Behavior Of Masonry Infill Walls Research Articles

In-plane behaviour of masonry infill walls with openings strengthened using textile reinforced mortar

A numerical study was carried out to simulate the in-plane behaviour of a 1:2.5 scaled one-storey one-bay masonry-infilled reinforced concrete (RC) frame retrofitted with textile-reinforced mortar (TRM). The study used ABAQUS finite element analysis (FEA) software and a three-dimensional (3-D) finite element method. Using a ductile design and details, the TRM-reinforced structure encountered in-plane displacement-control cyclic loads during the test. This study assesses how accurately a representative numerical model can replicate the results of an experimental test. Parametric research was conducted following the numerical model's calibration. To develop a suitable numerical model, suitable constitutive models based on the concrete damage plasticity (CDP) approach were used to characterize the nonlinear response of TRM, masonry infill, and concrete. The experimental findings, which aggrandize the response simulation, served as the basis for calibrating the models. Using a finite element framework and the simplified micro model technique, the masonry structure is simulated at the infill component level. The numerical model demonstrated accurately the ability to simulate the in-plane behaviour of the modified RC frame with infill walls, including its initial stiffness, deterioration, deformation-resisting ability, and failure patterns. Furthermore, a parametric study was conducted to determine the significance of the full-bond scenario between the RC frame infilled with masonry and the TRM considering: (1) the location of the strengthening material on the specimen and (2) the number of layers of the strengthening material. All retrofitted wall specimens showed a considerable improvement in in-plane performance; some features of the wall's behaviour were found to be strongly influenced by the parameters under examination. It can be observed that the specimen with two layers of TRM on both sides of the infill wall exhibit the maximum lateral load carrying capacity and maximum deflection resisting characteristics while the other retrofitted specimens controlled the deflection to some extent and significantly enhancing the load carrying capacities of the masonry system.

Numerical and Experimental Investigation on Cyclic Behavior of Masonry Infill Walls Retrofitted with CFRP

Numerical and Experimental Investigation on Cyclic Behavior of Masonry Infill Walls Retrofitted with CFRP

Experimental Analysis of Out-of-plane Behavior of Masonry Infill Walls Strengthened with Textile Reinforced Mortar and Wall Post in Autoclaved Aerated Concrete Frames

An experimental study was carried out to contribute to the rather limited data on the out-of-plane (OOP) behavior of masonry infills in reinforced concrete (RC) frames strengthened with the wall post and the textile-reinforced mortar (TRM). For this purpose, one unreinforced specimen served as the control, one specimen was reinforced with the wall post, and two specimens were reinforced with the TRM. They were fabricated and subjected to cyclic OOP loading until a drift ratio of 6%. Load and displacement values were recorded, and the research team discussed the failure mechanisms of the specimens. Results showed that the application of the wall post had the highest efficiency as it increased the load by about 3 times, while this value for TRM-strengthened walls was only 1.5. Strengthening modified the cracking, shifting it towards the middle parts of the wall, changing it from a brittle to a failure mode. Comparison of the envelope curves of specimens revealed significant improvements. The ultimate displacement and energy absorption capacity for the specimen reinforced with the post wall increased by 30% and 300% respectively. Similarly, for TRM-strengthened specimens, these values were 48% and 100%.

Macro-Modelling of IP-OoP Interaction in Unreinforced Solid Masonry Infills under Earthquake-Induced Actions: A Review

Unreinforced masonry-infilled reinforced concrete frames are a prevalent taxonomy class not only in the Mediterranean region but also in Europe and worldwide, where buildings of this type abound or are ubiquitous. Thus, somewhat expectedly, various earthquake events and sequences have repeatedly shown the poor seismic behaviour of masonry infill walls, which, in turn, have brought into question issues of the variability, uncertainty, and interaction of in-plane (IP) and out-of-plane (OoP) responses. The latter aspect is examined in this paper, which provides a systematic review concerning the conceptualisation and development of numerical macro-models for simulating the behaviour of solid infill wall panels taking their IP–OoP interaction into account. To this end, the most important parameters involved in the cyclic behaviour of unreinforced solid masonry infill walls are addressed first, and then the main models currently available in the literature are scrutinised and key features discussed, with emphasis posed on issues of accuracy/suitability and easiness or level of complexity/sophistication.

