Structural and Seismic Behavior of RC Buildings Retrofitted with External Wall Jacketing Due to Vertical Extension.

Abstract

Urban areas face a continuously growing demand for residential and commercial spaces, driving the need for spatial optimization. Consequently the vertical extension of existing structures becomes an economically viable, and also sustainable, approach. In this study This study investigates the structural evaluation and seismic rehabilitation of an existing four-story reinforced concrete, RC, building which is planned to receive three additional floors, so it turns into a seven-story system. Because the new configuration comes with a major rise in static gravity loads and also in dynamic lateral seismic forces, an integrated retrofitting strategy is worked out. The strategy mainly leans on reinforced concrete, RC, jacketing on the external walls, to substantially increase the building’s lateral stiffness and its seismic resistance, at least in a practical sense. Advanced 3D structural finite element models of the building, in both its existing and its extended variants, were developed using ETABS in strict compliance with ASCE 7-16 and ACI 318-19 provisions. The analytical approach utilizes a code-compliant Equivalent Static and Dynamic Response Spectrum Analysis, incorporating effective cracked section stiffness modifiers to account for material aging and cracking in the legacy frame. The evaluation follows a systematic step-by-step review across the structural components. The work follows a rather strict, step by step review and design procedure across the structural components, without skipping too much. It starts with the foundation stage, where soil bearing strength is checked and the footing enlargement is detailed to carry the added gravity and overturning effects. After that, the internal columns that face higher axial forces are examined and then retrofitted, together with the installation of external shear wall jacketing. Here the main emphasis is on how well the shear is transferred between the older and newer concrete interfaces. Toward the end, the existing floor slabs are checked for both modified bending demands and potential punching shear failures. The results of this thesis give a kind of broad template for forensic, and rehabilitation engineers. In particular it provides useful perspectives on how to handle stiffness distribution, and how to reduce torsional seismic effects that can show up when external wall retrofitting is applied in vertically expanded structures.