Seismic response of traditional buildings of Lefkas Island, Greece

This paper deals with the seismic response of the traditional buildings of Lefkas (also called ‘Lefkada’) Island in western Greece. These structures, with two up to four storeys, are met mainly in the old town of Lefkas, the capital of the island. The special structural characteristic of the traditional buildings of Lefkas (that is the issue of this article) is the dual load-carrying system used on ground floor level to handle vertical loads and seismic actions. The first main load-carrying system consists of single-storey stone masonry walls, while the second main load-carrying system consists of multistorey wooden frames at the inner perimeter of the ground-floor masonry walls. Therefore, the load-bearing system of the upper storeys, over the ground floor, consists of a wooden 3D frame with diagonal trusses that are infilled by walls of bricks and lime mortar. There is, also, a tiled wooden roof. During the earthquake of August 14th, 2003 ( M = 6.2 ) , partial collapse of the masonry walls took place in some cases at the low storey and some cracks around the openings were observed. In the upper floors, the load-bearing wooden frames did not suffer damage, but the brick infill cracked and out-of-plane falls were observed. In this paper, the analytical investigation of the seismic behaviour of such structures is developed, the identification of the main way of vibration of these systems is achieved, and both the explanation of the observed damages and the interpretation of the reasons for the development of these damages are performed. Finally, the results of a representative numerical model of a typical traditional building—from a series of examined models—with dual bearing system are presented and discussed, using as base excitation the two horizontal recorded components of the main earthquake ground motion that took place on August 14th, 2003, at Lefkas town, Greece.