Performance Of Unreinforced Masonry Buildings Research Articles

Historical Development and Seismic Performance of Unreinforced Masonry Buildings with Vertical Extensions in the City Centre of Barcelona

ABSTRACT This paper presents the historical development of the vertical extensions of unreinforced masonry buildings in the Eixample district of Barcelona and their impact on the seismic behaviour. Existing masonry buildings of Eixample present significant seismic risk because, despite the low to moderate seismic hazard of Barcelona, they show a marked vulnerability given their average height of six storeys and the substantial slenderness of the walls. Between the end of the 19th century and the beginning of the 20th century, the vertical extensions, known as remuntes in Catalan, were a common solution to the increasing demographic demand of the city. In their majority, these vertical extensions add a structural irregularity that represents a potential vulnerability factor not yet investigated. The present study focuses on Eixample’s remuntes, including their historical development, the description of their structural features, and the identification of their most representative configurations in the existing building stock. A seismic analysis based on the Finite Element Method is presented on a reference model without extensions and three others with the most recurrent configurations of remuntes. The seismic response is investigated through pushover analysis. The results provide a better understanding of the negative impact of the vertical extensions on the seismic performance.

Modelling of in-plane seismic behaviour of one-way steel or timber jack arch floors in existing buildings. Application to the Eixample district of Barcelona

The type of floor system has a decisive role in the seismic performance of unreinforced masonry buildings. The in-plane stiffness of the floors has to be adequately represented in the numerical modelling of existing buildings, as it can influence their seismic capacity. This paper investigates the seismic behaviour of one-way arch floor systems composed of steel or timber beams, and ceramic tile vaults. The main objective of the research is to provide a numerical procedure for the simplified modelling of jack arch floor systems in the seismic assessment of unreinforced masonry buildings. The presented approach aims to provide values for the orthotropic properties of simplified floor models composed of elastic 2D shell elements. The orthotropic elastic properties are computed and calibrated by means of comparisons with detailed 3D nonlinear models of the floors. The case study is a multi-storey existing masonry building of the historical “Eixample” district in Barcelona, which includes one-way arch floor systems. The Finite Element Method has been used for the numerical simulation of the seismic performance through nonlinear static (pushover) analyses. The results of the study contribute to a better understanding of the effect of the behaviour of one-way floors with steel or timber beams and tile vaults on the seismic response of masonry buildings. This work provides indicative values for the proper modelling of these particular floor slabs. The proposed methodology is also applicable to the numerical simulation of any other one-way floor system.

A three‐dimensional macroelement for modelling the in‐plane and out‐of‐plane response of masonry walls

SummaryThe seismic performance of unreinforced masonry buildings is commonly assessed using equivalent frame modelling. Its computational efficiency allows for a large number of analyses to be conducted, which are often required to account for epistemic and aleatoric uncertainties. To obtain a full description of the building response, in‐plane and out‐of‐plane failure modes need to be considered, though previous elements for equivalent frame models of unreinforced masonry buildings only account for the in‐plane response. This paper presents the formulation of a three‐dimensional macroelement for modelling the dynamic in‐plane and out‐of‐plane behaviour of masonry panels, which extends the approach of a previously developed macroelement to simulate the in‐plane response. The proposed three‐node, three‐dimensional macroelement is implemented in the software OpenSees and describes the main features of the in‐plane and out‐of‐plane behaviour of a masonry wall, including second‐order geometrical effects and a coupled shear/flexural response. It also allows for the use of complex material models. The proposed element is used to simulate experimental results for in‐plane shear‐compression tests and out‐of‐plane free vibration tests of masonry panels. The implemented element, as well as the example models, is openly shared through the repository https://github.com/eesd-epfl/OpenSees/wiki.

