Unreinforced Masonry Buildings Research Articles

The Influence of the Aggregate Configuration on the Seismic Assessment of Unreinforced Masonry Buildings in Historic Urban Areas

Unreinforced masonry (URM) buildings in historic urban areas of European countries are generally clustered in an aggregate configuration and are often characterized by façade walls mutually interconnected with adjacent ones. As a result, the seismic performance of buildings in an aggregate configuration can be affected by the mutual interaction between the adjacent units. This interaction, often called the aggregate effect, could significantly influence the level of the seismic vulnerability of URM buildings in aggregate configuration toward in-plane and out-of-plane mechanisms, the latter being the object of the present paper. Traditional methods for assessing the seismic vulnerability of URM buildings neglect the interactions between adjacent buildings, potentially underestimating the actual vulnerability. This study aims to derive fragility curves specific for UMR buildings in aggregate configuration and proposes an innovative methodology that introduces the aggregate effect into an analytical approach, previously developed by the authors for isolated URM buildings. The aggregate effect is modeled by accounting for the friction forces arising among adjacent facades during the development of out-of-plane overturning mechanisms by considering different scenarios, based on how façade walls interact with neighboring structures (e.g., whether they are connected to transverse and/or lateral coplanar ones). The proposed approach is applied to a real case study of an Italian historical center. The obtained results demonstrate that the aggregate effect significantly influences the fragility curves of URM buildings arranged in aggregate configurations. This highlights the importance of considering this effect and the usefulness of the proposed approach for large-scale assessments of seismic vulnerability in historic urban areas, contributing to sustainable disaster risk prevention.

Cost-effective topology optimization of masonry structure reinforcements by a linear static analysis-based GA framework

AbstractThe paper presents a novel optimization framework aimed at the minimization of seismic retrofitting-related costs for existing unreinforced masonry building structures. The framework provides topology optimization of reinforcements (reinforced plasters) to implement in masonry walls for the accomplishment of seismic safety checks under the reference seismic load combinations. Optimization is carried out by a genetic algorithm (GA) developed in MATLAB®, which controls a 3D finite element equivalent frame model of the masonry structure developed in OpenSees. The GA routine iterates the reinforcement configurations employing specific genetic operators. The feasibility of each candidate retrofitting solution is assessed by performing in-plane shear and flexural safety checks of masonry walls. The framework is finally tested with a case study masonry structure supposed to be made of average-quality or poor-quality masonry. Results will show that the proposed framework can effectively provide the minimization of seismic retrofitting costs for existing masonry structures, giving as output the optimal configuration of the reinforcements within the structural layout.

An Analytical Study of the Out-of-plane Seismic Performance of Masonry Walls Reinforced with High-Performance Fiber-Reinforced Cementitious Composites

Frequent earthquake occurrences in various regions of Korea have highlighted the urgent need that exists for the seismic retrofitting of unreinforced masonry buildings, which are particularly vulnerable to lateral forces. In this study, the out-of-plane seismic performance of masonry walls reinforced with high-performance fiber-reinforced cementitious composites (HPFRCCs) was evaluated using finite element analysis. ABAQUS was used to establish the analysis model, and the reliability of the model was validated by comparing the model results with shaking table test results. A parametric study of the reinforced masonry walls was thereafter conducted using the parameters of the reinforced sides of the walls (unilateral and bilateral) and thicknesses (10 and 20 mm). The analysis of the acceleration and displacement of the masonry walls revealed the beneficial effects of HPFRCCs on the out-of-plane seismic performance of the walls. The seismic performance of the walls was significantly enhanced when the HPFRCCs were applied to both sides of the walls.

