Pushover-based seismic risk assessment and loss estimation of masonry buildings

A pushover-based seismic risk assessment and loss estimation methodology for masonry buildings is introduced. It enables estimation of loss by various performance measures such as the probability of exceeding a designated economic loss, the expected annual loss, and the expected loss given a seismic intensity. The methodology enables the estimation of the economic loss directly from the results of structural analysis, which combines pushover analysis and incremental dynamic analysis of an equivalent SDOF model. The use of the methodology is demonstrated by means of two variants of a three-storey masonry building both of which have the same geometry, but they are built, respectively, from hollow clay masonry (model H) and solid brick masonry (model S). The probability of collapse given the selected design earthquake corresponding to a return period of 475 years was found to be negligible for model H, which indicates the proper behaviour of such a structure when designed according to the current building codes. However, the corresponding probability of collapse of model S was very high (46%). The expected total loss given the design earthquake was estimated to amount to 28 000 € and 290 000 €, respectively, for models H and S. The expected annual loss per 100 m² of gross floor area was estimated to amount to 75 € and 191 €, respectively, for models H and S. For the presented examples, it was also observed that nonstructural elements contributed more than 50% of the total loss.     

Shaking table study and modelling of seismic behaviour of confined AAC masonry buildings

The response of autoclaved aerated concrete confined masonry buildings to seismic ground motion has been studied. Three 1:4 scale models of residential buildings with the same distribution of walls in plan but different types of floors and number of stories have been tested on a uni-directional shaking table. Lightweight prefabricated slabs have been installed in the case of the three-storey model M1, whereas reinforced concrete slabs have been constructed in the case of three-storey model M2 and four-storey model M3. Model M1 was subjected to seismic excitation along the axis of symmetry, whereas models M2 and M3 were tested orthogonal to it. Typical storey mechanism, characterised by diagonal shear failure mode of walls in the ground floor in the direction of excitation has been observed in all cases. Taking into consideration the observed behaviour, a numerical model with concentrated masses and storey hysteretic rules has been used to simulate the observed behaviour. Storey resistance curves calculated by a push-over method and hysteretic rules, which take into account damage and energy based stiffness degradation hysteretic rules, have been used to model the non-linear behaviour of the structure. Good agreement between the experimentally observed and calculated non-linear behaviour has been obtained.     

A simplified methodology for the seismic assessment of masonry buildings with RC slabs

The present paper aims to contribute to the knowledge concerning the seismic assessment of load bearing masonry buildings with reinforced concrete slabs. The final goal of the present research was to propose a simple, yet accurate, methodology to assess the seismic safety of existing masonry buildings. The methodology here presented was based on the so-called ICIST/ACSS methodology with major improvements such as the extension to load bearing masonry wall buildings and the consideration of the effects of one of the most common strengthening solutions for masonry walls, here referred to as reinforced plastering mortar, as well as the possibility of considering four levels of increasing refinement: global, by alignment, by wall panel and by wall element. An extended research was performed on the existing methodologies to evaluate the seismic structural risk of load bearing masonry buildings, briefly describing methodologies similar to the one proposed, namely all of those that have in common the fact that they are based in the physical comparison between the resisting and acting shear forces at all storeys and along the two orthogonal horizontal directions. A case study is presented to check the applicability of the proposed methodology. The case study showed that the proposed methodology is relatively simple to apply and has a sufficiently good accuracy when compared with alternative methodologies. The degree of refinement of the analysis (global, by alignment, by wall panel and by wall element) must be taken into consideration and successively more complex analyses may be required when the results of simpler analyses are inconclusive.     

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

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.     

A framework for the seismic assessment of existing masonry buildings accounting for different sources of uncertainty

The current formulation of Eurocode 8 Part 3 and the Italian building code for the seismic assessment of existing buildings accounts for epistemic (knowledge‐based) uncertainties by means of the identification of knowledge levels with associated values of the so‐called confidence factors, applied only as a reduction of material strengths. This formulation does not always produce consistent results and it does not explicitly account for other sources of uncertainty. The paper proposes a probabilistic methodology for the quantification of appropriately defined factors, allowing consideration of the different sources of uncertainty involved in the seismic assessment of masonry buildings by means of nonlinear static analyses. This simple approach, also including an alternative formulation of the confidence factors related with material properties, allows to obtain results which are consistent with the acquired level of knowledge and correctly account for the different sources of uncertainty without requiring to carry out any stochastic nonlinear analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

多层砌体房屋抗震加固方法述评

本文讨论了多层砌体房屋抗震加固的原则,对目前常用的多层砌体房屋的加固方法进行了简要的论述,提出了各种方法的特点和适用范围以及需要注意的问题,并指出了将来可能的发展方向。     