Seismic Performance Evaluation of Unreinforced Masonry Buildings Retrofitted by Strengthening External Walls

Nonlinear static analysis and preliminary evaluation were performed in this study to evaluate the seismic performance of unreinforced masonry buildings subjected to various soil conditions based on the revised Korean Building Code. Preliminary evaluation scores and nonlinear static analyses indicated that all buildings were susceptible to collapse and did not reach their target performance. Therefore, retrofit of those building models was carried out through a systematic procedure to determine areas to be strengthened. It was possible to make most building models satisfy performance objectives through the reinforcement alone of damaged external shear walls. However, the application of a preliminary evaluation procedure to retrofit design was found to be too conservative because all the retrofitted building models verified with nonlinear static analysis failed to satisfy performance objectives. Therefore, it is possible to economically retrofit unreinforced masonry buildings through the fortification of external walls if a simple evaluation procedure that can efficiently specify vulnerable parts is developed.

Mechanical and bond properties of solid clay brick masonry with different sand grading

To evaluate the performance of unreinforced masonry buildings under different loading conditions such as lateral seismic load, the mechanical properties of masonry materials are required. Masonry is a composite material which consists of brick units and mortar joints bonded together. On the other hand, sand is the main ingredient of mortar and its characteristics such as grading can affect the physical and mechanical properties of mortar. In this research, a comprehensive experimental study was conducted to assess the effects of sand grading on the properties of mortar as well as masonry. Considering the main standard tests recommended for masonry as a composite material, the behaviors of masonry assemblages and prisms fabricated using three mortar mixes with coarse and fine sand grading were assessed to examine compressive strength, diagonal-shear strength, and brick-mortar shear and flexural bond strengths.

Probabilistic Model for Bed-Joint Shear-Sliding Strength of Clay-Brick Walls Based on Field Test Data

AbstractClay-brick unreinforced masonry is a very common practice in construction in many parts of the world. In this type of construction, earthquake-induced lateral loads are mainly absorbed by in-plane shear action of brick walls. Because of many inherent uncertainties, shear strength of brick walls is not a deterministic number. The fluctuating nature of the shear resistance can have a significant impact on the seismic performance of unreinforced masonry buildings. Therefore, the probabilistic features of shear-brick walls need to be investigated. ASTM C1531 is a standard test method for in situ measurement of masonry mortar joint shear strength. The test result would be an index of the wall’s shear capacity. In the present study, thousands of the aforementioned field test data are collected and analyzed not only to show the variable nature of wall shear strength, but also to derive the probabilistic characteristics of the parameter. These include mean, variance, standard error, and so on. However, th...

Experimental‐numerical research on the seismic performance of URM buildings made of lightweight AAC blocks / Experimentell‐numerische Untersuchung zum seismischen Verhalten von unbewehrten Mauerwerksgebäuden aus Porenbetonblöcken

AbstractMasonry walls constructed with lightweight AAC blocks and thin‐layer mortar meet the increasingly strict requirements of energy efficiency and sustainability. In this sense, they represent an excellent solution for modern buildings, not only for external cladding but also as loadbearing elements. Despite the possible advantages of using lightweight AAC masonry, a specific assessment of its seismic performance is mandatory in order to set design recommendations allowing to reach safety levels consistent with those required for other masonry types complying with EN 1998 standard requirements.A comprehensive study on the seismic performance of unreinforced masonry buildings made of lightweight AAC was carried out in an integrated experimental‐numerical approach. The experimental campaign provided the necessary information to setup a reliable numerical model to be extensively used to assess the seismic performance of a number of prototype AAC masonry buildings with different characteristics, by means of both linear and nonlinear static (pushover) analysis.The results of this systematic numerical assessment were eventually used to draft design recommendations, to set parameters (behaviour factors) to be used in linear analysis and to calibrate rules for simple buildings.

