Vulnerability Of Unreinforced Masonry Buildings Research Articles

Site effect influence on the seismic vulnerability of unreinforced masonry buildings in low to moderate seismic urban areas in Algeria

PurposeThis paper aims to develop preliminary damage scenarios for unreinforced masonry buildings located in low to moderate seismic hazard areas in Algeria, taking into account the specific site effects.Design/methodology/approachThree soil types were considered in this analysis according to the definition of the Algerian seismic code (RPA99/2003). Peak ground acceleration values were assigned to each soil type issued from a probabilistic seismic hazard analysis (PSHA). To highlight the effect of soil conditions on the seismic vulnerability analysis of masonry buildings, a site vulnerability increment is carried out, and the macroseismic Risk-UE method has been adopted and applied by developing two main seismic scenarios according to both return periods of the PSHA, 100 and 475 years, respectively.FindingsBased on the preliminary results of rock site condition, it can be outlined that the significant damage obtained for different earthquake scenarios discovered a substantial worldwide seismic risk to the building stock of the study area. Once the site effect is integrated into the analysis, more high values of vulnerability indexes and expected damages are obtained. Moreover, it can be concluded that soft soil (S3) is a little bit more influential than stiff soil (S2) on the final vulnerability index compared to (S1). However, the difference between the soil effect S2 and S3 on the vulnerability index can be neglected.Research limitations/implicationsResearchers are encouraged to test the mechanical approaches for more detailed outcomes of a specific building analysis.Practical implicationsThis research proves to the Algerian decision-makers that due to the site effects and the vulnerability of the masonry buildings, an urgent intervention program is required even for existing buildings located in low to moderate seismic hazard areas.Originality/valueSeveral seismic vulnerability types of research have been conducted in Algeria for the unreinforced masonry buildings in moderate to high seismic areas in which generally the soil effect is neglected. In this context, this research paper proves that due to the site effects and the vulnerability of the masonry buildings, special attention is required even for existing buildings located in low to moderate seismic hazard areas. With this conclusion, the requirement of taking into account the soli effect in the high seismic areas is even more pronounced and should be conducted.

Fragility curves for residential unreinforced masonry buildings prone to out-of-plane mechanisms: the case of the historical center of Sora

The earthquake events of the past and recent years highlight as the seismic protection of historical towns is a crucial and current issue in Italy, but also in many other earthquake prone areas of Europe, where severe damages and collapse of buildings have been observed after seismic events. In particular, significant damages have been detected in historic centers of small and medium towns, mainly characterized by unreinforced masonry buildings, highly vulnerable with regard to out-of-plane collapse mechanisms. In this context, the assessment of the seismic vulnerability of unreinforced masonry buildings is a fundamental issue, in that they represent the most widespread construction typology in Italian and European small and medium towns. One of the most effective approaches in predicting potential damages of building typologies, is based on the derivation of fragility curves. An important aspect that affects the construction of fragility curves is the choice of response spectra to define the seismic demand; both Italian code and European guidelines allow the use of natural records, but also propose to employ smoothed spectra, in that the first one is hardly applicable by practitioners. Nevertheless, the employment of the smoothed spectra does not allow for adequate considerations about the influence of record-to-record variability. Downstream of this brief discussion, the paper presents the evaluation of fragility curves for unreinforced masonry buildings typical of the Central Italy, prone to the occurrence of out-of-plane collapse mechanisms, by considering both the spectral-shapes directly derived from the Italian codes and spectra obtained by the selection of natural accelerograms.

An expeditious tool for the vulnerability assessment of masonry structures in post-earthquake reconstruction

AbstractPost-earthquake reconstruction activities need tools for assessing the vulnerability of structures, based on visual inspection and quick survey. So far, the public administrations in charge of granting the funds and monitoring reconstruction have adopted different methods taken from scientific literature or developed ad hoc for specific events. The time is ripe for a standard method to be developed, treasuring from the lessons learned in the field. This paper proposes an expeditious tool based on visual survey for the assessment of the seismic vulnerability of unreinforced masonry buildings, starting from available methods, whose parameters were reassessed and recalibrated, and scientific evidence from recent literature. The influence of the main structural features was considered to calculate a vulnerability index in the 0–100 range. The effects of materials and arrangement of masonry were quantitatively evaluated through the masonry quality index, which represents an advancement with respect to current practice. The method was validated on a sample of 50 masonry aggregates and nearly 200 structural units of L’Aquila, Italy, where reconstruction is underway after a destructive earthquake in 2009. The sample is representative of the built heritage of other earthquake prone areas in Italy and many European Countries and the proposed method is a step forward the development of a standard tool to be used in future post-earthquake reconstruction scenarios.

Optimal seismic retrofitting techniques for URM school buildings located in the southwestern Iberian peninsula.

