Non-linear finite element analysis of wall-beam structures

Abstract

The composite action between masonry wall and its supporting beam concentrates the vertical loading applied on the top of wall close to the beam supports. This produces bending moments much less than would be expected when the full load is acting directly on the beam. The study of this composite action is of economic importance since if the concept is utilised, a rational design of the beam will be achieved. This thesis presents a comprehensive material model and its incorporation into non-linear finite element computer model for the analysis of wall-beam structures made with brickwork of solid brick subjected to uniformly distributed load. The program is incremental in nature and capable of reproducing the non-linear behaviour caused by material non-linearity and progressive local cracking and crushing. The program is thus capable of modelling the behaviour of wall-beam structures subjected to non-linear load from first crack to final failure. The material model used in this program is derived from tests on representative samples of brick, mortar and small samples of brickwork. In the finite element model brick, mortar, concrete and steel are treated as separate materials along with the simulation of actual directional effects of mortar joints. A series of failure criteria have been adopted to model the different modes of failure experienced in the constituent materials. Due to the crack sensitive nature of the problem, particular emphasis has been given to the modelling of cracking and the post-cracking behaviour of the materials, especially the manner in which the local stresses in the fractured region are redistributed. The results of finite element model have been verified by comparison with experiments on brick masonry wall-beam structures subjected to uniformly distributed load applied at the top and extending over the full length and thickness of the wall. Comparison with published literature reveals that the present method can provide a more comprehensive prediction of behaviour of the wall-beam structure up to failure load. Sensitivity analyses of the various parameters defining the material model and the boundary conditions have been carried out. With the important parameters thus obtained, the finite element model has been used to carry out a comprehensive parametric study of the behaviour of storey height wall-beams subjected to uniformly distributed load. Based on the findings of this study, design recommendations have been proposed. As the computer program developed can handle general cases with arbitrary geometry, loading and boundary conditions, recommendations for investigations of various other wall-beam structures have been made.