Jun Gao

RCES composite structures, which combine the advantages of high bearing- and good anti-seismic capacity of ordinary steel reinforced concrete (SRC) with the characteristics of energy-saving and environmental protection of recycled concrete, are beneficial to promote the use of recycled concrete. However, the bond–slip behavior and load transfer mechanism are essential issues of RCES composite structures. This paper primarily focused on the load transfer mechanism and bond–slip behavior of RCES composite structures subjected to cyclic loading. A total of 14 specimens, which were designed with different replacement ratios of recycled concrete, cover thicknesses of H-shaped steel, transverse reinforcement ratios, and recycled concrete strengths, were tested to investigate the load transfer mechanism and interface damage. The results indicate that the whole loading procedure can be divided into four phases and four limit points. The bonding shear damage of a specimen develops rapidly, and most damage happened during 0~0.2 mm slip. The bonding stress values of chemical bonding stress τ_ca, friction resistance stress τ_f, and mechanical biting stress τ_m were calculated. Moreover, in order to reflect the influence of cyclic loading, a degradation factor ξ was proposed. The mean values of chemical bonding stress τ_ca: friction resistance stress τ_f: mechanical biting stress τ_m are 1:0.187:0.696, in which the chemical bonding stress is the largest, friction resistance stress is the second, and the mechanical biting stress is the least.

In the process of structural design and structural performance evaluation, the inference of the reliable life of the structure and the representative value of the material strength is a necessary work. The determination of material strength is the presumption of the quantile of the normal distribution, and the determination of the confidence level of the quantile of the normal distribution involves the noncentral t-distribution function. However, the calculation of the quantile is very complicated and is often provided in the form of a numerical table, which often involves multiparameter interpolation calculation, so it is not convenient to apply. The existing approximate calculation methods for noncentral t-distribution quantiles have strict application conditions, and the calculation process is relatively cumbersome. It is still difficult to meet actual needs in terms of fitting accuracy, application range, and convenience. In this paper, a new calculation method for noncentral t-distribution quantiles is proposed by introducing new probability expressions and related approximate distributions, based on theoretical derivation and numerical fitting. The comparative analysis results show that the method not only is convenient for calculation but also has the advantages of higher accuracy and wider application range, and it is more in line with the actual needs of engineering.

Methods for inferring the design value of the resistance based on test have long been studied extensively, but the existing methods have several limitations on unified guarantee rate ensurance and reliability control. Firstly, the rationales and deficiencies of the present methods in ISO 2394 : 2015 and EN 1990 : 2002 were generalized. Secondly, in view of the disadvantages, a new inferring method combining the probability model of resistance with statistical approach was put forward. The proposed method established a relationship among design resistance, probability characteristics of known factors, and statistical results of unknown factors and possessed a rigorous and sound theoretical basis on both conditions that the coefficient of variation of model uncertainty was unknown and full known. Lastly, a contrast work was carried out between the Eurocode method and the proposed method; the results showed that the latter method had a higher inferring value, which means a better inferring result.

In the current structure damage assessment process, different methods of selecting damage index threshold will significantly affect assessment results. OpenSees finite element software is used to build a 6-story RC frame structure model. Then, the inter-story drift and residual inter-story drift are used as single and double indices to calculate threshold values using the code method and the incremental dynamic analysis method. Evaluation results vary more significantly when the damage is evaluated using a single index. When the threshold is selected based using the code method with a double index, the results are more conservative. The stronger the correlation between the inter-story drift and residual inter-story drift is, the more conservative the results are.