Progressive collapse is a nonlinear dynamic behavior of structural systems. In order to study the progressive collapse resistance laws of reinforced concrete planar frame structures after failure of important members, an important member identification method based on strain energy of members was proposed. The effectiveness of the method was verified by taking a four-bay and eight-story reinforced concrete frame structure as the target. It was found that the method identifies important members with high effectiveness. On this basis, eight reinforced concrete frame structures with different beam spans or total number of floors were designed in accordance with code. Firstly, important members were identified based on the above method and the adverse structural member removal scenarios were formulated. Then, impacts of different total number of floors and structural span on progressive collapse resistance capacity of reinforced concrete planar frame structures were analyzed by adopting the nonlinear dynamic alternate path method. Finally, the approximate functional curve of reinforced concrete planar frame structures between proportions of columns removed from ground floor and degrees of structural collapse was fitted. The results indicate that after removal of center column at ground floor, structures are mainly carrying vertical loads by ground floor frame beams, and frame beams of remaining floors cooperate with ground floor frame beams to support loads. The decrease in total number of floors and the decrease in span can increase redundant load carrying capacity of structures, which has a positive effect on resistance capacity of frame structures to progressive collapse. Frame beam span has a significant effect on degree of structural collapse and total number of floors has a limited effect on degree of structural collapse. The relationship between proportions of columns removed from ground floor and degrees of structural collapse of reinforced concrete plane frame structures can be approximated by a logistic function.

This study analyzes 6 436 offshore ground motion records from 496 seismic events observed by seafloor observation network for earthquakes and tsunamis along the Japan Trench (S-net), aiming to investigate the frequency content characteristics of vertical ground motion components. Using random-effects regression with consideration of key factors like water depth and sediment layer thickness, we developed empirical models for vertical frequency content parameters. Significance tests and the Akaike Information Criterion (AIC) were employed to evaluate parameter validity and model goodness-of-fit. Results show that significant differences exist between horizontal and vertical frequency content distributions, highlighting the significance of the water depth parameter and setting condition. For S-net ocean-bottom stations (water depth: 102~7830 m), vertical frequency parameters shift toward shorter periods at depths less than 1500 m, while longer-period (longer than 0.8 s) records increase significantly at depths greater than 1 500 m. The water depth significantly affects vertical frequency content. Predictions for different tectonic types show consistent differences between vertical and horizontal models. Site terms exhibit significant differences between inner-trench and outer-trench stations, possibly influenced by the propagation paths of seismic waves and the topographical features associated with the outer ridge of the trench rather than sediment layer thickness. This study provides support for understanding offshore ground motion characteristics and assessing offshore seismic hazards.

In order to improve the seismic performance of traditional HDR(high-damping seismic isolation rubber bearings)bearings and their adaptability in simply supported beam bridges in high-intensity seismic zones, a new type of composite seismic bearing was developed based on the rational integration of steel bar dampers and HDR bearings, and its structural construction and mechanical behavior were described. Taking a specific specification product as an example, the vertical compression performance and horizontal hysteresis performance were demonstrated through finite element numerical simulation and experimental research. Then, a 5~20 m concrete simply supported beam bridge in an 8-degree seismic zone was taken as the object, and a finite element model was established using SAP2000 to study its seismic performance. The results showed that the vertical compression performance of the bearing met the standard requirements, and the horizontal hysteresis curve was more full than that of the HDR bearings. The finite element numerical analysis and experimental results were in good agreement with the theoretical skeleton model. Compared with the HDR bearings seismic system, the internal force response of the bridge pier increased to a certain extent after the use of the composite bearing, but it is still within the capacity range, and the displacement of the bridge beam end and the relative displacement of the pier-beam are significantly reduced, which can effectively avoid the occurrence of seismic damage such as beam-falling and collision of adjacent beams.

