Seismic response of traditional masonry buildings: Parametric study and evaluation

Post earthquake reconnaissance studies on masonry buildings have revealed as primary modes of failure diagonal cracking, out-of-plain bending and detachment of perpendicular connected walls. The rehabilitation of seismic resistance of these structures, the importance of which lies in maintenance and survival of the historical and cultural information they carry, usually is limited to repair options consistent with the architecture and the materials of the entity. However, these structures have to be handled through the framework of a rational and easy-to-apply methodology for assessment of their seismic capacity and definition of possible intervention scenarios when such a need is dictated from the assessment stage. The paper presents a simple procedure that is derived from first principles, using an equivalent single degree of freedom model to estimate seismic demands and the Mohr-Coulomb criterion to establish the dependable stone pier capacity. A parametric investigation is conducted to evaluate the stress amplification and effect on failure mode resulting from the presence of openings whereby important variables are, the area ratio and position of the openings. The primary conclusion drawn from the study is that masonry walls containing the greatest number of openings are the most vulnerable regardless of the direction of action of the earthquake (either in-plane or out of plane) as they represent the point of concentration of deformation demand in the structure. visual screening and detailed finite element simulation of historical buildings represent the two most remote ends in the spectrum of methods used today for the purposes of seismic assessment of structures. Rapid screening based on visual observation can only assess the condition of the structure and possible damages. Detailed F.E. solutions are fraught with uncertainty with regards the mechanical behavior of the materials, the extent of damage, and the actual state of interaction that occurs at the interfaces of different materials (e.g. timber and mortar or stones, soil with masonry, etc.); this approach is calculation-intensive and as such, it is most likely intended for the more important historical structures. Following the axiom that the intensity of the effort required to obtain a result, at least in the initial phase, should be compatible with the level of confidence associated with the input data and information, clearly alternative assessment procedures are required, lying between the two extreme options mentioned above, and tailored to the needs of seismic assessment of common traditional buildings. This paper presents such a simplified procedure intended to be used as a first order assessment tool of the seismic resistance of stone-masonry traditional houses. In the first phase, using simple mechanistic tools (a Mohr-Coulomb failure criterion and the Bernoulli hypothesis) the dependable base shear strength, VRd, of a typical structure under lateral seismic forces, VSd, is estimated. The VRd value depends on the gravity load, the hazard spectrum, the mechanical properties of the constituent materials, and the structural geometry. Structural adequacy is determined through the inequality: