34 ft Curtain wall Determine the lightest sections of A36 steel required for typi- cal beams AB and AC in Figure 10-38. The dashed lines rep- resent bar joists 24 in. on center. The spandrel beams AC carry only a small strip of floor but must support a precast concrete curtain wall that is 13-ft high. The weight of the wall is 40 lb per square foot of elevation. The floor load is 70 psf live and 30 psf dead, including an allowance for all structural members. The live-load deflection of beam AB must be less than L/360. and the total load deflection of AC must be less than L/270. 34 ft 25 ft Figure 10-38 Portion of a bar joist floor system