Sunday, April 28, 2013

Proposal For National Structural Code

Past experience and recent projects have now convinced me that we need a national structural code and/or a national technology code. A structural code could be the starting point with a technology code coming later. The technology code would capture all technology, everything artificial, everything done in and to the natural environment. But for now just consider the structural code.

The Australian Building Codes Board (ABCB) would like the Building Code of Australia (BCA) or now National Construction Code (NCC) to be the single point of reference for everything in the built environment. I don't believe this is appropriate. The BCA is fundamentally about habitable buildings, and in the main the performance criteria are for spaces not for the fabric of the building: the BCA has very little about buildings. Which as a point suggests the BCA is equally applicable to an open work space. Anycase, anything which is not a habitable building is classified as a class 10 building. If a building is class 10, then BCA requirements are found in BCA volume 2. Now BCA volume 2 is little more than a prescriptive solution for housing, and contains fewer performance criteria than BCA volume 1 2.

Personally I think BCA volume 2 should be scrapped and class 1 and 10 buildings put back in BCA volume 1. BCA volume 2 should have never been published, its a bad idea. In South Australia we had an SA Housing Code, this was described as a deemed to satisfy solution to the BCA as it was. That approach should have been retained. Whilst builders didn't like the BCA because it was performance based and didn't tell them what to do, they also didn't like that they couldn't try alternative technologies with the prior prescriptive codes.

BCA volume 2, should have been presented as a code compliant design solution, using brick veneer and timber framing. It should have set the bench mark for the presentation and publication of code compliant design solutions. Starting with adequate evidence-of-suitability for the construction methodology: the prescriptive solution in BCA volume 2, is not adequately proven suitable for purpose, and alternative technologies like rammed earth, straw bale, SIP's, plaster wall panels have to be demonstrated far more thoruoghly than the accepted traditional technologies. More importantly alternative technologies have to be demonstrated compliant with all kinds of rubbish the authorities pull out off a hat: I reiterate the BCA contains next to nothing regarding the characteristics of the building fabric. If starting from scratch brick and timber likely considered relatively stupid materials for constructing something as important as a home: bricks soak up water and timber gets eaten by termites: rubbish materials. BCA volume 2 should not have been part of the BCA, it should have been something else.

Now the SA Development Act and Regulations are not concerned with buildings, but concerned with modifications and changes to the use of land. After some exclusions for government authorities and use of crown lands, it starts referring to building works. Such building works need to be assessed against the building rules and the BCA is called up as part of the building rules. The building works contractors act is also concerned with building works. The building works contractors act is primarily concerned with housing. The industry concerned in all cases is the building and construction industry. Whilst may refer to the building of a bridge, a bridge is not considered a building, and is part of the construction sector not the building sector of the industry. How the design and construction of bridges is controlled I don't know, and the areas of jurisdiction start to blur depending on where a bridge is located or on what is considered to be a bridge. For example when is a foot bridge an industrial walkway? Does the footbridge have to be outside or does it refer to public space inside a large shopping centre? Small bridges and culverts on private property, what governs these? Sure we have a national bridge code, but it primarily relates to highways and railways? I doubt the code includes swinging canals.

So have two major codes for the built environment, the BCA and the bridge code. For the most part however building works are captured by the Development Act and go into the local city/district council for development approval. This therefore means initial review is against the Building Rules and that basically means the BCA, and if the building works do not relate to a habitable building then it means BCA volume 2 the presciptive solution for housing. A bridge is not a habitable building, it is therefore a class 10 building and governed by BCA volume 2, a prescriptive solution for housing. Common sense may prevail, however the law is not about common sense, it is about what is written and what is intended. For highway and railway bridges its obvious that the bridge code should control. Further more unlikely to be placed into council for development approval as design most likely placed out to tender by the approving authority in the first instance.

But bridges are not the only structure which are not habitable buildings. So if the BCA is the single point of entry for the built environment then the following are class 10 buildings governed by a prescriptive solution for housing:

1) Dam
2) Tall radio mast
3) Water tank
4) Silo's, Bins and Bunkers
5) Fixed Gantry Cranes
6) Industrial Chimneys
7) Oil refinery
8) Power Station
9) Large scale solar array
10) Wind turbine
11) Earth Retaining Structures and Coastal defence structures
12) Advertising Signs
13) Sports Safety nets
14) Agricultural Buildings/Shelters
15) Radar Dish
16) Large Scale Optical Telescope
17) Large open air machine and electrical systems

The above are all well beyond the scope of the BCA, and absolutely beyond the scope of BCA volume 2. Such are also way beyond the capabilities of building surveyors. Yet all likely to fall within the scope of the Development Act and require assessment against the building rules by building surveyors.

