Seismic Assessment Of Masonry Buildings Research Articles

Fragility curves for the seismic assessment of masonry buildings in historic centres prone to out-of-plane failure modes

Fragility curves for the seismic assessment of masonry buildings in historic centres prone to out-of-plane failure modes

Comparative study of alternative equivalent frame approaches for the seismic assessment of masonry buildings in OpenSees

The equivalent frame (EF) idealisation of masonry structures is widely used in engineering structures. Despite its simplifications, reliable numerical models can be produced to calculate the seismic behaviour of unreinforced masonry (URM) buildings. Different EF modelling approaches have been implemented in commercial software specifically conceived for performing nonlinear analyses on URM buildings (such as 3Muri, adopted in this study). Furthermore, the adoption of such an approach is also possible in general-purpose structural analyses software packages, such as OpenSees, through an ad hoc implementation of analysts. The aim of this paper is to compare various EF modelling approaches by adopting alternative nonlinear beam-elements in OpenSees belonging to the distributed and the lumped plasticity. To this aim, the responses of some benchmark cases study available in the literature from the “URM nonlinear modelling-benchmark project” within the context of ReLUIS projects have been adopted to preliminary test the reliability of the alternative approaches considered. In particular, they consist of some single panels and a trilith, for which the results of various software are already available. In the paper, the results obtained with OpenSees have been more in-depth compared with 3Muri, which is assumed as representative of a larger set of EF models adopted in engineering-practice (having already verified in previous works that it provides a reasonable scatter with other software package options). Then, the analyses have been extended as well to a 3D building representative of the neighbourhood of ‘El Plantinar’ in Seville. An accurate comparison has been carried out in terms of generalised forces, drifts and damage at an element and at a global scale. The results have shown that the method proposed in this manuscript allows using OpenSees to calculate masonry structures with the EF approach with a good agreement to other engineering-practice oriented tools. Thus, this outcome may constitute, in future research, the basis for exploiting the potential and versatility of OpenSees in accounting for other tricky phenomena: the soil-foundation-structure interaction.

Seismic Performance Assessment of Low-Rise Unreinforced and Confined Brick Masonry School Buildings Using the Applied Element Method

Masonry buildings are generally vulnerable to seismic action, as evidenced extensively in past earthquakes. In order to improve their seismic performance, several modifications have been introduced, such as reinforcing or confining the masonry. This paper presents a seismic analysis and fragility assessment procedure for non-engineered masonry building typologies, employing the applied element method (AEM). Compared to buildings with stiff diaphragms, the conventional pushover-based procedure is challenging for the seismic assessment of masonry buildings with flexible diaphragms, due to the lack of a global box-like behaviour. This study first presents a novel and validated method for nonlinear pushover analysis, independent of the type of diaphragm action on the building, by applying incremental ground acceleration and by considering suitable engineering demand parameters for the assessment of lateral capacity. Based on the failure mechanisms, a seismic performance assessment and fragility evaluation approach is then proposed, for reliable accounting of both the in-plane and out-of-plane failure modes. Finally, the proposed methodology is applied to a number of unreinforced and confined masonry school buildings with different seismic detailing levels, as often found in the Himalayan belt and beyond.

Development of expeditious methods for seismic assessment of pre‐code masonry buildings in Portugal

AbstractAlthough Portugal has not been hit by high‐magnitude earthquakes in recent years, its history is marked by tragic seismic events and it remains susceptible due to its geographical location. The Portuguese building stock is constituted approximately by 45% masonry residential buildings and most were built before the enforcement of the first seismic code in 1958. For several years, structural interventions in these buildings were allowed without the need to assess their seismic vulnerability. In 2019, a new law was approved to regulate the rehabilitation interventions to provide safety and comfort of existing buildings. The seismic assessment of existing buildings became mandatory and based on the procedures and requirements included in NP EN 1998–3: 2017 (Portuguese version of Eurocode 8 – part 3), which establishes the performance requirements and compliance criteria for existing buildings subjected to a certain level of seismic action. According to this normative requirements, analytical seismic vulnerability assessment and reliability‐based analyses were carried out on a large set of masonry buildings representative of the Portuguese housing stock, leading to the development of surrogate and expeditious method for seismic assessment in compliance with the reference method defined in the European standard. The method allows the seismic assessment of masonry buildings with rigid and flexible floors, without explicit numerical analyses, using only geometric parameters and the material properties. Compliance of results assessed by the proposed method and the corresponding values obtained by the code were carried out by confidence tests.

