2012 Week 44: State of Play

Past few weeks been drawing up a few cold-formed steel sheds, my dad doing the engineering. I will be doing workshop details later, probably last minute before Christmas to get the steel ordered and available for erection early next year in January, whilst the steel suppliers otherwise shut down.

Produced calculations for aluminium glazing channel to be used for frame less or cantilevered glass balustrade. Then tested the channel whilst otherwise testing the proposed laminated glazing. Everyone was hoping to break the glass but didn't happen. Proposing to retest the glazing as the grout didn't properly fill the channel.

Otherwise done calculations for several framed balustrades. Seems that balustrades are an ignored component in multi-storey building design. All very nice reducing the thickness of the slab, and getting an extra storey in the height: but the edge of the slab requires some substance into which the balustrade framing can be anchored. Most especially important, if the architects are opposed to base plates. Compound the hassles of getting adequate anchorage in the slab, with the problems of connecting the aluminium in the first place whilst trying to avoid welding. If weld aluminium then reduce its strength, so somehow the aluminium has to be connected to a base plate with out welding, or connected to other structure with out base plate. Then there is the issue that the aluminium tubes themselves don't have adequate strength, but this can be compensated for by the inserts used to attach to the support structure. So balustrades went from relatively simple to some what complex composite structures.

Also been working on design of golf safety net. These are large nets which are placed at the perimeter of a golf course to protect roads and housing from flying golf balls. I reduced the wind load to that typically used for light poles, antenna's and similar structures, rather than directly use the BCA criteria. Such structure is a class 10 structure and covered by BCA: volume 2, which some how seems inappropriate. I was only requested to check the poles. So there is no real  design of the sports safety net. I checked the posts for:

1) Drag force on the posts
2) Cable reactions normal to plane of the net.
3) Cable reactions in the plane of the net.

Not having any specification for the requirements of the net or the posts. That is I would expect the post supplier to have been provided with a specification for the post: either forces on the post, or the required size of the post. Not having any of this, using MS Excel I simply did a goal seek on the catenary  formula, to get the minimum cable tension which would achieve equilibrium for the forces normal to the net. I checked pier sizes using the Rutledge formula.

Got request for further information. Not having section property tables for the circular hollow section (CHS) proposed, I lazily used Multiframe steel designer to check the members. Seems I didn't make it clear that the post was checked for biaxial stresses: the forces normal to the net and those in the plane of the net. The forces in the plane of the net are higher than those normal to the net. These forces are an important factor to design of structures supporting flexible cables. If had a solid plate wall supported between posts then would only really have the forces normal to the plane of the wall to consider. For internal posts the lateral forces in the plane of the net cancel each other, on condition that the net either side of a post is equally loaded. For the end post this is not so, only got a net on one side, however the cables supporting the net also act as guy ropes for the post, so post size can be kept down.

The request wants the wind load to be increased or the posts designed for the breaking load of the cables on the basis that the cable should break before the post. I disagree with this philosophy: when tension cables snap they can cut people in two, take their heads off. The structure should be robust and ductile. The nets should break free of the cables releasing loads from cable and posts. If the cables get overloaded then the posts should fail by forming a plastic hinge at some point above the base, the posts folding up, and reducing their profile to the wind.

The basis of the wind loading code is not altogether to prevent collapse of a structure, since the design load always has potential to be exceeded, rather the main task is to keep the structure and its components anchored to the site.

My design philosophy therefore would be that first the net detaches from the cables, not fully but along at least one edge. By doing so the net releases load from the cables and the posts, it would move from being in a vertical plane to being horizontal: if the wind can keep it horizontal. My first thoughts were that the lower edge should detach. But second thoughts suggested that the top edge should detach, the net would then drop  under gravity: either to the floor or a lower level. The load on the post would then be reduced. This would therefore require that the attachments of the net differ along the two support edges.

If the nets fail to detach and release load then, the heads of the posts would be pulled closer together under the lateral loads. It would be preferable that the posts are tapered: either constant external diameter with varying internal wall thickness, or constant wall thickness with varying external diameter. The post then only has such strength as it needs at each height: if the nets are overloaded then the posts should bend and yield reducing profile to wind and avoid further loading which would lead to fracture. All would then be retained on site, but in need of repair. That's the philosophy, demonstrating suitability is another issue.

So been refreshing memory how to use lights by Dr. Vinicius F. Arcaro, University of Campinas, Brazil. Experimented with about 10 years ago, for sail-shade assessment, at which time I wrote MS Excel/vba subroutines to graphically display the model and results in IntelliCAD 2000, because the AutoCAD script (.scr) which it produces was incompatible with IntelliCAD. Thus far managed to build a model of one segment of the golf-net. To do so also made use of formfinding routines operating in GID. Idea is to consider the net as a coarsely woven fabric and so treat as tension membrane, supported on cables, rather than model the whole net. Though at this point not certain how going to do that.

Not sure of the benefit though if I have no control over the nets and support cables.

The other issue is to provide more information on the design of the piers, and a request that the piers be designed as laterally loaded piles.

Any case designing the posts for the breaking load of the cable would make the steel CHS posts massive, much larger than the timber matchsticks supporting a much larger golf-net standing near by. There is also another golf-net of the larger size to be provided at a future date.

So it seems to me that some design philosophy is required for the design of the nets. Yet another situation where buy something as if off-the-shelf and get engineering done for some bit, on an as needs basis. Get even more complex if the buyer and the certifier both turn out to be the same government authority. Now that definitely would be a lack of independence: and not in the best interests of the community.

Very little is as simple as it first appears.

The Building Code of Australia: Evidence-of-Suitability

A reference to the assessment methods, and requirements for evidence-of-suitability as found in BCA 2010, Building Code of Australia Class 2 to Class 9 buildings, Volume 1 (ABCB)

A0.9 Assessment Methods
The following assessment methods, or any combination of them, can be used to determine that a Building Solution complies with the Performance Requirements.
Evidence to support that the use of a material, form of construction or design meets a
Performance Requirement or a Deemed-to-Satisfy Provision as described in A2.2.
Verification Methods such as–
the Verification Methods in the BCA; or
such other Verification Methods as the appropriate authority accepts for determining compliance with the Performance Requirements.
Comparison with the Deemed-to-Satisfy Provisions.
Expert Judgement.

Part A2: Acceptance of Design and Construction
A2.2 Evidence of Suitability
(a) Subject to A2.3 and A2.4, evidence to support that the use of a material, form of construction or design meets a Performance Requirement or a Deemed-to-Satisfy Provision may be in the form of one or a combination of the following:
(i) A report issued by a Registered Testing Authority, showing that the material or form of construction has been submitted to the tests listed in the report, and setting out the results of those tests and any other relevant information that demonstrates its suitability for use in the building.
(ii) A current Certificate of Conformity or a current Certificate of Accreditation.
(iii) A certificate from a professional engineer or other appropriately qualified person which–
(A) certifies that a material, design, or form of construction complies with the requirements of the BCA; and
(B) sets out the basis on which it is given and the extent to which relevant specifications, rules, codes of practice or other publications have been relied upon.
(iv) A current certificate issued by a product certification body that has been accredited by the Joint Accreditation System of Australia and New Zealand (JAS-ANZ).
(v) * * * * *
(vi) Any other form of documentary evidence that correctly describes the properties and performance of the material,
(b) Evidence to support that a calculation method complies with an ABCB protocol may be in the form of one or a combination of the following:
(i) A certificate from a professional engineer or other appropriately qualified person which–
(A) certifies that the calculation method complies with a relevant ABCB protocol;
and
(B) sets out the basis on which it is given and the extent to which relevant specifications, rules, codes of practice and other publications have been relied upon.
(ii) Any other form of documentary evidence that correctly describes how the calculation method complies with a relevant ABCB protocol.
(c) Any copy of documentary evidence submitted, must be a complete copy of the original report or document.

Similar requirements can be found in Volume 2, for class 1 and class 10 buildings, but with different clause numbers.

Yes I know it should be BCA:2012, but I have little to zero use for the BCA, consequently hard to justify the expense every year.

To clarify I only have use of a single page in the BCA, a page which should be in AS/NZS1170. For the most part the BCA is just a partial catalogue of Australian Standards. Typically, designers make use of Australian Standards whether called up by legislation or not. Those who are not designers typically just propose, without demonstrating suitability for purpose. Suitability of purpose is dependent on a subjective judgement of what will be suitable: the task is to demonstrate that such level of performance will be achieved by a proposal.

The BCA requirements for demonstrating suitability and compliance, are only partial. Additional requirements may be required depending on jurisdiction. The additional requirements are typically forms to be filled in to meet local regulatory requirements. Manufacturers and suppliers should therefore seek to obtain designs and certifications which are independent of local requirements and which can readily be verified, accepted and approved in any jurisdiction. For example self-certification by RPEQ's in Queensland will meet opposition in South Australia, because it is not compliant with the requirements for a independent technical expert, further the certificates have inadequate information for independent technical assessment. Self-certification by designers and engineers, should therefore be avoided, no matter which jurisdiction operating in, since poor practice in the first instance.

I will write more on this later. I would prefer to be able to directly link to the clauses of the BCA, but this code is not readily accessible by all those it is imposed upon. If lucky you might get to view it at your local council office, or find it in your local library. Otherwise consult a building surveyor.