A framework for multi-risk assessment in a historical area of Lisbon

Historic areas have faced escalating risks due to population growth, urbanization, climate change, and increasing public awareness. Existing risk assessment methods often focus on individual hazards, necessitating a more integrated approach. This research introduces a comprehensive multi-risk model to assess the potential impacts of rainfall and earthquakes on Lisbon's historic city centre. The model considers key risk components – hazard, exposure, and vulnerability – providing a detailed evaluation. Pluvial flood hazards for different return periods were analysed using a proper hydrological model, and seismic hazards were estimated based on PGA values (0.035g–0.25g) with a 10 % exceedance probability over 50 years. Concerning the exposure, the paper integrates spatial distribution data acquired through satellite remote sensing and GIS tools, along with census data. Vulnerability assessments for ordinary unreinforced masonry buildings (URM) used the Risk-UE method and flood stage-damage curves. The results obtained through a multi-exposure and multi-vulnerability framework provide insight into the expected building losses: for a 475/500-year return period, the estimated losses are approximately 1150 M€ for earthquakes and 22 M€ for floods. The higher losses for earthquakes are attributed to structural damage, whereas flood losses are predominantly associated with indirect impacts and loss of contents. This study marks a novelty in the application of risk assessment methodologies in Portugal addressing multiple hazards and highlights the protection of the built environment to mitigate economic and human losses. The paper serves as a starting point for further assessments, offering an overview of the influence of multiple risks on urban settings.

Shaking table tests of a one-quarter scale model of concrete hollow block masonry houses retrofitted with fiber-reinforced paint

Unreinforced masonry (URM) buildings are prone to significant damage when subjected to ground motion. Some strengthening methods have been proposed to increase the seismic capacity. However, the widespread adoption of these methods faces various challenges, including economic constraints experienced by common people in developing countries, the complexity of implementation, efficiency, and seismic safety of each technique. This paper introduces a new retrofitting method of fiber-reinforced paint using fiberglass as the primary reinforcing material. The advantage of this technique lies in its simplicity and ease of application, with the added benefit of using the paint to improve the appearance of the house. Two 1:4 scale concrete hollow block (CHB) masonry houses were constructed to represent unreinforced masonry and retrofitted masonry structures using fiber-reinforced paint (FR-Paint). The shaking table test results indicate that the retrofitted house model showed improvements of up to 18 times in deformation capacity and up to 13 times in energy dissipation compared to the non-retrofitted house model. FR-Paint has a robust performance even in high input motion at a seismic intensity JMA of 7 (Japan Meteorological Agency). This confirms that this retrofitting method has a high earthquake-resistant performance.

Assessing fragility functions of unreinforced masonry buildings

The seismic vulnerability entrenched within the historical urban landscapes of Algeria serves as a poignant reminder of the pressing need for comprehensive risk management strategies, particularly concerning low and medium height unreinforced masonry (URM) structures. These architectural gems, rich in cultural significance, stand as tangible embodiments of Algeria's storied past. However, their susceptibility to seismic disturbances presents an immediate threat, demanding meticulous attention and innovative methodologies for effective risk assessment and mitigation. In a pioneering scholarly pursuit, this research embarks on an ambitious exploration, melding fragility functions and a sophisticated vulnerability index method to unravel the intricate tapestry of seismic risk assessment. Through the lens of fragility functions, the study delves into a nuanced analysis, probabilistically delineating the vulnerabilities entrenched within the complex framework of URM buildings. Furthermore, the meticulous derivation of vulnerability functions via the vulnerability index method enhances the granularity of risk assessment, providing a multifaceted perspective to discern vulnerabilities accurately. Central to this investigation is the Belouizdad district, a microcosm of historical significance nestled within the vibrant metropolis of Algiers. By scrutinizing seismic scenarios spanning a spectrum of intensities (ranging from VII to X), the study orchestrates a symphony of empirical data and analytical prowess, unraveling the potential seismic reverberations poised to impact the district's architectural heritage. In essence, this scholarly endeavor transcends the confines of mere academic pursuit, serving as a guiding light illuminating the path towards tailored seismic reduction policies. It stands as a clarion call to safeguard Algeria's architectural patrimony, fostering resilience amidst the tremors of uncertainty and ensuring the preservation of its cultural legacy for generations to come.