A Tool for the Rapid Seismic Assessment of Historic Masonry Structures Based on Limit Analysis Optimisation and Rocking Dynamics

This paper presents a user-friendly, CAD-interfaced methodology for the rapid seismic assessment of historic masonry structures. The proposed multi-level procedure consists of a two-step analysis that combines upper bound limit analysis with non-linear dynamic (rocking) analysis to solve for seismic collapse in a computationally-efficient manner. In the first step, the failure mechanisms are defined by means of parameterization of the failure surfaces. Hence, the upper bound limit theorem of the limit analysis, coupled with a heuristic solver, is subsequently adopted to search for the load multiplier’s minimum value and the macro-block geometry. In the second step, the kinematic constants defining the rocking equation of motion are automatically computed for the refined macro-block model, which can be solved for representative time-histories. The proposed methodology has been entirely integrated in the user-friendly visual programming environment offered by Rhinoceros3D + Grasshopper, allowing it to be used by students, researchers and practicing structural engineers. Unlike time-consuming advanced methods of analysis, the proposed method allows users to perform a seismic assessment of masonry buildings in a rapid and computationally-efficient manner. Such an approach is particularly useful for territorial scale vulnerability analysis (e.g., for risk assessment and mitigation historic city centres) or as post-seismic event response (when the safety and stability of a large number of buildings need to be assessed with limited resources). The capabilities of the tool are demonstrated by comparing its predictions with those arising from the literature as well as from code-based assessment methods for three case studies.

Linear static procedures for the seismic assessment of masonry buildings: Open issues in the new generation of European codes

Linear procedures (lateral static force method or modal response spectrum analysis) are the standard approach for the seismic design of new structures. On the contrary, nonlinear procedures, in particular incremental pushover analysis, should be used for the seismic assessment of existing buildings, because it is difficult to estimate the behavior factor of a building in the absence of a standardized capacity design. Moreover, in the case of existing buildings, the use of linear procedures provides results that are excessively conservative, therefore unreliable. Despite this, seismic codes consider linear procedures because of their theoretical simplicity and robustness with respect to model uncertainties and non-linear issues, a priori avoiding convergence problems. The paper deals with the critical issues related to the application of linear static procedures for the seismic assessment of masonry buildings. Methods proposed by the present draft of the Eurocode 8 (Part 3) and the new Italian Seismic code (NTC 2018) have been applied to a case study building, under two configurations (regular, irregular); in particular, the modelling options usually adopted by professionals have been considered. Results are compared with the assessment carried out through the nonlinear pushover analysis, which may be assumed as able to better estimate the actual seismic behavior. Anyhow, the aim of the paper is not a validation of the code procedures but a comparison between alternative allowed methods. Conclusions show that even by considering the recent improvements in the codes, in the regions characterized from medium to high seismic hazard, linear methods result almost inapplicable leading to almost all buildings not verified in contrast with the evidences of most recent earthquakes.

Confined and unreinforced masonry structures in seismic areas: Validation of macro models and cost analysis

Modern structural design requires consideration of sustainability parts from a life cycle perception, but also the initial design phase in which seismic actions have a substantial influence on the design of the structure. In recent times, the seismic assessment of masonry buildings by means of macro-element modeling methodologies has become popular, by application of performance-based evaluation techniques using nonlinear lateral load procedures (Pushover). This study addresses the endorsement of these methodologies by referring to two full-scale brick masonry structures subjected to a lateral loading conditions. The lateral load response of tested unreinforced masonry (URM) and confined masonry (CM) structures is compared with the response of the numerical models. The considered numerical models have good agreement for satisfactorily predicting the response of the experimental test and hence are capable of being used in a performance-based evaluation. Then, pointing to the characteristic housing of northern Pakistan and its typical design with a reinforced concrete (RC) building, the validated numerical models are used to estimate the hazard-resistant potentials of the URM and CM options for one, two and three story options, particularly in relation with maximum lateral load capacity. The load deformation response of both the typologies was also compared for the mentioned three story levels. It was observed that by confining the masonry its ductility capacity increases considerably, hence making it more suitable to be used in earthquake prone regions. Masonry structures are also compared regarding the construction costs compared to the RC typology. With regard to the dwellings studied, the projected lateral load behavior for masonry structures indicate the ability to withstand lateral loads adequately. These structures also allow a significant reduction in costs (up to 28%) compared to RC, hence appearing as challenging alternatives.

