Unreinforced Brick Masonry Research Articles

Experimental Investigation on the Flexural Performance of Brick Masonry Wall Retrofitted Using PP-Band Meshes under Cyclic Loading

Numbers of residential houses were damaged in some areas caused by earthquakes. The damages greatly affected the number of losses. Most of the houses in some countries are made of brick unreinforced masonry (URM) walls. Improving the structural performance of this kind of masonry has become important. For this reason, experimental study was conducted on the flexural performance of brick walls retrofitted with strapping band (polypropylene/pp-band). The walls were constructed using bricks produced manually with joint mortar ratio of 1 PC: 6 sand, that chosen to represent the actual field conditions of the communities in Indonesia. The aims of the study were to determine the out of plane flexural performance of the non-retrofitted and retrofitted brick masonry walls under cyclic loading by using some variations of the distance between pp-band. The walls were loaded to produce flexural bending that caused vertical and horizontal cracks. The results of the test showed that the retrofitted walls failed by large deformation. After crack, the strength reduced to about 25-50% of the crack load and then regained progressively as residual strength until 150% higher than the strength at crack load by large deformation due to the strapping band mesh. The wall with 10 cm pp-band distance should be used as optimum solution for retrofitting

Comparison of Numerical and Experimental Seismic Responses of FREI-Supported Un-reinforced Brick Masonry Model Building

Comparative study of numerically and experimentally obtained seismic responses of un-reinforced masonry building supported on in-house designed un-bonded fibre reinforced elastomeric isolator (U-FREI) are presented in this article. The effectiveness of U-FREI is established very clearly in terms of controlled dynamic response of the model building. Experimental studies are carried out on a shake table with elaborate instrumentations for measurement of acceleration and displacements at different floor levels. Numerical study of the model building supported on U-FREI is carried out to compare the results with experimental investigation. Multi-linear pivot hysteretic plasticity model is used to simulate the behavior of FREI, while plate elements are used for brick-masonry walls. Experimentally obtained force-displacement curves of FREI are used for defining the properties of multi-linear model representing FREI. The dynamic responses obtained from the numerical studies are compared with those from experimental investigations. This study indicates that the seismic responses of building supported on U-FREI can be numerically evaluated with quite reasonable accuracy. A good numerical model can be judiciously used at the preliminary design stage, followed by actual testing and construction of the base isolated building.

3D rigid block micro-modelling of a full-scale unreinforced brick masonry building using mathematical programming

In this paper, we present a three-dimensional limit equilibrium analysis of an unreinforced brick masonry building. The structure under investigation is a one-room one-floor building that has been selected from a full-scale test carried out within the framework of a joint USA-Pakistan research project. The structural model of the building is an assemblage of rigid blocks, which interact through no-tension contact surfaces with Coulomb friction. A micro-modelling approach is adopted where each masonry unit is modelled as a rigid body. The underlying limit analysis formulation is based on the concave contact model, with contact forces located at the vertices of the interfaces. Iterative calculations are carried out to deal with the non-associative friction behaviour. The numerical analysis is carried out with the aid of a computer program that provides as output the failure load and the collapse mechanism. The comparison with experimental outcomes shows that the adopted formulation is capable to predict the actual behaviour of 3D masonry structures with a reasonable computational effort.

3D rigid block micro-modelling of a full-scale unreinforced brick masonry building using mathematical programming

In this paper, we present a three-dimensional limit equilibrium analysis of an unreinforced brick masonry building. The structure under investigation is a one-room one-floor building that has been selected from a full-scale test carried out within the framework of a joint USA-Pakistan research project. The structural model of the building is an assemblage of rigid blocks, which interact through no-tension contact surfaces with Coulomb friction. A micro-modelling approach is adopted where each masonry unit is modelled as a rigid body. The underlying limit analysis formulation is based on the concave contact model, with contact forces located at the vertices of the interfaces. Iterative calculations are carried out to deal with the non-associative friction behaviour. The numerical analysis is carried out with the aid of a computer program that provides as output the failure load and the collapse mechanism. The comparison with experimental outcomes shows that the adopted formulation is capable to predict the actual behaviour of 3D masonry structures with a reasonable computational effort.

