This issue of Structures and Buildings is a great showcase for the breath of research across structural engineering remit, from insight into vulnerability of long-span timber structure in Italy, to mechanical model and seismic performance of frames with a self-centring connection.
The issue starts with vulnerability assessment of structures built before the adoption of the current framework of codes for seismic design is gaining the attention of many private and public entities (Gaspari et al., 2024). Long-span timber structures are often used as temporary post-event shelters or headquarters for rescue teams. Analysis of the safety of these structures is therefore important for helping decision makers plan any necessary retrofits and avoid any usage interruption in the case of major seismic events in the frame of post-catastrophe management.
In an experimental investigation (Hu et al., 2024), four full-scale specimens were tested under cyclic lateral loads to investigate the impacts of the wall sheathings on the seismic performance of the CFS wall. The failure process, failure mode, load–displacement curve, strength degradation, stiffness degradation, energy dissipation, deformation and strain variation of the walls were investigated. The failure modes of the walls were found to be failure of the connections between the CFS frame and the sheathing as well as crushing of the infill material. Compared with a specimen without sheathing, the peak load and lateral stiffness of the walls with sheathing were increased by 1.25–1.72 times, indicating that the sheathings played an important role in the lateral resistance of the wall. An analysis model and formulas for predicting wall lateral stiffness were developed. Comparisons between the calculations and experimental data showed that the proposed theoretical method was able to predict the lateral stiffness of the infilled CFS walls accurately.
This issue is moving to evaluating the applicability of seismic retrofit of an electric cabinet in a power plant (Lee et al., 2024). In order to improve the earthquake resistance performance of an electric cabinet, methods such as installing a vibration isolation device, increasing the number of connecting bolts between the cabinet bottom panel and base channel, welding a steel grid to the cabinet bottom panel, and so on, were considered and, in order to compare the performance in each case, a three-axis shaking table test was performed. As a result of comparing the seismic performance of each case according to the acceleration response, it was found that the reduction of seismic force was best when applying the vibration isolation device. However, there is a disadvantage in that the spatial and temporal limitations are large and the unit price is high for application in the field. For this reason, it is predicted that the method of ensuring the higher rigidity of an electric cabinet by increasing the number of connecting bolts, as proved through this study, would be a more economical and realistic seismic performance method in field applications.
Next, Pardeshi and Patil (2024) provides a comprehensive numerical study of an innovative coconut palm stem shaped headed shear connectors. An advanced nonlinear finite element (FE) models of push-out specimens were developed to study headed stud shear connectors embedded in a solid concrete slab. These models included the non-linear material properties of the concrete, steel beam, reinforcing bars, and headed stud shear connectors. The study examined how altering the shape of headed studs, inspired by the shape of a coconut palm stem, influenced the ultimate capacity of the shear connection. A detailed analysis was performed using FE models on 21 push-out specimens with varying concrete strengths, different CPSR stud shapes, and a traditional UCH stud. Failure and damage models were incorporated into the headed stud constitutive model to accurately simulate the failure mechanism after damage initiation. The following conclusions were drawn from the FE analysis.
The journey of this issue continues with a study on seismic response modification factor (R) evaluation for vertical irregular moment-resisting frame RC buildings by Ahmed et al. (2024). The value of the response modification factor (R) is influenced by various factors related to overall ductility and over-strength. In this study, actual R values were evaluated for cases of vertical irregularity in reinforced concrete buildings with moment-resisting frames (MRFs). A significant correlation was found between R and the vertical irregularity index, which was calculated based on the relative stiffness between adjacent stories. Three-dimensional numerical modelling was performed using ETABS for scenarios involving soft story and setback irregularities. Modal pushover analysis was employed to determine the inelastic seismic capacity. The results indicated that buildings with vertical irregularities have weaker inelastic seismic capacities compared to regular buildings. Consequently, R should be reduced by 15–40% before the design stage for buildings with single or combined vertical irregularities. Structures with both an asymmetric setback and a soft ground story exhibited the lowest R values, with R being highly sensitive to the vertical irregularity index (Vtm), showing an R-squared value of 80%. Therefore, the vertical irregularity index can be utilized to define the allowable vertical irregularity ratio, as well as the location and combination of vertical irregularities for each seismic zone.
The final paper in this issue is on the mechanical model and seismic performance of frames with a self-centring connection (Saeidzadeh et al., 2024). The structural performance of a novel self-centring pinned beam–column connection with friction dampers (SC-PC-FD) has been documented. A precise mechanical model for the SC-PC-FD connection is crucial for easy integration into common structural analysis and design software. This paper presents a simple mechanical model for the SC-PC-FD connection, verified through experimental and numerical studies on two-strand and four-strand configurations. The seismic performance of frames with SC-PC-FD connections was also evaluated using incremental dynamic analysis and compared to moment-resisting frames. One-, three-, and five-story building models with both connection types were designed and subjected to various earthquake records. The collapse margin ratios (CMRs) and fragility curves were obtained. The model accurately predicted the SC-PC-FD connection's behaviour, showing reduced maximum residual interstory drift ratios and fewer plastic hinges, while increasing CMRs.
