Long-term deflection of high-strength fiber reinforced concrete beams

The paper presents an experimental and theoretical study on the influence o f steel fibers and longitudinal tension and compression reinforcements on i mmediate and long-term deflections of high-strength concrete beams of 85 MP a (12,300 psi) compressive, strength. Test results of eighteen beams subjec ted to sustained load for 180 days show that the deflection behavior depend s on the longitudinal tension and compression reinforcement ratios and fibe r content; excessive amount of compression reinforcement and fibers may hav e an unfavorable effect on the long-term deflections. The beams having the ACI Code's minimum longitudinal tension reinforcement showed much higher ti me-dependent deflection to immediate deflection ratio, when compared with t hat of the beams having about 50 percent of the balanced tension reinforcem ent. The results of theoretical analysis of tested beams and those of a par ametric study show that the influence of steel fibers in increasing the mom ent of inertia of cracked transformed sections is most pronounced in beams having small amount of longitudinal tension reinforcement.