Effect of Uncertainties in Development of Fragility Curves for URBM Building

Seismic fragility analysis of Un-reinforced Brick Masonry (URBM) Buildings is useful for determining the possible extent of damage in the event of an earthquake. It is known that there are uncertainties with respect to both the mechanical properties of masonry and the characteristics of earthquake ground motion. This paper presents sensitivity studies: by considering Weibull distribution as candidate distribution for compressive strengths of brick and mortar and varying the Coefficient of Variation (COV); and by using 12 different earthquakes time histories available in the strong motion atlas of India separately. For this purpose a one room, single storey URBM building has been considered and the fragility curves have been obtained by integrating Improved storey shear modelling, Monte Carlo simulation and Incremental dynamic analysis. From the study, it has been observed that while using the Weibull distribution as candidate distribution for mechanical properties of masonry, fragility curves of URBM buildings are not significantly affected by the COV whereas they are sensitive to the choice of earthquake ground motion. Fragility curves obtained using different earthquake time histories show three bands. For the suite of earthquake time histories considered in this study, the observed fragilities are generally increasing with the epicentral distance. In other words observed fragilities corresponding to the far-field earthquake time histories are generally higher than those corresponding to the near-field earthquake time histories. Thus, for vulnerability analysis, selection of suite of earthquake time histories judiciously is more important than modelling the statistical variations in mechanical properties of masonry. Keywords: Coefficient of Variation, Incremental Dynamic Analysis, Seismic Fagility Curves, Sensitivity, Unreinforced Brick Masonry, Weibull Distribution

Effect of Uncertainties in Development of Fragility Curves for URBM Building

Seismic fragility analysis of Un-reinforced Brick Masonry (URBM) Buildings is useful for determining the possible extent of damage in the event of an earthquake. It is known that there are uncertainties with respect to both the mechanical properties of masonry and the characteristics of earthquake ground motion. This paper presents sensitivity studies: by considering Weibull distribution as candidate distribution for compressive strengths of brick and mortar and varying the Coefficient of Variation (COV); and by using 12 different earthquakes time histories available in the strong motion atlas of India separately. For this purpose a one room, single storey URBM building has been considered and the fragility curves have been obtained by integrating Improved storey shear modelling, Monte Carlo simulation and Incremental dynamic analysis. From the study, it has been observed that while using the Weibull distribution as candidate distribution for mechanical properties of masonry, fragility curves of URBM buildings are not significantly affected by the COV whereas they are sensitive to the choice of earthquake ground motion. Fragility curves obtained using different earthquake time histories show three bands. For the suite of earthquake time histories considered in this study, the observed fragilities are generally increasing with the epicentral distance. In other words observed fragilities corresponding to the far-field earthquake time histories are generally higher than those corresponding to the near-field earthquake time histories. Thus, for vulnerability analysis, selection of suite of earthquake time histories judiciously is more important than modelling the statistical variations in mechanical properties of masonry.

Assessment of mortar properties in vintage clay brick unreinforced masonry buildings

Mortar is a principal structural component of unreinforced masonry (URM) buildings, with mortar mechanical properties having an important influence on the behaviour of URM buildings when subjected to earthquake induced shaking. However, the mechanical properties of in situ mortar have long been known to be difficult to obtain. Recommendations on mortar properties for preliminary assessment of URM buildings, as well as details of field assessment procedures for in situ mortar characterisation have been previously suggested in national standards and guidelines in the USA, New Zealand and seismically active countries in Europe. An experimental study was implemented in order to investigate an improved characterisation procedure for vintage mortars, to be used by structural engineering practitioners with the aim to improve the accuracy of building seismic assessments, computer modelling and subsequent seismic retrofit designs. The tested mortar samples were extracted from 60 different vintage URM buildings throughout New Zealand. A non-standard mortar compression test procedure was developed, and an alternative in situ assessment technique to estimate mortar compressive strength was investigated. Supplementary tests to estimate the mortar aggregate/binder ratio and to predict the presence of cement in the mortar are also discussed.

Experimental Seismic Performance Evaluation of Unreinforced Brick Masonry Shear Walls

Unreinforced masonry buildings, constructed with stones or bricks, are common in the northern areas of Pakistan. In the October 2005 Kashmir earthquake, the seismic performance of stone masonry buildings was found to be poor, which was the primary source of fatalities. Unreinforced brick masonry (URBM) buildings, however, performed well even in severely jolted areas. The performance of URBM could have been much better if the affected buildings were constructed by using proper guidelines. Taking lessons from the disaster, an experimental investigation, based on typical geometry and precompression levels of the URBM shear walls in the affected region, was conducted to evaluate their seismic performance. Twelve walls were tested in the in-plane direction using quasi-static cyclic loading. First-story drift ratios for various performance levels in URBM buildings are proposed. The influences of relative precompression level and aspect ratio on the damage pattern, ultimate drift ratio, and equivalent viscous damping of the walls are examined.

