INFLUENCE OF TYPICAL TIMBER JOIST-TO-WALL CONNECTIONS ON THE PERFORMANCE OF UNREINFORCED MASONRY STRUCTURES OF THE KATHMANDU VALLEY

Abstract

Earthquake-resistant elements such as timber wedges in the joist-to-wall connection have been employed throughout traditional unreinforced masonry (URM) construction in the Kathmandu Valley. Even so, the damage pattern during the 2015 Gorkha earthquake of these traditional structures shows out-of-plane failure as a common occurrence. These private dwellings are typically old construction and the properties of the masonry are not known. The characterization of the mechanical properties of masonry is done through non-destructive tests for brick units and mud mortar. Three in-situ tests have been performed, namely the rebound hammer, pendulum hammer and penetrometer test. The results of the non-destructive found evidence of poor quality of the masonry mostly attributed to poor strength of mortar. This study investigates the effect of typical joist-to-wall connections in an attempt to gain insight into the failure modes and capacity of traditional structures through a parametric study. Detailed finite element models have been developed to carry out the parametric study on various connection typologies focusing on the level of joist insertion inside the wall and the use of timber wedges. A nonlinear static (pushover) analysis is performed on a traditional structure representing the typical building stock, to simulate the influence of the joist-to-wall connection in the seismic performance of traditional private dwellings. The analysis results are compared for structures with and without timber wedges. The capacity curves demonstrate a 1.3 to 1.5 times increase in the overall capacity of the structures with timber wedges compared to the structures without timber wedges. This finding is also supported by the observed failure mechanism where the coupling of parallel walls led to significant in-plane cracking for structures with timber wedges while vertical cracks at the intersection between orthogonal walls governed the failure of structures without timber wedges. This thesis is an attempt to contribute to the understanding of the structural behaviour of traditional construction in the Kathmandu Valley.