CIVENG 3J04 Lecture Notes - Limit State Design, Structural Load, Progressive Collapse
6 Jun 2013
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Document Summary
There are three main reasons for including safety considerations in structural design: (cid:120) the strength of materials or structural components may be less than expected (cid:120) overloads may occur (cid:120) the consequences of failure may be very severe. There are two basic methods: (1) factor of safety or working stress design method. Factor of safety = (ultimate resistance/ service load) = r/s. This assumes that both resistance r and load s are well defined, but in fact both the resistance and load of structures vary. Each of these may not affect equally the strength of all types and sizes of members, but nevertheless they are there. The following histogram shows typical variation of the yield strength of structural steel with mean strength of 394. 4 mpa. Note that strengths as low as 338 and as high as 487 mpa are reported. Therefore, the use of the mean value does not ensure a safe design.
