Historic Unreinforced Masonry Research Articles

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.

Structural design and engineering of Striatus, an unreinforced 3D-concrete-printed masonry arch bridge

This paper describes the structural design and engineering of “Striatus”, a 3D-concrete-printed unreinforced masonry pedestrian bridge built in Venice in 2021 as part of the Time Space Existence exhibition organised by the European Cultural Centre. The project combines the latest developments in 3D concrete printing with the structural principles of historic unreinforced masonry. Typically, the structural applications of 3D concrete printing are limited to elements such as columns and walls loaded vertically, perpendicularly to the horizontal printing layers, to formwork elements or secondary structural elements. Indeed, fabrication constraints, delamination issues and the low tensile strength of the concrete have been seen as limiting factors to 3D concrete printing for structural applications demanding resistance to bending or predominant loading directions not perpendicular to the printing layers. By using unreinforced-masonry structural principles, this paper shows that structural elements spanning space horizontally, such as a pedestrian bridge, can be built by using the 3D concrete printing components as the main structure, working only in compression, loaded perpendicularly to the printed layers. Furthermore, as a compression-only structure following masonry principles, Striatus enabled the use of unreinforced concrete without any mechanical or chemical connections between the elements and the separation of concrete and steel, only used for the supports and to equilibrate the horizontal thrust of the arch effect through the tension ties. This work shows how the application of unreinforced masonry principles to 3D concrete printing offers new opportunities in terms of structural design and represents a strategy to increase sustainability by reducing material consumption and allowing reusability and recyclability of the structure. Finally, this paper discusses the critical aspects related to the design of Striatus from an engineering and construction point of view.

In-plane shear strengthening of traditional unreinforced masonry walls with near surface mounted GFRP bars

In this study, the effectiveness of Near Surface Mounted (NSM) method, for in-plane shear strengthening of traditional and historical Unreinforced Masonry (URM) walls, is investigated through a comprehensive experimental study. For this purpose, square solid clay brick masonry wallettes (42 samples) with three different types of traditional mortars including gypsum mortar, lime-cement-sand mortar and lime-sand mortar are prepared and retrofitted with NSM Glass Fiber Reinforced Polymer (GFRP) bars. Then, diagonal shear tests are conducted to evaluate the in-plane shear behavior of the masonry wallettes. The effects of some key variables such as wall thickness, the retrofitted face of the wall, reinforcement ratio, and the type of paste for mounting the reinforcing bars, on the effectiveness of the retrofitting method are investigated. The results of the tests are presented in terms of the failure modes and the lateral shear stress-drift curves of the test specimens. Accordingly, the retrofitting method can enhance the in-plane shear strength, and the ultimate lateral drift capacity of the URM wallettes. According to the test results, the type of filler paste and reinforcement ratio influence the strength enhancement of the test specimens. Furthermore, in specimens retrofitted with the one-side retrofitting scheme, due to the asymmetry of walls under in-plane loads, an unexpected out-of-plane deformation is induced in the walls under in-plane load which adversely affects its global behavior.

Flexural Behavior of Reinforced Granite Members with Titanium Bars

Renovation and maintenance of heritage buildings to establish the cultural credibility of a country is an essential national task. To protect and maintain these structures, study of rehabilitation and strengthening methods for historical unreinforced masonry buildings has been a topic of experimental research. In Korea, significant historical structures made of granite stone require strengthening due to external destructive effects and internal degradation. Exposure to the elements has had an impact on granite stone resistance, resulting in separation and fracturing. To enhance structural behavior, pinning renovation techniques are essential. In this study, reinforcement by use of titanium bars was proposed as an effective method to improve the flexural strength of interconnected granite stones, which were applied in the restoration of Mireuksaji stone pagoda. Twenty specimens reinforced with titanium bars and epoxy resin were prepared, and a wide range of experiments were performed to determine strength performance of the structure based on various parameters. To provide a preliminary design guideline for reinforced epoxy-jointed granite segments, based on the current common practice in the design of concrete structures, failure of the specimens was classified as brittle or ductile. The results showed that adequate reinforcement following the proposed method can significantly enhance strength and ductility of the member.

