Retrofitting of RC Footings Subjected to Settlement Due to Earthquake

Abstract

AbstractRetrofitting of a structure is carried out after condition assessment, as the outcome of the assessment determines whether the damage taken place in the distressed building is within repairable limits or not. RC jacketing, steel jacketing and FRP wrapping are some of the methods for retrofitting of RC structures. The outcome of retrofitting of a structure that has priorly undergone damage due to earthquake are, increase in lateral strength and stiffness of the structure, increase in ductility of members present, thereby avoiding brittle failure of the structural members. The present work is a simulation of a practical work of retrofitting of isolated RC footings carried out in an existing old five storey RC structure used for commercial purpose that has been constructed in zone IV. A 3D model of the five storey RC structure along with isolated footings (plate elements) resting on the soil (solid elements) has been modelled in SAP2000. The soil on which the RC footings along with the structure stands upon has been modelled having three layers having the respective soil properties (unit weight, elastic modulus and Poisson’s ratio). Live loads conforming to IS 875-part 2 for commercial occupancy has been considered in the structure. Response spectrum method is adopted to carry out the earthquake analysis. In the present work, the assessment of settlement of isolated RC footings that is provided to support RC columns, present in the five storey RC structure subjected to earthquake loading is carried out initially. After assessing the settlement in the RC footings, retrofitting of the RC footings is carried out adopting section enlargement/RC jacketing method. Two different sizes of RC jackets (2 m × 2 m × 0.9 m and 2.5 m x 2.5 m × 1 m) are modelled and applied individually on to the existing RC footings, and the analysis was carried out. It was observed from the analysis results that, the RC jacket having a size 2.5 m × 2.5 m × 1 m that was actually provided around an existing RC footing (1.5 m × 1.5 m × 0.6 m) in the building, was found to restore the footing and the structure from further settlement due to the existing and seismic loads. As an alternate study, analysis was carried out considering steel columns having slab bases were introduced in between the existing RC columns whose footings had settled, to support the floor loads to possibly reduce the settlement of existing isolated footings along with the RC jackets around them.KeywordsRetrofittingEarthquake loadingIsolated footingFoundation settlementSection enlargementEncased columns with slab base