Experimental and analytical studies on the seismic behavior of reinforced concrete columns with light transverse reinforcement

Abstract

Structures made up of reinforced concrete columns with light transverse reinforcement are very common in a region of low to moderate seismicity, and are the predominant structural system in Singapore. Recent post-earthquake investigations have indicated that extensive damage in reinforced concrete columns with light transverse reinforcement occurs due to excessive shear deformation that subsequently leads to shear failure, axial failure and eventually full collapse of the structures. Therefore, a thorough evaluation of reinforced concrete columns with light transverse reinforcement is needed to understand the seismic behavior of these structures. For this purpose, an experimental program carried out on reinforced concrete columns with light transverse reinforcement subjected to seismic loading is conducted. Ten 1/2-scale reinforced concrete columns with light transverse reinforcement are tested to investigate the seismic behavior of these columns. The variables in the test specimens include column axial loads, aspect ratios, and cross sectional shapes. The specimens are tested to the point of axial failure under a combination of a constant axial load and quasi-static cyclic loadings to simulate earthquake actions. Experimental results obtained include hysteretic responses, cracking patterns, strains in reinforcing bars, displacement decomposition and cumulative energy dissipation. Next, an analytical approach, coupling flexure and shear deformations, is proposed to evaluate the initial stiffness of reinforced concrete columns subjected to seismic loading. A comprehensive parametric study is carried out based on the proposed approach to investigate the influences of several critical parameters. A simple equation is then proposed to estimate the initial stiffness of reinforced concrete columns. The applicability and accuracy of the proposed approach and equation are verified with the experimental data obtained from the current experimental program and studies in the literature.

Study of the residual axial capacities of shear-damaged reinforced concrete columns: Part 1—development of an evaluation model

“…Post-earthquake reconnaissance surveys indicate that the reinforced concrete (RC) columns of old buildings are often vulnerable to shear failure during earthquakes. Based on previous studies (Matsukawa, 2013; Nakamura and Yoshimura, 2002; Ousalem, 2006; Tran, 2010; Uchida and Uezono, 2003), the consensus is that shear failure can deteriorate both the horizontal and axial capacities of RC columns. If the axial load of a shear-damaged RC column with a significantly deteriorated axial capacity cannot be distributed to the neighboring columns by the surrounding beams and slabs, axial collapse may occur.…”

“…For RC buildings with earthquake-induced damage, several evaluation models have been proposed based on theory or experimental analysis to estimate the residual axial capacities of shear-damaged columns. These evaluation models can be divided into the following three types: (1) theoretical models (Elwood and Moehle, 2005; Matsukawa, 2013; Ousalem, 2006; Tran, 2010; Uchida and Uezono, 2003); (2) semi-empirical models (Kato et al, 2008; Nakamura and Yoshimura, 2002); and (3) empirical models (Japan Building Disaster Prevention Association (JBDPA), 2005). However, the residual axial capacities of RC frames have not yet been sufficiently studied, and the related previous studies are very limited (Elwood and Moehle, 2008; Ghannoum and Moehle, 2012; Murray and Sasani, 2017).…”

Study of the residual axial capacities of shear-damaged reinforced concrete columns: Part 2—experimental verification of an evaluation model

“…In previous studies, several evaluation models have been proposed to evaluate the residual axial capacities of the columns. These models can be divided into three types: (1) theoretical models (Elwood and Moehle, 2005; Matsukawa, 2013; Ousalem, 2006; Tran, 2010; Uchida and Uezono, 2003); (2) semi-empirical models (Kato et al, 2008; Nakamura and Yoshimura, 2002) and (3) empirical models (Japan Building Disaster Prevention Association (JBDPA), 2005).…”

Seismic assessment of existing reinforced concrete columns

“…Compar. ing with the case of columns with deformed rebars in Tran's tests (2010i19 ) and Tran and Li ' s tests,< 34 ) strain at different locations of longitudinal rebars in the column with plain rebars did not vary significantly as in columns with deformed rebars.…”

“…Five specimens in this study were designed to be similar to columns with deformed rebars in Tran ' s tests< 19 ) The comparisons also showed that for short columns (all specimens with shear span to depth ratios of 1.7) deformed reinforcement did not produce higher initial stiffness. The reason was because the flexural cracks occurred in columns with deformed rebars reducing its initial stiffness gradually.…”