Integrated framework to structurally model unreinforced masonry Italian medieval churches from photogrammetry to finite element model analysis through heritage building information modeling

A novel, integrated framework is proposed to assess the vulnerability of a case study unreinforced masonry (URM) Italian church by applying interacting modern tools including unmanned aircraft systems (UAS), “structure from motion” (SfM) photogrammetric survey equipment and software, and finite element method (FEM) analysis software in a complete heritage building information model (HBIM). The FEM model was used to perform both a modal response spectrum analysis and a validation pushover using stiffness adaptation analysis (SAA) to investigate the global behavior of the church and to identify the most critical local mechanisms for collapse potential. Once the most vulnerable components of the church were identified, macro-block analysis was used to estimate the capacity of these collapse mechanisms. Macro-block analysis is well established in the field and was proposed for use as one step in the proposed integrated framework with the aim of providing a holistic methodology that is sophisticated enough to identify the most vulnerable elements of URM churches, but also practical and efficient enough to be applied by practitioners. Traditionally, obtaining the necessary geometric information to correctly conduct the macro-block analysis of such complex buildings requires time-demanding and expensive surveying campaigns. Furthermore, accurately and precisely identifying the local failure mechanisms most influential to macro-block behavior is numerically demanding. The novelty of the current research detailed herein regards a proposed comprehensive seismic vulnerability analysis of historic URM churches with increased efficiency and accuracy of surveying and capacity modeling using modern tools in a fashion approachable by practitioners.

Seismic performance assessment based on displacement capacity of unreinforced masonry structures

The National Geological Museum is a representative building for the typology of historic unreinforced masonry structures built in Romania at the beginning of the XX century. The seismic behaviour was studied with respect to the displacement capacity, by comparing the initial structural configuration of the building with the retrofitted one. Taking into account the irregularities of the structure and the localized reinforced concrete jacketing works done in the 80s’, global results were proven to be misleading. Thus, relative floor displacements were used to study the behaviour of individual walls involved in local failures. Limit state thresholds based on relative displacements were used in order to calibrate the initial model with the post-earthquake damage assessment and then they were compared to the results obtained for the retrofitted model to establish the effectiveness of the strengthening works.

Roles of timber tie-rods to reduce seismic vulnerability of historical buildings in Egypt

Historical un-reinforced masonry (URM) buildings in Egypt from the medieval period generally comprise timber tie-rods that link the arches of arcades at the top of the column heads and along the arcade plane (in-plane). Usually, additional tie-rods are found perpendicular to the arcades (out-of-plane). Timber ties can also be used between facing tall URM bearing walls to minimise their buckling vulnerability. They play a considerable role in resisting seismic forces and minimising the deficiencies of URM buildings. A limited experimental investigation and a wide analytical campaign were conducted on two model buildings with the prevailing dimensions and materials of historical medieval buildings in Cairo by employing finite-element three-dimensional modelling. The focus of the work was the roles timber tie-rods play in the seismic stability of parallel-arcaded and cross-arcaded URM historical buildings. A proposal for enhancement of the seismic resistance of parallel-arcaded systems using a steel bracing system is provided.

Design Considerations for Retrofitting of Historic Masonry Structures with Externally Bonded FRP Systems

ABSTRACT Historic masonry buildings often require structural repair or retrofit to attain a satisfactory level of seismic resistance. This paper analyses the effect of externally bonded fibre-reinforced polymer (FRP) retrofitting systems on the global seismic response of such buildings in order to achieve the fundamental code-based requirements that refer to the structure’s state of damage for a specified limit state. As a case study, a three-storey historic unreinforced masonry (URM) building was selected. The first part of the paper presents an FRP design procedure for determining which vertical structural elements should be retrofitted and to what extent. As a result, six different FRP retrofitting layouts have been selected and analysed with the aid of non-linear static analyses in the second part of the paper. The paper concludes with a cost-feasibility study by introducing a cost-effectiveness index for FRP reinforcement that identifies the effectiveness of an FRP layout by accounting for the amount of retrofitting material used and comparing it with its effectiveness in improving the global seismic resistance.

