Earthquake engineering research and development have received much attention since the fi rst half of the twentieth century. This valuable research presented a huge step forward in understanding earthquake hazard mitigation, which resulted in appreciable reduction of the effects of past earthquakes. Nevertheless, the 2011 Tohoku earthquake and the subsequent tsunami resulted in major damage. This paper presents the timeline of earthquake mitigation and recovery, as seen by the authors. Possible research directions where the authors think that many open questions still remain are identifi ed. These are primarily based on the important lessons learned from the 2011 Tohoku earthquake.
A steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcing rebar made of an inner steel bar and outer FRP integrated in a pultrusion process. To promote the application of this new reinforcing rebar, this paper explores the mechanical properties of SFCBs and the performance of SFCB-reinforced concrete structures. Test results of SFCBs under uniaxial and cyclic tensile loading show that SFCB has a high elastic modulus, a stable post-yield modulus and a high ultimate strength. The tensile characteristics of SFCBs calculated according to the mixture law are found to be in good agreement with test results. A direct pullout test between SFCBs and concrete was conducted. The failure modes included SFCB pullout before or after inner steel bar yielded, which depended on factors like the steel/FRP ratio, effective bond length, and concrete strength. With its high-performance, especially with regard to anti-corrosion, and low cost, SFCBs are an ideal near-surface mounted (NSM) material to strengthen concrete beams. Experimental results show that NSM-SFCB strengthening can significantly increase both the section stiffness of the flexural members in the service stage and the bearing capacity in the ultimate stage. Concrete columns reinforced by SFCBs under horizontal cyclic loading were also tested, and the results show that concrete columns reinforced by SFCBs possess high initial stiffness, acceptable bearing capacity and good ductility. More importantly, SFCB columns had an obvious post-yield stiffness, which resulted in smaller residual displacement and, therefore, better post-earthquake reparability.
This article presents an experimental study on concrete beams strengthened with NSM reinforcements under monotonic static loading. The NSM reinforcements include commonly used steel bars, CFRP bars, and four different types of SFCBs. The main parameters of SFCBs considered in this study have been the types of FRP used (CFRP and basalt FRP) and steel/FRP ratio. The results show that (1) the stiffness during the elastic stage and the load capacity at the ultimate state of concrete beams strengthened with NSM-SFCB could be enhanced significantly; (2) the failure modes of the two concrete beams were as follows: the concrete beam strengthened with ordinary steel bar crushed after the steel bar yielded, while the beam strengthened with CFRP bar demonstrated a debonding of concrete cover on the beam soffit without any crushing of the concrete in the compression zone; (3) the steel/FRP ratio is of vital importance for the performance of beams strengthened with NSM-SFCBs. For SFCB with a high FRP/steel ratio, debonding of the concrete cover occurred after the yielding of the SFCB inner steel bars, while for beams strengthened with NSM SFCB with lower FRP/steel ratio, concrete crushing occurred after the rupture of the SFCB outer FRP; (4) compared with NSM-CFRP bars, NSM-SFCB can achieve the same anticorrosion properties at a much lower cost, which makes SFCB a competitive material for NSM strengthening of concrete structures.
The factory-produced steel-fiber reinforced polymer composite bar (SFCB) is a new kind of reinforcement for concrete structures. The manufacturing technology of SFCB is presented based on a large number of handmade specimens. The calculated stress-strain curves of ordinary steel bar and SFCB under repeated tensile loading agree well with the corresponding experimental results. The energy-dissipation capacity and residual strain of both steel bar and SFCB were analyzed. Based on the good simulation results of ordinary steel bar and FRP bar under compressive loading, the compressive behavior of SFCB under monotonic loading was studied using the principle of equivalent flexural rigidity. There are three failure modes of SFCB under compressive loading: elastic buckling, postyield buckling, and no buckling (ultimate compressive strength is reached). The increase in the postyield stiffness of SFCB rsf can delay the postyield buckling of SFCB with a large length-to-diameter ratio, and an empirical equation for the relationship between the postbuckling stress and rsf is suggested, which can be used for the design of concrete structures reinforced by SFCB to consider the effect of reinforcement buckling.
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