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Related:

1. SA Development Regulations: independent technical expert

SA Development Regulations: independent technical expert

Extract from SA Development Regulations

Division 1—Prescribed qualifications
85—Interpretation
In this Division—independent technical expert means a person who, in relation to building work—
     (a)     is not the building owner or an employee of the building owner; and     (b)     has not—     (i)     been involved in any aspect of the relevant development (other than through the provision of preliminary advice of a routine or general nature); or     (ii)     had a direct or indirect pecuniary interest in any aspect of the relevant development or any body associated with any aspect of the relevant development; and     (c)     has engineering or other qualifications that the relevant authority is satisfied, on the basis of advice received from a relevant professional association or a relevant registration or accreditation authority, qualify the person to act as a technical expert under these regulations.

Elsewhere there are several references to engineer:

(3) In subregulation (2)—professional engineer means a person who is—
     (a)     a corporate member of the Institution of Engineers, Australia who has appropriate experience and competence in the field of civil engineering; or     (b)     a person who is registered on the National Professional Engineers Register administered by the Institution of Engineers, Australia and who has appropriate experience and competence in the field of civil engineering.

These references typically differ only in the subregulations they relate to, and are generally concerned with roads, stormwater and earthworks.

First and foremost the primary requirement is independence.

At the simplest could say that:

Two idiots independently reaching the same conclusion is far better for the public interest, than one idiot acting as self appointed authority. It is through the continuing challenge from others that real competence is developed, not via a once off assessment and appointed position of authority. Far too many of the self-certifications flowing in from other states are worthless scrap paper. The certificates contain inadequate information to permit an independent technical check on the suitability of a development proposal.

It is not so much as that building officials in SA want to see the calculations, but that the requirements of the Building Code of Australia (BCA), is based on adequate evidence-of-suitability, and the certifications available are not considered adequate and the proposals are otherwise of questionable suitability.

At the simplest there is just a plain lack of effort defending the development proposals: besides a lack of evidence-of-suitability, the descriptions of the proposals are often also inadequate. The very lack of thought and consideration is the reason for the regulations being in the way. The regulations are only really a hindrance to those who choose not to do the right thing.

... more on the issues of independence later.

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Related:

1. The Building Code of Australia: Evidence-of-Suitability

Engineered Products and Evidence-of-Suitability

Really beginning to dislike civil engineers supplying services to manufacturers of supposedly engineered structural building products. Notice I didn't use the Americanism pre-engineered, this word itself probably stems from part of the problem. Civil engineers typically provide services for the custom design of one-off products. If live in an industrialised society probably got a million and one complaints about all the infrastructure provided: that is focus is not on the benefit provided but the deficiencies and inconveniences which have to be tolerated. Put simply the designs are inadequate. These are multi-million to billion dollar projects we are stuck with once constructed: the systems are extremely difficult to fix or get rid off. Quality design cannot be achieved by merely crunching numbers and complying with codes of practice. Quality design requires imagination, ingenuity and a certain amount of paranoia.

Now when engineers dump these mega-systems into our environment, their experience is developed from one mega-system to the next. As they learn more deficiencies in design become fewer, but the more that has to be learnt and done under the supervision of the experienced before an individual can start to practice: for society becomes less and less tolerant of the defects. Now consulting engineers are not really operating in a market based economy in the same way as manufacturers do. Manufacturers supply engineered products which either do or do not satisfy the needs of the end-user, supplied at the right time, in the right condition for the right price. Consultants supply a service (a product), and largely irrespective of the quality and suitability of the physical systems supplied. The community criticises the systems, but continues to employ the same group of consultants to produce more of the same: possibly hoping, fingers crossed, that they are gaining experience and the next system will be better. Whilst the systems often suffer faults in workmanship, that can often be directed back at the design, the design failing to be quality robust. If a design is quality robust then at the ideal, cannot help but make to the specification, and need to deliberately go out of the way to not build to specification. The steel reinforced concrete buildings which often fail during earthquakes in relatively poor countries are examples of poor quality robust design: whilst the reinforced concrete was adopted to minimise use of expensive steel, it should be noted that the steel still too expensive and scarce, and such steel was never going to make it into the concrete. Therefore to specify such buildings constitutes poor design. Whilst large scale manufacturing has adopted the principles of quality robust design (QRD), the building and construction industry has been relatively slow to adopt. Most ISO:9000 accredited consultancies, simply have systems concerned with managing flow of contract documents: not concerned with the quality of service or the quality of the designs for the systems specified.

I will make the assertion that given the lack of whole system design, these custom engineered systems in the built environment that consultants deal with: are anything but engineered. We do not refer to a Boeing 747, an Airbus A380, a Holden Commodore (GMH), a printer, a computer or a TV as being pre-engineered: they are all engineered products: or hopefully so.

Peoples typical contact with so called engineers, is when they have contact with a regulatory authority who sends them off to get an engineers report, engineers calculations or an engineers certificate. Engineering is not about meeting regulatory requirements, being registered and filling in silly forms. {Which is what RPEQ's (Queensland) and RBP's (Victoria) seem to think engineering is.}

Engineers do not have ESP or xray vision. They cannot come out to sight, kick the dirt look through walls and certify some construction as compliant with code of practice. Such activity is totally contrary to the basis of engineering, and something being engineered.

If something is engineered, then there is a technical specification describing what it is, in terms of its critical characteristics and expected performance under varying conditions. This extends to all its component parts and raw materials. There is also technical specification concerning the control of all inputs and the process of transforming raw materials into finished end-product. Engineering is always an activity prior to the existence of a product or execution of a process. Scientific observation, measurement and control of a process without prior engineering is applied science not engineering. Engineering specifies an expectation and aims to control the process of achieving such expectation.

Large manufacturing enterprises got divide into the designers and the makers, giving rise to the process of "over-the-wall-design": this is a very inefficient process, for products get specified which cannot be made. Manufacturing aimed to remove this inefficient process. The building and construction industry via the tendering and contracting process is built around "over-the-wall-design". More over the industry is now has a multitude of manufacturers who rely on external consultants: because all that engineering provides is the certificates of compliance to meet regulations.

When I asked a manufacturer about its product and the materials it uses, I don't expect the material supplier to direct me to some consultant civil engineer in another state. That is absolutely not acceptable. In similar manner I sure hope that manufacturers we work for, don't go around declaring we are their engineers.

If producing an engineered product then it needs a technical specification as previously described. If have an engineered product then it required engineered components and materials, ecah of which requires a technical specification. If supplying components or materials for an engineered product, then your product needs to be an engineered product and have a technical specification. That technical specification needs to identify all the physical properties, all the characteristics necessary to engineer the component or material into the larger engineered system.

If make steel, aluminium, glass, bolts, gears, chains, cables, nets,  etc... then if wish such products to be used in larger systems to be engineered to be compliant with codes of practice and regulations, then all these products require a technical specification. Further more require more than a simple certificate declaring product is compliant with some code: the business needs to be able to provide evidence that it is capable of making product compliant with a code. Such evidence needs to be generated on an on going basis, to verify that the process capability is being maintained. For the benefit of external parties, this capability should be audited on a regular basis by an external party, to witness and verify the claimed capability.

Certificates of compliance and/or conformance, professional licenses, along with permits of regulatory approval all largely represent worthless scrap paper. They all fail to provide a reliable indicator of an engineered product.

Take glaziers they install glass and certify compliant with the glass code AS1288. The certificates are worthless. The requirement of the installation is that it is compliant with the Building Code of Australia (BCA), in particular the structural provisions, which requires compliance with the deemed-to-satisfy provision in the form of the loading code AS1170. The glass code (AS1288) is a design code, the loading requirements to AS1170 first have to be determined before a design-solution can be selected from the available design-charts or otherwise determined from first principles. The certificates issued therefore are inadequate.

The Building Code of Australia (BCA) is largely independent of jurisdiction. That is anyone anywhere in the world can design a building product with the intent of achieving compliance with the BCA. The BCA itself contains some criteria for demonstrating compliance. The requirements are basically centred around providing adequate evidence-of-suitability. Ultimately such evidence would be submitted in a court of inquiry, as a consequence such evidence needs to be reliable and capable of independent verification. A certificate from someone in authority is not adequate evidence. A certificate has to be more than someone declaring the product to be good stuff. A certificate should at the minimum make reference to the technical specification of an engineered product.

Cannot simply declare the glass is to AS1288, or that the steel shed complies with AS1170 and AS4600, such declarations are worthless. The glass has to have a technical specification, the glass has to have specific mechanical properties such as elastic modulus, yield strength and ultimate strength, the chemistry of the glass may also be important. If there is no technical specification then there is no evidence the supplier can produce a glass installation which complies with AS1288. The materials namely the glass is an unknown entity being installed into a still larger assembly of unknown characteristics.

For the steel sheds people running around trying to get lighter frames. This may be an acceptable thing if there was a high level of consistency in the engineering of the product, but there is not. Those consulting civil engineers, I referred to at the beginning, simply issue some simplistic often highly deficient calcs-for-council, which will be used to dump a product into the built environment at the rate of a 1000 or more per manufacturer per year. At least with consultants custom designs there is some potential for improvement from one building to another. With other engineered and manufactured products, there is on going engineering to improve the product and better satisfy the needs of the end-user. Not so with manufacturers in the building industry, no in-house engineering, just rely on external consultants, and have no proper product design or proper management of design and engineering requirements: the engineering is always at the last minute when hit a regulatory requirement for more information. That is meet a problem with an individual project. In the main all these problems are due to poor engineering and inadequate evidence-of-suitability.

