Masonry Infill Research Articles

Experimental and numerical simulation of seismic behavior of reinforced concrete frames infilled with refractory straw blocks

Recent earthquakes have highlighted the vulnerability of infilled reinforced concrete structures due to the insufficient consideration of infill masonry walls' contribution to strength and stiffness. This study presents a novel refractory straw block (RSB) designed to address these challenges and improve the seismic performance of reinforced concrete (RC) frames. Unlike traditional infills, RSB is characterized by low-elastic-modulus, low-density, and high-ductility. Quasi-static tests were performed on three types of frames: unfilled, infilled hollow grouted bricks (HGB), and infilled RSBs. Failure model, stiffness, and load-displacement response of three specimens were investigated and analyzed. The results indicate that RSBs as infill material does not alter the failure mode and constitutive relationship of bare frame, while HGBs leads to shear failure. The peak load for the specimen IF-HGB was 69.3 kN at 1.1 % drift, compared to 38.8 kN at 2.4 % drift for the specimen IF-RSB, and 36.4 kN at 2.0 % drift for the specimen BF. The strengths of specimens IF-HGB and IF-RSB were 1.90 and 1.07 times that of specimen BF, respectively. The stiffness of specimen IF-HGB was 3.7 times that of the other specimens, but its allowable displacement was only 61 % of theirs. Dynamic time-history analyses were also performed on structures with no longitudinal infill (BF), with RSBs (SBF), and with fired bricks (FBF). At the design level of rare events (magnitude 8, PGA 400 gal), severe damage occurred, but collapse was limited. When the PGA increased further, the collapse probability of model FBF rose rapidly, whereas the collapse probabilities of models SBF and BF remained low and similar. Accounting for the confining effect of walls, model FBF showed a higher probability of severe damage than models SBF and BF, particularly under minor earthquakes. The maximum inter-storey drift ratio of the model SBF and FBF were respectively 1.2 times and 1.7 times that of the model BF, which shows that straw blocks as infill can greatly avoid the effect of infill on the seismic behavior of the structure. The study also emphasized the often-overlooked confining effect of masonry on columns, which can lead to unrealistic damage assessments and seismic shear force distributions.

Influence of masonry infills on seismic performance of BRB‐retrofitted low‐ductile RC frames

AbstractReinforced concrete (RC) frames with masonry infills represent a prevalent construction typology across the globe, including moderate to high seismic regions. Such structures are often characterized by high seismic vulnerability, and consequently, there is an urgent need for retrofit solutions to effectively improve their seismic performance. Buckling‐restrained braces (BRBs) represent one such solution. They are a type of dissipative device that can be included within the frames of an existing structure to increase its strength, stiffness, and energy dissipation capacity. Although a substantial amount of research has already been performed to understand the effectiveness of BRBs as a retrofit strategy, these studies have often neglected the contribution of masonry infills and the interactions between the infills and the BRBs. While masonry infills are usually overlooked in the analysis and design stage (owing to their brittle nature), past studies indicated that their strength and stiffness may significantly alter the structure's seismic performance, leading to undesirable and unexpected results. This study presents a detailed investigation of the impact of masonry infills on the seismic response and fragility of BRB‐retrofitted RC frames. A three‐story, three‐bay, low‐ductile RC frame has been selected for case study purposes. High‐fidelity finite element models are developed in OpenSees for combinations of infilled and non‐infilled structures—with and without BRBs. Nonlinear static and dynamic analyses are performed to evaluate the seismic response of the different configurations at local and global levels. Successively, cloud analyses are conducted by considering a set of 150 ground motion records to account for the record‐to‐record variability and develop seismic fragility curves. The present study sheds some light on the mutual interaction between the infill panels and BRBs retrofit intervention and highlights the critical aspects that must be considered in the design.

Exploring the seismic performance of corroded RC frames with masonry infills

Exploring the seismic performance of corroded RC frames with masonry infills

Seismic performance of Li-Tie type brick masonry infilled wooden frames considering joint damage: Degradation mechanism and hysteretic model

