Energy Absorption Capacity Of Rat-Trap Bond Masonry Under Base Excitation

Brick masonry does not exhibit much capacity to resist lateral loads and hence the masonry suffers heavy damage during earthquakes, which impart lateral loads to structures. In the Bhuj earthquake of Jan 26, 2001, that occurred in majority of masonry structures failed because they were built with un-reinforced brick masonry. The EBC code of practice for brick masonry, suggests the use of lintel band and roof band that introduce a rigid box-type behavior which will help the structure to improve its performance against seismic loads. But there are no Codal provisions for use of Rat-Trap bond masonry which has been found to possess good seismic resistance characteristics. Rat-Trap bond system consists of an array of headers and stretchers with bricks laid vertically on the edge to form a cavity within a set of two headers and two stretchers. In this investigation, an attempt has been made to study the behavior of un-reinforced Rat-Trap bond masonry of two categories viz., (i) with roof slab, and (ii) without roof slab. Shock-table tests on one-third scale masonry building models ( with and without roof slabs ) were carried out to study the behavior. The peak accelerations were recorded for each shock. The scaled bricks were obtained by cutting locally available bricks using special tools. The size of the masonry models was 2m x 1m x 1m. The amount of energy imparted during each shock was measured before total collapse both for Rat-Trap bond masonry models with and without roof slabs. The results of the tests revealed that the roof weight plays an important role in the design of Rat-Trap masonry systems subject to seismic loads.