Evaluation of Effective Moment of Inertia for Calculation of Short-Term Deflections of Steel Fiber Reinforced Concrete Flexural Members

摘要

The effect of discontinued, randomly distributed steel fibers on the effective moment of inertia (I_e) of lightly reinforced flexural members is evaluated through the testing of three pairs of specimens under four-point bending. The specimens consisted of a simply supported, 3660 mm long, 254 mm deep, and 610 mm wide one-way slab strip. All slab specimens contained minimum flexural reinforcement according to the ACI 318-14 Building Code. The first pair featured regular concrete (no fibers), while the second and third pairs included steel fibers in a volume fraction (V_f) of 0.26% and 0.38%, respectively. Beyond cracking, a substantial drop in the flexural stiffness was noticed in all specimens. The slabs with fibers, however, exhibited stiffer post-cracking response compared to their regular concrete counterparts. At yielding, a well-distributed cracking pattern was noticed in all test slabs, with maximum cracks widths of approximately 0.5 mm. It was found that the equation proposed by Bischoff (2005) to estimate the effective moment of inertia for concrete beams fits well the experimental data of the fiber-reinforced concrete slabs, given that the stiffening factor is set equal to one.