Damage index model and hysteretic viscous damping of masonry infill walls subjected to out-of-plane loadings

The definition of damage states for structural and non-structural elements is necessary to support the seismic vulnerability analyses and identify the most vulnerable elements that need to be retrofitted. The studies related to masonry infill walls focused on multiple experimental studies to characterize their in-plane and/or out-of-plane (OOP) behaviour. Some codes have already proposed damage states for masonry infill walls only under in-plane loadings. Also, the study of the normalized energy dissipation and the hysteretic viscous damping when subjected to OOP loadings were not explored. It is recognized that the OOP behaviour of masonry infill walls is still nowadays a topic needing further investigations. The main objective of this work is to propose damage index for infill walls under to pure OOP seismic loadings. For that, a detailed analysis of the damage observed in masonry infill walls tested under pure OOP loadings was performed. The damage observed in masonry infill walls made with different masonry units, with and without openings, is carefully detailed. After that, a pilot damage index model is proposed for masonry infill walls made of hollow clay horizontal brick units. The third objective of this work was the assessment and discussion of their normalized energy dissipation capacity and their hysteretic viscous damping. Some analytical formulations were proposed to estimate these parameters. A database containing thirteen OOP tests performed by three different authors was used to achieve these goals.

The out of plane behaviour of masonry infilled frames

The great interest about out of plane behavior of masonry infill walls has recently increased since it is a key point in the seismic modelling of framed structures. Their contribute to the whole seismic resistance of a framed building cannot be skipped. After a review of the literature on the subject, this paper presents a trilinear constitutive model for the out of plane behavior of masonry infills based on the tensile strength of the constituents. Comparisons with literature model are provided and the identification of the model is based on experimental tests.

Modelling of infill walls in reinforced concrete buildings under low-amplitude vibrations

A study was undertaken to analyse the capability of conventional finite-element (FE) models to represent the actual dynamic behaviour of masonry infill walls in reinforced concrete (RC) buildings under ambient conditions. Two commonly used modelling techniques were examined – shell elements and diagonal compression struts. An existing non-symmetrical, six-storey RC building was used as a reference structure. The dynamic characteristics of the real building were determined by an ambient vibration survey. Two FE models of the building were then constructed and the dynamic characteristics of the building were determined numerically. Comparisons of the experimentally obtained dynamic properties and those obtained using each numerical model revealed the most appropriate method for visualising the dynamic behaviour of RC buildings under low levels of vibration. The dynamic behaviour of RC buildings under earthquakes and the use of code-based period estimation formulas were then analysed. The results showed that each modelling technique affected the predicted dynamic frequencies substantially; choosing the most suitable model depends on the level of vibration.

The role of the openings in the out-of-plane behaviour of masonry infill walls

This research work aims to present an experimental study concerning the effect of the openings in the out-of-plane (OOP) behaviour of masonry infills in RC buildings. The experimental campaign comprises the OOP testing of three full-scale infill walls made up of horizontal hollow clay bricks, two of them with a central window and the remaining one with a central door. One of the specimens with a central opening was first subjected to a previous in-plane test and, after that, the damaged wall was subjected to an OOP test. All the tests consisted of applying a loading–unloading-reloading history of imposed displacements in the OOP direction through a uniformly distributed load. An innovative setup was used and adapted for each wall typology. The results are presented in terms of OOP force–displacement responses, damage evolution, relative stiffness and energy dissipation capacity. Finally, the test results are compared to each other to assess the effect of: i) the area of the opening; and ii) the previous damage. It was found that the openings reduced the maximum strength of 30% for undamaged panels, and it occurred for lower displacement demands. The increase of the opening area did not affect the peak load; however, it reduced their energy dissipation capacity significantly. The energy dissipation capacity reduced from 42% to 70%.