Performance and Retrofitting of Unreinforced Masonry Buildings against Natural Disasters – A Review Study

Un-Reinforced Masonry (URM) buildings are popular all over the world including Sri Lanka because of their durability, low cost, construction easiness and architectural character, need of less skilled labour, eco-friendliness and use of locally available materials such as ashlar or rubble, adobe and brick. However, these buildings have a higher probability of failing under natural disasters such as earthquakes, tsunamis and storm surges, floods, cyclones and landslides. In Sri Lanka, winds, landslides and floods have frequently occurred. In addition, a massive tsunami adversely affected the people in 2004 and its effects to islands on the Indian Ocean have been continued since December, 2004. Minor earthquakes have come off recently with experiences of wall cracks and no deaths. It is also believed that, there is a defused plate boundary in the making some 500 km south of the southern tip of Sri Lanka which might be the cause of these tremors or minor quakes. Further, an earthquake occurred in Colombo area in 1615, has caused around 2000 of human deaths. Therefore investigation of performance of URM buildings against these natural disasters and possible retrofitting methods are increasingly important. In this review study, an attempt is made to identify the performance of URM buildings against natural disasters and identify retrofitting methods that can be applied to existing building, to enhance the strength proper ties of structural components. Common failure mechanisms for URM structures consist of separation of walls at corners, diagonal cracking or vertical cracking in walls, separation of roofing from walls, out-of-plane wall failure, in-plane wall failure, shear cracks and de-lamination. These damages on a wall diminish the service life of building. In addition, different kinds of retrofitting methods: ferrocement, poly propylene mesh and bamboo reinforcement, for URM structures to be seismic resistant are presented. Mechanisms of failure of URM walls and effects of retrofitting techniques to reduce the damage are also discussed. ENGINEER, Vol. 47, No. 03, pp. 71-82, 2014

Implications of cumulated seismic damage on the seismic performance of unreinforced masonry buildings

The seismic capacity of a structure is a function of the characteristics of the system as well as of its state, which is mainly affected by previous damage and deterioration. The cumulative damage from repeated shocks (for example during a seismic sequence or due to multiple events affecting an unrepaired building stock) affects the vulnerability of masonry buildings for subsequent events. This paper proposes an analytical methodology for the derivation of state-dependent fragility curves, taking into account cumulated seismic damage, whilst neglecting possible ageing effects. The methodology is based on nonlinear dynamic analyses of an equivalent single degree of freedom system, properly calibrated to reproduce the static and dynamic behaviour of the structure. An application of the proposed methodology to an unreinforced masonry case study building is also presented. The effect of cumulated damage on the seismic response of this prototype masonry building is further studied by means of nonlinear dynamic analyses with the accelerograms recorded during a real earthquake sequence that occurred in Canterbury (New Zealand) between 2010 and 2012.

Performance of Unreinforced Masonry Buildings During the 2010 Darfield (Christchurch, Nz) Earthquake

The 2010 Darfield earthquake caused extensive damage to a number of unreinforced masonry buildings. While this damage to important heritage buildings was the largest natural disaster to occur in New Zealand since the 1931 Hawke’s Bay earthquake, the damage was consistent with projections for the scale of this earthquake, and indeed even greater damage might have been expected. In general, the nature of damage was consistent with observations previously made on the seismic performance of unreinforced masonry buildings in large earthquakes, with aspects such as toppled chimneys and parapets, failure of gables and poorly secured face-loaded walls, and in-plane damage to masonry frames all being extensively documented. This report on the performance of the unreinforced masonry buildings in the 2010 Darfield earthquake provides details on typical building characteristics, a review of damage statistics obtained by interrogating the building assessment database that was compiled in association with post-earthquake building inspections, and a review of the characteristic failure modes that were observed. It was observed that structures that had been seismically retrofitted appeared to perform well, with further study now required to better document the successful performance of these retrofit solutions.

