To be able to validate that the critical design effect of actions is being used, the design effects arising from all possible load combinations have to be investigated as part of the design process. Example 4.8.1 is given to show the load cases that have to be investigated in the case of a simply supported beam subjected to a permanent and a variable action.

In the remaining examples, unless otherwise stated, only the load combination(s) giving the greatest design effects have been considered, and these have been based on the use of the fundamental combination (equation (2.13)) at the ULS and the characteristic combination (equation (2.24)) at the SLS.

Example 4.8.1 A simply supported rectangular beam in an office area is secured to a supporting structure at A and B as shown in Figure E4.8.1, and functions under service class 1 conditions. It is subjected to characteristic permanent loading, Gk = 0.6 kN/m, a characteristic medium duration variable load Qk>1 = 1.2 kN/M acting downwards and a characteristic instantaneous duration variable load (wind action) Qk 2 = 0.6 kN/m acting upwards. The associated strength modification factors for the beam material are £mod,perm = 0.60, £mod,med = 0.80 and £mod,inst = 1.1 respectively.

Determine the design load cases that will produce the design effect for

(a) the equilibrium ultimate limit states (ULS);

(b) for the strength ULS, i.e. bending, shear and bearing;

(c) the design effect for the instantaneous deflection of the beam at the serviceability limit state (SLS).

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