Regulatory approval, such as development approval, is only concerned with checking that the proposed development complies with regulatory requirements to the extent assessed: it does not mean the development is actually suitable for purpose or 100% compliant.

The BCA has building-solutions and alternate-solutions. However the BCA is also highly lacking in defining the critical quality characteristics of a building and its component parts. In fact for a building code, it has very little content relating to buildings. Approval of new building materials for example is highly dependent on the individuals involved rather than the actual code. So straw bale, rammed earth, SIP's, ICF's, plaster wall panels, aerated concrete panels, polystyrene wall panels all problematic in terms of getting local approval. Yet its not as if the BCA deemed-to-satisfy materials like clay brick, concrete, steel, timber and glass actually have desirable characteristics in their own right as building materials. For example brick not particularly good, its soaks up water, that is why it is typically part of a cavity wall system.

Now when it comes to structural provisions of the BCA, it should be noted that AS1170, AS4600, AS1288 and all other Australian standards related to structures are all deemed-to-satisfy provisions. It is not necessary to use AS1170, it is necessary to meet the BCA performance criteria for structures. Deviating from the deem-to-satisfy provisions moves into BCA alternative solutions. Alternate solution or deemed-to-satisfy building solution, either way the fundamental requirement is to provide adequate evidence-of-suitability.

For a product to be engineered however it has do do more than simply meet BCA criteria, most especially at the end of the day, the performance criteria take precedence over the deemed-to-satisfy provisions, and when failure ultimately occurs the communities expectations and perceptions of what is considered fit-for-function over ride mere code compliance.

In terms of cold-formed sheds there is much that can be done to reduce frame size.

1) Adjust risk and life expectancy: {this changes: importance level, mean return period and wind speed}
2) Reduce internal pressure coefficients
3) Distribute wall wind pressure with height
4) Adjust serviceability requirements
a) Change serviceability risk and life expectancy
b) Change internal pressure coefficients
c) Change deflection limits
5) Allow stressed skin, or diaphragm design
6) Allow plastic or collapse method of design
7) Have monitored system with warning devices
8) Design mode of failure to be minimum hazard. (eg. failsafe)

Whilst such is possible there is requirement to justify the options taken, identify what constitutes fitness-for-function and suitability of purpose, then provide the evidence which demonstrates how the expected level of performance is to be achieved. It does not have anything to do with the BCA or any other national standard: providing such evidence is fundamental to science based design or design-science. The BCA and other national standards simply provide one set off criteria, one subjective judgement as to what one group of individuals considers to be suitable for purpose.

Something which merely complies with AS1170 and AS4600 is not fit-for-function. The codes only provide requirements for loads and the capacities of primary structural members, the structural capability of the components which enable those members to be connected together are largely ignored. The capability of the member is entirely dependent on the capability of the connections. In general the assessment of connections and the local effects on attached members is relatively inadequate. The engineering can be considered less than it should be, and the proposed structure does not comply with the structural performance requirements of the BCA, though it may appear to comply with the deemed-to-satisfy provisions AS1170 and AS4600.

The independent technical assessment required by the SA Development Act is entirely dependent on the knowledge and experience of the people making the assessment. Whilst some of these people are less competent than desired, the system is far better than having self-certifying RPEQ's and RBP's who never get questioned about not knowing what they are doing. When their self-certified products arrive in SA, then the certificates tend to be rejected, the agents for the product then seem to experience difficulty getting appropriate information to submit for approval and approach local consultants. If the products were properly engineered this would not be a problem.

It should be noted this is a different issue the other way round. When products from SA enter the other states, the issue is different: the suppliers have engineering calculations and drawings: what they don't have is an appropriate form filled in by the appropriate person. A good captive market those RPEQ's and RBP's have in Queensland and Victoria, but some contention of designing for the site and filling in silly forms does not constitute engineering. They seem to be getting away with dishing out high priced low quality rubbish. Registration, and licensing not very useful: not quality robust.

Certificates are not good enough, nor are calculations and drawings. Everything has to be part of an engineered whole, for it to be engineered and quality robust. Engineering is dependent on prior knowledge.

Now for some greater confusion. Has stated in prior posts, objective delete the word: engineer, and engineering from vocabulary. Since I have an idealistic perspective that engineering pushes forward the frontiers of science and technology. Engineering operates in a chaotic wilderness of uncertainty.

Going back in time, have an ancient building a stone wall, it gets so high then it collapses. The wall has to be built, resolving the problem was the work of an engineer. Designing stone walls is no longer the work of an engineer because the problem has been solved. To resolve the problem, the process is placed under observation and measurement, controlled and compared against an hypothesis regarding expected behaviour. The hypothesis is validated and the project is completed. The acquired knowledge is added to the body of prior knowledge. Attempting to solve problems as bump into them, is very expensive, wasteful of time and material resources, hazardous and otherwise highly inefficient.

It is preferable that prior scientific knowledge is available at design time, and all potential problems resolved and prepared for during the planning and design stage. For the vast majority of things this is possible, problems typically encountered are due to a lack of science, planning and design.

Applied science is important it makes observations, measures and collects data about systems, natural and artificial. Applied science may develop theories from the data to predict future behaviour of a system. Engineering science, adds the applied science knowledge to the engineering body of knowledge and expands and develops with respect to specific technological applications. For example idealistically, if we must have a division: then engineers designed and built the steam engine, applied science investigated and developed the science of thermodynamics, engineering science adopted thermodynamics and used it to further develop steam powered machinery. This further is added to the body of knowledge of technical science which enables the design of a steam powered device for a specific purpose.

Without a system developing the body of knowledge of technical science, just bumbling around in the dark hoping a product will achieve a desired level of performance.

So we can assess the performance of connections in hotrolled steel because the ASI and other organisations have sponsored research, either physical or literature, to compile and publish guidelines for connection design. No such research has been done for cold-formed steel design, not by industry organisations, nor public funded organisations for the common good, nor by businesses constructing products involving such connections. Everything is assumed ok on the basis of an authoritarian paper shuffling system.

Low quality imported steel, low quality imported bolts and other such issues are not a problem for a fully engineered product, produced by an engineered system. Nor does a lack of coordination, become a problem, just because of increasing availability of manufactured products to the building industry. So there is an increasing retail sector to the industry: but whether choose to make or buy still require a technical specification. Either a technical specification is sent to the supplier for them to comply with, or the supplier provides a technical specification against which the required specification can be compared to see if the product will be suitable. This should not be an exercise of paper shuffling  signature collecting, and identifying who to blame in future.

Manufacturers of engineered products should have technical personnel on staff. At the very minimum they should have adequate knowledge of the technical science for the product to be able to write technical specifications for the product. They should not rely on external consultants for design of their product, as generic as it may appear to be, unless they can properly manage the requirements for ensuring they have adequate evidence-of-suitability. The evidence-of-suitability relates to the product in its own right, and to the product as it relates to an end-users specific needs. An M16-PC(4.6) bolt may be suitable in its own right,  but from the technical specification for the bolt someone needs to determine if the bolt is suitable for a specific connection and thus provide a technical specification for the connection.

The technical specification and associated evidence-of-suitability all have to be adequate to the extent, that someone can independently verify the suitability with no other information beyond readily available publications. In terms of regulatory approval they are not going to conduct physical testing themselves to verify test results, the test results therefore have to be reliable on their own terms.

It should be noted that the onus is always on the proponent to defend the suitability of their proposal for development approval or any other regulatory approval. If going to test to demonstrate suitability, then should get that test witnessed by one or more independent parties: or otherwise send samples to at least two independent test laboratories. Also try to avoid having it tested and certified to the code: such is irritating when simply just trying to determine the products capability and all the lab can do is produce stock standard reports declaring compliant or non-compliant. Need to determine the products capability, its suitability for any specific purpose and compliance with any specific code is another set of issues: and not entirely with in the capabilities of the personnel of the test laboratories to judge.

We do not have a robust techno-scientific culture, and we need to develop such culture if we are to avoid some serious disasters in the future. The issue is not whether the product looks alright today, but whether the non-visual characteristics of the product will function as expected at some distant point in the future.


Sun 2012-Oct-21  02:12AM

Weight of Steel does Matter?

Shed Retailers
As previously indicated getting started in the cold-formed steel industry was relatively simple. Get some standard calculations for a single shed which envelopes the size range of expected market. On a given sale fill in some c-section hole punching sheets, and send them off to rollformer. Have delivered to site. As far as such supplier is concerned they have no control over fabrication costs, nor control over construction costs. Therefore only issue appears to be the cost of the steel, reduce the weight of steel and therefore reduce the cost.

Builder.
Steel erectors and other builders, have some control over construction costs, however any reduction in construction time results in lower fee for the job, and a need to get more projects per year, assuming their fees are time based. Often however their fees are based on $/sq.m of floor plan, some may charge $/tonne of steel erected. However tonnage doesn't really reflect the scope of the task. All that really changes from one shed to another is the area of the floor plan, which in turn increases the number of frames they have to erect. If frames get heavier then that may require moving from manual handling to need for mechanical handling. Increase in height of shed may also have an influence on costs due to need for people licensed to operate height related personal safety equipment (safety harnesses and fall arrest lines)

So as far as the builder is concerned construction costs are their fee and not something they wish to reduce, thus once again reducing the weight of the steel is the point of focus.

