Unreinforced Brick Masonry Buildings Research Articles

Seismic Performance Enhancement of Unreinforced Brick Masonry Buildings by Retrofitting with Reinforced Concrete Bands: Full Scale Experiments

Seismic Performance Enhancement of Unreinforced Brick Masonry Buildings by Retrofitting with Reinforced Concrete Bands: Full Scale Experiments

Modelling and Evaluation of the Seismic Capacity of Typical Brick URM Buildings of the Historical Center of Cuenca- Ecuador

The Historic Center of Cuenca (HCC) is located in the southern region of Ecuador. It is well known that our country is located on the so-called belt of fire of the Pacific Ocean, this area is characterized by having generated the most important seismic events in the history of mankind. More specifically, there are records that show that in the last 200 years the city of Cuenca has been exposed to earthquakes that have produced moderate to severe damage. These reasons make it possible to establish that the city of Cuenca and specifically its historic center could present important problems in the face of significant seismic events. Most of the buildings in the HCC date back to the middle of the 20th century and have used unreinforced brick masonry (brick-URM) to build their walls. This work is part of the Seismic Vulnerability Project: Seismic Damage Scenarios of the Built Heritage of the Historic Center of Cuenca. In the context of this vulnerability project, the objective of this work was to establish a family of pushover curves for three unreinforced brick masonry buildings typical of the HCC, based on a parametric pushover analysis. The definition of the typical buildings was based on an extensive work of architectural and geometric characterization of the traditional built heritage of HCC. On the basis of focusing the study on two-story buildings (the most common), the size of the floor area of the buildings (small, medium and large area) was assumed as a base parameter. Based on an analysis of the variability of different geometric and mechanical characteristics, and in order to study their influence on the pushover curves of the three typical brick URM buildings, the following study parameters were defined: 1) compressive strength of brick masonry, 2) lateral displacement capacity of brick-URM elements, 3) wall thickness. The pushover analysis was carried out with the Ruaumoko program. The model of the buildings responds to an equivalent portal frame macro-model scheme that has been formulated and validated by the authors of this paper. In order to consider the effects of the flexible floor on the dynamic response of this type of structures, a lateral load pattern that takes into account the contribution of higher order modes of vibration will be used in pushover analysis. The results will be discussed in terms of the incidence of the variability of the study parameters on the basic characteristics of the pushover curves. These results will be an essential input for the next stage of the project consisting of damage estimation for different levels of seismic action expected in the city.

Seismic performance of a Low-Cost base isolation system for unreinforced brick Masonry buildings in developing countries

Unreinforced masonry (URM) buildings are one of the most common type of constructions in developing countries, due to their reduced cost and ease of fabrication. However, the traditional non-engineered nature of these buildings combined with the poor mechanical performance of their structural materials pose a major threat to their earthquake performance, often resulting in heavy damage and losses. This study investigates the possibility of improving the response of typical URM buildings in developing countries, using a novel low-cost fibre reinforced elastomeric isolators (FREIs) developed with recycled rubber (RR). Detailed three-dimensional finite element analyses were carried out on the fixed-base (FB) and base-isolated (BI) configurations of the prototype building subjected to a set of strong recorded ground motions, considering both the design basis earthquake (DBE) and maximum considered earthquake (MCE). The numerical model of the URM building was developed using non-linear shell elements and bilinear springs that respectively simulated the hysteretic behavior of masonry walls and RR-FREIs. Numerical results show a significant reduction in both the accelerations and inter-story drifts of the BI configuration when compared to the response of the FB building. The global elastic response and corresponding enhanced seismic performance of the BI building under DBE confirm the effectiveness of the proposed base isolation system in protecting non-engineered URM buildings from seismic events with medium-to-high intensity.

Seismic Capacity Assessment of Unreinforced Brick Masonry Building Performed According To Eurocode

Brick Masonry Building with cement sand mortar is a common type of building typology in Nepal. Regardless of being one of the eldest construction technology, the behavior of masonry building is still a matter of study. The uncertainty in the behavior of masonry structures is due to material heterogeneity, complex behavior under different loading conditions and may be due to less research in this arena. Different modeling strategies are used and proposed worldwide to design and to identify the seismic performance of Masonry Building. The analysis strategy ranges from the simple linear method, equivalent frame method, static nonlinear method to dynamic nonlinear, which may be chosen according to engineering design aims and research purpose. In this attempt, authors choose two degrees of freedom 3D model of Unreinforced Brick Masonry Structures which catches both overturning and hysteresis mechanisms due to the shear response implemented by the TREMURI program with static nonlinear procedures. This verified method of modeling and analysis is applied to assess the performance of three different Unreinforced Brick Masonry buildings of the same plans with different numbers of storey.