A New Macro-Element for Predicting the Behavior of Masonry Structures under In-Plane Cyclic Loading

A new macro model for the finite element modeling of unreinforced masonry (URM) exhibiting in-plane nonlinear cyclic behavior is proposed. The ultimate objective is to predict the seismic response of multi-story URM buildings. The macro model enables the modeling of URM shear walls with a limited number of degrees of freedom (DOF) at low computation times. The macro model consists of a deformable elastic frame supported by diagonal struts with nonlinear behavior aiming to capture all dissipative phenomena occurring during seismic events. The nonlinear constitutive behavior of diagonal struts is inspired by models documented in the literature, ensuring a robust foundation for the proposed approach. This paper first provides a comprehensive review of the principal models currently available for URM analysis. It then articulates the rationale behind the development of this new numerical model, aiming to address the limitations encountered in existing methodologies and to offer a simple and fast tool for predicting the seismic behavior of URM buildings. Afterward, the new model is presented and tested with the simulations of two experimental campaigns performed on different URM walls. The comparison between experimental and numerical results shows that with a limited number of DOF and parameters, it is possible to obtain a prediction of the experimental results with satisfying accuracy.

Seismic retrofit cost model for Italian masonry residential buildings to support territorial-scale risk analysis

Over the last 50 years, earthquakes forced the Italian Government to pay emergency, recovery and reconstruction costs amounting to 180 billion euros, i.e., about 3.6 billion euros per year. These figures underline the poor seismic resilience of Italy and therefore the need for sustainable risk mitigation plans at national level.Within this context, this study aims to provide a seismic retrofit cost model for Italian unreinforced masonry (URM) residential buildings, to support territorial-scale risk analysis. To this end, well-established intervention techniques, suitable for being analyzed on a large scale, were selected. These interventions include strengthening of masonry walls, stiffening and anchoring of floors, improving the wall system connection, and their possible combinations. First, for each of the selected interventions, the related cost items (obtained via a work-breakdown-structure procedure) were identified. Second, their unit cost was either retrieved from Italian price lists or estimated according to market analysis ad hoc conducted. Third, a quantity-survey-method approach was implemented to a set of 445 URM buildings to estimate the retrofit costs per square meter (€/m2) of investigated retrofit interventions. Lastly, based on the estimated cost of retrofitting of these buildings, parametric cost models were developed to inform seismic risk analyses at various territorial scales, depending on the available building information (i.e., exposure data).The cost models here developed and proposed can be used to support the design of cost-effective seismic mitigation measures, i.e., to identify retrofit solutions that are technically effective but also economically sustainable at large territorial scale.

Damage assessment of unreinforced masonry buildings incorporating damage accumulation

AbstractRecent earthquakes have shown susceptibility of unreinforced masonry (URM) buildings to damage accumulation in seismic sequences or long duration ground motions. Current structural modelling approaches commonly disregard the damage accumulation in URM buildings or they are unable to accurately capture this phenomenon unless sophisticated FEM models are employed. Such models are not feasible in risk‐based applications given the required large number of dynamic analyses needed to develop robust fragility and vulnerability curves. On the other hand, the common displacement‐based engineering demand parameters (EDP), such as inter‐story drift ratio, fail to capture the impact of damage accumulation in simpler, more manageable models. An alternative is to use advanced damage indices that are capable of monitoring the monotonic accumulation of damages. This study proposes a displacement‐ and energy‐based damage index that uses, as the basis, the Park and Ang damage index, modified and calibrated through experimental data of individual URM elements. Our calibration procedure maps the physical observed damage states to the hysteretic response of the elements. Consequently, damage on the individual elements is aggregated to define a global damage state at building level. Validation is carried out based on an equivalent frame model of a building tested on a shake table. Additionally, the model is subjected to multiple ground motions of seismic sequences and to long‐duration ground motions to evaluate the performance of the proposed damage index. In comparison with displacement‐based damage measures, the proposed damage index shows a superior ability to capture cumulative damage, even when simplified models are employed.

Damage Evaluation and Seismic Assessment of a Typical Historical Unreinforced Masonry Building in the Zagreb 2020 Earthquake: A Case Study—Part I

The city of Zagreb, the national capital and economic hub of Croatia, is situated in a seismically active region and hosts a significant array of historical buildings, from the medieval to Austro-Hungarian periods. These buildings possess varying but generally high degrees of vulnerability to seismic loading. This was highlighted in the Zagreb earthquake of 22 March 2020, emphasizing the need for seismic retrofitting in order to preserve this architectural heritage. In this paper, the seismic capacity of one such unreinforced masonry building is considered through a number of analysis methods, including response spectrum, pushover, and out-of-plane wall failure analyses. Given the advantages and disadvantages of the individual methods, their applicability and value in a seismic analysis is considered. Ambient vibration measurements before and after the Zagreb 2020 earthquake, used for model calibration, are also presented. Conclusions are drawn from each individual analysis and later compared. In conclusion, no single analysis method considers all relevant failure modes, and a combination of nonlinear static or dynamic analysis and out-of-plane analysis is recommended. Due to the large volume of the material, it is published in two parts, with ground motion record selection, dynamic analysis, and a comparison of the results published in part two.

