The estimation of the initial stiffness of columns subjected to seismic loadings has long been a matter of considerable uncertainty. This paper reports a study that is devoted to addressing this uncertainty by developing a rational method to determine the initial stiffness of RC columns when subjected to seismic loads. A comprehensive parametric study based on a proposed method is initially carried out to investigate the influences of several critical parameters. A simple equation is then proposed to estimate the initial stiffness of RC columns. The applicability and accuracy of the proposed method and equation are then verified with the experimental data obtained from literature studies.

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.

Six full-scale nonseismically detailed reinforced concrete interior beam-wide column joints were tested to investigate the seismic behavior of the joints. Axial compression loads varying from zero to high magnitude, as well as quasi-static cyclic loading simulating earthquake actions were applied. The overall performance of each test assembly was examined in terms of lateral load capacity, drift, stiffness, energy dissipation capacity, and joint shear strength. Three levels of axial compressive column load were investigated to determine how this variable might influence the performance of the joint. The tests also explored the effects of centerline eccentricity on the performance of interior beam-wide column joints subjected to earthquake loading. All the specimens failed at the joint panel with gradual strength deterioration, low attainment of structural stiffness, and bond degradation. The low attainment of stiffness and strength was attributed to the bond deterioration of the longitudinal bars through the joint core. It is concluded that special reinforced concrete interior beam-wide column joints with nonseismic design and detailing, could possess the inherent ductility for an adequate response to unexpected moderate earthquakes.

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