Volume loss fatality model for as-built and retrofitted clay brick unreinforced masonry buildings damaged in the 2010/11 Canterbury earthquakes

Building volume loss can be directly correlated with earthquake fatalities and is therefore considered to be a better damage descriptor for estimating risk to occupants than traditional damage states. Empirical volume loss studies are limited and the study presented herein represents what is likely the first attempt to develop a relationship between commercial unreinforced brick masonry (URBM) buildings attributes, ground motion, and fatalities based on empirical data. Data from two New Zealand earthquakes was utilized to develop a model that predicts the probability of a URBM buildings being in a volume loss damage states (VDS) and the associated probability of an occupant fatality. To demonstrate application of the model, two New Zealand earthquake scenarios are presented and discussed. The model is intended to be applied at a broad scale, to capture an average response over a large number of New Zealand URBM buildings, with applicability to other countries having stocks of comparable URBM buildings.

Structural Performance Characteristics based Seismic Damage Gradation Schema for Single Storey URBM Buildings in India with a Rigid Diaphragm

ABSTRACT Damage gradation is the important aspect in obtaining fragility curves and hence in the estimation of expected damage during hazardous events. This paper presents a new schema for seismic damage gradation, simply referred to as damage gradation, for use in vulnerability analysis of single story unreinforced brick masonry (URBM) buildings with a rigid diaphragm. The new schema for damage gradation is based on structural performance characteristics instead of the fixed limiting values of drift ratios or drift ratio thresholds, for which appropriateness and justifications are provided. The schema is, DG1: earlier of initiation of non-linearity in any of the component piers or attainment of 33% of peak base shear of the building, DG2: attainment of peak base shear of the building, and DG3: fall-off resistance to 60% of peak base shear of the building. The schema is arrived at based on study of capacity curves, along two principal horizontal directions, of a representative set of 35 typical URBM buildings and by establishing, (1) it is inappropriate to adopt the conventional fixed limiting values of drift ratios for damage gradation and, (2) the applicability of drift ratio thresholds is also limited.

Simulating the damage extent of unreinforced brick masonry buildings under boulder impact using three-dimensional discontinuous deformation analysis (3-D DDA)

Abstract The main material of brick masonry buildings is discontinuous masonry material. This study presents a critical review of the damage characteristics of masonry and the methods for studying the behavior of masonry. The damage extent of brick masonry buildings under boulder impact is analyzed using an approach based on three-dimensional discontinuous deformation analysis (3-D DDA). A “block-joint” model is established to represent the brick and mortar of the building, which is based on the discontinuous characteristics of the masonry material. On this basis, a benchmark model is used to validate the 3-D DDA. Using this approach, the velocity distribution and several displacements of key points of the building blocks are obtained to compare the damage extent of the building under six different cases that consider in-plane or out-of-plane boulder impacts to the building at different heights. The size and material parameters of the building model are based on the most common buildings in the field of investigation. These results can be used to show the failure process of buildings on a continuous basis or to quantitatively compare the damage extent of different types of buildings. By analyzing the force condition of the basic element blocks, the results demonstrate that the damage extent of the building is related to the impact direction, impact height, location relationship between the damaged part and the impact position, and constraint condition.

Seismic Capacity Assessment of Confined Brick Masonry Building: An Experimental Approach

Brick masonry is widely used for building construction throughout the world. However, unreinforced brick masonry buildings performed poorly in the 2005 Kashmir earthquake, in Pakistan, resulting in a decline in the use of brick masonry. In order to investigate and quantify the performance of brick masonry against the seismic forces by confining it through typical stiffer, line elements (column and beams), a full-scaled room model of an area 3048 × 3658 mm (10 × 12 ft) and height of 3353 mm (11 ft) was constructed using confined brick masonry. The model was tested under quasistatic loading system. Crack pattern was noted at the end of each loading cycle. The response of the model was interpreted through a hysteresis curve, which was then idealized by a bilinear curve. A comparison of the results has been made with four different studies done on the similar model made of unreinforced brick masonry before and after retrofitting and unreinforced concrete block masonry before and after retrofitting previously tested at the same testing facility.

