Dynamic Modelling of Ujjayanta Palace—A Heritage Load-Bearing Masonry Building

Abstract

This paper discusses the modelling of the Ujjayanta Palace building, a highly asymmetrical load-bearing masonry structure, for the purpose of carrying out time history analysis for earthquake inputs. The analysis enabled the ductility-based design, which was a major requirement for seismic retrofitting of the heritage building. The building is situated at Agartala, the capital of the state of Tripura. The building has a number of piers which are assumed to carry the axial gravity loads and the lateral seismic forces. The asymmetry in the plan and elevation necessitated the development of a relatively simple model which includes the lateral sway modes as well as the torsional modes of vibration. Thus, the scheme included calculation of the location of the mass and stiffness centre in each floors. The in-plane and the out-of-plane stiffness of the masonry piers were included in the formulation of the stiffness matrix. The seismic mass lumped at the floor levels were obtained in accordance with the provisions of IS-1893 (2002). After setting up the coupled equations of motion, which included three degrees-of-freedom (translations in the two horizontal directions and rotation about the vertical axis passing through the mass centre) for each floor, the mass matrix and stiffness matrices were obtained. Later, the seismic forces were computed in each of the masonry piers by solving the equations of motion using a numerical integration scheme. The earthquake inputs were taken by considering the site-specific earthquake parameters. This dynamic analysis enabled the crucial computation of the deformation of the masonry piers, following which a containment reinforcement scheme was detailed.