Experimental characterization of the out-of-plane behaviour of masonry infill walls made of lightweight concrete blocks

Masonry infill walls are widely spread over the reinforced concrete buildings due to different demands. The buildings' thermal energy efficiency is a top priority nowadays since many of the existing building stock comprises buildings with low energy performance. The buildings' external envelope is undergoing a transformation with the vertical hollow concrete blocks' appearance with high thermal and acoustic demands. However, recent evidence from a strong earthquake shows that the masonry infill walls are quite vulnerable to out-of-plane loadings and were responsible for many casualties, injuries and economic losses. Based on that, this work's main objective is to study the out-of-plane (OOP) behaviour of masonry infills made with vertical hollow concrete blocks. The experimental campaign comprises the OOP testing of three full-scale infill walls made up of these masonry units, one of them as-built without previous damage, one with previous damage due to an earlier in-plane test and the third one retrofitted. All the tests consisted of applying the loading–unloading-reloading history of imposed displacements in the OOP direction through a uniformly distributed load. The results will be presented in terms of OOP force–displacement responses, damage evolution and energy dissipation capacity. The test results are compared to assess the previous damage effect and the retrofit technique's effectiveness. A final study is presented concerning the masonry unit and slenderness effect with other literature results.

Experimental Investigation on the Possible Effect of Previous Damage, Workmanship and Test Setup on the Out-of-plane Behaviour of Masonry Infill Walls

ABSTRACT The poor out-of-plane behaviour of masonry infill-walls (MIW) in recent earthquakes, resulted in several casualties and economic losses. The main objective of this work is to present an experimental campaign comprised of four out-of-plane tests of full-scale MIW with the main goal to assess the possible effect of the previous damage, workmanship and test setup in the MIW out-of-plane behaviour. From the results, it was observed that the existence of the prior damage reduced the out-of-plane strength and energy dissipation of about 30% and 70%, respectively. The workmanship can introduce variations in the MIW response from 10% to 30%.

Effect of prior in-plane damage on the out-of-plane behavior of masonry infill walls

Out-of-plane collapse is one of the most important failure modes for masonry infill walls in frame structures during earthquakes and may result in significant economic loss, blocked evacuation pathways and even injuries and fatalities. To investigate the effect of prior in-plane damage on the out-of-plane behavior of masonry infill walls, a series of full-scale masonry infilled RC frame specimens that conform to the Chinese practice were subjected to sequential in-plane and out-of-plane quasi-static loading. The results show that the out-of-plane strength of the masonry infill walls was reduced by 22% and 47% at 1/500 and 1/200 prior in-plane drift ratios, respectively, whereas the out-of-plane stiffness was not significantly affected by the prior in-plane damage. Based on the test results of the present experiment and the collected data available in the literature, an empirical equation was derived to relate the out-of-plane strength reduction factor with both the prior in-plane drift ratio and the slenderness of the wall panel. According to the equation, the out-of-plane strength starts to degrade when the in-plane drift ratio reaches approximately 0.1% to 0.3% depending on the wall slenderness. Both the rate and extent of the strength degradation are greater for slenderer wall panels. Through a numerical example, we demonstrate that neglecting such an in-plane-out-of-plane interaction may lead to substantial underestimation of the loss by seismic damage of masonry infill walls in buildings.

Recent Findings and Open Issues concerning the Seismic Behaviour of Masonry Infill Walls in RC Buildings

The extension of the damages observed after the last major earthquakes shows that the seismic risk mitigation of infilled reinforced concrete structures is a paramount topic in seismic prone regions. In the assessment of existing structures and the design of new ones, the infill walls are considered as nonstructural elements by most of the seismic codes and, generally, comprehensive provisions for practitioners are missing. However, nowadays, it is well recognized by the community the importance of the infills in the seismic behaviour of the reinforced concrete structures. Accurate modelling strategies and appropriate seismic assessment methodologies are crucial to understand the behaviour of existing buildings and to develop efficient and appropriate mitigation measures to prevent high level of damages, casualties, and economic losses. The development of effective strengthening solutions to improve the infill seismic behaviour and proper analytical formulations that could help design engineers are still open issues, among others, on this topic. The main aim of this paper is to provide a state-of-the-art review concerning the typologies of damages observed in the last earthquakes where the causes and possible solutions are discussed. After that, a review of in-plane and out-of-plane testing campaigns from the literature on infilled reinforced concrete frames are presented as well as their relevant findings. The most common strengthening solutions to improve the seismic behaviour are presented, and some examples are discussed. Finally, a brief summary of the modelling strategies available in the literature is presented.