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.

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.

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.

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.

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.

Equivalent frame model and shell element for modeling of in-plane behavior of Unreinforced Brick Masonry buildings

Although performance based assessment procedures are mainly developed for reinforced concrete and steel buildings, URM (Unreinforced Masonry) buildings occupy significant portion of buildings in earthquake prone areas of the world as well as in IRAN. Variability of material properties, non-engineered nature of the construction and difficulties in structural analysis of masonry walls make analysis of URM buildings challenging. Despite sophisticated finite element models satisfy the modeling requirements, extensive experimental data for definition of material behavior and high computational resources are needed. Recently, nonlinear equivalent frame models which are developed assigning lumped plastic hinges to isotropic and homogenous equivalent frame elements are used for nonlinear modeling of URM buildings. The equivalent frame models are not novel for the analysis of masonry structures, but the actual potentialities have not yet been completely studied, particularly for non-linear applications. In the present paper an effective tool for the non-linear static analysis of 2D masonry walls is presented. The work presented in this study is about performance assessment of unreinforced brick masonry buildings through nonlinear equivalent frame modeling technique. Reliability of the proposed models is tested with a reversed cyclic experiment conducted on a full scale, two-story URM building at the University of Pavia. The pushover curves were found to provide good agreement with the experimental backbone curves. Furthermore, the results of analysis show that EFM (Equivalent Frame Model) with Dolce RO (rigid offset zone) and shell element have good agreement with finite element software and experimental results.

Deterministic and Probabilistic Earthquake Scenarios for the Seismic Risk Analysis of URM Buildings

Barcelona, as well as a large number of cities in the Mediterranean basin, has a housing stock composed of a large number of unreinforced brick masonry buildings. Motivated by different factors, the enlargement of the city (Eixample in Catalan) was held from the second half of the 19th century and the beginning of the 20th, a period in which a large number of buildings of this type were built, many of which are still used as dwellings. Although the buildings were built individually, some of them are linked to adjacent buildings by the side walls. This feature leads to the analysis of the buildings as isolated structures and also as an aggregate. Barcelona is located in a seismic region of low to moderate hazard, with macroseismic intensity between the grades VI and VII of the European macroseismic scale EMS'98. Based on the deterministic and probabilistic response spectra for the different types of soils present in Barcelona obtained in the work of Irizarry (2004), the seismic risk of four individual buildings and an aggregate is evaluated. The buildings are modeled and analyzed using the TREMURI program and MATLAB routines under the guidance of RISK-UE project.

Experimental Seismic Performance Evaluation of Unreinforced Brick Masonry Buildings

This paper presents an experimental study on the performance of a full-scale unreinforced brick masonry (URM) building system tested under quasi-static loading at the Earthquake Engineering Centre, University of Engineering and Technology in Peshawar, Pakistan. The configuration and materials used in the single-story URM building are typical of those found in the northern areas of Pakistan affected by the 2005 Kashmir earthquake. This study is a part of ongoing research for the earthquake impact assessment of the city of Abbottabad. Combined shear and flexural behavior was observed during the test. The experimental data was analyzed and is presented in the form of force-deformation hysteresis loops and envelope curves. Based on the measured data, different performance levels have been established. The measured response of the test structure is also compared to the estimated response obtained using three capacity evaluation procedures and the two are found to be in good agreement.

Experimental Behavior of Full Scale URM Building Retrofitted with Ferrocement Overlay

This paper presents a study on the behavior of a damaged full scale unreinforced brick masonry building, retrofitted with ferrocement overlay and cement based grout injection, tested under cyclic loading. Damage mechanism and force-deformation behavior of the retrofitted structure are compared with its pre-damaged response to quantify the beneficial effects of retrofitting scheme. The lateral load capacity of the retrofitted building was significantly improved and the damage mechanism was transformed from mixed compression-flexural-shear mode to a more stable flexural rocking mode. The energy dissipation capacity, however, remained unchanged and the deformation capacity was slightly decreased.