This paper aims to study different seismic retrofitting techniques to test the reduction of the seismic vulnerability of unreinforced masonry buildings. Three techniques have been considered in a case study: adding steel or carbon fibre reinforced polymer grids in the walls and steel encirclements in the openings. The performance-based method has been used to that purpose. Nonlinear static analyses have been performed to obtain the capacity and fragility curves, the performance point and the damage level states. Moreover, an analysis of the cost-benefit ratio has been carried out. Results have shown that the three techniques have produced considerable improvements. The addition of encirclements has reduced the deformation resulting in a slight increase of the structure’s stiffness. Adding steel grids has produced the maximum peak strength increase while adding polymer grids has produced the largest ultimate displacements. Adding encirclement has had the best cost-benefit ratio.

Effect of out-of-plane behavior on seismic fragility of masonry buildings in Turkey

This study focuses on the evaluation of seismic safety of unreinforced masonry buildings in Turkey by using fragility curves generated for two behavior modes of load bearing walls: in-plane and out-of-plane. During generation of fragility curves, a force-based approach has been used. There exist two limit states in terms of base shear strength for in-plane behavior mode and flexural strength for out-of-plane behavior mode. To assess the seismic vulnerability of unreinforced masonry buildings in Turkey, fragility curves generated for in-plane behavior were verified by the observed damage during the 1995 Dinar (Turkey) earthquake and fragility curves generated for out-of-plane behavior were verified by the observed damage during the 2010 Elazig (Turkey) earthquake. The verification results reveal that the proposed fragility-based procedure can provide an alternative for the seismic safety evaluation of unreinforced masonry buildings in Turkey. Using this procedure, it becomes possible to investigate a large population of masonry buildings located in regions of high seismic risk in a short period of time. The obtained results are valuable in the sense that they can be used as a database during the development of strategies for pre-earthquake planning and risk mitigation for earthquake prone regions of Turkey.

Assessment of the seismic vulnerability of unreinforced masonry buildings

A methodology for seismic vulnerability analysis of URM buildings is presented. It includes the estimation of capacity curves for typical building classes, as well as vulnerability (fragility) curves in terms of peak ground acceleration (PGA). The methodology for developing vulnerability curves is based on a hybrid approach, combining statistical data with appropriately processed results from nonlinear static analyses that permit extrapolation of statistical data to intensities for which no data are available. The data used are statistical, derived from Greek earthquakes, the Thessaloniki 1978 and the Aegion 1995 events, with some additional data from the Pyrgos 1993 earthquake used for comparison purposes. The databases of the first two earthquakes are briefly presented and processed using a filtering technique. The resulting hybrid vulnerability curves correlate PGA to the probability that a building type exceeds a particular damage state.

OUT-OF-PLANE SEISMIC RESISTANCE OF MASONRY WALLS

Seismic vulnerability of unreinforced masonry buildings is studied by means of simplified out-of-plane collapse mechanisms that take into account connections with transversal walls. According to experimental evidence, the analysis assumes that failure is reached with a rigid body motion of a part of the facade that falls down. Two classes of mechanism are examined: the overturning of the facade due either to a vertical crack at the connection or a diagonal crack on the transversal wall, both defined resorting to a simple model of masonry fabric, viewed as a regular assembly of rigid blocks and elastic plastic joints with friction but no cohesion. The use of simplified mechanisms give rise to an explicit evaluation of the seismic resistance to changes in the geometry and in the masonry fabrics, that could be used by practising engineers. This formulation is developed for both static horizontal actions and ground velocity peak, in the belief that the latter probably gives a better approximation of seismic action, while also providing, by comparison with the results of static forces, an estimate of the behaviour factor for unreinforced masonry. Eventually, the analytical forecasts are compared with numerical results obtained by means of the distinct element method.

Damage from 20th century earthquakes in eastern Canada and seismic vulnerability of unreinforced masonry buildings

This paper has been prepared as a reminder of past damaging earthquakes in eastern Canada and as a testimony of the damage suffered; isoseismal maps of five selected eastern Canadian earthquakes are presented as well as illustrations of their effects. Although features of the four older historical events reviewed herein are reasonably well documented (although not to present standards), data of engineering significance needed to perform accurate seismic-resistance evaluations have been for the most part lost owing to the time elapsed. Hence, the damage examples presented herein should not be construed as a comprehensive survey but rather as a sampling of noteworthy failures. Since most of the structural damage produced by these earthquakes was suffered by unreinforced masonry buildings, an overview of the seismic risks they constitute and their main modes of failure is presented. The first step of a coordinated seismic risk reduction plan is also formulated; its application is recommended for the mitigation of economic and human losses in future eastern Canadian earthquakes. Key words: case histories, earthquakes, eastern Canada, seismic risk reduction plan, structural damage, unreinforced masonry buildings.