Fabricators + in-house Engineering
In some countires hotrolled steel sheds are engineered to suit the needs of the project. These sheds are either in hotrolled steel sections, or more commonly fabricated tapered beams welded up from flat plate. So here they have contol of fabrication, and also often control of construction. But once again, as with the builder, they have no real wish to reduce the cost of the activities which are seen as their income, and so the focus is still the weight of steel.

Optimum Solution is not Minimum Weight Solution
The flaw in all these cases is equating the weight of the steel to the cost of the steel. The real issue is the cost of materials, not the weight of steel. Further it is not the cost of materials on an individual project, but the cost of materials across many projects.

Hollow steel sections (HSS), such as SHS, RHS and CHS are typically considered expensive materials, and yet they found a market in small residential sheds and light industrial sheds, as did the use of hotrolled steel angles. They found a market because they were relatively light weight materials, and could be fabricated into welded trusses or bolted trusses. For a one-off project, the use of such sections and such fabrication would typically be considered far too expensive compared to the use of a single section in the form of a universal beam (UB) or possibly parallel flange channels (PFC). But for high demand small sheds, the smallest UB and PFC some what impractical and over sized. There was cost benefit in fabricating light roof trusses. Many home owners preferred sheds with trussed roofs they could store long items in the roof space, and otherwise use the bottom chord for a block and tackle to hoist engines from their cars. Then cold-formed c-sections emerged in the market, for a time trussed roof's held their place but slowly lost more and more market. The c-sections being light weight sections from high strength steel could and can span the required distances for small sheds without the need to expend time fabricating trusses. With c-sections no need for skilled welders, and possibly eliminate the need for bolt trusses. However as spans increase cold-formed sections bolted to form trusses can start to encroach on the market held by hotrolled UB's.

So in this we can see that cost includes fabrication and materials. At one time more fabrication could cut total costs by reducing the cost of materials used, that this then changed to lower cost materials bringing about a reduction in fabrication. The important characteristic about rollformed c-section, is that a significant amount of fabrication can be automated in the punching and rollforming process: and it is fairly rapid. {Maximum around 100 ft/min, or 30m/min}.

Whilst there is likely variability in rollforming feedrate say going from C7510 to C30030, I hazard it is off minor significance to productivity compared to length rollformed. The importance of this is that the retailers, do have some control over fabrication. For example can choose C7510 girts at 600 c/c or C15012 girts at 1200 c/c. {c/c = centre to centre}. If adopt the larger section, then have fewer rings around the girth of the building, that is the net length of section required is less compared to the smaller section. Therefore hazard it will take less time to rollform the total length of C15012 required compared to the total length of C7510 required. {Few in any supply C15010} If using coil of same total diameter, and strip of same thickness, then have the potential to get more complete jobs from the one coil, and therefore fewer coil change overs for the rollformer. Not sure about total length in a coil, but assuming it is 2000m, then say shed requires either 500m of C7510 or 250m of C15012, then from one coil can get either 4 sheds or 8 sheds.Sure the strip width is wider for the C150 than it is for the C75, but total volume of steel approximately the same. {The C150 requires slightly more steel: due to differences in flange sizes, and also differences in outer girt requirements.} However it is the total cost of supply which needs to be considered, and also the timing of supply. It should be noted that a  several years BHP held a seminar for consultants and they pointed out that some 80% of the cost of steel was in the cladding and cladding support system, but little effort was and is put into its design.

With respect to fabricators with in-house engineers, once again it is a flawed concept to assume that the value lies in them getting the weight of the steel to a minimum and therefore minimum cost frames. The benefit of going to such fabricators is that they can optimise the design to better meet their fabrication facilities and available resources. If get a consultant to design a shed and then go out to tender, then the shed will not relate to any fabricators production capability nor their available resources. If consultant says fabricate by folding, fabricator will want to weld up from plate: the fabricators will have alternative preferences to the design consultant. A consultants design may specify 250UB but the optimum design from a fabricator maybe from 310UB, because they have such steel lying around the workshop which is not going to be used for anything, and is tied up capital. In another situation the fabricator may have 250UB lying around and the consultant specfies 310UB, but fabricator can weld cover plates, castellate, or fabricate in a variety of ways from plate and their available sections to create a more economical structure. Most especially the case if the price of steel is on the rise, and most fabricators have to buy steel now whilst a handful of fabricators have stocks of steel bought previously at lower price. So in some countries (eg. India), holding stocks of flatbar and plate, and welding up into I-sections to suit the job, is more economical than using hotrolled UB's, UC's. The optimum solution, the minimum cost solution is highly dependent on circumstances.

Now in a market where increasingly software is being used to get minimum section size to suit a job, it may appear that getting the minimum section size is essential to minimum cost solution. I will hazard to say not so. During the 1990's there was a shift, from minimum cost optimisation to maximum profit optimisation: the purpose of a business is to maximise profit not minimise cost. Further more the minimum cost of everything is zero, don't do it. If choose to do something then it costs what it costs.

Business is a real world experiment, therefore costs and prices are not certain, they are highly variable. Buy something for one price doesn't mean can sell it at equal or greater price, it may be necessary to sell it at lower price to free warehouse space and cut inventory costs. Similarly can push prices up and up, until sales volume drops off. With higher prices can make same profit for less effort, sometimes this is necessary. By raising prices can cut demand, and therefore reduce the need to expand production facilities or otherwise generate the funds to expand production facilities. The latter is key, those who want to supply useful gooods, versus those who simply want profits for personal luxuries.

Those who want to supply will expand production facilities, they will eliminate waste, they will improve quality, and add value to their products. They may also cut per unit production costs, but not necessarily cut sales price to the full extent possible because the market will already be happy or partially happy with the existing market price.

The minimum size of structural section which can be demonstrated compliant with a code of practice is the lowest quality, lowest value product which it is legal permissible to sell to the market. Anything not compliant with the code of practice is considered defective, until demonstrated otherwise to be suitable for purpose and the codes modified accordingly. It is not science it is politics. It should be noted that the codes are actually deficient: for example the wind loading code is based on horizontal flow of air over a building typically producing suction or uplift on the surfaces: in non-cyclonic regions the primary storm event is a violent downdraft: rather than roof being lifted of the building more likely to have buidling flattened against the ground. Similarly the Australian interior is likely to experience tornado activity: also not covered by the codes. When it comes to the crunch, the requirement is not whether it complied with the codes but whether or not it was actually suitable for purpose.

Therefore there is a problem if shed manufacturers are running around trying to find engineering which will justfy smaller compliant section sizes to compete. If the cost of the frame is an issue, then I say they are not offering any major benefit over the custom design project and going out to tender to find a contractor. The problem with tender/contract is that the fabricators typically use relatibely crude and cumbersome fabrication processes, with relatively poor capability at replicating parts. No one is going to spend ten's of thousands or a few million dollars to make a die for replication of a few dozen parts. Something which could be stamped from sheet metal in a few seconds, will be fabricated from heavier gauge steel probably at the rate of an hour or more per part and these parts in turn will have an influence on the nature of associated parts. So to start with the consultant engineer cannot produce minimum weight solution in first place, unless the crude fabrication techniques are the only practical techniques for the size of structure. Buildings fit into classes, some classes have high demand, those high demand classes are suited for automation of repetitive components. However, to permit mechanisation and automation, it may be necessary to work with more robust components, and that may result in an increase in weight of material compared to the structural requirement. Whilst weight has increased, the per unit production cost have decreased and the volume produced per unit time increased.

The building industry zero inventory approach does not altogether deliver at the right time, nor to the right quality: not really something that manufacturing industry should be aiming for. Some inventory is necessary to buffer the flows required to satisfy the market at the right time.

Take example from another industry. Several years back I ordered a desk, there were different sizes available in terms of widths of the tables. I ordered the smaller width. The width I ordered wasn't in stock, and needed to be made, but they had a larger version available. They offered me the larger version at the same price as the smaller version: I didn't really want the larger version, but then again I didn't really want to wait either, so I accepted the larger version. They got rid of stock occupying space, I put my desk to work sooner.

Reducing the section size, is reducing the value of the shed structure, whilst increasing the section size makes the shed more robust. Shed retailers have the potential to negotiate with their preferred rollformer, and compare sales forecasts of shed sizes, against demand for various size c-sections. By doing so, they can cut the operational costs of the rollformer, and share in the cost savings, by buying high volume of a specific larger section at lower price, whilst prices of other sections are higher.

It should be noted that the rollformers want to sell steel, so reducing weight of steel sold not good for them. Rollformers entering the shed and carport industry, is so that they can sell more steel, but they have to balance this with competing against their customers. Their customers, may just decide to buy their steel from elsewhere. However, there should be more added value to the shed, than to the c-section. If trying to sell more steel then reducing weight of steel structure doesn't make sense: unless shed price has more added cost than added value and consequently sales of sheds are low.

It should be noted that many DIY's have priced materials and consider they can fabricate and build themselves for much lower than they can buy shed from any supplier. So suppliers do need to consider the other costs, and their desired profits. The buyer has to be able to see value, rather than cost and profits going to owners.

