Many existing reinforced concrete buildings in developing countries located in seismic areas do not possess sufficient strength and ductility characteristics to resist the effects of severe earthquakes. Among other deficiencies, improper detailing of reinforcement and poor quality of materials are major causes of poor seismic performance. More specifically, inadequate lap splice lengths provided at floor levels on plain column longitudinal bars, particularly when concrete strength is low, is a widespread deficiency that has not been investigated in detail to date. Information on the behavior of such columns under earthquake actions is extremely important for reliable assessment of the seismic safety of many existing structures with detailing deficiencies and poor construction quality. In this study, the effect of lap splice length on the cyclic lateral load behavior of low-strength RC columns with plain longitudinal bars (14 mm diameter) was investigated experimentally. The specimens were designed to represent columns with low axial loads. The geometric ratio of the longitudinal reinforcement and the volumetric ratio of the lateral reinforcement of the columns are 1% and 0.8%, respectively. The test program included five RC columns with lap splice lengths of 25, 35, 44 and 55 times longitudinal bar diameter, as well as a reference specimen with continuous longitudinal bars. Test results clearly demonstrated that presence of 180-degree hooks at the ends of the lap splice reduces the negative influence of the inadequate lap splice length on RC member performance, even in the case of low-strength concrete. All specimens reached their flexural strengths and did not experience considerable strength degradation until large drift levels. Test observations were supported with findings of a fiber-based analytical model, which also demonstrated the influence of hooks on improving the bond slip behavior along inadequate lap splices.
The present study investigates elastic buckling behavior of open-section shell segments under action of a central radial load. A design parameter is expressed to characterize the influence of fillet radius on load-bearing capacity. A reduction factor equation is developed as a multivariate function of shell parameters, which evaluates the amount of decrease in load-bearing capacity of the structure caused by the corner fillet. In addition, an expression to predict limit load of the shell structure under clamped end conditions is introduced. Furthermore, a parametric study is performed to reveal the influence of fillet radius and radius-to-thickness ratio on the limit load as well as deformation patterns of the open-section shells. Results show that corner fillets have a significant effect on the limit load of the open-section shell segments under in-plane loading.
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