Effect of post-yield stiffness of longitudinal reinforcements on the progressive collapse behavior of concrete beam-column sub-assemblages
Qin Weihong1,2 Liu Xinyu1,2 Hui Zhuo1,2 Xie Peng1,2 Huang Zhentao1,2
1. Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University,Nanjing 211189, China;
2. National Prestress Engineering Research Center, Southeast University, Nanjing 211189, China
Abstract：In order to study the effect of the post-yield stiffness of longitudinal reinforcements on the progressive collapse behavior of concrete frame structures after the failure of a middle column, the pseudo-static loading experiments on four specimens of one-half scaled beam-column sub-assemblages with two-span beam were carried out. Three specimens were reinforced by Steel-FRP Composite Bars(SFCBs)with different secondary stiffness ratios, while the control specimen was reinforced by ordinary steel bars for comparisons. The load/axial force-displacement curves, the failure modes, the strain development of longitudinal reinforcements and the capacity at each stage of SFCB specimens were analyzed and compared with those of the control specimen. Test results show that after the flexural action stage, SFCB specimens were under the secondary stiffness plus compressive arch action(SSCAA), which is significantly different from the compressive arch action of the control specimen. After the yielding of longitudinal reinforcements, the capacity of SFCB specimens at each stage was greatly enhanced compared with that of the control specimen. Based on the principle of virtual work, calculation formulas for capacity of SFCB specimens at the stage of flexural action and at the stage of SSCAA were established, and the theoretical calculation results agreed well with the test ones. The effect of secondary stiffness ratio of longitudinal reinforcements on the enhancement of the progressive collapse resistance of specimens was revealed by the theoretical formulas. Based on the above analysis, it was suggested that the maximum value of the secondary stiffness ratio of SFCBs should not exceed 0.30.
