Unreinforced Masonry Infill Walls Research Articles

Dynamic behaviors of unreinforced and spray polyurea retrofitted brick masonry infill walls under blast loads: Shock tube test and analyses

Unreinforced masonry infill walls (MIWs) are prone to crack, fragment, and even collapse under blast loads, threatening the safety of building structures, as well as the inside occupants and equipment. Spray polyurea (SPUA) has been proven to be an excellent retrofitted material for MIWs to improve their blast resistance. Aiming to study the dynamic behaviors of brick MIWs under far-field range blast loads, the successive blast tests on seven unreinforced and SPUA-retrofitted brick MIWs with different thicknesses and boundary constraints were first carried out based on the developed compressed air-driven large cross-section (3m×3 m) shock tube. It was indicated that the blast resistance of MIWs significantly improved by increasing wall thickness and strengthening boundary constraint; SPUA coating can improve the blast resistance of MIWs and effectively suppress the debris generation and splash. Then, the equivalent single degree of freedom model based theoretical calculation and the simplified micro-model based numerical simulation methods previously established by authors were briefly introduced. Additionally, the dynamic behaviors of seven examined MIWs were further predicted and compared with test results, which verified the applicability of theoretical calculation and numerical simulation methods. Finally, the improved damage and failure evaluation criteria of unreinforced and SPUA-retrofitted MIWs were given, and the charge weight and standoff distance diagrams of typical MIWs were proposed based on the validated theoretical and numerical methods as well as the improved criteria, which would provide a helpful reference for blast-resistant evaluation and retrofitted design of brick MIWs.

Tie system to upgrade out‐of‐plane performance of infill masonry walls

AbstractThe objectives of this study were to investigate the out‐of‐plane behavior of unreinforced masonry (URM) infill walls and to identify the effectiveness of tie systems that were proposed to enhance the infill stability under both in‐ and out‐of‐plane effects. This study examined three types of tie systems: a full‐length tie system (prototype), a staggered tie system and a half‐length tie system. For this purpose, four 1/4‐scale, single‐story, one‐bay masonry infilled reinforced concrete (RC) frame specimens with and without the proposed tie systems were sequentially tested under in‐plane static cyclic loading and out‐of‐plane dynamic excitation. In the experimental study, two series of shaking table tests were conducted to investigate the out‐of‐plane behavior of the infill walls. The first series compared the fundamental out‐of‐plane performance of three proposed tie systems, and the second series verified the effectiveness of the full‐length tie system to prevent infill out‐of‐plane failure under an excitation simulating the severe floor response in medium‐rise buildings. The test results indicated the following: (1) the presence of the tie systems caused minor differences in the in‐plane capacity and ductility of each specimen, (2) the effectiveness of the full‐length and staggered tie systems was superior to that of the half‐length tie system, and (3) the full‐length tie system not only prevented the infill out‐of‐plane failure but also significantly reduced the infill damage under realistic excitation conditions. The above research outcomes provide a useful contribution of the infill to upgrade the seismic resistance of buildings.

Effect of Infills on the Response Modification Factor for Infilled Reinforced Concrete Frame Buildings

RC frames with unreinforced masonry infill walls are the most common type of building. Unreinforced masonry walls are often not considered by engineers in the design process, although walls and frames interact during strong ground motion, leading to structural responses deviating radically from what is expected in the design. Under lateral load, reinforced concrete confining members (frames) act in tension or compression, depending on the direction of the lateral seismic pressures. Meanwhile, masonry walls act as diagonal struts prone to compression. This research aims to develop the effect of masonry infills and their distribution on the value of the resulting response modification factor. For this purpose, a parametric study was performed on five, seven, and ten-story' buildings modeled as bare and infilled frames. Infill ratio, panel aspect ratio, unidirectional eccentricity, and bidirectional eccentricities were the parameters investigated. Each proposed model's resulting response modification factor was compared to the value cited in different international codes. It was concluded that this value differs depending on several parameters and cannot be constant for a certain structural system. The novelty of this research is the deduction of a general equation to calculate the response modification factor as a function of the percentage of infills and the eccentricity, while presenting two different methods to calculate it. Doi: 10.28991/CEJ-2023-09-12-09 Full Text: PDF