Modelling methods of historic masonry buildings under seismic excitation

Historic masonry buildings in seismically active regions are severely damaged by earthquakes, since they certainly have not been explicitly designed by the original builders to withstand seismic effects, at least not in a ‘scientific’ way from today’s point of view. The assessment of their seismic safety is an important first step in planning the appropriate interventions for improving their pertinent resistance. This paper presents a procedure for assessing the seismic safety of historic masonry buildings based on measurements of their natural frequencies and numerical simulations. The modelling of the brittle nonlinear behaviour of masonry is carried out on the macro-level. As an example, a recently completed investigation of the seismic behaviour of the Aachen Cathedral is given, this being the first German cultural monument to be included in the UNESCO cultural heritage list in 1978. Its construction goes back to the 9th century a.d. and it is considered as one of the finest examples of religious architecture in Central Europe. The investigation is based on measurements of the natural frequencies at different positions and numerical simulations using a detailed finite element model of the Cathedral.     

Consideration of aging and SSI effects on seismic vulnerability assessment of RC buildings

At present, the seismic vulnerability assessment of reinforced concrete (RC) buildings is made considering fixed base conditions; moreover, the mechanical properties of the building remain intact in time. In this study we investigate whether these two fundamental hypotheses are sound as aging and soil-structure interaction (SSI) effects might play a crucial role in the seismic fragility analysis of RC structures. Among the various aging processes, we consider the chloride-induced corrosion based on probabilistic modeling of corrosion initiation time and corrosion rate. Different corrosion aspects are considered in the analysis including the loss of reinforcement cross-sectional area, the degradation of concrete cover and the reduction of steel ultimate deformation. SSI is modeled by applying the direct one-step approach, which accounts simultaneously for inertial and kinematic interactions. Two-dimensional incremental dynamic analysis is performed to assess the seismic performance of the initial uncorroded ( \(\hbox {t}=0\) years) and corroded ( \(\hbox {t}=50\) years) RC moment resisting frame structures, having been designed with different seismic code levels. The time-dependent fragility functions are derived in terms of the spectral acceleration at the fundamental mode of the structure \(\hbox {S}_{\mathrm{a}}(\hbox {T}_{1}\) , 5 %) and the outcropping peak ground acceleration for the immediate occupancy and collapse prevention limit states. Results show an overall increase in seismic vulnerability over time due to corrosion highlighting the important influence of deterioration due to aging effects on the structural behavior. Moreover, the consideration of SSI and site effects may significantly alter the expected structural performance leading to higher vulnerability values.     

A nonlinear macroelement model for the seismic analysis of masonry buildings

The macroelement technique for modelling the nonlinear response of masonry panels is particularly efficient and suitable for the analysis of the seismic behaviour of complex walls and buildings. The paper presents a macroelement model specifically developed for simulating the cyclic in‐plane response of masonry walls, with possible applications in nonlinear static and dynamic analysis of masonry structures. The model, starting from a previously developed macroelement model, has been refined in the representation of flexural–rocking and shear damage modes, and it is capable of fairly simulating the experimental response of cyclic tests performed on masonry piers. By means of two internal degrees of freedom, the two‐node macroelement permits to represent the coupling of axial and flexural response as well as the interaction of shear and flexural damage. Copyright © 2013 John Wiley & Sons, Ltd.     

Empirical seismic vulnerability analysis for masonry buildings based on school buildings survey in Iran

School facilities in Iran, in particular masonry schools, have shown poor performance during past earthquakes and can be identified as one of the parts of the country’s infrastructure that is most vulnerable to earthquakes. Hence, in this paper a method to perform index-based damage assessment for brick masonry schools located in the province of Yazd, the central region of Iran, using a comprehensive database of school buildings, is proposed. The database was obtained from the field survey forms applied for each observed school to collect the features of and damage to the structure. The results of a vulnerability index method developed in Iran are employed as input data to obtain empirical fragility curves for the school inventory. The Macroseismic model and GNDT II level method are two empirical methods combined in this procedure. Finally, the procedure is verified using damage survey data obtained after recent earthquakes (1990 Manjil–Rudbar earthquake and 2003 Bam earthquake) that occurred in Iran.     

