Seismic Behavior of R/C Beam Using High Strength Longitudinal Rebar

Abstract eng:
Recently, many high-rise Reinforced Concrete buildings are built using high strength materials in Japan. The combination of high strength concrete and high strength rebars is a good match for seismic members. However, middle rise reinforced concrete buildings are constructed using concrete with strength in the range of 21 to 60N/mm2, and rebars with yield strength between 350 and 500N/mm2. To conduct research to use combined high strength rebars and normal strength concrete, it is important to rationalize reinforcing bar work on middle rise reinforced concrete buildings. But few experiments have been conducted to confirm the seismic behavior obtained by combining rebars with yield strength of about 600N/mm2 and concrete with strength between 21 and 60N/mm2. Therefore, a total of 13 beam specimens were tested to evaluate the seismic capacities and the design method. The specimens are 1/2 scaled beams. The beams were subjected to anti-symmetrical reversal loads as seismic motion of a frame structure. As common parameters, the section shape was 300mm*400mm at 1/2 scale and the shear span ratio was 2.5, and the main bars used were rebars with yield strength ranging from 628 to 640N/mm2. The failure mode of the beam members was varied and planned for concrete strength from 21 to 60N/mm2. The actual strength of the concrete was 22.5N/mm2 for Fc21, 38.7N/mm2 for Fc36, and 64.9N/mm2 for Fc60. The test confirmed the load-bearing capacity during bending failure, shear failure and bond-splitting failure. This experiment also revealed that the load-bearing capacity equations induced by many past research projects are effective. The strength equations of several failure are verified by this test and by past studies. The skeleton curve for seismic design using these testing data is proposed. The skeleton curve is composed of initial stiffness, a degrading ratio after cracking and yield strength. The degrading ratio for beams using high strength longitudinal rebars is newly proposed by this paper. Not only a test, but also an analytical study was carried out to grasp the detailed behavior of beams. The design method including its criteria and structural capacity can be proposed for use for design of low or middle rise R/C buildings in an earthquake-prone country.

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