OUT-OF-PLANE BEHAVIOUR OF UNREINFORCED MASONRY INFILL PANELS

Abstract

The study presented herein, aims at investigation of out-of-plane behaviour of unreinforced masonry infill panels in frame buildings. In the present study, the focus has been on the out-of-plane action due to inertia effect of the panels. The URM infill panels, with different geometric configurations and boundary conditions, have been tested under static and dynamic out-of-plane loading. The thesis also presents, non linear static and dynamic analysis of the URM infill panels using Distinct Element Method (DEM). The investigations have been carried out on URMpanels made of burnt clay half scale bricks. First, compressive strength and the Modulus of Elasticity of the masonry have been determined by compression test on prisms. A study has been performed on small size masonry panels of two different thicknesses, by testing them in one way out-ofplane bending, parallel and perpendicular to joints, under displacement controlled loading. The bending strength of the panels has been calculated based on grosssection, taking into account the self-weight of the panels. The load-deflection curves and Modulus of Rupture have been obtained in the two orthogonal directions. It has been observed that as the thickness of unrestrained panel increases, the flexural tensile strength perpendicular to bed joints decreases. The ratio of Modulus of Rupture in the two orthogonal directions has also been computed and observed to be close to the values given in masonry codes and those reported by other investigators. To study the influence of end restraint on the flexural strength perpendicular and parallel to joints, similar tests have been carried out, with the supported edges restrained against rotation. The restrained panels have shown a significant increase in average bending strength about both the axes, accompanied by large deflections at ultimate state, demonstrating considerable ductility. The value of Orthogonal Strength Ratio, R for the restrained panels has been observed to be less than the corresponding values for unrestrained panels. The observed compressive strength, Modulus of Elasticity and flexural tensile strength perpendicular to joints has been used for the analytical simulation of URM panels under out-of-plane static and dynamic loading, using DEM. The classical Mohr-Coulomb criterion has been used to simulate the failure of masonry within the in DE model blocks and slip at joints between the blocks. The elastic properties and tensile strength of masonry have been taken directly from the test results, while the normal and shear joint stiffnesses and cohesion in the masonryhave been obtainedby a sensitivity analysis. The friction angle has been taken as 35°, from the literature. The DE model was able to simulate the behaviour and failure pattern of unrestrained and restrained panels, under out of plane bending for both the orientations of the bed joints. The simulated load-deflection curves, for panels with different boundary conditions and thicknesses, have been found to be close to those obtained, experimentally. An experimental study has been carried out on one-way and two-way spanning unreinforced burnt clay brick masonry infill panels, constructed within rigid reinforced concrete frames, under dynamic loading. The panels were tested on Shock Table, subjected to primarily impulsive motion, characterised by high acceleration, high frequency and short duration. The two-way spanning infill panels have also been tested with window and door openings. Modes of failure of the various panels, the sustained peak acceleration and observed displacements have been presented. The mode of failure in one-way spanning panels subjected to out-of-plane dynamic loading has been characterised by cracks along the bed joints in the middle and at the top of the panel, with full brick thick panel displaying significant arching action. In two-way spanning panels, significant arching action has been observed in all of the tested panels. In case of two-way spanning panels, the crack pattern depended on the slenderness ratio of the panel. In half brick thick panel (/z/f=28), the crack pattern was similar to the yield line pattern of two-way slab. In case of thicker panels, after initial horizontal cracks in the middle and top, vertical cracks were observed along the centre-line in the upper half of the panel. In case of infill panels with window and door openings, the cracks originated from the corner of the openings and progressed diagonally to the corners of the panels. The damage in the various panels at different shocks has been quantified in terms of Damage Index. The behaviour of the various panels under dynamic loading has also been simulated using DEM. The blocks in the DE model have been assumed to be linear elastic, while the contacts at the interface between the blocks, and between blocks and the frame, have been assumed to follow an elasto-plastic law with Coulomb-slip criterion. The IV modes of failure and the displacements obtained from the DE model have been compared with the experimental results and found to be in good agreement