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Finding out the most effective parameters relating to the resistance of reinforced concrete connections (RCCs) is an important topic in structural engineering. In this study, first, a finite element (FE) model is developed for simulating the performance of RCCs under post-earthquake fire (PEF). Then surrogate models, including multiple linear regression (MLR), multiple natural logarithm (Ln) equation regression (MLnER), gene expression programming (GEP), and an ensemble model, are used to predict the remaining load-carrying capacity of an RCC under PEF. The statistical parameters, error terms, and a novel statistical table are used to evaluate and compare the accuracy of each surrogate model. According to the results, the ratio of the longitudinal reinforcement bars of the column (RLC) has a significant effect on the resistance of an RCC under PEF. Increasing the value of this parameter from 1% to 8% can increase the residual load-carrying capacity of an RCC under PEF by 492.2% when the RCC is exposed to fire at a temperature of 1000 °C. Moreover, based on the results, the ensemble model can predict the residual load-carrying capacity with suitable accuracy. A safety factor of 1.55 should be applied to the results obtained from the ensemble model.

In the present study, the performance of reinforced concrete tunnel (RCT) under internal water pressure is evaluated by using nonlinear finite element analysis and surrogate models. Several parameters, including the compressive and tensile strength of concrete, the size of the longitudinal reinforcement bar, the transverse bar diameter, and the internal water pressure, are considered as the input variables. Based on the levels of variables, 36 mix designs are selected by the Taguchi method, and 12 mix designs are proposed in this study. Carbon fiber reinforced concrete (CFRC) or glass fiber reinforced concrete (GFRC) is considered for simulating these 12 samples. Principal component regression (PCR), Multi Ln equation regression (MLnER), and gene expression programming (GEP) are employed for predicting the percentage of damaged surfaces (PDS) of the RCT, the effective tensile plastic strain (ETPS), the maximum deflection of the RCT, and the deflection of crown of RCT. The error terms and statistical parameters, including the maximum positive and negative errors, mean absolute percentage error (MAPE), root mean square error (RMSE), coefficient of determination, and normalized square error (NMSE), are utilized to evaluate the accuracy of the models. Based on the results, GEP performs better than other models in predicting the outputs. The results show that the internal water pressure and the mechanical properties of concrete have the most effect on the damage and deflection of the RCT.

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