Capturing a greater share of the market does not require decreasing unit price, it requires grabbing the markets attention and selling them the function and value they need. People don't want sheds they want buildings for a specific purpose: domestic workshop, hobby room, double garage, storage room, chicken shed, stable, mechanics workshop, warehouse, self-storage units. Each of these buildings has characteristics beyond the performance of the portal frames comprising the structure. There are doors, windows, ventilation, shelving and a multitude of internal and external requirements. If the buildings are off-the-shelf as buyers tend to expect then suppliers would have such designs already available. Once again the unit price of say a stable from one supplier may be less than from another, because they have optimised that particular type of building. On the other hand the higher priced supplier may win the sale because of perception of higher quality product, and much safer for the horses stabled.

It is upto sellers to identify value in their products, and sell that value to prospective buyers. I know one supplier who was an agent for one brand of shed, and otherwise also custom built sheds. Samples of the branded shed were erected at their display site: they kicked and pushed and shook the branded shed and said they were happy to supply that shed, or for slightly higher fee they could supply their own more robust built shed. Its not necessary to reduce price to make a sale. However its difficult to kick and make the larger sheds shake, also not so convenient to have installed on a display site. So for the larger sheds a different kind of customer education and information activity is required.

If think the competition are using smaller section sizes, then that suggests that comparitive information is available in the environment: if only the fact the building site is accessible at some point. Therefore there should be no problem releasing decent technical specifications, which properly inform buyers of what to expect.

Yes I know, civil engineers representing the ASI shed group are all into custom design for the site, and therefore the requirements are uncertain, and so are into promoting an uneconomical infinite spectrum of goods. Once again, just because a lighter structure is possible for the site, does not make it the lowest cost structure, nor the optimum solution for a given set of conditions. Structures can be pre-engineered for a given set of conditions, those conditions can be compared against the project conditions, and a stock standard solution adopted. One manufacturers stock standard solutions should not be the same as anothers. This differentiation means they sell more specific products, to specific markets.

For example the cold-formed carport industry as largely moved away from using c-sections, to more customised boxed sections (actually variation of two channels designed to clip together), these custom box sections are specific to a single manufacturer, consequently their carport and verandah tables cannot be used to size a carport whilst buying steel from elsewhere. Whilst the development approval process, attempts to protect investment in RD&D, it has little control over what happens after approval. So city councils can reject a carport proposal submitted by one carport builder based on another suppliers tables. But little control and ability to check, that a builder submitted a proposal based on one suppliers tables and then bought c-section from elsehwere. It is largely this activity that pushed the industry to introduce a product which is more unique, of course everyone who wants to jump on the bandwagon is dreaming up their own variation of a stylish box section. With such sections its not so simple for the salespeople and buyers to compare section sizes, and argue about weights.

Whilst structural design is important, it is really architectural and industrial product design that the shed industry is in need of, not structural engineering. Each structural section has a limiting envelope for a given set of parameters: determining that envelope is a once of exercise. The issue is once have such envelope, what can be done with the section to create useful buildings: what value can be reaped from such standard design.

For example many people build American barn style sheds as holiday shacks. This is something of a waste as they then proceed to construct a substantial amount of timber framing internally for plaster board linings. But they have a building envelope constructed rapidly, and now can proceed at own pace as a DIY, fitting out the interior. Cold-formed steel buildings provide for rapid enclosure of space: that is value. Further the real standard design is a portal frame: not really a shed. That portal frame has more uses than providing the frame for a shed: those frames can be used in housing where large open spaces are required free from bracing walls. But for such purposes the frames would need to be stiffer,  to better control deflections, and that would push up section size.

Manufacturers should set their own performance criteria for their product, and not rely on regulatory authorities to impose.

When a business is offering a broad range of products, or more to the point offering nothing in particular, then it shouldn't be so concerned about the loss of sales based on price. Consulting engineers arguing about under cutting of fees typically offer nothing in particular. Shed suppliers offer nothing in particular. Not surprising therefore that some other business offering nothing in particular wins the sale on the basis of lowest price.

Products will always be compared on price, if that is the only observable difference. Suppliers need to differentiate their products: that is the combination of goods and services. Engineers are not all the same, noticeable from the fact that sheds are not all the same yet designed to same performance based codes. If sheds, and shed suppliers are not all the same, then why the focus on price, and the focus of weight of steel contributing to price difference? One reason is that the suppliers are too small, none really has a real product, they are really just retailers for pallets of steel: and often completely lacking instructions explaining how to assemble into a shed, and also lacking parts. They may advertise sheds, they may promote sheds, they may have pictures of sheds supplied in the past (or others have supplied): but they have little to no evidence they can supply the shed the current customer is seeking.  For the price what does or can the customer expect?

From many of the shed suppliers, all the customer can really expect is a pile of steel, and a lot of hassle getting development approval, along with a building which is a problem to assemble on site.

Buyers of light industrial and commercial sheds really need to be wary of unexpectedly becoming owner-builder, or otherwise leaving it to some salesperson to play architect and civil engineer in an attempt to make building and site compliant with requirements for development approval.

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Related Posts:

Cold-Formed Steel Shed Industry: part:#1

Cold-Formed Steel Shed Industry: part:#2

Cold-Formed Steel Shed Industry: part:#3

PEB, PEMB, PMBS Cold-Formed Steel Sheds and Canopies #pt2

Height Versus Span Design charts for Steel Sheds

The Section Weights ...

Weight of Steel does Matter?

Kleinlogel Rigid Frame Formulas

Manufactured Structural Products And Simplified Wind Classification

Other Blogs:

Shed Design: pt#1 (Basic Procedure

The Section Weights ...

From the illustration in previous post, the weights of the sections:


C250-24 8.17kg/m
C200-19 5.74kg/m
C150-24 5.67kg/m

Note that often the deeper section is lighter and stiffer, and the better section to choose if deflections are a controlling issue. The design chart I got the sizes from is based solely on strength, and low internal pressures. When I produced the chart it was to indicate the state of the industry, not as recommended sizes to use, but a reference datum to improve upon. Also to provide an opportunity for the industry to stop wasting time determining section sizes and put some effort into connection design and testing. Put simply, the heights and spans cannot be fully realised because few if anyone actually has connections capable of providing  the moment resistance required, to produce a rigid frame.

Though it should be noted that greater heights and spans are possible, by adopting still lower internal pressure coefficients, and taking shielding into consideration. But if the connections don't have resistance compatible with the structural form, then its all nonsense.

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Related Posts:

Cold-Formed Steel Shed Industry: part:#1

Cold-Formed Steel Shed Industry: part:#2

Cold-Formed Steel Shed Industry: part:#3

PEB, PEMB, PMBS Cold-Formed Steel Sheds and Canopies #pt2

Height Versus Span Design charts for Steel Sheds

The Section Weights ...

Weight of Steel does Matter?

Kleinlogel Rigid Frame Formulas

Manufactured Structural Products And Simplified Wind Classification

Other Blogs:

Shed Design: pt#1 (Basic Procedure

PEB, PEMB, PMBS Cold-Formed Steel Sheds and Canopies #pt2

Industry must be picking up, projects hanging around from end of last year finally got go ahead, and enquiries from old and new in the shed/canopy industry. Some looking for software, whilst others have issues with size of sections their designs currently use and being unable to compete.

The cannot compete because of size of structural section doesn't make sense to me, and never as and probably never will. I know it is possible to put a product in the market which is some 8 times more expensive than all other products in the market, and for that product to grab the majority of the market displacing all other players. And I know that this is because of a better product design: stronger, more durable, more robust, functionally safer, and better aesthetic.

I also know that the costing methods employed in the building industry are over simplistic and unrealistic, being based on $/metre or $/tonne. These approaches are fine for ball park figures determined by quantity surveyors to determine if project is feasible for the intended buyer. But such costing methods are inappropriate when in a highly competitive market. Highly competitive market does not mean that supplier should keep dropping their costs, rather they should be able to identify cost, quality and value.

I read somewhere that 2/3 of manufacturing costs are tied up in inventory. But do not be confused, this did not relate to funds tied up in raw materials stuck in a warehouse, nor to finished product locked in a warehouse. It related to the costs associated with managing an excessive number of components and excessive variety of products. Benefit comes from the discipline of Design for Assembly (DFA).

For example if have a product which comprises several parts which are bolted together, then that represents a large number of components to be designed, documented, fabricated and handled. If redesign so that can be welded together,then at the minimum eliminated all the bolts, nuts and washers, and replaced with welding wire. Further redesign however can eliminate the welding wire, and simplify to a few die-cast or injection moulded parts which simply clip together. Still further design and can reduce to a single part. There is a lot of cost tied up in having multiple parts.

A few years back the ASI developed a rationalised costing methodology in an attempt to get better pricing of steel structures rather than based simply on $/tonne, it had cost factors for various fabricated parts and assemblies. Unfortunately it is probably seen as too complex and time consuming to be used for one-off-projects. The shed and carport industry however is a different matter: for a single design is used for production of multiple units. Determining cost, waste and lack of quality is important to staying in business.