Effects of Lateral Constraints and Geometrical Characteristics on Deformation Capacity of the Persian Historic Unreinforced Masonry Shear Walls under Uncertainty Conditions

In the most structural codes, deformation capacity of the unreinforced masonry shear walls is estimated based on their structural behavior(failure mode) and aspect ratio. In this paper, deformation capacity was determined for the Persian historic brick masonry walls by considering the effects of various parameters such as lateral constraints, aspect ratio and thickness. Also, to take into account the uncertainties in material and geometry of the walls in their deformation capacity, partial factor γdu was proposed, somehow, deformation capacity of shaer wall is determined by multiplying this factor in the computed deformation. Accordingly, the in-plane behavior of 48 different specimens of masonry walls with four lateral constraint configurations (contribution of transverse walls and also top slab), four distinct aspect ratios(height to length) of 0.5, 0.75, 1.0 and 1.5, three traditional wall thicknesses of 0.20, 0.35 and 0.50 m, under pre-compression load of 0.10 MPa were computed using nonlinear pushover analyses. Then, the obtained force-deformation curves were idealized by bilinear curves (linear elastic – perfectly plastic) to make them easier for comparison objectives as well as to be more adopted in practical purposes. The latter results indicated that deformation capacity of the shear walls decreases by stiffer lateral constraints, more thickening; and decrease in height-to-length aspect ratio. In addition, it was observed that the transverse walls (vertical constraints on two sides, and at two ends of the base shear walls) were more efficient in reducing deformation capacity than the top slab (horizontal constraint). As a result, according to the numerical calculations, the ultimate drift value for the Persian historic brick masonry walls determined between 1.3% and 2.7%. Eventually, the partial factor of γdu to consider uncertainty in modulus of elasticity and thickness assessment in deformation capacity of the Persian historic masonry shear walls achieved in the range of 1.3 to 1.7.

Characterization of mechanical behaviour of grey clay brick masonry in China

Grey clay bricks (GCBs) are a traditional and unique masonry material for Chinese buildings, and their application is especially prevalent in traditional Chinese architectures. Despite that structural analyses of historical constructions have been a popular area of focus in recent studies, information on the behaviour of GCB masonry structures is still lacking. In this paper, a comprehensive characterization of the mechanical behaviour of GCB masonry by using experimental and numerical methods is presented and discussed. Characterization tests were primarily carried out to determine the mechanical strengths of GCB, cement-based and lime-based mortar, and the bond behaviour between them. Then, a series of tests was performed on GCB masonry prisms and panels to evaluate the compressive, flexure and shear behaviours of GCB masonry, respectively. Finally, numerical models based on the experimental results were setup and further implemented for analysing the nonlinear response of a historical unreinforced masonry building in Macau to obtain the safety level. The combined experimental and numerical investigation evaluates important parameters for the mechanical behaviour of GCB masonry and delivers updated understandings of the structural behaviour of existing GCB masonry buildings in China.

Seismic damage and fragility assessment of ancient masonry churches located in central Chile

An assessment of damage and seismic fragility of historical unreinforced masonry churches located in Chile’s central valley was carried out employing the results of a field survey of 106 ancient churches, after the 2010 Maule earthquake. The observed damage was correlated with recurrent failure mechanisms of unreinforced masonry structures, by taking into account 22 local mechanisms involving macro-elements on these churches. The average damage level suffered by each church was computed considering the global and local behaviors of the structures through a damage index computed as a weighted mean of the levels of damage observed for each mechanism. The results of this damage index method are used to obtain Probability Mass Functions and suitable probabilistic tools are used to propose Empirical Fragility Curves (EFCs) for these structures. The EFCs are directly usable by stakeholders involved in risk assessment aimed to the prioritization of possible future damage mitigation strategies and other decision making processes relative to this historical heritage.

Material property testing for the refurbishment of a historic URM building in Yangon, Myanmar

The architecture of Yangon, Myanmar has been heavily influenced by British colonisation from the mid-1800s, with a large portion of the historic building stock being constructed of unreinforced masonry (URM). The city’s historic buildings have regularly been exposed to the ravages of war and natural disasters, as well as low levels of maintenance despite a rapidly growing population. One of the primary needs when assessing a building for refurbishment and/or retrofit is to characterise the constituent material properties. On-site material investigation was undertaken in a large historic building originally constructed in (circa) 1896, with multiple renovations and expansions made at different times. The original structure is comprised of unreinforced loadbearing Laterite stone and clay-brick masonry walls. In-situ testing and sample extraction were conducted at 14 discrete test locations throughout the building and consisted of: (i) bed joint shear tests in clay-brick masonry with 16 tests throughout the building; (ii) in-situ deformability (aka ‘flat-jack’) tests on the Laterite stone masonry and on the clay-brick masonry; (iii) laboratory compression tests and petrographic examinations of individual clay-bricks, Laterite stones and mortar samples. The findings from the materials characterisation are presented herein with the aim of serving as guidance for engineers assessing similar historic buildings in Myanmar and other Southeast Asian countries, where few characterisation studies on local, historic materials – particularly on Laterite stone masonry – have been publicized.