Numerical Investigation on the Influence of In-Plane Damage on the Out-of-Plane Behavior of Masonry Infill Walls

This study presents a finite element model to investigate the bidirectional seismic behavior of masonry infill walls. The test data are utilized to verify the numerical model. The comparison between the analytical and the experimental results indicates that the finite element model can successfully predict the failure mode, stiffness, and strength of the masonry infill wall. Based on the model, the effects of aspect ratio (height to length), slenderness ratio (height to thickness), and masonry strength on the out-of-plane (OOP) response of infill wall with in-plane (IP) damage are explored. Considering the aspect ratio, slenderness ratio, and masonry strength of infill wall, the OOP behavior of infill wall with and without IP damage is studied. Finally the reduction of the stiffness and strength in the OOP direction, due to the IP damage, is discussed.

Effect of masonry joints on the behavior of infilled frames

The present paper investigates the behavior of masonry infill walls and the effect of the interfaces between the masonry wall units (joints), on the global behavior and on the local infill-frame interaction. The investigation focuses on the case of failure of a supporting column that may trigger a progressive collapse of the building. Experimental results of a new testing method are presented. The experimental technique enables analysis of the contact zone and the contact tractions, and their variations during the loading process. The purpose of this study is to explore and quantify the effect of the joints on the global and local behavior of the composite infill-frame structure. The study examines the contact zone between the infill wall and the frame and its variation with loading, and compares the new data with available expressions that are found in the literature. A comparative experimental study that includes three large-scale unreinforced masonry infill walls with identical geometry and identical Autoclaved Aerated Concrete (AAC) masonry units, but different joints' properties is presented. The results show that the joint properties have a significant effect on the ultimate load, the initial stiffness and the energy dissipation with differences of about 50%, 85% and 70%, respectively. It is also shown that the length of the contact zone changes during loading in all three specimens and its size depends on the joints characteristics. The different contact lengths that are calculated by available simplified models are smaller than the experimentally measured contact region by more than 30%.

Modelling the out-of-plane behaviour of masonry walls retrofitted with engineered cementitious composites

The out-of-plane behaviour of masonry infill walls retrofitted using engineered cementitious composites (ECC) is investigated numerically in this paper. The behaviour of beam-like masonry specimens, considered to provide a simplistic representation of masonry infill walls, subjected to static four-point bending testing is investigated numerically through the use of nonlinear finite element analysis. The specimens are strengthened using a thin layer of ECC which is fully or partially bonded to their lower face (acting in tension). The numerical predictions obtained are validated against relevant test data and are used to provide insight into the mechanics through which the ECC layer enhances the out-of-plane behaviour of the subject specimens in terms of strength, stiffness and deflection. It was found that the specimens retrofitted with a partially bonded ECC layer exhibit more ductile behaviour (deflection) compared to those retrofitted with a fully-bonded ECC layer (the latter exhibiting higher load-carrying capacities). Finally, the validated models are employed to carry out a parametric study to investigate the effect of different design parameters, associated mainly with the properties of the materials used, on the behaviour of the specimens considered.

Enhancing the out-of-plane performance of masonry walls using engineered cementitious composite

Abstract A novel technique for enhancing the out-of-plane behaviour of masonry infill walls is proposed herein. The technique involves the use of a thin layer of engineered cementitious composite (ECC) which is fully or partially bonded onto the face of masonry walls. To investigate the feasibility of this technique, the present research focuses on studying the behaviour of a series of beam-like masonry specimens with or without an ECC retrofitting layer subjected to a four-point bending load. The load is applied monotonically to failure at rates of 1 mm/min or 200 mm/min. The results show that the ECC-retrofitted specimens exhibited a significant enhancement in the out-of-plane performance in terms of strength, stiffness and deflection compared to the un-strengthened specimens. It is observed that specimens with a partially bonded ECC layer out-performed their counterparts having a fully bonded ECC layer. The partially de-bonding technique is found to allow the ECC layer achieve its full ductility potential. The results also reveal that specimens subjected to an elevated loading rate exhibited a greater load-carrying capacity and stiffness but lower deflection.