This paper investigated the influence of the damage to column-foot (C-F) joints and the gaps of mortise-tenon (M-T) joints on the seismic behavior of Li-Tie style timber frames with masonry-infilled wall. Five full-scale Li-Tie type brick masonry-infilled timber frames, two without the joint damage, two with the damage to C-F, and one with the gaps of M-T joints, were cyclically tested. The failure modes, mechanical and deformation mechanisms were revealed. The second-order effect, strength degradation law, and the changing laws of the equivalent viscous damping coefficient and strain of the specimens were analyzed. The results showed that when the maximum inter-layer drift ratio was less than 2.4 %, the second-order effect of Li-Tie type timber structure with the masonry infill can be ignored. The masonry infilled timber frames considering the joint deterioration suffered a large strength degradation degree, and a more significant loss of the peak load and ductility. The equivalent viscous damping coefficient of the masonry infilled timber frame considering C-F damage increased by up to 24.67 %, while that of the one including the gaps of M-T joint decreased by 6.67 %. The C-F damage led to an increase in the strain at the beam end, the damage to M-T joint resulted in an decrease in the strain at the beam end. However, the damage to C-F and the gaps in M-T joint had little influence on the strain distribution in the C-F area. Based on the hysteretic, stiffness and strength degradation characteristics, and tests results of the specimens, the new tri-linear hysteretic models of Li-Tie type brick masonry infilled wooden frames with and without the joint damage were established and verified. Good agreement between the model predictions and test results was observed.

Effect of prevalent irregular configuration of infills on the seismic collapse of Indian RC buildings

Rapid urbanization and land scarcity obligated the urban population for multi-use of Reinforced Concrete (RC) buildings to meet both residential and commercial purposes together. Un-Reinforced Masonry (URM) infills are often placed irregularly in plan and or elevation of the buildings in some floor(s), particularly in the ground floor to suit the need of occupational requirements accompanied by the inherent irregularities due to openings for doors and windows to meet functional requirements for residence. Seismic performance of infilled frame highly depends upon degree of infill-frame interaction, and it is of utmost importance to classify infilled frame buildings in various Model Building Types (MBTs) based on the type of irregular placement of infills in addition to the parameters affecting seismic performance. Based on field pilot surveys carried out in Indian cities, URM infilled buildings have been classified into 14 different MBTs. Seismic performance of the prevalent categories of MBTs have been evaluated through Incremental Dynamic Analysis (IDA). It has been observed that irregular placement of infills increases the seismic collapse risk significantly, and reduces collapse capacity to approximately 50% as compared to ideal uniformly infilled building. Global collapse occurred due to failure of structural members in the vicinity of irregularity created due to infills.

Nonlinear dynamic study on existing masonry-infilled concrete frames retrofitted with timber panels

This study investigates the dynamic performance of a timber-based seismic retrofit for existing reinforced concrete (RC) buildings, named RC-TP. The core of the proposed retrofit intervention is the replacement of the existing masonry infills with structural timber panels that are connected to the concrete elements using metal dowel-type fasteners and a timber subframe. The unreinforced frames were designed according to codes in force in the 60 s and 70 s, considering exclusively gravity loads to simulate a condition common to a large part of the built heritage across Europe. The seismic performance of single-storey single-bay frames before and after the application of the RC-TP retrofit was assessed via nonlinear simulations, for which the incremental dynamic analysis method was adopted. The results of the extensive dynamic study show the effectiveness of the RC-TP retrofit in increasing the seismic acceleration resisted by the frames and their base shear capacity and in promoting a more ductile failure mechanism. Some general considerations helpful in guiding the implementation of the retrofit system were also drawn.

Code-based brittle capacity models for seismic assessment of pre-code RC buildings: comparison and consequences on retrofit

The existing Reinforced Concrete (RC) buildings stock is often characterized by a significant seismic vulnerability, due to the absence of capacity design principles, even in regions with high seismic hazard, such as Italy. Approximately 67% of existing RC buildings in Italy have been designed without considering seismic actions (GLD), resulting in very low transverse reinforcement amount in beams and, particularly, in columns. Additionally, beam-column joints typically totally lack stirrups. Consequently, shear failures under seismic actions are very likely for this pre-code building typology, often limiting their seismic capacity. However, the assessment of shear failures in beams/columns or joints varies significantly from code to code worldwide. The main goal of this work is to quantify the impact of different code-based brittle capacity models on the seismic capacity assessment and retrofit, focusing on GLD Italian pre-1970 RC buildings. This comparative analysis is carried out by first considering three current codes, emphasizing their, even significant, differences: European (EN 1998-3-1. 2005), Italian (D.M. 2018), and American (ASCE SEI/41 2017) standards. Then, shear capacity models prescribed by the current drafts of the next generation of Eurocodes are implemented and compared to the current models. The assessment includes: (i) a parametric comparison among models; (ii) the evaluation of case-study buildings capacity in their as-built condition and after shear strengthening interventions. The latter is performed on 3D “bare” models, due to the lack of practical guidance in most codes on modelling masonry infills.

