Research On The Short-term Flexural Stiffness And Deflection Behavior Of GFRP-reinforced Concrete Beams

Based on the existing research achievements and broa d consensus at home and abroad, fiber reinforced polymer bars(FRP) can be applied to the new-built concrete structure reasonably instead of rusty steel bars, especially the bridge structure. However, FRP material has lower elastic modulus and no yield poi nt. Lower initial stiffness, larger deflections, wider cracks and brittle failure mode are presented in FRP reinforced concrete(RC) beams compared to concrete beams reinforced by steel bars. Thus, a series of problems about behavior at the serviceability limit state(SLS) and related mechanism of the FRP RC beams could not be ignored and need to be solved immediately.This paper focused on the flexural behavior of GFRP RC beams at SLS,three series of eight one-third scaled tests of concrete beams reinforce d GFRP bars were carried out. The datum, such as material stains, mid-span displacements, cracking width and depth, were measured at each loading stage, especially before 2 times the cracking load. Then the degree of stiffness degradation after cracking, deflection limit, crack width limit, and concrete stress limit at SLS were analysed selectively. In summary, mid-span deflection limit of l0/250 was the control parameter influencing serviceability of GFRP RC beams.Furthermore, the finite element(FE) soft ware, ABAQUS, and theoretical calculation models were adopted to simulate test models.The accuracy of established finite element models was validated with the comparison between FE and test datum. Based on this, further study about the influential factors, such as reinforcement ratios, concrete strength, cover thickness(the ratio between the effective depth and the gross depth), cross section types, rebar arrangement, on the flexural behavior of GFRP RC beams was carried out.Different theoretical calculation models were compared to test results. It was shown that, the guide for design and construction of concrete reinforced with FRP bars would bring out significant errors when it was used to predict the deflection and other performance of GFRP RC beams. B ased on the test datum, and consulted to related codes and recommendation s, this paper systematically analysed the factors determining the SLS, and proposed theoretical formula about SLS.