First-order approximation towards empirical seismic vulnerability assessment of low-cost unreinforced masonry buildings in South Africa

The 5 August 2014 Orkney earthquake in South Africa caused significant damage to low-cost unreinforced masonry buildings. After the earthquake, post-earthquake surveys were conducted to assess damage and deduce the intensity experienced by these buildings. During these surveys, only buildings that were reported as damaged were investigated. This study conducted an empirical seismic vulnerability assessment using data collected from those surveys. However, for a comprehensive assessment, the data should include all buildings in the study area. Hence in this study, a first-order approximation was applied to gather sufficient data to construct fragility curves for low-cost unreinforced masonry buildings in South Africa. The damage probability matrix technique was used for fragility curve construction. The fragility curves were constructed using the intensity and damage data, statistical models, and model fitting techniques. The fragility curves obtained in this study predicted comparable but slightly lower damage compared to other curves for unreinforced masonry buildings of similar typology. Although the method applied was able to produce fragility curves comparable with other studies, it is recommended that in order to get a reliable fragility curves all the buildings in the study area should be investigated including those that suffered little to no damage.

Observed failure modes in existing URM buildings after November 26, 2019 earthquake in Albania

This study explores the vulnerability of Unreinforced Masonry (URM) structures to seismic events, aiming to uncover the causes of failure and propose reconstruction strategies. Despite often being devastated in powerful earthquakes, URM buildings show damage even in mild to moderate seismic events. Field assessments after a magnitude 6.4 earthquake near Durres, Albania, in 2019, revealed severe damage in masonry buildings and adobe dwellings. Weak structural connections, insufficient roof support, and the absence of bond beams in load-bearing walls were identified as key contributors to the observed damage. The survival of masonry buildings post-earthquake does not guarantee seismic safety. The study recommends reinforcement techniques like shotcrete application, space reduction, and corner reinforcement, along with innovative methods such as Fiber Reinforced Polymer (FRP) use, for existing undamaged unreinforced buildings. These measures aim to prevent damage in the aftermath of destructive earthquakes, offering insights for the resilience of URM structures.

Modelling of in-plane strengthening of unreinforced masonry buildings: a numerical comparison between traditional and FRCM jacketing

Modelling of in-plane strengthening of unreinforced masonry buildings: a numerical comparison between traditional and FRCM jacketing

The diagonal shear behavior of masonry walls fabricated with historical lime-based mortar and retrofitted with near surface mounted method

The historical monuments in different regions of the world were constructed using local materials. Sarooj was a lime-based mortar utilized extensively in the construction of Unreinforced Masonry (URM) buildings in some Middle Eastern countries in the past centuries. However, few studies have been conducted on the mechanical properties of masonry fabricated with Sarooj and strengthening of the elements in which this type of mortar was used. In the present study, the in-plane shear behavior of URM wallettes fabricated with Sarooj mortar and retrofitted with Near Surface Mounted (NSM) Glass Fiber Reinforced Polymer (GFRP) bars is investigated through an experimental and numerical study. In this regard, first, diagonal shear tests are conducted on square wallettes. The test specimens include bare and retrofitted wallettes. The type of paste used for filling the grooves in the NSM method and the retrofitted face of the wallettes are the main variables whose effects are investigated in the experimental program. In addition to the NSM method, the in-plane behavior of walls retrofitted with a novel technique named Epoxy Filled Joint (EFJ) is investigated in the experimental phase of the present study. Then, through a numerical study, the wallettes retrofitted with the NSM method are simulated in Finite Element (FE) software Abaqus following a macro-modeling approach. The results of the experimental study confirmed that the strengthening of the URM wallettes with the NSM method not only enhanced their ultimate in-plane shear strength, but also improved the ultimate drift capacity of the wallettes. Furthermore, the shear stress-drift curves obtained from the FE model were in good agreement with those obtained from the tests. In addition, the test results showed that the EFJ method significantly increased the in-plane shear strength of the wallettes.

