Tuesday, October 09, 2012

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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