Mutual Effect Between Moisture Transfer and Mechanical Response in Infill Masonry Walls of Reinforced Concrete Building Envelope

The external envelope of buildings with reinforced concrete structures (RCS buildings) is subjected to environmental actions, particularly related to wind-driven rain (WDR), external humidity variations, and rising dampness, which can cause significant variations in moisture content to their unreinforced masonry (URM) infill walls, mainly associated to water penetration across that envelope. The consequent moisture transfer across the envelope can change the mechanical response of the URM infill walls and lead to their cracking, which could aggravate the referred water penetration, with a subsequent increase in the risk of building envelope degradation. In reverse, the effects of mechanical loads on moisture transfer across that envelope can be also relevant, in terms of change in the moisture content of these URM infill walls. The aim here is to analyze this type of mutual effect between moisture transfer and mechanical response in URM infill walls of RCS buildings. Essential elements about the characteristics of moisture transfer across URM infill walls and of the interface resistance with moisture flows are summarily described, and the essential evaluation of the mechanical behavior of URM infill walls when subjected to moisture variations is carried out. Moisture transport characteristics are discussed, focusing on analyses of the behavior of masonry elements when subjected to moisture variations. An initial assessment of the mechanical behavior of URM infill walls when subjected to different moisture variations is made through a compression test of a brick masonry specimen with variable moisture content. Following that analysis, an evaluation is made of the moisture transfer in URM infills, as well as the influence of the interface between layers in that moisture transfer and, subsequently, an assessment is made of hygromechanical couplings. Finally, elements for prevention about the causes of degradation of URM infill related to humidity and mechanical actions in the RCS building envelope are discussed.

Ultrasonic Pulse Velocity Testing for Monitoring the Degradation of Infill Masonry Walls and Access Their Impact on the Durability of the Envelope of Buildings with Reinforced Concrete Structure

Buildings with reinforced concrete structure (RCS buildings), including unreinforced masonry (URM) infill walls, can be negatively affected by anomalies in their envelope, such as cracking and water penetration, which worsen the aesthetic aspect and reduce the safety and level of comfort of those buildings. To access the relevance of these anomalies and their evolution along service life, a corresponding survey and monitoring during service life are essential. Non-destructive test methods (NDT), in particular ultrasonic pulse velocity (UPV) testing, are currently used in that survey and monitoring. In the context of monitoring the degradation of the URM infill walls and access their impact on the durability of the RCS building envelope, UPV testing can be a type of NDT method to be used, considering that it can contribute to the evaluation of the state of conservation of the construction elements, such as masonry and concrete. It is intended here to access the potential use of UPV testing in the monitoring of anomalies related to the degradation of building facades due, particularly, to cracking and to water penetration associated with WDR (wind driven-rain). The preliminary assessment of the use of UPV testing is made through the previous analysis of the results of the application of UPV testing for the detection of sub-surface and surface cracking in compression tests of masonry specimens. Following that analysis, an evaluation is made of the conditioning aspects of the use of UPV testing to access durability problems of the building envelope. Particularly, the main characteristics of cracking with interest for the assessment of the potential use of UPV testing are generally discussed. And, finally, an evaluation is made of the risk of water penetration through the cracks, for potential use of UPV testing in monitoring the presence of humidity in the cracks.

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.