In rough terms once a structure is engineered, then the quantity of steel in the structure is fixed: however the steel can be redistributed to achieve fewer parts and lower labour costs. Costing a building on the basis of $/tonne therefore doesn't give an accurate cost of the building. Similarly steel erectors basing their fees on plan area of building doesn't give an accurate indicator of cost. Such costing approaches also hinders any improvement and innovation in the industry. Reduce the number of operations, or reduce the time to construct a building, and there is no cost benefit because the tonnage of steel not changed and the floor area not changed.

Now the cold-formed shed or carport industry is seen as an easy entry by builders, since little setup cost. Get a standard design which envelopes most of the buildings in expected market. Then fill in purlin punching sheets and send off to rollformer. Then a pallet of steel: girts, purlins, frame and cladding is then delivered direct to site, another pallet coming from supplier of any fittings required. A workshop may be required, if frame members have to be mitre cut and end plates welded. This requires the rollformer to deliver to the workshop rather than to site, thus involving additional processes, handling and transportation costs. Since the traditional cold-formed shed has welded end plates, the latter approach has been the more common. So straight off there is a cost difference for new players who can use straight cut c-section direct from the rollformers, and who have some standardised connection components. Such cost difference means that one supplier has potential to supply a given shed in larger c-section.

Should also consider the basis of standard calculations. Shed manufacturers want standard calc's on the cheap, so they state the span and size of c-section they want to use and then want calc's for maximum height, they can then use such calc's for any building which falls within the span and height envelope. One manufacturer wants to use C25024, another C20019: depending on wind loading: C25024 can get to height of 6m plus, whilst the C20019 to around 4.8m. But the majority of the market for both suppliers is 2.7m high, for which C15024 would be suitable.

{On notation: C-sections and z-sections are typically described by depth and base metal thickness (BMT), so C15024, refers to c-section 150 deep made from 2.4mm thick steel. On site can only measure the total coated thickness (TCT), which is the BMT plus thickness of galvanised coating. The notation isn't very useful because it ignores the breadth of the flange and dimensions of the lip used to stiffen the flange, such vary between manufacturers, so not altogether interchangeable.}

So its not really a structural issue, its a matter of the economics of getting designs. Most fabricators get designs on an as needs basis. The consequence of which, is that the designs rarely envelope one another in a rational manner. They therefore do not have designs which indicate the limitations of the available c-sections. Further more there is no mandated size for the structural sections, the fundamental requirement is that the structure is suitable for purpose, and that involves more than assessment of stress and strain, or strength and deflection.

We have the pre-engineered timber framing code AS1684, because in the past builders working on the same new development complained about the size of timbers used and argued about not being able to compete. Why can they use 70x35 F7 studs and I have to use 90x45 F7 studs? Well the answer isn't about minimum strength of the structure, but quality and robustness of the structure. For example, I know a builder who wouldn't use anything less than 45mm thick for the wall studs. The reason is that 35mm is too thin when it comes to installing plaster board panels. When 70x35's are used additional studs have to be installed where the plasterboard sheets butt: this may be at every 2nd stud. However it is unlikely that the plasterboard installer will have the extra timbers and install: it is an interruption to their workflow, and extra cost and operation. If the builder puts in the extra stud, chances are the plasterboard will be installed differently and the butt joints won't aligned with the extra studs. The production process is therefore more quality robust if the larger 70x45 studs are installed throughout. By having the pre-engineered solution in the form of AS1684, builders can check the minimum structural requirement and then factor in all the other issues themselves, and thus avoid arguments with the engineer of having oversized the structure. Unfortunately it does contribute to fostering the mentality: that its the law how large a structural section should be. There is no such law.

This mentality leads to industry associations writing silly letters to Standards Australia, complaining about internal pressure coefficients. We cannot compete because others in the industry are using lower internal pressure coefficients: its the law that the internal pressure coefficient should be ??. No it is not, there is no law. The fundamental law is that the structure is fit for function, suitable for purpose as demonstrated by compliance with various performance criteria of the Building Code of Australia (BCA). The BCA is the subjective opinion of a committee or individual people: it is not science. Hence we argue, why do we have to design for this load, where does this load come from. So make a change to probabilistic design, then argue why 1/500 probability of exceedance for wind loading, why not 1/1000.? Simple answer we tried 1/1000 from 1989 to 2002, building industry complained about increase in wind load compared to previous permissible stress design. So as a matter of subjective opinion and judgement the value was changed to 1/500, increasing risk of failure. It is not however necessary to wait till the codes change, it is upto designers to justify their design decisions. For example prior to 2002, I was using the probabilistic models in the appendices to wind loading code (AS1170.2) on a regular basis to assess carports and verandahs which had been constructed without approval. The construction took place many years before, the city councils discovered and imposed a requirement to seek development approval or remove. By making use of the appendices and commentary, need was shown for the methods, that 1/1000 not suitable for all structures. The result being that the methods were shifted to the main body of the code, and expanded.

There is no sense in taking pride in merely complying with the code of practice. Such attitude simply says the supplier would produce rubbish if no code of practice was in place. A quality supplier is one who sets the standard, who designs to their own standards, and their standards exceed those which are mandated. Further more their standards continue to surpass mandated standards even when the mandated are improved.

We appear to have an industry, that wants to say this is the legal size of c-section to use, if supplier using anything else then illegal, shutdown their operations, so that I can have more of the market. Not really business, complaining to parental government, rather than stand on own two feet. The suppliers which loosing business too, follow the same code, they get approval. Designers using the same codes, and working from the same customer brief will design two different buildings. If not either they are both hopeless designers or the codes are too restrictive. Performance based codes are not too restrictive, prescriptive codes are too restrictive.

So one supplier has design based on C25024, not because that is the minimum size which can be demonstrated suitable, but because, that is the size specified in their enveloping design, if they had more designs they could use smaller section. If the industry had software, as it increasingly does, then all would be getting closer to the C15024 of the example. But there are still a multitude of parameters to judge, which have to go into the design, which can result in a still smaller section size, or which may result in a larger section size. Design is subjective, and even science based engineering design does not produce a single result because the inputs are subjective.

Now from the example in the first place, the market place does not have a supplier who is supplying the minimum size section, only a supplier using a smaller section. So straight out minimum size section is not the issue, just lower price than competition. Now if the suppliers all have sheds based on different size sections, then customer is not comparing apples with apples. Now retail sector already introduced unit costing, or was that had imposed on them. The purpose of the unit costing is so that customer can getter a better feel for comparative prices. That is the larger can of food has a lower $/gm than the smaller can, so whilst the smaller can costs less, the buyer is paying more $/g for the contents. However, the smaller cans have added value to some users, and so there is more to consider than $/g. However for the shed customer $/tonne or $/m may be a useful comparison. But not if the manufacturer has costed all buildings on the same $/tonne or $/m rates. The customer needs assisting with value analysis, which is going to be a problem for the industry because they cannot value their own products, so how is the customer going to assess comparative value. Can only really be competing on price alone, when comparing like with like: exactly the same product. Comparing like with like is retail sector, and the primary issues are not the goods bought, but proximity and convenience of access to supplier, and quality of service provided by supplier.

Shed and carport suppliers do not supply the exact same collection of goods and services, they do not have anything which can be compared like for like, they cannot compete on price. If potential customer makes a decision based on cost to them, then the other suppliers have failed in the sale of their goods and services: not in the magnitude of their price. Dropping the price is not the requirement, making the customer aware of the value of the goods and services offered is the requirement. In the main most customers are just plain unaware of how appallingly useless most shed suppliers are at getting development approval.

Which raises another issue. Elsewhere in the world they refer to pre-engineered buildings (PEB), or pre-engineered metal buildings (PEMB), or pre-engineered metal buidling systems (PMBS). For the most part there appears little pre-engineered about the structures and buildings and, high end software is used to achieve rapid custom design. However, whilst the terms PEMB and PMBS are seemingly used interchangeable, I think a distinction should be drawn between buildings and building systems. A pre-engineered building system (PBS) is a collection of pre-engineered components which can be used to design a large variety of buildings. Whilst a pre-engineered building (PB), is an entire building possibly designed from a PBS, there can be no custom variations what so ever to a PB. A kit form garden shed or lawnmower locker is a PB. Light industrial buildings however are more typically PBS, which require custom engineering to transform PBS into a building. The cold-formed shed and carport industry in Australia does not have a PBS, it has standard calculations for portal frames (gable frame). To fit doors larger than the spacing of the frames, they crop the columns, the standard calculations then become invalid, for now have a different rigid frame. To meet customer requirements, salespeople are making unacceptable changes to what is closer to a PB. The result is either delays in getting council approval, or approval being granted by building surveyors who have poor understanding of the structural form and treat in similar manner to timber framed house construction: namely lintel required to support the rafter of the cropped frame. The process would be equal to car salesman agreeing to supply customer with a 3 wheel version of a 4 wheel car, because the customer thinks would be cheaper to maintain. Cheaper to maintain possibly, but not going to get except for major RD&D investment, at significant expense and over at least 5 years.

The building industry can only do things by calculation if there has been research to validate the calculation models. The cold-formed shed businesses are not putting in the RD&D they rely far too much on external consulting engineers. Engineers, who in many cases should stick to concrete, for they have inadequate knowledge of steel design, and don't put effort in to achieve necessary competence. Why would they, if they rarely get asked for such designs, because its mostly for standard calc's or variations to on an as needs basis every few years, if not long periods of 10 years or more: and then back to concrete design. Get the picture as to why the connections are not fully assessed, and thus can be demonstrated inadequate. Full engineering can push the others out off the industry, not necessary to drop price. More necessary to demonstrate have a quality product: both in terms of goods and services.

