Effectiveness of Base Isolation Systems for Seismic Response Control of Masonry Dome

Abstract

AbstractDomes are constructed historically over the last many centuries. They are doubly curved structures, without angles and corners. The most important advantage of dome structures is that they enclose an enormous amount of column-free interior space, in addition to providing decent aesthetic sight. Historically, domes were built of masonry material. Masonry structures have very low ductility, and hence they are weak in resisting the lateral loads. Most of the domes are designed for gravity loads using simple geometrical rules, considering the dome as an arch of identical section. Due to the absence of reinforcement in the masonry domes, their thickness must be kept high to resist the tensile stresses. Because of their large thickness, masonry domes attract a large magnitude of seismic forces due to higher mass thus, making them vulnerable to earthquake excitations. Due to earthquake forces, the masonry domes are subjected to tensile forces at the bottom rings and as a result, cracks are developed in the bottom parts of domes. The conventionally designed and constructed masonry domes are vulnerable to severe damage or total collapse under strong seismic excitations. To preserve these ancient structures of historic importance from being damaged due to seismic excitations, base isolation can prove to be a very effective technique. In the present research, seismic response of the case study masonry dome of span 25 m, located in Maharashtra, India, is investigated analytically. The specific objectives of the study are (i) to analyse the seismic performance of the fixed base masonry dome structure under real earthquake ground motions, (ii) to analyse the seismic performance of the masonry dome installed with base isolation systems, viz. lead rubber bearings (LRB) and friction pendulum systems (FPS) and (iii) to compare the seismic performance of the fixed base masonry dome with that, installed with LRB and FPS. The response of the base-isolated dome is obtained using SAP2000 by performing nonlinear time history analysis and is compared with the corresponding response of the conventional dome without base isolators. The nonlinear time history analysis is performed considering real earthquake ground motions of PGA ranging between 0.1 g and 0.35 g. The effectiveness of base isolation technique in improving the response of the dome is explored. The major evaluation criteria considered are tensile stresses, base shear and displacement at the apex point of the dome. It is observed that the seismic response of the base-isolated dome diminishes significantly in comparison with the conventionally constructed dome, depicting the effectiveness of the base isolation strategy. Both, the elastomeric and sliding systems, are found to be very effective in decreasing the response quantities, substantially. The force–displacement loops for both the isolators show considerable energy dissipation. The original uniqueness and aesthetic value of the historical monumental dome are maintained unaltered, even after employing base isolators at the foundation level of the dome.KeywordsMasonry domesBase isolationLead rubber bearingFriction pendulum systemNonlinear time history analysisSAP2000