Effect of unreinforced masonry infill walls with and without ECC layer on the performance of RC framed structure

Effect of unreinforced masonry infill walls with and without ECC layer on the performance of RC framed structure

Evaluation of seismic vulnerability assessment building using rapid visual screening method: case study at the Faculty of Islamic Economics and Business of Islamic State Prof. KH. Saifuddin Zuhri University

Indonesia is one of the nations that is more prone to earthquakes due to its location at the intersection of the Indo-Australian, Eurasian, and Pacific plates. This study aims to find out the vulnerability and final score of the Faculty of Islamic Economics and Business of Islamic State Prof. KH. Saifuddin Zuhri University used the RVS method based on FEMA P-154, where this method is one of the earliest methods used to evaluate the vulnerability of a building, and has a final value limit of 2. If the final score is more than 2, then the building under review has a low vulnerability to earthquakes and vice versa. This building is one of the mid-rise buildings in Purwokerto which was established in 2019. Based on RVS analysis, the final score was 3.6 for the category of concrete moment-resisting frames (C1) and 1.4 for the category of concrete frames with unreinforced masonry infill walls (C3). Thus, the results showed this 6-story building has a vulnerability to earthquakes with a high category of a high probability of damage to level 3 and a very high probability of level 2 damage.

Damage of Infill Masonry Walls due to Vertical Loads in Buildings with Reinforced Concrete Structure

Buildings are subjected to deformations of their reinforced concrete structure due to vertical loads that can lead, in certain cases, to the significant cracking of the unreinforced masonry (URM) infill walls, therefore requiring the development of specific knowledge of these types of deformations in order to minimise them. Aiming the evaluation of buildings with reinforced concrete structures subjected to vertical deformations, the mechanical characteristics of their infill masonry walls, as well as of their interface with the supporting concrete elements, are here analysed. The basic compression behaviour of brick masonry is assessed particularly through the previous analysis of a vertical compression test of a masonry specimen. The mechanical behaviour characteristics of the constituents (bricks, and mortar joints) are analysed to account for their influence on the compression behaviour of masonry infill, aiming particularly for the prevision of their cracking in case of vertical deformations of the supporting reinforced concrete (RC) elements. Based on that evaluation, the analysis of masonry walls subjected to vertical deformations of their supports is made through the assessment of the relevant characteristic behaviour of masonry wall-beam/slab assembly in case of vertical load. A general modelling approach of the behaviour of URM infills and the interaction with their supports is generally accessed. Finally, the preventive control of deformations of masonry wall-beam/slab assembly is discussed.

Numerical simulation of RC-masonry infill wall system strengthened with textile reinforced concrete

Masonry walls are generally considered non-load-bearing elements in most concrete or steel-framed structures. Being a heterogeneous structure, the masonry system effectively enhances the strength and lateral stiffness of the overall panel when subjected to horizontal forces. But the recent unsatisfactory performance of unreinforced Masonry Infill Walls (MIW) during in-plane seismic loading has caught the attention of many researchers for the last few years. To overcome these detrimental effects, strengthening the MIW frame is considered the best procedure to enhance the horizontal load-carrying capability of the system. Numerous studies evaluating various parameters affecting the behaviour of MIW were conducted using Fiber Reinforced Cementitious Material (FRCM) as a strengthening material. This paper conducted a validation study that includes numerical simulation of the experimental research carried out at Wellington Institute of Technology in which nine 2:3 scaled single bay and single story Reinforced Concrete Frame with Masonry Infills (RCFMI) specimens strengthened with different fibers (basalt, carbon, and glass) of FRCM was tested under in-plane seismic/cyclic loads. The study went into detail on creating a numerical model replicating the non-linear structural cyclic behaviour of an infill wall bound by a reinforced Concrete frame and subjected to displacement-controlled in-plane lateral stress. The numerical analysis was performed in the Finite Element Method (FEM) programme ABAQUS using a streamlined micro-model approach. To simulate the non-linear behaviour of the masonry blocks and concrete, the Concrete Damage Plasticity (CDP) model was employed. The tested specimen was retrofitted with glass fiber grid diagonal bands, each with a width equal to 1/6 of the infill diagonal length. This analysis was used to create the numerical model. The validation demonstrated that the numerical model could faithfully simulate the behaviour and forecast the strength of masonry infill walls with RC frames. The findings of the observations are explained in the form of load–displacement hysteresis loops and excursion curves. The numerical results demonstrate excellent agreement with the experimental data, a significant impact of FRCM on the system's dynamic behaviour, and an improvement in MIW effectiveness with FRCM under cyclic loading is observed.