Design procedure for a timber-based seismic retrofit applied to masonry buildings

An innovative timber retrofit was investigated at the EUCENTRE and at the University of Pavia, Italy, as part of a comprehensive research campaign on the seismic vulnerability of existing unreinforced masonry buildings subjected to induced seismicity in The Netherlands. The retrofit system consists of timber frames, connected to the masonry piers and to the floor diaphragms, and oriented-strand board sheathing nailed to the frames and to flexible timber diaphragms. Starting from the main critical aspects observed in experimental tests, the proposed solution was conceived to enhance the in-plane and out-of-plane capacities of masonry piers, improve the overall wall-to-diaphragm connections, increase the floor diaphragm stiffness and strength, and allow possible integration with energy efficiency upgrades. This paper, the first of a series of two, focuses on the conceptual bases of the seismic retrofit system and on the analytical equations that can be used for the design of its components. Moreover, a step-by-step design procedure is presented to guide the reader through the application of these equations. A companion paper [1] will discuss the validation of the analytical formulation with the experimental data from quasi-static cyclic and dynamic shake-table tests on building components and complete specimens.

Full-scale cyclic tests on a stone masonry building to investigate the effectiveness of a one-side application of the composite reinforced mortar system

The results of an experimental study on a full-scale, two-storey rubble stone masonry building, strengthened with a Composite Reinforced Mortar (CRM) system applied on the external face of the walls, are herein presented. The CRM system consisted of a mortar coating reinforced with Glass Fiber Reinforced Polymer (GFRP) mesh and injected steel transverse connectors, which connect the separated wythes of the masonry. The aim of the research is to investigate the effectiveness of this strengthening technique. The study concerns two cyclic experimental tests: the first was carried out on the unreinforced masonry building up to a damage level not far from the ultimate limit state. Then, the building was repaired, strengthened with the proposed technique, and tested again. The second test was carried out up to a near-collapse condition. This allowed to evaluate the effectiveness in terms of seismic performances provided by the reinforcement.The cyclic horizontal load, with increasing amplitude, was applied to each of the two longitudinal walls of the building by means of servo-controlled hydraulic jacks pinned to a vertical steel beam. This beam allowed the distribution of the total lateral force between the first floor and roof level, in the fundamental mode shape. The experiments proved the effectiveness of the proposed strengthening method: with respect to the unreinforced masonry building, the resistance increased by 2.4 times, the displacement capacity by 4 times and the total dissipated energy by about 7.2 times. These benefits were due to the GFRP mesh reinforced coating’s capability to prevent the formation of isolated thick cracks, instead promoting a wider dispersion of many closely spaced thin cracks. Moreover, the importance of transverse connectors in preventing the separation of the masonry leaves in the strengthened walls was also clearly observed.

Explicit Method in the Seismic Assessment of Unreinforced Masonry Buildings through Plane Stress Elements

The complex nonlinear behaviour of unreinforced masonry (URM), along with the interaction between structural elements, still represents a challenge for the seismic assessment of existing URM buildings. A large variety of mathematical tools have been developed in the last decades to address the issue. The numerical work herein presented attempts to provide some insights into the use of FEM models to obtain reliable results from nonlinear dynamic analyses conducted with explicit methods. Through plane stress elements, two in-plane mechanisms were studied to identify optimal parameters for unreinforced masonry elements subjected to dynamic actions. The results were then compared with outcomes generated by an implicit solver. Subsequently, these parameters were used in nonlinear dynamic analyses on a building section for the seismic assessment in both unreinforced and reinforced conditions. The element type, hourglass control, damping, and bulk viscosity influence the dynamic response, mainly when the nonlinearities become larger. The hourglass control techniques employ a scaling factor to suppress the occurrence of spurious modes. Values ranging from 0.01 to 0.03 have shown effective results. When the stiffness-damping parameter for Rayleigh damping is of a similar order of magnitude or lower than the time increment without damping, the time increment remained in feasible ranges for performing analysis. Additionally, the bulk viscosity can stabilise the response without causing substantial alterations to the time increment if the values are under 1.00.