Back to Design for Assembly (DFA) issues. It would be inappropriate to price c-sections or any structural section soley on the basis of $/tonne of the raw material. The difference in price of a C25024 and a C15024 should not be merely the difference in weight. Australia's shed industry currently built around c-sections, rest of world largely built around tapered sections fabricated by welding plates. With tapered sections, typical structural form is a 3-pinned arch: the heaviest part of the section being at the knee. Alternative to welding up from plate, there is the option of cutting an approriate sized universal beam (UB) diagonally and then welding on additional flange plates to create tapered sections. From this approach, in very rough terms, can see that halving the amount of steel compared to using a constant size section: {eg. get 2 rafters from the one length of UB}. Similarly when using c-sections back to back to form I-sections, it is apparent that end frames have half the load width, and therefore only a single c-section is required for end frames. However, when making frames in UB, making the end frames from parallel flange channels (PFC) is a false economy. It introduces additional components, to be detailed, fabricated, handled and transported, and fitted into the production schedule, all for the sake of 2 frames in the over all structure. Further more at a future date the end frame causes problems with extension of the building: since now require a UB frame as no longer end frame but internal frame.

Now with tapered beams and c-sections, may consider that primary input is steel plate or steel coil strip so cost should be soley derived from a $/tonne rate for raw material. But not so, doing so is not realistic cost of supply. Looking at c-sections, manufacturers have a large variety of depth and thickness combinations. To provide this variety they need steel coils of differing thickness, and differing widths. If the raw steel strip coils, are say 2400mm wide, then the rollformer needs to slit these coils into widths suitable for each size of c-section, which may be based more on current demand than optimum layout for the coil. There will thus be waste narrow width of coil of no use to the rollformer. One way to achieve greater economy, is to buy coil already slit to the width required for the c-sections, the supplier of the coils has a different set of economies and can sell the narrow coil strips to businesses which do sheet metal work involving stamping and blanking.

Since C7510 is commonly used for girts and purlins, or more generically cladding rails, it is to be expected that this would have a relatively low price compared to C30030 which is rarely used. It is also to be noted that many of the rollformers only have a single production line. So to change from C7510 to C30030 requires shutting down the line, resetting the tooling, changing the feedstock, starting the rollforming with a lead strip which becomes waste. Due to the waste strip to get the processed started, it is preferable that once a coil is loaded it is entirely rollformed into section. But since part of the production process involves punching holes into the flat sheet, then rollforming into a section and cutting to required length: it is preferable than rollforming be to meet orders. If not too meet orders then can only rollform to typical production length of 12m, without any holes. Stock lengths of c-section have different economic order quantities (EOQ), than rollformed to order. So for example the thick rollformed Duragal channel (upto 8mm) is typically not economical for builders to use for beams in house renovations  because minimum order length of 6m from some suppliers is too expensive and a waste of material for the typical projects. Builders need suppliers who can supply lengths to order, for such suppliers the offcuts have markets.

A shed manufacturer rolllforming their own materials can achieve benefits by having at least 3 production lines:

1) Cladding Rails
2) Cladding
3) Main frame

Though cladding rails the same size as the main frame can have benefits, and thus reduce the number of production lines. There are benefits also to be had from plain channels which nest, and so can be used as top and bottom plates, studs, as well as splices for other members. Now changing from C25024 to C15024, is less of a burden than changing to C20019. The former only requires change in feedstock strip width, whilst the latter requires change in BMT and feedstock strip width. Additionally with respect to the main frame, changes in section size also require changes in the components required to fasten the frame together. Keep changing the size of section to meet the minimum structural requirement of the frame is not economical, not to mention it causes delays in supply.
One reason for using c-sections over UB's has to do with DFA. If use UB's then typically have cleats welded to the UB's to which the c-section girts and purlins bolted. If use c-sections, then the c-section frame is punched, and the cladding rails are bolted flange to flange with the main frame. The cleats are thus eliminated and the number of bolts reduced from 2 to 1, also bolt changed from being in shear to being in tension. Still further reduction can be achieved by using Tophat's for cladding rails: no pre-punching is required for these, they are fastened in place with self-drilling screws.

The greatest reduction of all is just to have the cladding: no frame, no girts, no purlins. This is the approach taken by USA buildings direct, which has a deep cladding profile, used to build arched buildings. Which appears to be a derivative of the Nissen and Quonset huts of World War II. Not sure how they put light fixtures and such in, without putting holes in the building fabric, but should be ways, not all that different than shell of a car, ship, or aircraft. Anyone, running around finding consulting engineers, to produce standard calc's for lighter shed structures, is not the way to innovate and compete. Engineers need to be on staff, and continuously assessing variations in design, take both end-product and production process into consideration.

Often automation requires heavier sections than manual operations, but the benefit is faster production and more consistent quality of product. Drilling holes manually is slow, and welding is preferable. But manual welding is a high skilled activity, so when the skill not available bolting is preferable. Hotrolled sections typically had to be drilled manually. The drilling was slow, however, cleat plates being small, easy to handle can be punched to form holes. More than that, cleats can be cropped to length and punched with holes in a single operation. So producing cleats and welding to a UB, is faster than drilling holes along the length of the UB for flange to flange bolting. But then rollformed sections came along, these can be punched with holes rapidly, so if suited for frames, can produce a steel framed building more rapidly than with hotrolled steel.  Though it should be noted that prior to hotrolled sections, the traditional way to produce an I-section, was from plate and angles, and lots of rivets: thus lots of rivet holes would have been required. Thus expect that where these riveted beams were being used that technology would develop for rapid production of holes, and so it is that automated beam lines would have taken their initial form. Today there are hi-tech CNC automated beam lines for drilling and welding of hotrolled sections and otherwise fabricating castellated sections and tapered sections. But I hazard that where c-sections are suitable, then c-sections would dominate the market sector. It should also be noted that c-sections typically fabricated from steel with yield strength of 450MPa, whilst hotrolled steel typical strength is 300MPa. Given we don't have mandatory deflection limits, the higher strength steel gives a lower weight structure than the hotrolled steel. If deflections are considered in design, then makes little difference because elastic modulus (E) is the same for both strengths of steel: and a section with appropriate second moment of area needs be found (inertia Ixx, Iyy).

Since deflections are not mandated, once again different designers can make different judgments about appropriate deflection limits and consequently will produce differing designs: one lighter than the other. But does this mean the lighter structure automatically costs less. The simple answer is no. The ligher structure likely to require more fabrication: tapered beams versus UB. If using C-sections, the lighter structure may require more frames placed at closer sections, it may require more flybracing, and it may require connection components not held in stock due to little demand for. Each and every manufacturer has to determine their own production economics, and not compare product to others on assumption of similar production costs.

If a manufacturer or supplier starts off using C150's then they want to get the maximum range of possible buildings from those C150's, so as not to require fabricating additional connection components for say C200's, or should they move into using say C250's? Where does the larger sector of the market lie, would they be better off introducing frames from C250 and having slightly oversized for some buidings, or introduce C200's and loose some projects because cannot accomodate?

We have the simplified wind loading code AS4055, due to economics of manufacturing. It is easier to produce windows and doors suited for wind class N1, than to mess around producing such products for a continuous spectrum of loading conditions. Its better to design for a step class of loading conditions, than a continuous spectrum. Similarly the residential slab and footing code is written around stepped classes, rather than a continuous spectrum. Sure if at the lower end of the class, then custom design may prove more economical on paper, but that doesn't mean that it is viable to get the materials or components. For example the span tables for wind class N1 and N2 are the same: this is largely because something other than wind loading is controlling member size. However, if at the lower end of wind class N2, it may be economical to get tie-down system designed for the AS1170.2 wind load, rather than for the wind class. But if choose to do that, then future attachment of a carport may be problematic, because won't have any reserve in the connections for the extra uplift from the attached carport. Cheaper now, problem in the future. And even if do this for tie-down, the off-the-shelf framing brackets which choose to use, likely to have some surplus capacity, since cannot get the calculated capacity exactly. Further the windows will still have to be N2, if want custom designed then they will be more expensive. Custom designed and custom manufacturerd costs more than stock standard off-the-shelf.

The reason people buy cold-formed sheds is because they want to avoid the delays of design, they want buildings which are already approved for purpose, and so development approval will be a simple matter, and fast. They also want the buildings supplied fast. Delays caused by not getting approval, by not having the right materials in stock, by not having the right designs available, all becomes an irritation to the buyer. The buyer could have gone to an architect and engineer in the first place, then shopped around to find a builder, and got prices on more or less the same thing from each builder. But they didn't because this industry, said it had buildings available, could organise development approval, and custom manufacture. Problem there: is no reference to custom design. Development approval just seen by suppliers as a need to supply a picture of intjention: scribble on an order form. As long as stick within constraints of their standard calc's not a problem, but they are sales people not technical people, they have no idea when they step outside the scope of their standard designs, they rely soley on council to request further information.