From a structural viewpoint the BCA is an expensive pile of scrap paper. The ABCB deliberately removed the annual probability of exceedance from AS1170 loading code and placed in the BCA, so that structural engineers would have to look at the BCA. But only need the page with the annual probability of exceedance, the rest of the structural provisions is a long list of Australian standards. Builders and plan drafters may never read standards, but engineers and similar use the standards catalogue as a major source of reference. No matter what is being designed, Australian standards are reviewed to find community expectations of standards of performance. The standards catalogue contains far more than the BCA, the BCA is nothing. Sure the BCA contains options for fire rated construction, but such is primarily an architectural design issue, not a structural issue. The architect primarily decides the materials and form of construction when it comes to habitable buildings, not the engineers. If owner and architect choose a particular set of conditions then the BCA may impose concrete construction: but it is within the scope of the architect and owner to change the conditions and avoid the concrete, and do so without the assistance of an engineer. If they insist on a particular path, and oppose the use of concrete then may be able to employ the services of a "fire engineer" and enable alternative materials such as steel cladding on steel framework to be used. But such is generally a BCA alternative solution, and really beyond the scope of the BCA to provide guidance.

The BCA is something of a joke, and extremely dangerous to be called up in legislation and imposed by law. The wording and language in the BCA is wrong. Alternative solutions are near impossible, as the BCA assessment methods basically discard the performance requirements and replace with deemed-to-satisfy provisions. Deemed-to-satisfy provisions can be inadequate and fail to satisfy performance requirements. Things beyond the scope of the BCA are squeezed within its scope by regulating authorities who have less than the necessary competence to perform their assessment role properly across the full range of building works which they may encounter.

As I indicated in earlier post the steel structures code AS4100 does not cover torsion, nor does it cover the design of connections: in particular it does not cover the localised bending and buckling of plates in the vicinity of the connections. This is not entirely a problem because there are industry manuals which cover the deficiencies. The problem is that the BCA is called up by legilsation, and it in turn calls up AS4100: thus AS4100 is considered law and mandatory, whilst the industry manuals are not. More over I have worked on contract as a structural drafter, and the supervising engineers were not aware of the manuals I was using to detail steel work connections. On the otherhand I know next to zip about concrete, then again I do know there are issues regarding detailing steel reinforcement: like got to be able to get concrete around it otherwise its not reinforced concrete its just a steel cage. Once again the engineers don't check these things and are unaware of the available industry manuals. Whilst I may prefer the CSI Steel designers manual, I am otherwise referring to Australian publications like the Steel Designers Handbook by Gorenc and Tinyou. Then again I don't really need the ASI to translate American and Eurocodes into an Australian approach for connection design: not the least of which is the ASI is too slow.

Part of the issue is what to include in the codes. For example AS4100 does not state how to calculate the bending moment in a beam. It has some guidelines for use of linear elastic analysis, use of moment amplification factors, non-linear analysis and plastic design. But the basic purpose of AS4100 is to define the maximum resistance which can be used to compare against the calculated bending moment. By the same token therefore would not expect it to define how to calculate the stresses in the plate elements of a connection. The problem is that it is not always clear cut, the division between applied stress and available resistance. In such situations empirical formula may give plate thickness directly, and there is no way to derive such formula from geometry: just have to go repeat the experiments to validate the formula: and no one working in an office is going to go do that.

Other issues to consider are:

1) Consistency (materials codes are clearly biased by politics and economics of industry sectors)
2) Repetition
3) Completeness

The loading code AS1170 series of standards presents an incomplete picture to practising engineers, and is expensive. Compare cost of wind loading code AS1170.2 excluding commentary to the American ASCE7-05 which covers all loading situations and full commentary. It is said that snow loading is little relevance to most Australian engineers, so keeping it separate keeps costs down. No it doesn't, it increases costs, as there are extra covers and other repetitive sheets forming it into a separate yet connected publication. Combining all of AS1170 into a single code would put all loading requirements into the hands of all structural engineers, giving them plenty of opportunity to study and learn the codes before they bump into need to use and have to rush out and get other portion of loading code.

But cannot do this because each portion is managed by a different Australian Standards committee. Which then becomes another issue: the codes are revised at different dates. Thus for example, the earthquake code was slow to be converted to limit state format. And another example is tests carried out to AS1170.2:1989 wind loading code against criteria in the BCA rather than to the current version of AS1170.2:2011.