Behavior factor estimation for seismic design of unreinforced masonry buildings

The use of new geo-sourced construction materials in seismic areas requires the assessment of the structure ductility in order to properly design the building. This research aims to propose a procedure for behavior factor estimation in case of using a new construction material. In particular, in this paper, the proposed methodology is applied to an unreinforced masonry building in an average-risk seismic zone. Before application for seismic design, the reliability of the selected equivalent frame modeling approach is validated by comparison of dynamic features obtained from both numerical and operational modal analysis. An existing stone masonry building is selected as case study to validate the modeling approach. A measurement campaign provides the structural response to ambient vibrations and structural damping. After validating the model in elastic conditions, the building ductility capacity is estimated using a numerical pushover analysis, for different load combinations and distributions, according to the European design code, under the assumption of perfect plasticity. The proposed procedure provides a behavior factor obtained specifically for the analyzed building, using a relationship between ductility demand and behavior factor deduced from dynamic analysis. The average ductility demand is estimated numerically, for a set of synthetic acceleration signals compatible with the Eurocode elastic response spectrum and a given behavior factor. Finally, it is suggested to verify the near collapse limit state of the building structure not only in terms of target to capacity displacement ratio but also in terms of load ratio, since it can be more restrictive in some instances.

Shaking table tests of masonry wall reinforced with steel-bar truss units linked by spring dampers

Since unreinforced masonry buildings are vulnerable to earthquakes, various studies have been conducted to improve their seismic performance. In this study, spring dampers were added to steel-bar truss units to improve the performance of the reinforcement method, and shaking table tests were performed to evaluate their seismic performance. Furthermore, a full-scale I-shaped masonry wall was prepared by considering the inner walls of masonry buildings, and steel-bar truss units linked by spring dampers were installed on both sides of the specimen. For the unreinforced specimen, the horizontal spectral acceleration calculated for the flexible components was 0.54 g, the seismic loading level was sequentially increased by 20%, and in-plane excitation was performed. The experimental results showed that the unreinforced masonry specimen resisted up to 220% of the designed seismic acceleration, whereas the reinforced masonry specimen resisted up to 320%. At the end of the experiment with the unreinforced masonry specimen, the response peak acceleration and drift ratio of the reinforced specimen were approximately 36% and 50% lower than those of the unreinforced masonry specimen, respectively. This implies that the diagonal bars constituting the truss units reduced the story drift ratio by suppressing shear deformation, and the vertical bars prevented cracking by introducing an additional axial force on the masonry wall. The experimental results demonstrated that the reinforcement method efficiently improved the seismic performance of the masonry wall in terms of stiffness, ductility, shear force. Because this study was conducted with only one variable, i.e., the presence/absence of the strength method, further research with various variables such as a number of steel-bar truss units, prestressing force level, spring stiffness of spring damper is required to verify the practical applicability of the method.

Shape Memory Alloy‐Based Seismic Retrofit of an existing URM Building

AbstractMasonry buildings constitute a considerable part of the existing building stock and are often related to significant architectural and cultural value. Empirical construction, accumulated damage, material heterogeneity and anisotropic behavior deteriorate their structural and seismic capacity, increasing thus the risk of undergoing severe damage and even collapse. To enhance these buildings' performance, various retrofit schemes have been developed and have been included in current codes and standards, mostly utilizing conventional materials and improvement of their intervention techniques. Recently, research efforts are oriented to the application of emerging metal materials with advanced properties endowed with re‐centering abilities that conventional materials lack, aiming to achieve vibration control and mitigate potential structural damage.This work investigates the use of shape memory alloys (SMAs) for the seismic protection of masonry buildings focusing on the exploitation of their superelastic effect, namely the ability to revert to their original shape after being subjected to large deformations. The research adopts a case study approach, developing an SMA based retrofit scheme to be applied to an existing listed unreinforced masonry building in Thessaloniki. For the purposes of the study, finite element modeling is performed, while response spectrum analysis is carried out to assess the effectiveness of the introduced retrofit strategy.