With the aim to model the seismic behavior of steel reinforced concrete (SRC) frame columns, in this research, hysteresis and skeleton curves were obtained based on the damage test results of SRC frame columns under low cyclic repeat loading and the hysteretic behavior of the frame columns was further analyzed. Then, the skeleton curve and hysteresis loops were further simplified. The simplified skeleton curve model was obtained through the corresponding feature points obtained by mechanical and regression analysis. The nonlinear combination seismic damage index, which was developed by the test results and can well reflect the effect of the loading path and the number of loading cycle of SRC frame columns, was used to establish the cyclic degradation index. The strength and stiffness degradation rule of the SRC frame columns was analyzed further by considering the effect of the accumulated damage caused by an earthquake. Finally, the hysteresis model of the SRC frame columns was established, and the specific hysteresis rules were given. The validity of the developed hysteresis model was verified by e comparison between the calculated results and the test results. The results showed that the model could describe the hysteresis characteristics of the SRC frame columns under cyclic loading and provide guidance for the elastoplastic time-history analysis of these structures.

Previous research shows that freeze–thaw cycles represent one of the most dangerous threats to reinforced concrete (RC) structures. However, there is almost no experimental data on the effects of freeze–thaw cycles on the seismic behavior of RC columns showing flexure-shear failure. In this study, three columns with the shear span-to-depth ratio of 2.5 were subjected to different numbers of freeze–thaw cycles (FTCs) and pseudo-static testing. The seismic performance indexes of the specimens were analyzed in terms of hysteretic behavior, skeleton curves, shear deformation, and energy dissipation. The test observations show that the failure patterns of the test columns altered from the flexure dominated to shear dominated, owing to the more severe deterioration in shear capacity induced by freeze–thaw attack than in flexure capacity. The test results also indicate that freeze–thaw cycles significantly decrease the ductility and energy dissipation of test columns, and they increase the contributions of shear deformation to the total deformation.

The purpose of this paper was to systematically investigate the influence of acid rain environments on the seismic behaviour of a reinforced concrete (RC) column. Six RC column specimens with shear span ratios of 2.84 were tested under low cyclic reversed loads after being subjected to accelerated corrosion tests in an artificial climate. The corrosion level and stirrup ratio were used as the control variables. The corrosion ratios of the longitudinal rebars ranged from 0 to 13.17%, and the corrosion ratios of the stirrups varied from 0 to 6.75%. The seismic behaviours of the column specimens were analysed with respect to visual damage, failure mode, hysteresis behaviour, load‐carrying capacity, deformation capacity, stiffness degradation, and energy dissipation behaviour. The test results showed that the appearance characteristics of the six column specimens exhibited varying degrees of visual damage as a result of the simulated acid rain exposure. All six specimens were dominated by similar flexural‐shear failures under low cyclic reversed loads, regardless of the distinctions in the corrosion levels or stirrup ratios. For the specimens with the same ratios of stirrup, as the corrosion level increased, the load‐carrying capacity, deformation capacity, stiffness, and energy dissipation capacity were continuously decreased. For the specimens with the same levels of corrosion, the higher the stirrup ratio was, the stronger the restraint effect of the stirrups on the concrete, and the seismic behaviours of the specimens were obviously improved.

In order to study the restoring force characteristics of corroded steel frame beams in an acidic atmosphere, based on different corrosion damage degrees, tests on the material properties of 48 steel samples and six steel frame beam specimens with a scale ratio of 1/2 under low cyclic repeated loading were conducted. According to the test results, the relationship between the weight loss rate and the mechanical properties of corrosion damage steel was obtained by numerical regression analysis, and the hysteresis curves and skeleton curves of the corroded steel frame beams were also obtained. The simplified trilinear skeleton curve model of the corroded steel frame beams and the expression of the corresponding feature points were determined by analyzing the failure process. The strength and stiffness degradation rule of the steel frame beam was analyzed furtherly. The hysteresis rule was established by introducing the cyclic degradation index which considers the effect of different corrosion degrees, and finally the restoring force model based on the corroded steel frame beams in an acidic atmospheric environment was established. Comparison with the test results show that the skeleton curve and the restoring force model established in this paper can accurately describe the seismic performance of corrosion damaged steel frame beams and can provide a basis for the seismic calculation analysis of corroded steel structures in an acidic atmosphere.