Comparison of dynamic behaviours of retrofitted and unretrofitted cob material walls

Abstract

This paper presents the results of shaking table tests of shear wall panels made of cob materials. A proposed low-cost retrofit design was applied on one of the panels. The retrofitting was carried out with vertical bamboo sticks and horizontal layers of plastic coated steel wire mesh. A similar wall panel without retrofit was used as a control specimen. The wall panels were 1 m in height and length each with a thickness of 150 mm. The height and thickness were selected to simulate one-third model dimensions of the prototype walls employed in cob buildings in Balochistan, Pakistan. The walls were instrumented with accelerometer and string pots to measure acceleration and displacement, respectively. The decay in the dynamic characteristics of the retrofitted wall panel was less than the unretrofitted control wall panel. The displacement and acceleration of the unretrofitted control specimen increased drastically after a peak ground acceleration (PGA) of 1 g (0.33 g in the prototype domain). The acceleration response of the control specimen decreased at a PGA of 2.25 g (0.75 g in the prototype domain) and it failed by toe crushing at a PGA of 4.55 g (1.52 g in the prototype domain). No significant damage or change in the behaviour of the retrofitted wall panel was observed up to a PGA of 5.19 g (1.73 g in the prototype domain). The applied in-plane moment on the unretrofitted wall panel reached to a maximum value at a PGA of 1.23 g (0.41 g in the prototype domain) whereas the retrofitted wall was subjected to similar maximum moment at a PGA of 3.43 g (1.14 g in the prototype domain). The results clearly indicate that the proposed retrofit design is effective in improving the in-plane response of the cob shear wall and can be used for both the existing and new cob structures.