A Multi-hazard Risk Assessment of Buildings in Padang City

The main purpose of an earthquake risk assessment is to assess the potential loss of buildings in earthquake prone regions and to provide enough information to employ suitable mitigation strategies. The Mw 9.1 great Sumatra earthquake in 2004 and the Mw 9.0 Japan earthquake in 2011 have highlighted the importance of a multi-hazard risk assessment framework that includes the effects of both earthquake and its associated hazards such as tsunami. The multi-hazard risk assessment of buildings requires several stages including earthquake and tsunami hazard analyses, the vulnerability analysis of buildings, building inventory as well as the risk estimation of buildings in the investigated area, which are discussed in this paper. The method on how to incorporate these stages into a multi-hazard risk assessment framework is also presented. The developed risk assessment framework is then used for the city of Padang that has a considerably high earthquake and tsunami hazard with great exposure to population and infrastructures. The estimated risk obtained in this study is expressed in terms of Pure Risk Premium (PRP) for different building categories commonly found in Padang including unreinforced brick masonry (UBM), confined brick masonry (CBM), reinforced concrete frame with masonry infill (RCI) and steel structures. The earthquake PRP(s) obtained in this study are comparable with the latest insurance rates released by MAIPARK. MAIPARK is an insurance company specialized in earthquake reinsurance, which also provides earthquake statistics and sets a benchmark for earthquake insurance pricing in Indonesia. Tsunami PRP(s) for different building categories in the area are also presented in this paper; however, no comparison can be made due to the unavailability of tsunami insurance premium data for Indonesia. Based on the results, it can be concluded that building risk associated with tsunami in Padang is considerably lower than that of earthquake, due to infrequent occurrence of tsunamis in the area. The earthquake and tsunami risk of buildings in Padang is predicted to be £54.5 million and £30.8 million per annum, respectively.

Shake Table Evaluation of Low-Cost Strengthening Technique for Unreinforced Brick Masonry Columns

Shake Table Evaluation of Low-Cost Strengthening Technique for Unreinforced Brick Masonry Columns

Assessment of earthquake-induced damage in Quebec city, Canada

A methodology is developed for first-order assessment of the seismic risk involving seismic hazard, local building inventory, and evaluation of respective vulnerability. Central to the vulnerability analysis is the concept of fragility functions used to determine the probability of exceedance of a specified damage state, where the nonlinear structural behaviour is defined by capacity curves. A new set of continuous hazard-compatible fragility functions is proposed for rapid risk assessment on urban and regional scales in interactive spreadsheet application. To demonstrate the method, it was applied in a dense urban environment of downtown Quebec City, Canada, for damage assessment of low-rise wood light frame and unreinforced brick masonry buildings. Earthquake scenario with M6.2 and distance 10km from the centroid of the study area was developed from deaggregation of the seismic hazard defined by the current National Building Code of Canada-NBCC 2010. The ground shaking was represented with a simplified site-specific response spectrum, fully defined with spectral accelerations at 0.3 and 1.0s. The results show that as much as 61% of the considered buildings would sustain certain degree of damage. The influence of epistemic uncertainties in the ground motion prediction and the site-class on damage estimation is evaluated.

Analytical method for the assessment of unreinforced brick masonry walls subjected to eccentric compressive loads

Slender unreinforced masonry walls are likely to fail due to mechanism formation when they are subjected to eccentric compression loads causing second order bending effects. A practical analytical formulation is herein presented to provide an accurate calculation tool for these cases. The proposed method is compared with Eurocode-6, ACI-530, Southwell Plot method (semi empiric), a Finite Element Analysis and experimental tests. The results show that the proposed method and ACI-530 are accurate at calculating the load-bearing capacity of the most slender walls and the less slender cases respectively. The Southwell Plot method achieves the best performance although its applicability is limited.