State-of-the-Art Report on Seismic Performance of Unreinforced Masonry Buildings

The author is commended for the summary of the progress in the reduction of earthquake hazard in unreinforced masonry buildings. However, the author repeats a common misunder­ standing of the Agbabian, Barnes, and Kariotis (ABK) methodology (Methodology 1984). The statement made in the ABK methodology is over a realistic range of building and soil characteristics, the ground motion is transmitted through the end walls with little amplification. This statement is not equivalent to saying these walls are infinitely rigid in plane. The ABK research studied the behavior of unreinforced masonry (URM) walls supported on flexible soils to support this assumption. The data obtained by the sensors placed in the Old Gilroy Fire Station (Plots 1990) support this assumption. The amplification of the ground displacements at the roof level was about 13 mm and 11 mm on a single pulse at the beginning of the record, and an average of 4 mm during the remaining period of ground shaking. This is a maximum amplification of the peak displace­ ment of 11 %. The amplification at the second-floor diaphragm was probably less than one-half of at the roof as its height is 3.76 m above the base, and the height of the sensor at the roof above the base is 8.1 m. The studies by Tena-Colunga (1992) identified that the dynamic response of the structure is controlled by the diaphragm action. And the diaphragm response is controlled by the input motion at its end. This is the key concept of the ABK methodology (Methodology 1984). The loading of the end shear wall results from its own mass and the diaphragm's dynamic response. There is no, and there need not be, assumption of rigid in-plane wall response. The inertial forces at any level in the end wall, applied to the end wall, are equal to the dynamic response forces of the diaphragm instead of to an arbitrarily assumed distribution of inertial forces. The discusser also disagrees with the assumption made by the author the objective of the U.S. codes and standards used to reduce earthquake hazard is to mitigate the risk of life loss and The ABK methodology was not intended solely to mitigate the risk of life loss or injuries. Mitigation of this risk is obtained by the reduction of property damage. The design-level ground motion used in the ABK research for the highest risk seismic zone had a spectral velocity of 0.76 mls (Seismic 1981). The design-level ground motion recommended in this highest-risk seismic zone by the Handbook for the Seismic Evaluation of Existing Buildings (FEMA 1992) is 0.61 mls for S2 type soils. The use of these codes and standards does meet historical pres­ ervation goals. It should be recognized the predicted earthquake damage resulting from design-level earthquake has a small probability of occurrence. The discusser has seen many instances in which features of historic buildings were lost in an attempt to save them.

Closure to “State‐of‐the‐Art Report on Seismic Performance of Unreinforced Masonry Buildings” by Michel Bruneau

Closure to “State‐of‐the‐Art Report on Seismic Performance of Unreinforced Masonry Buildings” by Michel Bruneau

State‐of‐the‐Art Report on Seismic Performance of Unreinforced Masonry Buildings

A large proportion of North America's older building inventory is of unreinforced masonry (URM), constructed in the absence of mandatory earthquake design requirements, and unquestionably recognized as the type of construction most vulnerable to earthquakes. Awareness of this seismic hazard is relatively new in eastern North America. In addition, the nature of the seismic risk and other engineering constraints there shed a new and different perspective on the problem. This state‐of‐the‐art paper on the seismic performance of URM buildings summarizes knowledge that has already gained some acceptance in parts of North America, and outlines current limitations. Concerns regarding the seismic performance of existing URM buildings are formulated in an eastern North American seismicity context. The various failure modes of URM buildings or components subjected to earthquake excitation are described, and, when possible, illustrated. The state‐of‐practice as required by North American building design codes and standards is summarized. A special analytical procedure of the Uniform Code for Building Conservation, largely inspired from the Agbabian, Barnes, and Kariotis (ABK) methodology for the mitigation of seismic hazards in existing buildings, is reviewed.

The Borah Peak, Idaho Earthquake of October 28, 1983—Performance of Unreinforced Masonry Buildings in Mackay, Idaho

Damage to buildings in Mackay, Idaho during the October 28, 1983 Borah Peak earthquake was largely limited to unreinforced masonry construction, including the unreinforced masonry chimneys of wood frame dwellings. Except for chimneys, which typically collapsed or were severely damaged, the level of damage was only slight to moderate, even though the earthquake resistance of the construction was very low, even for unreinforced masonry.