An in-fill beam is a component in the floor framing system for an office buildin

Question

An in-fill beam is a component in the floor framing system for an office building. The spacing of the in-fill beams is 10 feet and the beam's span is 30 feet. The span is simply supported. The superimposed dead loading applied to the floor system is 60 psf. The superimposed live loading applied to the floor system is 100 psf. Assume the in-fill beam weighs 55 pounds per linear foot. Address the following to complete this problem: a.) Assume that load and resistance factor (LRFD) design is used. Compute the maximum factored bending moment (i.e. the required strength or demand) that the beam should be sized (or designed) for. Which AISC-LRFD loading combination controls? b.) Assume allowable strength design (ASD) is used. Determine the required moment strength (i.e. the demand) to be used for design. Which AISC-ASD loading combination controls?

Explanation / Answer

Triburatry width of beam = 10feet

Beam span = 30 feet

Superimposed dead load, SDL=60psf

Superimposed dead load on beam = 60*10 = 600plf

Live Load =100 psf

Live load on beam = 100*10 = 1000 plf

dead weight of beam = 55plf

a) Total dead load on beam = 600+55=655 plf =0.655klf

Total live load on beam = 1000 plf=1 klf

moment on beam at midspan due to dead load = 0.655*302/8 = 73.69 kip-ft

moment on beam at midspan due to live load = 1*302/8 = 112.5 kip-ft

Per LRFD,the govering design combination is 1.2DL+1.6LL

Required strength = (1.2*73.69)+(1.6*112.5) = 268.4kip-ft

b)Per ASD, the governing combination is DL+LL

Required strength = 73.69+112.5= 186.2kip-ft

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