Dry Masonry Strenghtening through Basalt Fibre Ropes: Experimental Results against Out-of-Plane Actions

One of the most important characteristics that historical masonry should have is that of a monolithic behavior. Without these basic feature, no structural analysis could be considered reliable. If this characteristic is absent, strengthening bearing masonry giving it a transversal monolithic behavior is one of the first retrofitting actions to do so as to improve its seismic performance. Hence come out the idea to develop a new consolidation technique specially formulated for historical masonry. Stitching masonry through continuous flexible elements is an innovative technique, able to connect the several masonry components and to attribute to it a monolithic behavior according to the principles that govern the intervention on existing buildings: minimal intervention, compatibility, reversibility, respect of authenticity, matter conservation, control of the visual impact and possibility of recognizing the intervention. Basalt fibers ropes of 4 mm of nominal diameter (declared by manufacturer), have been used in this experimental program as continuous flexible element. The technique has been already tested and proved to be effective for improving the behavior against “in-plane” actions. Good results has been obtained also excluding synthetic adhesives (resins), with an enhancement about reversibility. In this paper, the results of an experimental campaign aimed to evaluate the technique effectiveness against “out-of-plane” loads are presented. Reinforced and unreinforced brick masonry specimens have been tested simulating vertical bending mechanism activation to evaluate the stitches contribute.

Strength Performance of Unreinforced Brick Masonry Walls under Flexo-Compression Load. Analytical Methods

The structure of many historical buildings relies on unreinforced masonry load-bearing walls. In the case of large slenderness or significant eccentricity of the vertical compressive loads the mechanism formation failure mode is likely. Considering the second order bending effects and the tensile strength of the masonry is essential to accurately calculate the load-bearing capacity of these structures, which is required for maintenance tasks. An analytical methodology has proposed with this aim. This original method, the Southwell plot method and the formulations from two standard codes (ACI-530 and Eurocode-6) are applied to calculate the resistance of 18 experimentally tested walls to conclude that the proposed methodology brings correct results, the standards are conservative and the Southwell plot method is the most suitable for the analysis of the considered cases but it is not always applicable.

Geometric characterisation and out-of-plane seismic stability of low-rise unreinforced brick masonry buildings in Auckland, New Zealand

The 2010-2011 Canterbury earthquakes and corresponding Royal Commission reports have resulted in changes to the legislative environment and led to increased public awareness in New Zealand of the earthquake performance of unreinforced masonry (URM) buildings. As a result, building regulators, owners, tenants, users and heritage stakeholders will be facing a unique challenge in the near future where assessments, improvements and demolitions of URM buildings are expected to occur at an unusually high rate. Auckland is the largest city in New Zealand and because of the relative prosperity of Auckland during the period 1880-1935 when most URM buildings were being constructed in New Zealand, the city has the largest number of URM buildings in the country. Identifying those buildings most at seismic risk in Auckland’s large and varied building stock has warranted a rapid field assessment program supplemented by strategically chosen detailed assessments. Information that can be procured through rapid field inspections includes the building geometric typologies (e.g., heights, building footprint geometry and isolated versus row configuration), elevation type (e.g., perforated frame versus solid wall), wall construction (e.g., solid versus cavity, number of leaves) and basic construction material type (e.g., clay brick versus stone). Furthermore, investigation into the architectural history, heritage status and functional usage of Auckland’s URM buildings will affect the direction of retrofit strategies and priorities. As the owner of a large and varied portfolio of URM buildings as well as the local organisation responsible for assessing building safety, Auckland Council is developing exemplar inspection, assessment, prioritisation and retrofit strategies that will target the seismic risks associated with URM buildings, in particular, so as to preserve and enhance safety and the economic and community value of these special buildings. Collaboration amongst Auckland Council, The University of Auckland and GNS Science has resulted in a state-of-the-art rapid quantitative assessment program applied to a sampling of typologically representative URM buildings in Auckland.

Material properties of existing unreinforced clay brick masonry buildings in New Zealand

The material properties of New Zealand’s heritage clay brick unreinforced masonry (URM) buildings were investigated and are reported herein. Material data was collected from a total of 98 New Zealand clay brick URM buildings and a database was compiled that was comprised of various masonry material properties. The intention behind the reporting of information and data presented herein was to provide indicative values to the professional engineering community to aid as preliminary input when undertaking detailed building assessments for cases where in-situ testing and brick and mortar sample extraction are not feasible. The data presented is also used to support the relationships for URM material properties that have been recommended by the authors for incorporation into the next version of the NZSEE seismic assessment guidelines for URM buildings. Although researchers from Europe, USA, India and Australia have previously studied the material properties of clay brick unreinforced masonry, knowledge on New Zealand URM material properties was poor at the time the study commenced. Therefore, a research programme was undertaken that was focused on both in-situ testing and laboratory testing of samples extracted from existing New Zealand clay brick URM buildings.