It is also clear that AS1170.2 is for buildings, everything else is an after thought thrown into the appendices. Yet everyone blindly states, their product no matter what it is has to be designed to comply with AS1170.2 wind loading. Even if dealing with buildings there are large gaps in AS1170.2 tables, so not all buildings are within its scope. Generally however it is considered impractical to carry out wind tunnel tests for small residential structures to fill in the gaps, and a lot of judgement calls are made. But this can lead to inconsistency or a hard time with regulators who are not able to make decisions for themselves.  So something is required to fill in gaps in the loading code, such as at present the lack of information for solar panel installations mounted on roof tops (buildings and canopies).

The materials codes do not follow a consistent set of guidelines, so its not so much a question of learning mechanics but learning the style of an industry sector. The steel structures code AS4100 and cold-formed steel structures code AS4600 have different but similar approaches: why? One uses alpha-m , the other uses Cb, why the difference? One (AS4100) uses moment amplification and makes a big thing out of it and causes confusion, the other AS4600 hides it in the clauses for checking member capacity? The aluminium structures code AS1664 uses similar approach for effective section modulus to AS4600, yet it is lost in the midst of the code. The aluminium structures code calculates limiting stresses whilst all other codes calculate resistances, this is stated because mechanical use aswell as structural. This is a poor excuse, as resistances are just as useful to mechanical, and AS4600 calculates limiting stresses but converts into resistances. Mean while the timber structures code AS1720, as another approach to lateral stability again, and whilst it calculates resistances it doesn't differentiate between section capacity and member capacity as the other codes do, the result is that it calculates member capacities, and then in combined action expressions multiplies by factors to basically undo the member capacity calculations and produce section capacities. The equations would be simpler if section capacities were calculated first. Further when timber structures code changed to limit state, it retained the 30% overstress on wind loading, it should have removed this. Such over stress wasn't removed until AS1170.2 was further revised and regional wind speeds were reduced. AS1720 also uses the capacity reduction factor to take another bite off importance factor. It calculates capacities of joints rather than allowing assessment of the individual components of a connection. It presents some concepts which can be misleading and therefore hazardous if applied incorrectly. I really dislike its presentation of double shear, and in general the code seems incomplete and thrown together.

Most of these codes can be replaced by a single code, with different materials properties, instead of being aligned with the traditional practice of a given industry. Further all the codes could then be updated at once. All these committes for different codes is silly. Australia just doesn't have the population to waste on such nonsense. This is reflected in the slow update of some codes, apparently 30 years lapsing for some codes before revised.

The significant overlap between all the materials codes is one example of repetition as well as inconsistency. The timber framing code AS1684.1, the metal framing code AS 3623, and NASH specification for steel framed housing are all unnecessary. Basically all these codes present a set of rules for the design of individual structural elements of pinned and braced building structures. Incomplete rules, for there is a lack of information to assess the ceiling diaphragm and/or floor diaphragms on which the structures depend. Once again its industry politics, timber versus steel. Its a waste, especially for designers, who have to go get each of these different codes and waste their time becoming familar with, and making reference to, when could otherwise simply get on with using the loading code.

If design something to timber structures code AS170, then there is need to compare against AS1684 span tables. Then question why are AS1684 members so large, or why so small, why don't my calculations come out the same. The members in AS1684 in some situations are larger because they check serviceability requirements not otherwise mandated, or otherwise use extreme value loads for a range of suitable situations: there is some conservatism in there to allow for the breadth of use of the span tables. Other situations using AS1720 get larger members because AS1684 has thrown in fudge factors to share and distrubute loads, they have declared superior testing of timber taking place and material strengths are higher than in AS1720, over stress permitted not otherwise considered, and axial forces fundamental to the function of the structural forms in AS1684 are ignored. So members selected from AS1684 span tables not fully compliant with AS1720. But the approach taken by AS1684 is an acceptable one, and if acceptable for timber then why not other materials. The inefficient answer to that is to write similar codes for other materials hence AS3623, and its replacement NASH specification for steel framing for housing. All lacking a bigger picture.

At its simplest a structural code would merely take the BCA structural provisions, and then have the BCA refer to the structural code. However the structural code is for all structures not just habitable buildings. So the national structural code (NSC) would have to also reference:

1) BCA
2) The bridge code
3) Crane Code
4) Industry guides for Bins and Silos
5) Standards for light poles
6) Standards for lattice towers
7) Other Australian Standards and or industry manuals.

Where Australian standards not available, then reference would be to ISO, Euro, British, American codes with order of preference given and where possible the actual codes called up. The code would also identify shortfalls and the need for further research, this can be given in an informative appendix.