Seismic Vulnerability Assessment of Historical Unreinforced Masonry Buildings in Osijek using Capacity Spectrum Method

Seismic Vulnerability Assessment of Historical Unreinforced Masonry Buildings in Osijek using Capacity Spectrum Method

Experimental shear testing of timber-masonry dry connections for the seismic retrofit of unreinforced masonry shear walls

Abstract The mechanical coupling of timber products to the masonry walls of unreinforced masonry (URM) buildings is generating considerable interest in terms of seismic vulnerability mitigation. An extensive experimental investigation on timber panel to masonry wall connections realised with screw anchor fasteners is presented. A total of 64 shear tests under monotonic, cyclic and semi-cyclic loading conditions were performed on site in a historic URM building. The examined parameters were: masonry type, timber panel product and material, load-to-grain direction, fastener geometry and steel grade. The outcomes of the campaign are then reported and discussed focusing on the strength and stiffness properties and on the dissipation capacity and residual strength of the connection under cyclic load. Moreover, a log-normal distribution fitting is proposed for the maximum load and slip modulus measurements of all the cyclic test configurations analysed. Finally, the principal experimental observations are listed along with recommendations for future work or use in practice.

Seismic Vulnerability of Historical Masonry Aggregate Buildings in Oriental Sicily

ABSTRACTThe seismic vulnerability assessment of historical UnReinforced Masonry (URM) buildings is a very complex task since it is strongly related to a great variety both of geometrical layouts and of masonry mechanical characteristics. In this article, some results of a Catania University research project, denomined “FIR 2014”, focused on the seismic vulnerability estimation of historical buildings, built in Catania after the 1963 earthquake, are presented. First, a detailed typological analysis of the considered urban fabric, characterized by typical residential masonry buildings, has been performed. Such analysis allowed recognizing an elementary structural modulus, which has been studied according to different geometrical layouts representative of isolated or aggregate buildings. The results of nonlinear static analyses, performed by applying an innovative macro-element approach, allowed for the assessment the seismic vulnerability of typical URM buildings coherently to the Italian seismic code. The adopted macro-element strategy for the seismic assessment of aggregate masonry buildings, although related to a specific historical center, may be applied to similar urban fabrics and can also be used for the calibration and validation of fast seismic assessment strategies, particularly useful for the evaluation of the seismic risk at urban scale.

Classical Temples and Industrial Stores: Survey Analysis of Historic Unreinforced Masonry (URM) Precincts to Inform Urban Seismic Risk Mitigation

ABSTRACTOamaru, Winton, and Invercargill feature some of New Zealand’s most intact heritage precincts that are confronted by ongoing threats of seismic activity. The 2010/2011 Canterbury earthquake sequence and Canterbury Earthquakes Royal Commission of 2012, identified a nationwide trend through the proportion of deaths that occurred in public places as a result of the prevalent historic unreinforced masonry (URM) building stock. The reported study was undertaken to address urban safety and seismic risk mitigation through the lens of heritage conservation. The range of classically designed public buildings and industrial warehouses in the South Island of New Zealand were often produced by singular architectural practices, using locally sourced materials and construction techniques. It is vital to incorporate an examination of unique architectural qualities within urban seismic risk assessment and mitigation. Historic urban layout, architectural deployment of masonry, and extent of retrofits were recorded through onsite visual surveys via Geographical Information Systems and three-dimensional representation technologies. Extending the scope of information collected for engineering seismic risk assessment by focusing on the historical architectural context informs the selection of future mitigation measures. Oamaru, Winton, and Invercargill present intriguing case studies for multidisciplinary analysis, prior to testing urban-scale survey approaches within comparable historic centers across New Zealand.

