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.

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.

Carbon fiber reinforced polymer materials are widely applied in structure strengthened engineering because of the many advantages of carbon fiber reinforced polymer. However, the debonding damage between the carbon fiber reinforced polymer and host structures occurs frequently, which might lead to the brittle failure of structure components, especially flexural ones. In this paper, an electromechanical impedance-based method, an important technique in structural health monitoring, was adopted to detect the debonding damage of carbon fiber reinforced polymer plate-strengthened steel beam by using lead zirconate titanate (PZT) transducers. A carbon fiber reinforced polymer plate-strengthened steel beam specimen was fabricated in the laboratory and two PZT sensors were attached at different locations on the carbon fiber reinforced polymer plate. The impedance signatures with variation of the different degrees of the debonding damage were measured by an impedance analyzer. The root-mean-square deviation method and the cross-correlation coefficient method were used to quantify the correlation between the electromechanical impedance and the debonding damage degree. The results reflect that an electromechanical impedance-based structural health monitoring technique can serve as a good method to detect the debonding damage of carbon fiber reinforced polymer plate-strengthened steel structures.

In recent years, researchers have been concerned with the seismic resilience of structures under salt-erosion environments. As an important part of the resilience assessment, loss estimation, particularly considering the structural loss caused by salt erosion, become a research hotspot. This study presents a methodology to develop loss estimation for deteriorating reinforced concrete (RC) structures by combining it with a quantitative analysis method. The replacement cost of a deteriorated structure was defined to establish a deteriorating reinforcement model based on the loss of a corroded section. The deteriorating reinforcement model was further utilized to establish a post-earthquake loss estimation function of the structure owing to chloride-induced corrosion by considering the cumulative effect of chloride erosion and earthquakes on deteriorating RC structures. Sigmoidal functions were used to simulate post-earthquake recovery paths depending on the extent of damage after an earthquake. Then, the structural resilience was estimated by combining it with a time-varying function. Finally, the resilience assessment calculation of a three-story RC structure example model was considered, and the applicability of the research method established in this study was verified. The calculation results show that the structural loss increased with an increase in the chloride erosion time at any specific PGA and led to a gradual decrease in the structural resilience. Reinforcement corrosion has a significant effect on structural resilience under earthquakes, and ignoring the effect of chloride salts on a structure can lead to an overestimation of resilience.

TBM tunnels crossing fault fracture zones require support systems for the control of deformation; ideally, these systems should be economically and computationally feasible to design. Conventional numerical optimization involves repeatedly evaluating high-fidelity models, and the associated computational burden increases rapidly as structural variables and competing objectives are introduced. This study develops and applies a surrogate-assisted multi-objective optimization framework for a steel-reinforced concrete hybrid segment support system in a tunnel located in a fault fracture zone. The framework combines Optimal Latin Hypercube Sampling (OLHS) for design-space coverage, Kriging surrogate modeling for rapid response prediction, SHapley Additive exPlanations (SHAP) for parameter importance interpretation, and the Non-dominated Sorting Genetic Algorithm II (NSGA-II) to conduct a Pareto search. Two engineering objectives—tunnel crown displacement and haunch displacement—are predicted using the surrogate model, while a material-based support cost index is evaluated independently from the design variables. The selected compromise solution reported in the original analysis reduces the crown displacement, haunch displacement, and support cost index by 7.02%, 9.28%, and 12.84%, respectively, relative to the reported original scheme. Direct numerical analysis of the selected continuous optimum yields crown and haunch displacements of approximately 2.25 and 1.27 mm, respectively, consistent with the surrogate-based results. Although available field monitoring observations provide an additional engineering consistency check, the short monitoring duration and incomplete documentation of the underlying project data limit claims of full-scale causal validation. The main contribution of this study is therefore the integration of expensive numerical analysis, interpretable surrogate modeling, multi-objective optimization, and engineering-level verification for the investigated hybrid segment system.