The structural performance of mid-rise buildings with a soft first story is a critical issue in earthquake-prone regions. This paper presents a detailed assessment of both the seismic performance and the structural reliability of a confined masonry mid-rise building with a soft reinforced-concrete first-story irregularity located in Mexico. This structure was designed according to outdated building codes to reflect construction practices that remain common in some parts of the country. Nonlinear dynamic analyses were conducted using ETABS v21. To simulate various seismic scenarios, ground motion records associated with return periods of 72, 475, and 975 years, respectively, were implemented. The results demonstrated that maximum inter-story drift is predominantly concentrated at the first story, exceeding the performance thresholds for immediate occupancy, life safety, and collapse prevention. Furthermore, a probabilistic performance assessment was developed considering the randomness of inter-story drift responses. Then, reliability index (β) was calculated for each seismic scenario. In all cases, β values remained consistently below the minimum recommended limit. These findings confirm the formation of a soft-story mechanism at the first level and are relevant for buildings designed under construction provisions like those used in the present case study.

Seismic excitations induce floor accelerations that can damage non-structural components and, in extreme cases, contribute to global structural failure. Although floor acceleration demands have been widely studied, their integration into probabilistic seismic performance and reliability frameworks remains limited within Performance-Based Seismic Design (PBSD). This study addresses this gap by proposing a reliability-based framework that incorporates the stochastic nature of floor accelerations through their probability density functions. Five-story steel and reinforced concrete (RC) buildings, designed according to Mexican codes, were analyzed using nonlinear dynamic simulations in PERFORM 3D under 33 ground motions corresponding to immediate occupancy (IO), life safety (LS), and collapse prevention (CP) levels. Structural reliability was quantified using the probability of failure ($p_f$) and the reliability index (β). Results show that peak accelerations occur at the roof level, with higher demands in the steel structure. For the IO level, β ranged from approximately 2.29 to values above 4.0 in steel buildings, while RC structures reached up to β ≈ 4.97. At LS and CP levels, RC buildings maintained β values generally above 3.0, whereas steel structures showed values as low as β ≈ 1.32. The Kernel distribution best captured response variability, reflecting high dispersion ($C.V.$ > 30%). The proposed framework enhances PBSD by linking acceleration demands with reliability-based decision-making.

This study presents a probabilistic assessment of the seismic performance of a mid-rise soft-first-story building retrofitted using a hybrid strengthening strategy, addressing the limited integration of hybrid energy dissipation systems within a reliability-based framework for vertically irregular structures. The structure consists of a confined masonry system with a reinforced concrete irregular first story, where buckling-restrained braces (BRBs) are implemented at the ground level and shear-link energy dissipation devices are incorporated at the upper stories. The retrofit aims to mitigate deformation concentration at the soft story while promoting a more uniform distribution of seismic demands along the building height. The proposed methodology is based on bidirectional nonlinear time-history analyses conducted in ETABS v21, using ground motion records associated with return periods of 72, 475, and 975 years. Inter-story drift ratios are treated as random variables to account for record-to-record variability, and probabilistic models are employed to estimate exceedance probabilities and reliability-based performance metrics. The original structure exhibited low reliability levels, with β values ranging from 1.30 to 2.05 across performance levels, indicating a high probability of unacceptable performance and a pronounced soft-story mechanism. After retrofitting, the structural reliability increased significantly, reaching mean values of 7.76 and 7.65 at the immediate occupancy level, 7.43 and 7.73 at life safety, and 7.42 and 7.32 at collapse prevention for the EW and NS directions, respectively. These values greatly exceed the commonly accepted target of β = 3.5 and are associated with probabilities of unacceptable performance on the order of 10 ^-14 to 10 ^-15 . Overall, the hybrid retrofit strategy effectively eliminates the soft-story mechanism, ensures a stable redistribution of seismic demands, and significantly enhances the reliability and seismic resilience of buildings with vertical irregularities.

Existing bridges represent a significant challenge for structural engineering due to aging, increased traffic demands, and lack of original design information. This paper presents an investigation of the structural behavior of the Miguel Hidalgo Bridge, located in Culiacán, Sinaloa, México, which has remained in service for over a century. A preliminary visual inspection identified deterioration mechanisms, including cracking, exposed reinforcement, damaged bearings, and localized structural deformations. Given the absence of original design documentation, a structural health monitoring (SHM) strategy was implemented to assess its condition. The SHM methodology integrates field instrumentation using accelerometers for operational modal analysis under ambient vibration and GPS receivers for displacement measurements, complemented by a geometric survey and material characterization through non-destructive techniques. These data were used to develop and calibrate a three-dimensional finite element (FE) model, which was employed to evaluate structural performance under service loads in accordance with AASHTO provisions. Results indicate that the bridge satisfies serviceability criteria; however, certain components exhibit deficiencies in load-carrying capacity. These findings highlight the importance of integrating monitoring data with numerical modeling to support decision-making related to maintenance, rehabilitation, and extension of service life in existing bridge infrastructure.