Methodology for practical seismic assessment of unreinforced masonry buildings with historical value

Abstract

Summary Historical constructions are part of the world heritage, and their survival is an important priority. Comprising mostly unreinforced, load‐bearing masonry, heritage buildings may date anywhere from antiquity to the 19th and early 20th century. Being exposed to the elements over the years, they are in various states of disrepair and material degradation. Based on postearthquake reconnaissance reports, these structures occasionally behave rather poorly, even in moderate seismic events, undergoing catastrophic damage and collapse, whereas retrofitting is governed by international conventions regarding noninvasiveness and reversibility of the intervention. The complexity of their structural systems (continuous structural components, lack of diaphragm action, material brittleness, and variability) challenges the established methods of condition assessment of preretrofitted and postretrofitted heritage constructions. The most advanced state of the art in materials and analysis tools is required, far more complex than with conventional buildings. Thus, an assessment procedure specifically geared to this class of structures is urgently needed, in order to assist engineers in this endeavor. The objective of this paper is the development of a performance‐based assessment framework that is palatable to practitioners and quite accurate in seismic assessment of unreinforced masonry buildings with no diaphragm action. The underlying theoretical background of the method is illustrated with reference to first principles: global demand is obtained from the design earthquake scenario for the region, using empirical estimates for the prevailing translational period of the system; deformation demands are localized using an approximation to the translational 3‐D shape of lateral response, estimated using a uniform gravitational field in the direction of action of the earthquake; acceptance criteria are specified in terms of relative drift ratios, referring to the in‐plane and the out‐of‐plane action of the masonry piers. The quantitative accuracy of the introduced procedure is evaluated through comparison with detailed time‐history dynamic analysis results, using a real life example case study. Qualitative relevance of the results is evaluated through comparison of the location and extent of anticipated damage estimated from the proposed assessment procedure, with reported records of the building damages that occurred during a significant past earthquake event.

An engineering approach for evaluating the dynamic response of acceleration‐sensitive secondary systems in flexible structures

“…The alternative that gives the most accurate picture of Ψ PRD,i , yet requires the largest computational effort, is the Inertial Pushover Analysis (IPA). 56 Throughout this analysis procedure, the 3D primary structure is modeled by the Finite Element Method (FEM), considering either elastic or inelastic member response and analyzed quasi-statically. The load combinations considered are (a) the action of the vertical loads for the seismic load combination G+ψ E ⋅Q 54 and (b) the action of a notional lateral field of accelerations, A i , applied in each of the two principal directions and/or in the vertical direction, depending on the type of earthquake loading (see Figure 3).…”

“…As demonstrated in Pardalopoulos and Pantazopoulou, 56 the inertial pushover analysis can be performed on any structure, regardless of its type (eg, steel, reinforced concrete, masonry, timber), plan view, and height. This means it can be performed on torsionally sensitive structures, on structures with setbacks and on structures with soft story formation, irrespective of any level of diaphragm action.…”