Seismic Vulnerability of Code Compliant RC Frame Building with Unreinforced Masonry Infill Walls

Unreinforced masonry (URM) infill walls in Reinforced concrete (RC) buildings are normally designed as non-structural elements. However, in the past, the post-earthquake response of the RC frame building showed that URM infill walls increase the strength and stiffness of the RC frame buildings. Further, it is also observed that URM helped to prevent the disastrous destruction by acting as a structural member in RC frame. In the present study, the performance assessment of a four-storey URM infill RC frame with different infill configurations, namely bare and Open Ground Storey (OGS) is done using fragility analyses. Nonlinear masonry material is modelled as the equitant three strut model in ETABS. Nonlinear static pushover analysis is applied for the analysis of the configured RC frames. The probability of damage states is determined by firstly converting pushover curves into capacity curves and accordingly, performance-point values of Spectral acceleration and Spectral displacement for seismic demand Zone-V (Elastic Response Spectra as per IS 1893:2016) using the capacity-spectrum method (ATC-40) are determined. The fragility function used is an approximation of the continuous to discrete distribution. Fragility curves and mean damage matrix are derived to compare performance with each other. From the vulnerability analyses, it is observed that the OGS framed RC building performs better as compared to the bare frame.

Nonlinear truss modeling method for masonry-infilled reinforced concrete frames

This paper presents a new modeling approach for masonry-infilled, reinforced concrete (RC) frames, based on the nonlinear truss analogy. The unreinforced masonry infill walls are modeled with truss cells containing horizontal, vertical and inclined elements. Zero-length macroelements are also used to account for the localized damage on mortar joints. The frame members are modeled with a recently proposed scheme that can account for inelastic response and can capture the effect of shear damage and failure of RC columns. The modeling approach is validated through analysis of experimentally tested masonry-infilled frames, and its capability in capturing the strength and damage patterns is evaluated. A sensitivity study is also provided, to elucidate the impact of several model parameters on the obtained analytical results.

Out-of-Plane fragility of In-Plane damaged unreinforced masonry infills in low rise reinforced concrete buildings

ABSTRACT Unreinforced masonry (URM) is commonly used to make infill walls in reinforced concrete (RC) frame buildings. Such infill walls are highly vulnerable to out-of-plane (OOP) seismic loading and this can result in huge economic losses and human casualties. Therefore, fragility assessment of URM infill walls under seismic loads is important in view of performing large-scale risk analysis. In this paper, OOP fragility functions are provided based on a numerical investigation supported by a macro-element model. The fragility is calculated assuming the uncertainty in the geometric and mechanical properties of infills instead of the variability in the seismic input. Further, the effect of in-plane (IP) and out-of-plane (OOP) interaction is taken into account. Finally, the sensitivity of the results to the infill position in low rise buildings is discussed. Experimental data available in the literature are used for the validation of the output. Overall, the results indicated lower vulnerability in the OOP direction for infill walls without IP damage and high vulnerability in the OOP direction in the presence of previous IP damage. The vulnerability was found also increasingly proportional to the positioning of the panels at higher floors where the spectral acceleration of the structure is higher too. The proposed procedure can be extended to other types of infill walls depending on the construction technique of the site of interest, obtaining different and specific fragility curves for large-scale risk analysis.

