Abstract
The study aims to research the influence of salt fog corrosion cycles on seismic performance of reinforced concrete (RC) frame beam-column joints in coastal atmosphere. Based on low cyclic loading tests of six RC frame beam-column joint specimens, this study analyses the failure patterns, hysteresis loops, load carrying capacity, displacement, backbone curves, and energy dissipation capacity of corrosion-damaged RC frame beam-column joints. The effect of salt fog corrosion cycles and axial compression ratios are tested repeatedly. The results show that with the same level of axial compression of the frame joint specimens, as the increase of salt fog cycles, the strength, ductility, energy dissipation, bearing capacity, and deformation capacity of joints degenerated to different degrees． When the corrosion level is the same, the stiffness degradation appeared to be more apparent as the increase of axial compression ratio. Then, the behavior degeneration rule of the RC frame beam-column joints is analyzed and formed according to the results of the test; the degeneration restoring force models of corroded RC frame beam-column joints is formed and verified based on Clough’s three-line degenerate restoring force model and the introduction to cyclic degeneration index. The results show that the restoring force model can better describe the hysteresis characteristics of the beam-column joints of corroded RC frames. The research is a theoretical reference for the seismic analysis of the RC frame structure affected by coastal atmospheric environment.
Highlights
Reinforcement corrosion is the main cause of deterioration of reinforced concrete (RC) structures [1, 2]
Considering the limitation of the dimensions of the environmental chamber used in this study, the geometric reduction ratio of the joint specimen was 1 : 3. e main research parameters were the axial compression ratio and the degree of steel corrosion, and the design parameters of joint specimens are shown in Table 1. e joint specimens were 2.2 m long, 1.45 m high, and the cross-section of the beam was 150 × 250 mm2, the cross-section of the column was 200 × 200 mm2, the concrete strength grade was C30, the longitudinal bars of the beam-column members were all HRB335, and the stirrups were all HPB235
Six RC frame beam-column joint specimens were subjected to rapid artificial climate corrosion test in the coastal environment, and they were tested under lateral cyclic loads. e effects of cumulative mass loss rates and axial compression ratios on strength, ductility and energy dissipation capacity of beam-column joints were analyzed, and the restoring force model of corroded RC frame beamcolumn joints was studied. e following conclusions can be drawn from the test results: (1) For the RC frame beam-column joints, the corrosion of the stirrups was more severe than the longitudinal reinforcements
Summary
Reinforcement corrosion is the main cause of deterioration of RC structures [1, 2]. Longitudinal reinforcement corrosion will result in the decrease of effective cross-sectional area, the degradation of mechanical properties, and weakening the bond performance between the steel bar and the concrete [3]. Stirrups corrosion will reduce the restraint on the core concrete [4], which will deteriorate the performance of RC structures [5]. Because of the higher level of air humidity and chloride ion, the steel cumulative mass loss rate in coastal atmosphere is faster than that in the general atmosphere. Chloride ion erosion is the main cause of steel bars corrosion in coastal atmosphere [6]. China is a country with a long coastline and frequent earthquakes, and RC structures in coastal atmosphere are located in the earthquake regions as well
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