Put simply if not buying a shed to put garden lawnmower in, then get drawings produced by an independent party. Take these drawings to the shed producers, and get proper quotes. In first instance drawings don't have to be engineering drawings. The drawings just need detail to obtain planning consent. If planning consent obtained, then can consider requirements for building rules consent. If buying a shed still don't need engineering drawings, but do have to cover all the architectural building issues of the building code. Once got the architectural issues resolved then shop around for service and price. {Don't need building rules consent,just documentation with a high likelyhood of getting the consent without modification.}

If go direct to an engineer, then chances are they will not design anything which is available from any of the shed suppliers. Treat similar to housing. Get plans drawn up, then shop around builders. The builder choses a  timber supplier, and the timber supplier gets a timber estimator to do a materials take-off to the timber framing code (AS1684) or otherwise choose a truss manufacturer and they use software to size the truss members. Once a materials take-off is produced, it is submitted to council to obtain final development approval. All other BCA  issues have however been resolved before the timber framing is sized. Most shed manufacturers and suppliers do not build the shed, nor do they do any of the required siteworks such as carparks, stormwater drainage. So that low cost shed can suddenly become a pallet full of steel dumped on site, waiting for someone to build.

If shed supplier doesn't erect the steel work, they may recommend a builder, if they do so, then they are required to offer at least 3 names of builders. Now some suppliers, have the sheds built, using the services of one or more builders. This can be a cost absorbed in the overall price of the shed, or itemised. These suppliers are typically locked into steel erector fees based on $/sq.m some may base on $/tonne. I will hazard a guess that the original fees were based on $/tonne for hotrolled, but cold-formed steel is lighter construction, so converted original fee into $/sq.m rates. Costs and pricing are complex, at the very core is the need to make enough money for food, clothing and shelter, no matter how much work get. The firefighter has to maintain their skills and make a living whether fighting fires or not. Similarly the welder has to make a living, no matter how much welding work available. Therefore hourly rates are not something which can be fixed or locked in at higher values. Time is money, and selling time is nonsense.

If I modify the design of a shed so that the steel erector can construct more sheds in a year, it doesn't mean that they can win work to build more sheds, or that there are more sheds around to be built. If there is lower demand for sheds, it doesn't mean that the price will drop, the builders have less work to obtain their annual income from, the unit cost per shed will slowly increase, and the number of players in the market reduce. It is a complex juggling and balancing act.

But the building industry in particular seems focused on them over there are breaking the law, their products not up to spec, whilst my product over here twice as good as needs to be. Take them out off the industry. Its really technically inept, and plain nonsense. If product is truly better than the competition, then it will sell at significantly higher price. So if loosing sales to lower priced product, then as a supplier, you have little to no understanding of the real value of your product, nor the real needs of the customer.
Assuming customer is driven by price. {eg. they make $200 /year and after food, have $2 surplus at end of year. So buying a $2000 shed as a home, is a 1000 years of savings} Then the aspect of the price to tackle is not the magnitude, but the payment methods. If have to get a loan, then a higher price, means a larger mortgage and higher interest payments. Builders dealing with large volumes of money daily, therefore should get better deals on loans, and therefore potential to offer lower interest rates. The issue is also the total cost of the project, not just the cost of the building. Therefore need to assist the buyer to understand what the total costs are, so that they can negotiate with suppliers. With one supplier the shed may be a higher price, but the site works at a lower cost than another: yet the total costs for the two are the same. But is what the buyer is getting really the same.

Now if the buyer is driven by price and willing to spend time shopping around, are they also willing to spend time getting to understand the differences between products: to become informed and educated about the product. See the building industry in particular is based mostly on supposedly "secret" knowledge, and a lack of sharing, a lot of bluff. There is a fear of getting caught out, a fear of loosing advantage if others know what you are doing. Yet it is through an educated and informed market place that low quality suppliers are pushed from the market. Informed buyers don't buy based purely on price. However, quality and value are matters of individual perception, so sellers have to develop and build those perceptions.

The cold-formed shed industry basically competes on basis: my rubbish is cheaper than theirs, so buy my rubbish. No why would a surf life saving club, be buy a cheap shed to store thousands of dollars worth or life saving equipment? They would only do that because they didn't give any thought or consideration to their needs, and what would make the most suitable building. If buy a camera, a mobile phone, a car, a computer, then have technical specifications available to assist in making choices. If buy a shed or carport, no technical specifications, just silly brochures with pictures of buildings, not necessarily those built by the supplier. They do not supply technical specifications, because they don't have any. If they did have specifications, they would also consider it telling others what is required to start in the industry. Also there is no accounting for getting approval for one thing, and buying and installing something else.

But once again not always clear cut. There are accusations of selling rural sheds for suburban regions. Such may be so, but what is a rural shed? For the most part, rural sheds are designed to the farm structures code, which permitted a 20% over stress: but not on every rural shed, a shed had to meet specific criteria for that to apply. Buildings with large numbers of workers would not comply. Further just because a code of practice permits lighter structures, does that make economic sense to the individual

For a business, even though not required, it may well be beneficial to have buildings constructed for post-disaster level of importance. Then when a disaster happens, the business is first off the mark, supplying people again. Similarly will that cheap farm building, provide adequate protection to pigs and chickens? That million dollar thoroughbred horse, does it want to be stabled in a cheap shed?

The cost of a structure is not purely dependent on its weight, there is all the associated manufcaturing costs. Even if section size can be reduced, there is no particular reason to do so: as it decreases resistance, decreases durability and robustness, and reduces life expectancy of shed and increases risk of failure. basically it decreases its value.

Now if all supplier has to do is order c-section from rollformer, it may appear that cost of c-section is controlling issue. Still however, the different suppliers have differing over head costs, and the workers different expectations of lifestyle they wish to support. More sales staff, then probably more people sat around doing nothing failing to make sales: but still however needing a basic income to keep going. Further there is still the differing costs of the connection components used by different suppliers.

Even though ordering the c-section, rather than rolling in-house, there is still the economics of excessive variety and availability to consider. Set some standards, eliminate some customer choices, and put a larger volume of larger size c-sections through the rollformers facilities and get trade discount, because reduced the rollformers change over costs and the variety of coil strip they have to have on hand.

The more functions in the supply chain under the control of the one supplier, the more waste which can be removed from the process. So cannot reduce the cost of erection when locked into subcontract at $/sq.m, but bring in-house and the costing can be changed. Move more fabrication off-site and into factory, can implement more automation, faster production and still more unit cost reductions.

See! Personally I don't care that C20019 is adequate for a main frame, because I wouldn't want the frame unless it is 3mm thick or greater, but there is no C20030, so may settle for C20024. Then again walls of brick veneer houses are typically 240mm thick, so therefore a C25024 may be the preferred size to go with. Similarly wouldn't want C7510 girts and purlins, stick with C25024 installed between frames rather than to outer surface. Having chosen a larger section, wouldn't stick with typical 3m spacing, would increase this to limits of the C25024. That is having chosen C25024, design structure to suit.

Those C7510 cladding rails, were originally for fencing. They are relatively dismal sections, and can barely span the 3m spacing of typical frames. The result is that cladding is not installed at its maximum span. Cladding another issue of economics, for manufacturers are always trying to make deeper profiles which span greater distances, problem is they also have less coverage: so whilst have fewer cladding rails to install have more cladding sheets to install. Further greater distances between purlins (roof cladding rails) represents increased hazard working on the roof, either during construction or during future maintenance operations. Whilst for the walls, typicall window sill at 900mm and window head at 2100mm, so for typical small workshop/office need at least 4 girts (wall cladding rails, around the girth). For taller buildings, should girts match spacing of some expected future multiple storeys or mezzanines, or simply relate to maximum cladding spans.

Another issue when considering weight, this is Australia, not the USA, UK or Europe, the weight of snow crushing the building is not an issue. The critical loading condition is wind loading, uplift forces, if make the structure lighter, then have to find some other means of providing the weight to hold it down. The solution is usually a lot of concrete in the footings. Concrete may be cheaper than steel, but drilling the piers could be a problem. Also if floor slab to be installed some time after shed has been built then the weight of concrete in slab not available to assist building hold-down, so larger footing piers required at the beginning.

There are more than the structural mechanics issues to consider, to achieve a building structure which can be supplied at the right price, at the right time, in the right condition.

Clearly some of the larger players have better advertising and promotional campaigns than some of the other players, but they don't necessarily have better products. There is little point in smaller players competing with them across the full range of products. Smaller players need to find the right niche market, and out perform the bigger players in that market sector. For example win the larger buildings on the quality of both goods and service. Sure may still loose some on price, but that just means still haven't got the right product: the appropriate combination of goods and services, and still otherwise failed to educate the public.

Think small local retailer versus supermarket. The supermarket is going to beat the small local retailer on price, the small retailer therefore has to determine the right combination of goods and services that the supermarket cannot supply: specialisation. Rather than looking to compete, look at diversification. Problem with shed industry is everyone jumping on same bandwagon, everyone wanting a piece of the same pie. If seek diversity in the industry, then require innovation, and result is creation of a different pie to offer.

If have exactly the same product, then the cost difference would have to be your profit, wouldn't it? Now if the product varies, then what would the cost difference be? Want the public asking questions about the product, not the price. People can cost the materials retail, and then determine they can get the design done, and build themselves for less money. If that happens, then suppliers have got their product all wrong. Given we have a large DIY and owner-builder population, the building industry really needs to improve its product: goods and services.

Mon 2012-Oct-08  00:11

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