Comparative fragility methods for seismic assessment of masonry buildings located in Muccia (Italy)

The current paper focuses on a sector of the historic centre of Muccia, in the district of Macerata (Italy), affected by the seismic sequence that involved Central Italy in 2016. The main goal is comparison, in terms of fragility curves, among two vulnerability assessment methodologies (empirical and mechanical). The study area has been structurally and typologically identified according to the Building Typology Matrix (BTM). Physical vulnerability analysis of the urban-sector was performed through application of an index-based method, specifically for masonry building aggregates. An isolated masonry building, damaged after the seismic sequences, has been selected as a case study. For the assessed building, empirical fragility curves are presented according to Guagenti & Petrini’s correlation law. Furthermore, a numerical model has been set up by using the macro-element approach, which has allowed to perform non-linear static analyses. Mechanical properties of masonry were defined according to the New Technical Codes for Constructions (NTC18), assuming a limited knowledge level (LC1). Refined mechanical fragility functions have been derived and compared to the empirical ones.Analysis results have shown that the empirical method tends to overestimate by 5% and 10% the expected damage for slight and moderate thresholds. For PGA values greater than 0,3 g the damage levels decreased by 30% and 20%, with reference to the near collapse and collapse conditions, respectively.

Public Housing in Florence: Seismic Assessment of Masonry Buildings

Florence is known all over the word for its historical and monumental buildings; however, most part of residential buildings have been made in the XX century, and they present all the critical issues proper of recent housing. Florence is one of the first Italian cities to have experienced the public housing. Its public housing population consists mostly of masonry buildings, and it does not comply the requirements provided by the current seismic legislation. This work is aimed at evaluating the seismic performance of a masonry building-type belonging to the public housing population of Florence. A typical public housing intervention, consisting of 18 masonry buildings, has been assumed as case-study. The seismic input has been described according to the Italian Code prescriptions, by considering the effective soil stratigraphy, and considering the effective mechanical properties of each layer. The seismic performance of the case-studies has been checked by performing a nonlinear static analysis. The results are expressed in terms of seismic performance, defined as the ratio between the seismic capacity and the corresponding demand. The obtained results evidenced the role of the building features on the seismic assessment of the buildings.

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.

Displacement-based seismic assessment of masonry buildings for global and local failure mechanisms

AbstractSeismic fragility functions provide an easy mean to estimate the vulnerability of structures, develop damage scenarios and quantify number of structures with different damage states for a given seismic hazard. This paper presents the derivation of fragility functions for different types of masonry structures in Pakistan using a European standard methodology. It included structures with reinforced concrete floors and wooden/steel floors with truss roof. The first class of masonry structures is considered with the in-plane shear damage in masonry walls with abrupt collapse of structure at the ultimate deformation capacity of in-plane walls. Masonry structures of second class are considered with the collapse of out-of-plane facade walls in case of the absence of ring beams and ties and presence of weak wall-to-wall and wall-to-floor connections. Monte Carlo simulation is used to generate random structures with different geometrical and mechanical properties, which are analyzed using fully probabilist...

A macro‐model with nonlinear springs for seismic analysis of URM buildings

SummarySeismic assessment of existing unreinforced masonry buildings represents a current challenge in structural engineering. Many historical masonry buildings in earthquake regions were not designed to withstand seismic loading; thus, these structures often do not meet the basic safety requirements recommended by current seismic codes and need to be strengthened considering the results from realistic structural analysis. This paper presents an efficient modelling strategy for representing the nonlinear response of unreinforced masonry components under in‐plane cyclic loading, which can be used for practical and accurate seismic assessment of masonry buildings. According to the proposed strategy, generic masonry perforated walls are modelled using an equivalent frame approach, where each masonry component is described utilising multi‐spring nonlinear elements connected by rigid links. When modelling piers and spandrels, nonlinear springs are placed at the two ends of the masonry element for describing the flexural behaviour and in the middle for representing the response in shear. Specific hysteretic rules allowing for degradation of stiffness and strength are then used for modelling the member response under cyclic loading. The accuracy and the significant potential of the proposed modelling approach are shown in several numerical examples, including comparisons against experimental results and the nonlinear dynamic analysis of a building structure. Copyright © 2016 John Wiley & Sons, Ltd.

