Cyclic behavior assessment of low-rise unreinforced masonry building augmented with steel framework: Experimental and numerical investigations

In rural and hilly regions of the Indian subcontinent, general vernacular buildings are of unreinforced masonry (URM) construction and are often designed without seismic design principles. Strong ground shaking in these regions in the recent past has demonstrated the inherent brittle nature and lack of tensile resistance of the existing URM buildings, resulting in extensive damage and loss of life. In the present study, a single-story, unsymmetrical red clay brick building, representing a typical rural educational facility in India, was strengthened using steel as framing and confining members. The architectural layout was in accordance with the local building traditions, and the structural steel members were used for confinement of the URM walls. The connections of the steel frame were designed and detailed for load combinations in compliance with the Indian standards and the concepts of the capacity design to force the damage in the members before the failure of connections. To evaluate the performance of this composite structure, a full-scale model consisting of the steel frame with brick masonry walls was built and by employing the regional methods of construction and subjected to quasi-static displacement loading to examine its cyclic response and failure patterns. Incremental reverse cyclic loadings were applied to the structure to capture: (i) the force-deformation hysteresis, (ii) the yielding of critical steel members, (iii) interaction of steel-masonry components, and (iv) the initiation and propagation of cracks. Subsequently, a calibrated numerical model of the building was developed based on the experimental results, wherein brick infill was modeled as equivalent strut elements. Key observations from the full-scale quasi-static testing and numerical study confirmed enhanced lateral strength, stiffness, and deformation capacity of the steel-masonry building. Moreover, the observed crack propagation and failure pattern offer critical insights in finalizing appropriate retrofitting measures for steel-masonry composite structures.