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Open Ground-Storey (OGS) buildings, widely adopted for functional openness, are highly vulnerable to seismic collapse due to stiffness irregularity at the ground storey (GS). The magnification factor (MF), defined as the amplification applied to GS column design forces, acts as a practical strengthening measure to enhance GS stiffness and thereby mitigate the soft storey failure mechanism. While earlier studies recommended fixed MF values, their lack of adaptability often left stiffness deficiencies unresolved. This study develops a rational framework to quantify and predict the required MF for OGS columns, enabling safe yet functionally efficient design. A comprehensive set of three-dimensional reinforced concrete OGS models was analyzed under seismic loads, covering variations in plan geometry, ground-to-upper-storey height ratio (Hr), and GS infill percentage. Iterative stiffness-based evaluations established the MF demand needed to overcome stiffness deficiencies. To streamline prediction, advanced machine learning (ML) models were applied. Among these, black-box models achieved high predictive accuracy, but Symbolic Regression (SR) offered an interpretable closed-form equation that balances accuracy with transparency, making it suitable for design practice. A sensitivity analysis confirmed the Hr as the most influential parameter, with additional contributions from other variables. Validation on additional OGS configurations confirmed the reliability of the SR model, while seismic response comparisons showed that Modified OGS (MOGS) frames with the proposed MF achieved improved stiffness, reduced lateral displacements, uniform drift distribution, and shorter fundamental periods. The study highlights the novelty of integrating interpretable ML into structural design, providing a codifiable and practical tool for resilient OGS construction.

The purpose of this study is to update the non-linear modeling of soft storey RC frame building for performance based design. The qualitative and quantitative assessment of different strength and ductility parameters of tested building components including the different types of reinforcing steel have been presented. The cyclic performance of tested G+2 soft storey RC frame building of ¼ scale is evaluated and the components test results are applied successfully for performance evaluation of prototype soft storey RC frame buildings under different modes of failure. It indicates that the non-linear characteristics of reinforcement used in different components of building frame have significant influence on the global failure pattern particularly assuring a flexure mode of failure.

Cyclic testing has been carried out on two 1/4 scale of (G+2) soft storey RC frame building models to evaluate the nonlinear performance under cyclic loading. The first model has been designed only for gravity loading and the second model has been designed for gravity and earthquake loading. The different pushover parameters of the frames such as load-deformation curve, displacement and storey drift profile and the failure pattern have been evaluated. These parameters are used for up-gradation and comparison of the nonlinear analytical modeling of the soft storey RC frame building. The nonlinear analytical models have been updated at three stages i.e. linear range, nonlinear range and finally at failure stage. The % of error between the experimental and analytical results for different pushover parameters has also been evaluated.

The 2020 southern Puerto Rico earthquake sequence highlighted the severe seismic vulnerability of informally constructed two-story reinforced concrete (RC) houses. This study examines the failure mechanisms of these structures and assesses the effectiveness of first-floor RC shear-wall retrofitting. Nonlinear pushover and dynamic time–history analyses were performed using fiber-based distributed plasticity models for RC frames and nonlinear macro-elements for second-floor masonry infills, which introduced a significant inter-story stiffness imbalance. A bi-directional seismic input was applied using spectrally matched, near-fault pulse-like ground motions. The findings for the as-built structures showed that stiffness mismatches between stories, along with substantial strength and stiffness differences between orthogonal axes, resulted in concentrated plastic deformations and displacement-driven failures in the first story—consistent with damage observed during the 2020 earthquakes. Retrofitting the first floor with RC shear walls notably improved the performance, doubling the lateral load capacity and enhancing the overall stiffness. However, the retrofitted structures still exhibited a concentration of inelastic action—albeit with lower demands—shifted to the second floor, indicating potential for further optimization.

Multi-story, reinforced-concrete (RC) building structures with soft stories are highly vulnerable to damage due to earthquake loads. The soft story causes a significant stiffness irregularity, which has led to numerous buildings collapsing in previous seismic events. In addition to the structural collapse, the failure of non-structural components (NSCs) has also been observed during past earthquakes. In light of this, this study investigates the effect of a soft story and its location on the seismic behavior of a supporting building and NSCs. The soft story is assumed to be located on the bottom (ground), middle, and top-story levels of the considered building models. Story displacements and inter-story drift ratios are evaluated to assess structural behavior. The floor response spectra and the amplification effects of NSC on the floor acceleration responses are studied to understand the behavior of NSCs. The analysis results revealed that the bottom soft story exhibits a considerable vertical stiffness irregularity, and its position substantially affects the floor response spectra. The amplification in the floor acceleration response was found to be greater at the soft-story level. This study reported that middle soft-story buildings exhibit the most remarkable amplification in the component’s acceleration. Finally, peak floor response demands are compared with the code-based formulation, and it is found that the code-based formulation’s linear assumption may lead peak floor response demands to be underestimated or overestimated.

This paper investigates the behavior and the failure mechanism of a double deck bridge constructed in China through nonlinear time history analysis. A parametric study was conducted to evaluate the influence of different structural characteristics on the behavior of the double deck bridge under transverse seismic motions, and to detect the effect of bi- directional loading on the seismic response of this type of bridge. The results showed that some characteristics, such as the variable lateral stiffness, the foundation modelling, and the longitudinal reinforcement ratio of the upper and lower columns of the bridge pier bents have a major impact on the double deck bridge response and its failure mechanism under transverse seismic motions. It was found that the soft story failure mechanism ：is not unique to the double deck bridge and its occurrence is related to some conditions and structural characteristics of the bridge structure. The analysis also showed that the seismic vulnerability of the double deck bridge under bi-directional loading： was severely increased compared to the bridge response under unidirectional transverse loading, and out-of-phase movements were triggered between adjacent girders.

The masonry infill of RC frames structures is generally considered as non-structural. The design of the concrete frames is often made by ignoring the influence of the masonry infill, which is only accounted for its mass. The experience on buildings submitted to earthquakes shows that masonry infill walls completely change the behaviour of bare frames due to increased initial stiffness and low deformability. The way in which masonry infills affect the RC frames members is difficult to predict, as different failure modes can occur either in the masonry or in the surrounding frame. In addition to local effects, the position of the masonry infills at different levels can lead to structural irregularity, with a strong influence on the global seismic response of the building. Less infilled stories, also called soft stories, have a particularly unfavourable behaviour under seismic loads, as frame members at these levels are more susceptible to failure. This paper analyses the differences in the behaviour of bare and infilled frames through numerical modelling. Nonlinear push-over analyses of infilled frames are carried out under in-plane vertical and lateral loading. The infill panels are modelled as equivalent single diagonal struts. Several force-displacements laws are considered for these diagonals.