Most importantly the code would capture all structural forms and give basic guidelines and simplifications permitted for various categories of structures, and make explicit common practices such as allowing 10% overstress.

The code would also identify accepted reference manual, and classic texts and papers which form the basis of structural mechanics and structural design. For example designing a water storage tank using finite element method (FEM) may be considerd unacceptable if there is industry manual on storage tank design. It seems to be an increasingly common practice to simply accept FEM as giving the right answer. When I was studying FEM was considered to be far from the right answer, having an error of 20% or more, and only to be used as a design guide, with it being absolutely necessary to build and test prototypes to validate and calibrate the FEM model. But FEM is being used for massive one-off structures on assumption of model being valid: bad practice.

Engineering takes place at the frontiers of science and technology. Civil, structural and mechanical disciplines are not operating at the frontiers, the technologies they deal with are parametric variations of well established technologies. Placing something inferior into the built environment is not acceptable. Somebody somewhere has typically worked it all out before.

Tall industrial chimney stacks getting over stressed due to wind excitation not acceptable, but do we have any guidelines available? Sure I have some historical documentation from the UK, but does Australia have any current documentation? If cannot find an Australian standard is there some obscure industry association? There is no point some specialist coming out off the woodwork after a chimney collapses and makes national and international news.

We need one point of reference for structural design. Want to design a sail shade, then these are the reference papers which should be used. Designing as a cable-net and tension membrane too complex, then this is the simplified approach permitted if sail shade lies with in a given set of constraints.

The requirements for becoming a competent structural designer all outlined in the structural code, these are the topics, the papers and reference manuals should be familiar with. And it doesn't involve getting a master of business administration (MBA) and becoming a chartered executive engineer: it requires competence in structures not accounting.

It is a code because it is to be sustained and maintained on a regular basis, it is to be kept upto date, by guardians of the knowledge. The code can also list in appendices, acceptable software, such software does not have to be used, but such software is used as a point of reference. Criteria for testing and approving software can be given. Also of extreme importance is identifying national experts in various areas of practice and with respect to various structural forms. These national experts need connecting to a long chain of future successors. Who replaces Trahair for hotrolled steel, Hancock for cold-formed steel and Holmes for wind loading?

We primarily have regulations because someone figured there was a shortfall, not because that somebody knew the answer. Good regulations capture everything and have generic rules which lead to specifics. Poor codes have specifics, impose themselves on everything and pose a greater hazard than having no code at all.

The Building Code of Australia (BCA) makes a poor National Structural Code. The BCA should reference an all encompassing structural code. And both of these should be referenced by an even more all encompassing technology code: fusiion, genetics, nanomachines, space exploration. What are the constraints on research and testing? For these technologies even the testing of prototypes poses a hazard to the greater community.

It seems that there are many so called engineers who don't understand the fundamentals of their role, and they are simply code pushers, and have no grasp of the concept of design. Large numbers of so called civil engineers especially, are capable of little more than pushing numbers through codes of practice and saying yes complies? If not in the code they don't check it, or even think about it.

A comprehensive structural code will highlight that their continuing professional development (CPD) has been rubbish, that they don't know very much and not operating at the level of engineer, and barely operating at the level of engineering associate. The code will define a basic methodolgy to the approach of design and evaluation of design proposals.

It should also be noted that the existing regulations generate far too much scrap paper. So guidelines are also required for the presentation of calculations, suitability of certificates, and methods for providing rapid and efficient assessments and approvals of common structural forms. We should not be hampered by the past tradition of working calculations out with pencil and paper automatically producing documentation. People seem to go out of their way to find mathematical type set like packages to achieve such presentations and largely there is little value, and all they do is produce more scrap paper. Calculations are a means to an end, not an end in themselves. So whilst a calculation needs doing it doesn't necessarily need presenting some where.

Also those checking calculations are not performing their proper role, their task is independent assessment of the proposal. The proposal is shown on drawings not calculations: and independent means with out influence and guidance of the design calculations. So the approving authority doesn't need any calculations, and assessment is faster and easier than finding a design-solution. Assessing existing construction however takes longer and is more complex than design: this is because most illegal construction also deviates from the validated mathematical models, and testing cannot be carried out. Basically assessing stuff people have built without approval is frustrating. That aside, if have a design proposal which has been designed, not just dumped on paper, then assessing compliance with a code should be relatively easy if have the appropriate tools. The problem as indicated in previous blogs, is people putting effort into developing tools appropriate to their job. The lack of appropriate tools results in inconsistencies between similar projects and unnecessary amounts of time expended on the project.

So I see what I can do about setting up a Blog to start an open source structural code.