Seismic fragility assessment of low-rise stone masonry buildings

Many historic buildings in old urban centers in Eastern Canada are made of stone masonry reputed to be highly vulnerable to seismic loads.Seismic risk assessment of stone masonry buildings is therefore the first step in the risk mitigation process to provide adequate planning for retrofit and preservation of historical urban centers.This paper focuses on development of analytical displacement-based fragility curves reflecting the characteristics of existing stone masonry buildings in Eastern Canada.The old historic center of Quebec City has been selected as a typical study area.The standard fragility analysis combines the inelastic spectral displacement,a structure-dependent earthquake intensity measure,and the building damage state correlated to the induced building displacement.The proposed procedure consists of a three-step development process:(1) mechanics-based capacity model,(2) displacement-based damage model and(3) seismic demand model.The damage estimation for a uniform hazard scenario of 2% in 50 years probability of exceedance indicates that slight to moderate damage is the most probable damage experienced by these stone masonry buildings.Comparison is also made with fragility curves implicit in the seismic risk assessment tools Hazus and ELER.Hazus shows the highest probability of the occurrence of no to slight damage,whereas the highest probability of extensive and complete damage is predicted with ELER.This comparison shows the importance of the development of fragility curves specific to the generic construction characteristics in the study area and emphasizes the need for critical use of regional risk assessment tools and generated results.     

Simple and complex modelling of timber-framed masonry walls in Pombalino buildings

Timber-framed (TF) masonry has been developed as an effective lateral-load resisting system in regions of high seismicity such as Southern Europe. A salient feature of the ‘last generation’ of TF buildings is the presence of diagonal members that may consist of two diagonal braces. The present study focusses on alternative modelling procedures, ranging from simple to rather complex, for this interesting type of traditional structure. All models are applied to study the behaviour of full-scale specimens of diagonally-braced TF panels. The complex model is based on plasticity with contact surfaces for the connection between timber diagonals and masonry infills. A parametric analysis using this model shows that masonry infills affect only slightly the lateral force carried by this TF panel configuration. Furthermore, two simple modelling techniques are put forward for application in the analysis of large, realistic structures incorporating TF walls. The first one is directly connected to the complex modelling and is based on substructuring. A nine-step procedure is developed and is found to properly reproduce the response of the test specimens. The second simple model is a phenomenological one, developed on the basis of observed behaviour during tests and is a complete hysteretic model; however, for comparison purposes, all models are evaluated here with respect to the prediction of the envelope (pushover) curve for the walls tested under lateral loads.     

Evaluation of the seismic response of masonry buildings based on energy functions

This work is based on energies evaluated from the responses of 12 stone and brick masonry systems subjected to 58 shaking table tests. The evolution of input energy during a damaging base excitation is correlated to the change of the damage patterns of the considered buildings. The comparison among energies dissipated and absorbed by the buildings during the various shocks gives some hints on strengthening strategies. It is found that damage to spandrel beams produces a more significant energy absorption than other types of damage. Copyright © 2001 John Wiley & Sons, Ltd.     

配筋混凝土砌块砌体高层模拟结构抗震分析

以上海园南小区配筋砌块砌体高层住宅作为原型结构，通过变化结构的一些基本参数，模拟成一系列新的结构，对模拟结构进行了抗震分析，研究了结构参数对配筋砌块砌体结构抗震性能的影响。     

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 Elaz?? (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.     

Twin lintel belt in steel for seismic strengthening of brick masonry buildings

A single-room, single-storey full-scale brick masonry building with precast RC roofing system was tested thric eunder displacement controlled lateral cyclic loading, to assess the effectiveness of the basic repair and seismic strengthening techniques. Initially, the virgin building specimen was loaded laterally to failure, In the second stage, the damaged building was repaired by stitching across the cracks, and tested under the same lateral loading. In the third stage, the twice-damaged structure was repaired once more by stitching and strengthened by twin lintel belt in steel and vertical corner reinforcement,and re-tested. The building strengthened by twin lintel belt in steel showed about 28% higher strength under lateral loading than the virgin building.     

Nonlinear modelling of the seismic response of masonry structures: Calibration strategies

Bulletin of Earthquake Engineering - In this paper, a simple and practitioners-friendly calibration strategy to consistently link target panel-scale mechanical properties (that can be found in...     

Experimental investigation on the seismic performance of masonry buildings using shaking table testing

Masonry buildings worldwide exhibited severe damage and collapse in recent strong earthquake events. It is known that their brittle behavior, which is mainly due to the combination of low tensile strength, large mass and insufficient connection between structural elements, is the main limitation for their structural implementation in residential buildings. A new construction system for masonry buildings using concrete blocks units and trussed reinforcement is presented here and its seismic behavior is validated through shaking table tests. Dynamic tests of two geometrically identical two-story reduced scale (1:2) models have been carried out, considering artificial accelerograms compatible with the elastic response spectrum defined by the Eurocode 8. The first model was reinforced with the new proposed system while the second model was built with unreinforced masonry. The experimental analysis encompasses local and global parameters such as cracking patterns, failure mechanisms, and in-plane and out-of-plane behavior in terms of displacements and lateral drifts from where the global dynamic behavior of the two buildings is analyzed comparatively. Finally, behavior factors for the design recommendations in case of unreinforced masonry are also evaluated.