Seismic assessment of masonry buildings accounting for limited knowledge on materials by Bayesian updating

Several building codes propose methodologies to account for epistemic uncertainties in the seismic assessment of masonry buildings by selecting a knowledge level and reducing material strengths by means of the associated value of the confidence factor. Previous works showed that, in the case of masonry structures, this approach has various limitations, such as the lack of proper consideration of experimental tests performed. This article focuses on the issue of imperfect knowledge on material properties of existing masonry buildings and proposes a probabilistic methodology for the assessment, based on Bayesian updating of mechanical properties. The use of a Bayesian approach allows to update the values of the material properties assumed a priori as knowledge on the building increases, by taking into account all the experimental information gathered during the assessment process. A large number of simulated assessments is carried out and the values of the confidence factors on material properties are defined through the comparison between the obtained results and those of the reference structure, assumed to be perfectly known. These factors are useful in a more general framework for the assessment of masonry buildings accounting for different sources of uncertainty.

Consideration of modelling uncertainties in the seismic assessment of masonry buildings by equivalent-frame approach

The choice of modelling strategy and analysis options has a significant influence on the results of the seismic assessment of existing buildings and therefore it is very important to have an idea of the dispersion in the results due to different hypotheses regarding the structural model. This paper concentrates on pushover analysis, considered as the reference method currently adopted by engineers for the seismic assessment of existing masonry buildings, and on the equivalent-frame macro-element approach, assumed to be a satisfactory compromise between computational effort and accuracy in the results. A logic tree approach is used to treat the different considered options, including the definition of the geometry of the equivalent frame, the distribution of loads among the masonry piers and on the horizontal diaphragms, the degree of coupling between orthogonal walls, the definition of the cracked stiffness of structural elements and the modelling of masonry spandrels. By assigning a value of probability to each end branch of the tree, the distribution of the peak ground acceleration corresponding to the selected limit states can be obtained and, from this distribution, a quantitative estimate (in probabilistic terms) of the effect of modelling uncertainties on the seismic response of masonry structures is derived.

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

SUMMARYThe 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.

Simplified indexes for the seismic assessment of masonry buildings: International database and validation

Heritage masonry buildings are particularly vulnerable to earthquakes because they are deteriorated and damaged, they were built with materials with low resistance, they are heavy and the connections between the various structural components are often insufficient. The present work details a simplified method of seismic assessment of large span masonry structures that was applied to a database of 44 monuments in Italy, Portugal and Spain, providing lower bound formulas for different simplified geometrical indexes. Subsequently, the proposed thresholds are validated with data from the 2010–2011 Canterbury earthquakes, which includes 48 stone and clay brick masonry churches. Finally, fragility curves that can be used to estimate the damage as a function of the peak ground acceleration (PGA) are also provided.

Possibilities and comparison of structural component models for the seismic assessment of modern unreinforced masonry buildings

This paper addresses the possibilities of structural component models for the seismic assessment of masonry buildings using pushover analysis. The ultimate goal is to allow efficient design of new unreinforced masonry buildings in seismic areas. Different modelling strategies are presented and the implementation of a simple design tool based on structural component models is described in detail. The different approaches are applied to a two-storey building with regular plan and elevation, allowing for a comparison between them. The results indicate that macro-modelling using structural component models and pushover analysis are adequate approaches for the seismic assessment and design of unreinforced masonry buildings, as the tools require very low computational resources, allow easy interpretation of results and provide satisfactory accuracy.

Modeling and vulnerability of historical city centers in seismic areas: a case study in Lisbon

Historical city buildings are an integral part of the built heritage to be preserved, and their safety is a primary requirement in seismic areas. Collapse of ancient masonry buildings due to seismic actions occur mostly due to overturning of the perimeter walls. This paper addresses the issue of seismic analysis and vulnerability of historical city centers, with a specific case study: the 18th century downtown part of Lisbon, Portugal. The finite element method was adopted for a number of different analyses, introducing non-linear behavior of the materials. From the analysis, the following issues have been addressed: (a) seismic vulnerability of this type of constructions; (b) influence of the group of buildings on the seismic behavior of the individual buildings that compose a single compound; and (c) methodology for action. It is believed that the conclusions obtained with respect to the seismic assessment of masonry buildings can be extrapolated for the wide variety of historical city centers.