On December 18, 2023, the Jishi mountain earthquake revealed damage to 750 kV surge arresters. In order to improve the seismic performance of existing pillar-type electrical equipment in substations, the intermediate layer was selected as the isolation part for modification. Two intermediate isolation schemes were proposed: steel wire rope damper and composite seismic isolation bearing. The original surge arrester and isolation structure were modeled using the ABAQUS finite element method. Ten sets of seismic waves were input for finite element analysis, and the stress of bushing root, top acceleration and displacement responses of each structure were extracted to compare and analyze the isolation efficiency of the intermediate layer. The results show that under seismic action, the intermediate isolation structure of the steel wire rope damper can effectively reduce the stress of bushing root and top acceleration of the surge arrester, but it has a significant amplifying effect on the top displacement, which can easily cause wire tension damage. The intermediate isolation scheme with composite seismic isolation bearing can improve the vertical stiffness of the intermediate layer structure, so that the root stress and top acceleration of the original structure bushing decrease by more than 40%, and the peak displacement of the top is only increased by 12.56%, so as to achieve a good seismic isolation effect. The intermediate isolation device with composite seismic isolation bearings exhibits good seismic isolation efficiency and is an effective retrofit measure to improve the seismic performance of existing 750 kV surge arrester.

A simplified method for calculating the longitudinal movement and cumulative displacement of the stiffening girder in long-span suspension bridges under random traffic flow is proposed. In this method, the suspended stiffening girder system is equivalent to a single-degree-of-freedom (SDOF) vibration system. Based on this SDOF system, the longitudinal vibration equations of the suspension bridge’s stiffening girder under moving loads and random traffic flow are derived. A rapid calculation method for the stiffening girder’s longitudinal vibration response under random traffic flow is proposed. Taking an example of a long-span suspension bridge and using existing traffic measurement data, random traffic flow samples are generated based on the Monte Carlo method. These samples are then treated as random loads on the SDOF system. The SDOF vibration equation is solved, and the results are compared with ANSYS dynamic analysis results. The findings reveal that under random traffic flow, the stiffening girder undergoes longitudinal movement and accumulates a significant displacement. This cumulative displacement consists of both static and dynamic components, with the latter contributing more significantly. Compared to the finite element transient dynamic analysis, the displacement response results obtained from the simplified SDOF system show minimal differences in extreme values and root mean square(RMS) values (less than 5%), although there is a slightly larger difference in cumulative displacement (approximately 13% ~ 19%). This indicates that the simplified vibration model can capture the stiffening girder’s longitudinal movement characteristics under random traffic flow. The proposed simplified method greatly simplifies the analysis of the stiffening girder’s longitudinal movement under random traffic flow, enabling response evaluation and parameter optimization in the preliminary design stage.

In order to expand the application of perfobond leiste (PBL) shear connectors, the low-cycle reciprocating loading tests were conducted on one steel reinforced concrete composite shear wall and four steel plate concrete composite shear walls with PBL shear connectors. The failure mechanism and seismic performance of the specimens were studied. The results show that the failure modes of shear walls under horizontal loads can be divided into two types including bending failure and bending-shear failure. The aspect ratio of the walls, the configuration of steel core plates and the arrangement of the PBL shear connectors are important factors affecting failure modes. PBL shear connectors can facilitate steel core plates working well with the concrete. Besides, the configuration of steel core plates can improve the bearing capacity of the walls. The bearing capacity of shear walls decreases with the increase of aspect ratios, and the vertical arrangement of PBL shear connectors is better than the horizontal arrangement of PBL shear connectors. Based on the design of compression-bending capacity of steel reinforced concrete columns recommended in EN 1994-1-1:2004, a design formula of compression-bending capacity for steel plate concrete composite shear walls with PBL shear connectors is proposed. It is verified that the design formula can accurately calculate the compression-bending capacity of the shear walls with large aspect ratios by comparison.

In order to investigate the effectiveness of treatment measures for silt subgrade in high seismic fortification areas, vibration table model tests were conducted on pure silt subgrade and reinforced silt subgrade. Based on a comparative analysis of the failure characteristics and dynamic response laws of the two models, the influence mechanism of reinforcement on the seismic performance of silt subgrade was explored. The experiment shows that after the peak acceleration of seismic load reaches 0.25 g, the experimental pure silt subgrade gradually experiences cracking, fragmentation, and sinking failure. After adding four layers of geogrids on the slope side of the subgrade, the seismic resistance of the silt subgrade can be effectively improved. When the peak acceleration of the seismic load is loaded to 0.35 g, although cracks also appear on the reinforced silt subgrade, the subgrade can still maintain good integrity. Under seismic loads, reinforced silt subgrade and pure silt subgrade have basically the same acceleration and dynamic soil pressure response rules. The acceleration amplification factor increases nonlinearly with the increase of subgrade height, and decreases with the increase of seismic load. Under the same load, the amplification factor on the slope side of the subgrade is larger than that on the centerline side, but the difference between reinforced silt subgrade is smaller. The dynamic soil pressure of both models shows a pattern of “larger on both sides and smaller in the middle” in the height direction of the subgrade. In the direction of the subgrade cross-section, the dynamic soil pressure on the centerline side of the subgrade is greater than that on the slope side. Due to the influence of subgrade structure, the potential fracture surface of reinforced silt subgrade under seismic loads will form at the end of the reinforced body and within the low pressure compaction zone. Reinforcement is an effective measure to improve the seismic performance of silt subgrades. In practical engineering applications, the length of the reinforcement should not be less than 0.65H, and there should also be sufficient anchoring length.