Finite-element analysis of out-of-plane behaviour of masonry infill walls

Masonry infill walls should have sufficient out-of-plane stability to ensure the safety of people and the performance of safety-relevant components. The behaviour of masonry infill walls under out-of-plane loading, which is caused by earthquakes due to the mass and inertia of the wall, is crucial to the overall safety of buildings. A simplified micro non-linear three-dimensional finite-element method for simulating the behaviour of masonry infills under out-of-plane loading is presented in this paper. Appropriate experimental data from the literature are utilised to examine the capability of the model. A parametric study is presented using the connection conditions of the wall and frame, the slenderness ratio, the compressive strength of the masonry and the aspect ratio as parameters. It is shown that the model can simulate the various crack patterns observed in experimental studies reported in the literature. Based on the results of the parametric study, a simplified formula is developed to compute the out-of-plane load resistance of a masonry infill wall. A comparison of the results from the simplified formula and experimental data indicates that the formula can be employed to predict the out-of-plane strength of masonry infill walls in reinforced concrete frames with acceptable accuracy, except for those with extremely small slenderness ratios.

Experimental study of the out of plane behavior of masonry infill walls with exterior insulation systems

The objective of this study is to evaluate the out of plane behavior of a masonry infill wall provided with an exterior thermal insulation system. For this purpose there were constructed two 1:1 scale specimens of masonry infill walls in order to compare a simple wall with one having already applied an exterior thermal insulation system composed by a polystyrene insulation and a protection layer of plaster and a glass fiber mesh. The load was applied through a horizontal force, acting at the mid height of the wall. Both specimens were tested in displacement control, using alternate force with 3 cycles per loading step. As it was expected, an increased stiffness and out of plane resistance was observed for the wall provided with the insulation system. Various observations were noticed related to the technology and overall behavior of the infill masonry wall.

Resistance of Reinforced Concrete Frames with Masonry Infill Walls to In-Plane Vertical Loading

Numerous studies have been conducted on the in plane behavior of masonry infill walls to lateral loading simulating earthquake action on buildings. The present study is focused on a problem that has almost not been studied regarding the vertical (opposed to lateral) in-plane action on these walls. This may be of concern when a supporting column of a multi-storey reinforced concrete frame with infill masonry walls undergoes a severe damage due to an extreme loading such as a strong earthquake, car impact or military or terror action in proximity to the column. The loss of the supporting column may cause a fully or partly progressive collapse to a bare reinforced concrete frame, without infill masonry walls. The presence of the infill masonry walls may restrain the process and prevent the development of a progressive collapse. The aim of the present study is to test the in-plane composite action of Reinforced Concrete (RC) frames with infill masonry walls under vertical loading through laboratory experiments and evaluate the contributions of infill masonry walls, in an attempt to examine the infill masonry wall added resistance to the bare frame under these circumstances. Preliminary results of laboratory tests that have been conducted on reinforced concrete infilled frames without a support at their end, under monotonic vertical loading along that column axis will be presented. The observed damages and failure modes under vertical loading are clearly different from the already known failure modes observed in the case of lateral loading.

Shaking table testing for masonry infill walls: unreinforced versus reinforced solutions

SummarySeveral factors influence the behaviour of infilled frames, which have been a subject of research in the past with moderate success. The new generation of European design standards imposes the need to prevent brittle collapse of the infills and makes the structural engineer accountable for this requirement, yet it fails to provide sufficient information for masonry infills design. Therefore, the present work aims at understanding the seismic behaviour of masonry infill walls within reinforced concrete frames, using both unreinforced and reinforced solutions (bed joint reinforcement and reinforced plaster). For this purpose, three reinforced concrete buildings with different infill solutions were constructed at a scale of 1:1.5, all with the same geometry, and were tested on the shaking table of the National Laboratory for Civil Engineering, Portugal. All solutions performed adequately for the design earthquake, with no visible damage. Still, the experimental tests show that the double‐leaf‐unreinforced infill walls underperformed during a large earthquake, collapsing out of plane by rotating as rigid bodies with multiple configurations. Also the reinforced concrete buildings collapsed, because of the adverse interaction with the infill walls. The infill walls with bed joint reinforcement and reinforced plaster did not collapse out of plane, because of their connection to the concrete frame, which is an essential requirement. Copyright © 2016 John Wiley & Sons, Ltd.