Out-of-Plane Behavior of URM Infill: Accuracy of Available Capacity Models

The aim of this paper is to check the accuracy of analytical capacity models available for the prediction of out-of-plane strength of unreinforced masonry (URM) infill walls. The accuracy of the available models is checked by detailed comparison with the existing experimental results. In doing so, both types of capacity models are evaluated: Type I for the prediction of the strength in the undamaged state, and Type II for the prediction of strength reduction in the in-plane damaged state. Results from the calculations are discussed, and the best among the available models are recommended. Furthermore, the influence of orthotropy of the infill masonry in the out-of-plane capacity predicted by the models is discussed. The paper also highlights the prospect of using the capacity models in the cases of infill-beam gap and infill with openings. In the paper, the best pairs of models (composed by a model for the prediction of the out-of-plane strength in the undamaged state and a model for the prediction of the reduction of the out-of-plane strength in the damaged state, not necessarily provided by the same author) for URM infill walls, are suggested for the first time.

Prediction Equations for Out-of-Plane Capacity of Unreinforced Masonry Infill Walls Based on a Macroelement Model Parametric Analysis

In the seismic performance assessment of reinforced concrete (RC) frames, a reliable estimation of the capacity of unreinforced masonry (URM) infill walls is of utmost importance to ensure structural safety conditions. With particular attention to the out-of-plane (OoP) capacity of URM infill walls after in-plane (IP) damage, the issue of defining reliable analytical prediction models for the assessment of the capacity is an ongoing study. In this paper, empirical equations are proposed for the evaluation of the infilled frame’s OoP capacity, with or without IP damage, based on an extensive numerical parametric analysis, focusing on the influence of the key parameters that govern the mechanical model. The OoP capacity of URM infill walls, considering the variation in their geometrical and mechanical properties, was evaluated by using a macroelement model. The OoP strength was found to be largely influenced by the compressive strength, slenderness ratio, aspect ratio, and, additionally, level of IP damage. The reduction of OoP strength and stiffness due to IP damage was largely governed by the strength and the slenderness ratio of the URM infill wall. The reliability of the proposed model was also proved by comparisons with experimental results and some of the analytical models already available in the literature. The proposed equations provide reliable estimates of the OoP capacity by strongly indicating the suitability of the adopted macroelement model in capturing the OoP response of URM infills.

Investigating the Effect of Masonry Infill Walls on the 2D RC Structural Systems with Asymmetry along the Elevation

Reinforced concrete (RC) frames with unreinforced masonry infill panels are common structural building systems all over the world. Although many analytical investigations and experimental observations emphasize the contribution of masonry infills to the overall stiffness and strength of the structures, their effects are not considered by the engineers in the design and the analysis calculations. Due to the variations in the actual behavior of the infill walls and using different parameters to define the infill walls in modeling and capacity calculations, they have unpredictable effects on the global response of the structural systems. The purpose of this study is the simulation of a collapse mechanism scenario that may be developed during the earthquake through applying incremental equivalent static load. Infill panels were represented using equivalent compression diagonal struts and their effects on the behavior of RC structural systems having asymmetrical placement of unreinforced masonry infill walls along the elevation has been scrutinized. The equivalent static load was applied to the structural system in +/-X directions to focus on the effects of using only one diagonal strut. It has been observed that the influence of the infill panels on the structural system has beneficial effects in decreasing the story drift, which may be attributed to the contributory effect of the infill panels on the lateral stiffness of the structural system. Furthermore, the axial forces and bending moment diagrams have been plotted for each increment in the equivalent static load, which can give insight to understand the significance of masonry infill walls.

Effects of mortar compressive strength on out of plane response of unreinforced masonry walls

