Unreinforced masonry (URM) buildings, prevalent in historic urban centers, often constitute an architectural typology of kinematically coupled clusters, where independent structural units are built in direct adjacency. Despite this, seismic performance assessments typically analyze these buildings as isolated structures, a common practice that overlooks the interaction between neighboring structures, resulting in unrealistic demands and fragility estimates. This research studies this dynamic coupling by modeling three distinct URM building archetypes and assembling them into seven different two- and three-unit clusters to evaluate the influence of building position and differences in strength and stiffness between neighboring structures. Using a three-dimensional equivalent frame approach that captures both in-plane and out-of-plane behavior of masonry walls, fragility curves for each isolated unit were derived from nonlinear response history analyses, using a suite of actual ground motions and following the multiple stripe analysis methodology. Then, fragility curves of the buildings within the clusters were also developed and compared with those of the isolated structural units. Results show a complex, configuration-dependent interaction. While weaker buildings (i.e., lower in-plane stiffness and lower strength capacity) benefit from the support of stronger neighbors, this support renders the stronger units more fragile, an effect that intensifies with increasing stiffness disparity. The collapse sequence is initiated by the most vulnerable unit, regardless of its position within the cluster, which can trigger a progressive collapse that compromises adjacent, otherwise stable, structures. This study provides quantitative evidence that assessing URM buildings in isolation is not only flawed but unconservative. Therefore, the seismic fragility of URM buildings cannot be quantified in isolation; it needs a holistic approach, developing cluster-level models for realistic performance assessments of historic urban centers.
Masonry infill walls, soil–structure interaction (SSI), and failure mechanisms of reinforced concrete (RC) members are critical factors governing the seismic response of RC frame buildings. Unlike ductile RC frames, limited-ductility RC structures are more susceptible to brittle and premature failure modes due to their restricted deformation capacity and potential shear-critical behavior. Although the seismic effects of masonry infill walls have been extensively studied for RC frames with intermediate and high ductility, the comprehensive evaluation of limited-ductility RC frames considering the coupled effects of masonry infill walls and nonlinear SSI remains insufficient. This study investigates the seismic response and vulnerability of limited-ductility RC frame buildings subjected to mainshock–aftershock earthquake sequences. Two representative 2- and 4-story RC frame buildings designed in accordance with UBC97 are considered. Two-dimensional nonlinear numerical models are developed and analyzed in OpenSees, incorporating flexure–shear interaction in RC members to capture the shear-critical behavior of limited-ductility frames, while masonry infill walls and the supporting soil are explicitly modeled using nonlinear constitutive formulations to represent structural and soil nonlinearities. Bare and masonry-infilled frames are subjected to nonlinear response-history analyses using 20 selected mainshock–aftershock ground-motion sequences. Seismic performance is evaluated through Incremental Dynamic Analysis (IDA), and fragility curves are developed using HAZUS damage state definitions to quantify the probability of exceeding different performance levels. The results indicate that masonry infill walls increase the seismic capacity by up to 50
Composite concrete-filled shear walls have been proven to be an efficient lateral load-resistance system owing to their great strength, stiffness, and ductility. Nevertheless, their behavior under sequential hazards, particularly post-earthquake fire, remains poorly understood. For this investigation, a finite element analysis of the problem was developed in ABAQUS and first verified against previous experimental data to validate the numerical approach. After validation, a comprehensive parametric investigation of composite shear walls was conducted. The numerical procedure included heat-transfer analysis, monotonic lateral loading, cyclic analysis following the ATC-24 loading protocol to evaluate hysteretic behavior, and sequential post-earthquake fire analysis. The parameters examined included wall configuration, boundary-element length, surfaces exposed to fire, and lateral loading ratio. The outcomes demonstrated that boundary elements greatly improved the ambient lateral strength and deformation capacity, leading to increases of 6.3–13.5
