Ap

1 + KakrCul

DPc = loss of prestress at time composite topping slab is cast, excluding initial elastic loss Icomp. = moment of inertia of composite section ddf = deflection due to differential shrinkage and creep between precast section and composite topping slab

= Fycs12/8£cJcomp. for simply supported beams (for continuous beams, use the appropriate factor in the denominator)

e comp comp ycs = distance from centroid of composite section to centroid of slab topping F = force resulting from differential shrinkage and creep Ecc = modulus of composite section a = creep strain at time t divided by ultimate creep strain = t°-60/(10 + t0-60)

8.8.4 Long-Term Deflection of Composite Double-Tee Cracked Beam [2,5] 8.8.4.1 Example 8: Deflection Computation of a Double-Tee Beam

A 72-ft (21.9 m) span simply supported roof normal weight concrete double-T-beam (Figure 8.13) is subjected to a superimposed topping load WSD = 250 plf (3.65 kN/m) and a service live load WL = 280 plf (4.08 kN/m). Calculate the short-term (immediate) camber and deflection of this beam by (a) the Ie method and (b) the bilinear method as well as the time-dependent deflections after 2-in. topping is cast (30 days) and the final deflection (5 years), using the PCI multipliers method. Given prestress losses 18%.

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