A large number of seismic investigations have shown that the damage caused by nonstructural components could not be ignored, and with the increasing maturity of the response spectrum method, it has become an important method for the seismic response analysis of nonstructural components. However, the current method of generating response spectrum was mostly used for multi-story structures, and the method of generating response spectrum for large-span structures was still not clear. Therefore, this article establishes nine types of single-layer cylindrical reticulated shell structural models on the basis of ABAQUS and Python. Through numerical analysis, the representative nodes of the single-layer cylindrical reticulated shell were identified by comparison, and the spectral characteristics of the three-way acceleration response spectrum were investigated and analyzed, and the fitting form of the node response spectrum was established, and the fitting formula of the three-way acceleration response spectrum of the single-layer cylindrical reticulated shell nodes was proposed. In addition, this article further determined the calculation formula of each characteristic parameter through the fitting analysis, and investigated the relationship between the peak acceleration amplification factor, the peak spectral acceleration amplification factor and the effective distance of the nodes, the structural rise-to-span ratio and the roof mass based on the representative nodes. The research results in this article could be used to approximate the seismic response of the single-layer cylindrical reticulated shell non-structural components, and could provide a valuable reference for the generation of response spectrum for other large-span structures.

To enhance the protection of masonry pagodas and improve the damping performance of suspension pendulum damper (SPD), a novel SMA composite pendulum damping system is proposed, integrating shape memory alloy (SMA) into SPD. This system enhances the inertia force generated by the pendulum within SPD by leveraging the super elasticity and high damping characteristics of SMA, thereby improving the overall energy dissipation capability of the damping system. Initially, the study outlines the process of obtaining the equivalent restoring force of SMA through stochastic equivalent linearization. Subsequently, it establishes the SDOF computational model of the SMA composite pendulum damping system by drawing parallels with the SDOF computational model of SPD. The paper elucidates the structure and operational principles of the damping system, followed by an exploration of the effects of two control parameters on its performance. Further, the study applies both SPD and the new composite pendulum damping system to a masonry pagoda. The structural vibration response is analyzed under three distinct seismic excitations following the implementation of the damping system using ABAQUS software. The findings reveal that the SMA composite pendulum damping system outperforms SPD in vibration control under various seismic excitations, demonstrating its superior applicability.

In order to improve the seismic performance of reinforced concrete (RC) frames, carbon fiber-reinforced polymer (CFRP) was used to retrofit reinforced concrete frame structures. The effects of CFRP on the failure mode, the energy dissipation characteristics, the lateral stiffness degradation patterns, the ultimate bearing capacity degradation and the ductility of RC columns were investigated by the pseudo-static tests. The results show that the peak bearing capacity, initial stiffness and ductility of the CFRP reinforced model are increased by 43.89%, 39.27% and 30.10%, respectively. Based on the parametric study of the finite element model, the contribution of CFRP to the seismic upgrading effect of RC columns was quantitatively revealed, and the optimized design of CFRP retrofitted was proposed. The results indicated that the peak load, ductility and energy dissipation capacity of the whole structure are improved by using CFRP full-wrap reinforcement and strip reinforcement models with different coverage areas. The damage degree of column decreases, the damage degree of beam increases, and the failure mode changes from “column hinge” to “beam hinge”. Simultaneously, different CFRP reinforcement areas and the distance between strip-shaped CFRP have different reinforcement effects on concrete structures. Based on the investigation results, the recommended ratio of the width of CFRP strip to its spacing is 1.00 to 1.25.