A methodology for development of seismic fragility curves for URBM buildings

This paper presents a simple methodology that integrates an improved storey shear modelling, Incremental Dynamic Analysis and Monte Carlo Simulation in order to carryout vulnerability analysis towards development of fragility curves for Unreinforced Brick Masonry buildings. The methodology is demonstrated by developing fragility curves of a single storey Unreinforced Brick Masonry building for which results of experiment under lateral load is available in the literature. In the study presented, both uncertainties in mechanical properties of masonry and uncertainties in the characteristics of earthquake ground motion are included. The research significance of the methodology proposed is that, it accommodates a new method of damage grade classification which is based on 'structural performance characteristics' instead of 'fixed limiting values'. The usefulness of such definition is discussed as against the existing practice.

Failure mechanism of compressed short brick masonry columns confined with FRP strips

The article addresses the issues of strengthening and stabilisation of compressed masonry structures by inorganic FRP fabrics. The confinement of a masonry column with fabrics of carbon fibres with a high modulus of elasticity and high tensile strength relieves the transverse tensile stresses in the masonry and increases the ultimate deformation and the ultimate load. The experimental research of brick masonry columns under concentric load performed to-date has pointed out the necessity of adopting a different approach to assessing the load-bearing capacity or residual load-bearing capacity, which takes into account the different failure modes of reinforced and unreinforced brick masonry.

In-plane strengthening of clay brick unreinforced masonry wallettes using ECC shotcrete

New Zealand’s stock of unreinforced masonry (URM) bearing wall buildings was principally constructed between 1880 and 1935, using fired clay bricks and lime or cement mortar. These buildings are particularly vulnerable to horizontal loadings such as those induced by seismic accelerations, due to a lack of tensile force-resisting elements in their construction. The poor seismic performance of URM buildings was recently demonstrated in the 2011 Christchurch earthquake, where a large number of URM buildings suffered irreparable damage and resulted in a significant number of fatalities and casualties. One of the predominant failure modes that occurs in URM buildings is diagonal shear cracking of masonry piers. This diagonal cracking is caused by earthquake loading orientated parallel to the wall surface and typically generates an “X” shaped crack pattern due to the reversed cyclic nature of earthquake accelerations.Engineered Cementitious Composite (ECC) is a class of fiber reinforced cement composite that exhibits a strain-hardening characteristic when loaded in tension. The tensile characteristics of ECC make it an ideal material for seismic strengthening of clay brick unreinforced masonry walls. Testing was conducted on 25 clay brick URM wallettes to investigate the increase in shear strength for a range of ECC thicknesses applied to the masonry wallettes as externally bonded shotcrete reinforcement. The results indicated that there is a diminishing return between thickness of the applied ECC overlay and the shear strength increase obtained. It was also shown that, the effectiveness of the externally bonded reinforcement remained constant for one and two leaf wallettes, but decreased rapidly for wall thicknesses greater than two leafs. The average pseudo-ductility of the strengthened wallettes was equal to 220% of that of the as-built wallettes, demonstrating that ECC shotcrete is effective at enhancing both the in-plane strength and the pseudo-ductility of URM wallettes.

Strengthening of unreinforced masonry using welded wire mesh and micro-concrete – Behaviour under in-plane action

Unreinforced masonry (URM) buildings constitute a significant part of existing building inventory worldwide. Past earthquakes have shown that these buildings are highly vulnerable to earthquakes. Application of of Ferro-cement (welded wire mesh with micro-concrete/mortar) is one of the commonly used techniques for seismic retrofitting of such buildings. The present experimental study performed on unreinforced brick masonry panels strengthened by Welded Wire Mesh (WWM) and micro-concrete, aims to investigate the efficacy of this technique in enhancing the shear and ductility capacity of masonry. A set of six unreinforced and twelve strengthened panels are subjected to diagonal compression tests. Two different reinforcement configurations, simulating field application, are evaluated. The effect of strengthening on in-plane shear behaviour of URM walls, including failure modes, modulus of rigidity, shear strength, maximum drift, and pseudo ductility, are investigated. The results show that the strengthening using Ferro-cement results in significant enhancement in shear strength and ductility of unreinforced masonry.