Crack expansion of concrete is the initial damage stage of structures, which may cause greater damage to structures subject to long-term loads or under extreme conditions. In recent years, the application of intelligent materials to crack self-repair has become a hotspot among researchers. In order to study the influence of factors on the self-repair capability of shape memory alloy (SMA) wire concrete beam, both theoretical and experimental methods were employed for analysis. For the convenience of experiment, composite materials (epoxy cement mortar and silicone polymer clay) instead of concrete were used. The SMA wires were externally installed on and internally embedded in epoxy resin cement mortar beams and silicone polymer clay beams. Comparison of crack repair situation between two installation methods turns out that both methods possess their own advantages and disadvantages and should be employed according to the actual situation. The influence of unbonded length on the self-repair capability of embedded type SMA wire beams and the necessary minimum unbonded length to achieve self-repair function were studied. The results state clearly that the longer the unbonded length is, the better the crack repair situation is.

Sliding mode variable structure control (SMVSC) has very strong robustness, which has been widely applied in permanent magnet synchronous motor (PMSM) speed regulating system. Constant rate reaching law approach speed is related to the sliding mode reaching gain. The higher the sliding mode reaching gain, the faster the reaching speed, and then the stronger chattering. In this paper, a new reaching law is designed on the basis of constant reaching law. With the analysis of MATLAB, the new reaching law not only increases the approach speed of the sliding mode, but also has a better inhibition effect on chattering. It provides a reference for further experiments.

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When a structure is subjected to an earthquake sequence, the high rate of aftershocks after the mainshock and cumulative damage caused by the earthquake sequence make the structure very dangerous. Considering the uncertainty in seismic occurrences, structural damage is often predicted using a seismic risk analysis. This approach has become a main measure for seismic disaster assessment, and provides a reasonable reference for post-earthquake emergency response decision-making and pre-earthquake seismic design. Therefore, it is of great significance to study a seismic risk analysis considering the effect(s) of aftershocks. In this study, the aftershock hazard is estimated for a post-mainshock environment based on an aftershock probabilistic seismic hazard analysis. Considering the uncertainty regarding the mainshock and aftershock occurrences, in addition to the functional relationship between the mainshock and aftershock parameters, the aftershock seismic hazard is estimated for the pre-mainshock environment. The mainshock fragility and aftershock fragility of regular girder bridges are evaluated based on the Kunnath damage model. Finally, considering the damage accumulation in bridge structures, the seismic hazard and seismic fragility are combined to establish a post-mainshock aftershock seismic risk framework and pre-mainshock mainshock-aftershock seismic risk analysis framework. Based on these, the mainshock risk and mainshock-aftershock risk are compared to verify the importance of considering the aftershock effects in seismic disaster assessments. The aftershock risks for the bridges of different post-mainshock damage states are compared, and the influence of the initial damage after the mainshock on the damage to the structure in the post-mainshock environment is studied.

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