Fragility curves and loss estimation for traditional timber-framed masonry buildings in Lefkas, Greece

The 2003 earthquake in the Greek island of Lefkas, has revived the interest for the local anti-seismic technique based on the use of timber-framed masonry, whose adequate performance during the earthquake revealed the merits of this rather sophisticated, albeit traditional, construction. A key feature of the Lefkas structures is their dual structural system. The secondary system is activated once the ground storey stone masonry piers of the primary system (which includes timber-framed masonry in all storeys) fail. In this regard, two different structural models are presented herein to simulate the response of each system. A macro-model based on nonlinear (NL) strut elements and point plastic hinges is intended to model the timber-framed masonry. NL analyses are carried out for one, two and three storey buildings, which represent the most common cases in Lefkas. Furthermore, an investigation is carried out regarding the foundation of the buildings resting on soft alluvial deposits. Pushover curves are derived from the NL analyses of the buildings and are then converted to capacity curves using the characteristics of the predominant mode. On these curves four damage states (slight damage, moderate damage, heavy damage, and collapse) are defined on the basis of criteria related to the actual response of the building. Then, fragility curves in terms of spectral displacement are generated, adopting a log-normal statistical distribution. These curves are converted into PGA values using a selected response spectrum. Utilising these fragility curves a seismic loss scenario for the 2003 Lefkas earthquake is developed for the timber-framed masonry stock of Lefkas city.