Nonlinear analysis of contemporary and historic masonry vaulted elements externally strengthened by FRP

This paper addresses numerical modeling and nonlinear analysis of unreinforced masonry walls and vaults externally strengthened using fiber reinforced polymers (FRP). The aim of the research is to provide a simple method for design of strengthening interventions for masonry arched structures while considering the nonlinear behavior. Several brick masonry walls and vaults externally strengthened by FRP which have been previously tested experimentally are modeled using finite elements. Numerical modeling and nonlinear analysis are performed using commercial software. Description of the modeling, material characterization and solution parameters are given. The obtained numerical results demonstrate that externally applied FRP strengthening increased the ultimate capacity of the walls and vaults and improved their failure mode. The numerical results are in good agreement with the experimentally obtained ultimate failure load, maximum displacement and crack pattern; which demonstrates the capability of the proposed modeling scheme to simulate efficiently the actual behavior of FRP-strengthened masonry elements. Application is made on a historic masonry dome and the numerical analysis managed to explain its structural behavior before and after strengthening. The modeling approach may thus be regarded a practical and valid tool for design of strengthening interventions for contemporary or historic unreinforced masonry elements using externally bonded FRP.

Compression and Cyclic Shear Behavior of Lime Mortar Brick Masonry

Most of the British regime engineered heritage brick masonry in northern India is either purely in lime mortar or in lime-surkhi (crushed brick aggregate) mortar. Lime mortar constituting majorly of historical brick masonry stock and influences substantially the dynamic characteristics was investigated. The heritage buildings are highly vulnerable against seismic actions especially in the highly active tectonic regions of Himalayan foothills. Material properties of Historic Unreinforced Brick Masonry (HUBM) in lime mortar are critical to be evaluated for assessment but it is difficult to test the in-situ constituents due to intervention constraints governed by civic bodies on such heritage structures and hence exhaustive testing has been carried out on contemporary lime masonry. Compression tests have revealed the design, yield, ultimate strength and feasible inelastic material properties suitable enough to characterize the cyclic behavior of historical brick masonry in India. Elastic modulus, shear modulus and Poisson ratio have been evaluated to be on the lower side as compared to contemporary mortars constituted masonry. Parameters such as damping, hysteresis behavior, energy dissipation and stiffness degradation characterizing the seismic behavior in elastic and inelastic range suggested the improved performance of brick masonry with increase in compressive strength of lime mortar.

Numerical and Experimental Validation of a 3D Macro-Model for the In-Plane and Out-Of-Plane Behavior of Unreinforced Masonry Walls

ABSTRACTThe behavior of historical UnReinforced Masonry (URM) buildings subjected to earthquake loading is usually governed by a complex interaction between the in-plane and out-of-plane response of masonry walls. In modern masonry building, the in-plane behavior of masonry walls is generally guaranteed in the structural design, but thin non-structural masonry infills are often vulnerable to out-of-plane actions. A reliable prediction of the combined in-plane and out-of-plane behavior of URM walls requires rigorous nonlinear finite element models, whose complexity and computational cost are generally unsuitable for current engineering applications, motivating the research of alternative numerical approaches. This article presents a study for validation of a 3D macro-model intended to simulate the combined in-plane and out-of-plane behavior of unreinforced masonry walls, against experimental results available in the literature and FEM simulations. The model is based on a three-dimensional macro-element whose kinematics is governed by seven degrees of freedom only. The mechanical behavior of the element is based on a fiber discretization approach that adopts basic material parameters. The performance of the proposed macro-element strategy is assessed by means of nonlinear static analyses performed on masonry walls, for which both numerical and experimental results are available in the literature.

Experimental study on the behaviour of masonry pavilion vaults on spreading supports

Over the years, historic unreinforced masonry vaults have been proved to be particularly vulnerable to dynamic actions and large displacements. This paper focuses on the investigation of the structural behaviour of a pavilion vault on spreading supports by means of experimental tests on a 3D–printed scale model made of discrete blocks. Both the collapse mechanisms and the ultimate displacement capacity are analysed. The reliability of this method for investigating the collapse of vaulted structures is validated by drawing analogies with crack patterns of real vaults. The experimental data are compared with the results obtained by thrust line analysis. A good prediction is obtained by making specific assumptions that take into account three-dimensional effects, which demonstrates the importance of thrust line analysis also for 3D collapse.