Seismic performance of single layer cylindrical lattice shells
Creators: name: Cedron Fernandez De Cordova, Francisco Javier
Publisher: name: Imperial College London
Year: 2020

description: This thesis examines the seismic behaviour and design of single layer cylindrical lattice shells, commonly used in applications such as train stations or sports halls. Although their design against gravity loads and buckling is well documented, their behaviour under seismic loading has received less attention, particularly when dealing with the development of design procedures in codes of practice. In this research, a parametric assessment is firstly carried out to determine the main factors influencing the dynamic characteristics of such shells, with a focus on key geometric ratios as well as mass properties and boundary conditions. As a result of this study, expressions are derived for the estimation of the fundamental period and associated mode of vibration as well as mass participation ratio, for the purpose of preliminary and simplified design. The seismic response of typical forms of single layer cylindrical lattice shell configurations, representing a wide range of rise to span ratios, is then assessed within the linear elastic range under selected earthquake excitations. Axial forces and bending moments from the various seismic loading scenarios are compared to those produced by gravity, with emphasis on the salient influence of the geometric rise to span ratio of the structure. Particular focus is also given to the relative influence of the horizontal and vertical seismic components on the internal actions, and the significance of their combined effects as a function of the shell geometry. Based on the results and observations, a simplified method for the estimation of internal forces produced by seismic actions is proposed. In order to provide a means for evaluating the underlying inelastic behaviour, the nonlinear static, or pushover, response of the shells is assessed. The plastic mechanisms that develop are examined and characterised for shells of various rise to span ratios. A simple pushover approach, which is suitable for this structural form, is suggested using a force profile obtained from the fundamental mode shape. The peak angle change is also proposed in this thesis as a novel damage parameter which is particularly suitable for characterising the inelastic global and local demands in shells of different geometries. The pushover assessments are subsequently followed by detailed incremental dynamic analyses in order to evaluate the nonlinear time history response of the shell structures under realistic earthquake excitations. The results provide detailed insights into the influence of the horizontal and vertical excitations on the nonlinear inelastic seismic response, and illustrate the suitability of the peak angle change as an inelastic deformation measure for shells of different geometries. The main findings from the linear and nonlinear assessments are highlighted within the discussions, culminating in an illustrative case study. Special attention is given to findings which are of relevance to performance based assessment procedures as well as simplified design approaches.