In this study, the out-of-plane response of infill walls that are widely used in Turkey and the surrounding regions were experimentally investigated. Several out-of-plane wall tests were performed in the laboratory, with the walls specimens produced with lateral hollow clay bricks (LHCB) and different mortar qualities. The walls were tested in their out-of-plane (OOP) direction under static load conditions and evaluated based on the load-bearing and energy dissipation capacities, crack propagations, mortar strengths, and initial stiffnesses. These walls are experimentally investigated to understand the effects of the mortar strength on the infill wall structural behaviors and to assess the effectiveness of the out-of-plane strength formulations. It was found that when the mortar strength is low, the first major crack occurs at the mortar, however, because of the arch mechanism efficiency in this situation the OOP load-carrying and energy dissipation capacities of unreinforced walls can be significantly increased. When the first major crack in the wall occurs in the brick itself, the arc mechanism is provided with delicate sections in the brick, which leads to strength decreasing in the walls. In this case, excessive deviations occur in the out-of-plane strength formulations estimates. This study shows that the arc mechanism, the damage start region and progress can change significantly unreinforced masonry (URM) infill walls behaviors.

SEISMIC BEHAVIOR OF UNREINFORCED CONCRETE MASONRY INFILL WALLS

The majority of new and existing building inventories in the Middle East consist of reinforced concrete skeletal structures with outer shells composed of unreinforced masonry infill walls. In the absence of any mandatory seismic design requirements, these buildings will sustain catastrophic damage when exposed to high seismic activity. Investigating the behavior of such infill walls when exposed to ground motion is therefore an important topic. Experimental tests using shake table out-of-plane ground motion of the 1940 El Centro earthquake displacement are conducted on 3:10 scaled specimens of a single story reinforced concrete frame with a masonry infill wall in between. The test specimens are constructed with the same materials and construction practices commonly used in the region. Displacements and strains are compared with a finite element model of the frame. Moreover, the observed overall behavior of the infill is compared to that of the computer model. The recorded strains in the mortar joints exceeded cracking limits, whereas the overall stability of the wall in out-of-plane bending was not compromised. Recommendations on the use of these structural elements are formulated.

Experimental in-plane seismic strengthening of masonry infilled reinforced concrete frames by engineered cementitious composites (ECC)

The present study aimed to evaluate the performance of engineered cementitious composites (ECC) retrofit technique for unreinforced hollow clay brick masonry infill wall in non-ductile reinforced concrete (RC) frames subjected to in-plane cyclic loading (quasi-static loading). To this aim, the mechanical properties of ECC and masonry elements were tested. Then, four 1/3-scale, one-story, single-bay RC frames were fabricated. Among these specimens, one frame was tested without infill wall (BF), one frame with unretrofitted infill wall (IF-E0), and specimens IF-SF-E20 and IF-DF-E20-2 were retrofitted by using an overlay ECC on the masonry infill wall on one side and both sides, respectively. The retrofitted specimens provided higher lateral load capacity, stiffness, and energy dissipation capacity up to 215%, 32%, and 102%, respectively, compared to the unretrofitted specimen. Further, the proposed strengthening technique prevented brittle premature failure in the masonry infill walls and partially maintained the integrity of unreinforced infill walls. Also, the obtained backbone curves of specimens were idealized. Based on the results, the displacement ductility factor of the retrofitted specimens decreased up to 50%, but also the force reduction factor and the overstrength factor of them increased up to 19 and 68%, respectively. At the end of the paper, a simplified analytical method is proposed to calculate the peak strength of retrofitted masonry infilled RC frames. The results obtained from this method were close to the experimental results.

ATC Mw7.1 Puebla-Morelos earthquake reconnaissance observations: Structural observations and instrumentation

After the 2017 Puebla-Morelos earthquake, the Applied Technology Council (ATC) funded a mission to Mexico City to collect structural, geotechnical, seismological, and damage information on concrete structures. The collected data set includes 70 reinforced concrete buildings and contains photos, design drawings, ground motion records, ambient vibration data, and reconnaissance observations, where available. This article presents the most important structural observations and instrumentation findings. The data show that, in buildings with a flexible lateral system, the unreinforced masonry infill walls resisted substantial load and prevented more severe damage to the structural system. Many previously retrofitted buildings failed in locally unreinforced areas, because retrofits did not comprehensively strengthen all weaknesses in the building. Significant damage was also observed in buildings with weak story irregularities and buildings founded on weak soil.