Experimental In-Plane Shear Performance of Masonry Infill Walls Assembled with Cementitious Matrix–Grid Composites

This paper presents a study on strengthening infill walls using composite materials to enhance shear capacity. The cementitious matrix-grid (CMG) material was employed for this purpose. Various configurations of the CMG, including single or double layers, applied to one or both sides of the wall, with or without anchorage, were tested. The study consisted of two stages. Initially, the mechanical properties of the bricks, mortar, and CMG mortar were determined using twenty-seven specimens. In the second stage, ten specimens, divided into five groups with one group left unstrengthened, underwent shear tests. Shear strength and shear strain relationships were determined for each specimen. Comparative analysis between strengthened and unstrengthened specimens revealed the effectiveness of the strengthening technique. The strengthened specimens exhibited superior structural performance compared to the control specimens. Specifically, the average maximum shear strength of all strengthened specimens surpassed that of the controls. Moreover, double-layer strengthening notably improved ductility. The findings suggest that applying a double layer of CMG to both sides of the wall with anchorage is the most effective method for strengthening. CMG composites significantly enhance the shear strength of infill walls and promote ductile failure. The comparisons of different strengthening combinations can contribute significantly to the existing literature and the construction sector by offering retrofitting options that can be tailored to address various economic and temporal, as well as target strengthening considerations.

Cross‐laminated timber for seismic retrofitting of RC buildings: Substructured pseudodynamic tests on a full‐scale prototype

AbstractThis paper presents an experimental study on an innovative timber‐based retrofit solution for reinforced concrete (RC) framed buildings, with or without masonry infills. The intervention aims to enhance seismic resistance through a light, cost‐effective, sustainable, and reversible approach integrating energy efficiency upgrades. The method employs cross‐laminated timber (CLT) panels as infills or external retrofitting elements, mechanically connected to the RC frame through steel fasteners. The system is combined with thermal insulation for improved energy efficiency. The seismic performance of the proposed retrofit technique was assessed experimentally on a full‐scale building model at the European Laboratory for Structural Assessment (ELSA). The experiments included tests on two five‐story building configurations: a masonry‐infilled RC building as a reference and the same structure strengthened with CLT panels. Each building was subjected to unidirectional earthquake simulations of increasing intensity using the pseudodynamic (PsD) testing method with substructuring. The physical substructure of the hybrid model consisted of the first story of a two‐story mockup built and retrofitted in the laboratory, while stories two to five were simulated numerically. The paper discusses major observations from the tests, comparing the damage evolution and hysteretic responses of the two configurations. The experiments yielded promising results, showing that the suggested retrofit solution significantly increased displacement and energy dissipation capacity. The retrofitted building survived earthquake intensities up to 50% higher than the non‐retrofitted counterpart, exhibiting only slight structural damage. These pioneering experiments provide compelling data on the high effectiveness of the proposed CLT‐based retrofit system in enhancing the seismic performance of full‐scale RC buildings.

The Influence of Open-Ground Floors on the Impact of RC Columns Due to Seismic Pounding from Adjacent Lower-Height Structures

The substantial influences of masonry infills used as partition walls on the seismic behavior of multistory reinforced concrete (RC) structures have long been recognized. Thereupon, in this study, considering open-ground floors due to a lack of infills (pilotis configuration), the structural pounding phenomenon between adjoining RC buildings with unequal story levels and unequal total heights is investigated. Emphasis is placed on the impact of the external columns of the higher structure, which suffer from the slabs of adjoining shorter buildings. The developing maximum shear forces of the columns due to the impact are discussed and compared with the available shear strength. Furthermore, it is stressed that the structures are partially in contact, as is the case in most real adjacent structures; therefore, the torsional vibrations brought about due to the pounding phenomenon are examined by performing 3D nonlinear dynamic analyses (asymmetric pounding). In this study, an eight-story RC frame structure that is considered to be fully infilled or has an open-ground floor interacts with shorter buildings with ns stories, where ns = 6, 3, and 1. Two natural seismic excitations are used, with each one applied twice—once in the positive direction and once in the negative direction—to investigate the influence of seismic directionality on the asymmetric pounding effect. Finally, from the results of this study, it is concluded that the open-ground story significantly increases the shear capacity demands of the columns that suffer the impact and the inelastic rotation demands of the structure, whereas these demands further increase as the stories of the adjoining shorter building increase.

Macro-modelling of GFRG infilled RC frames incorporating pivot hysteretic model

GFRG (Glass Fibre Reinforced Gypsum) panels present a viable alternative to conventional masonry infills in masonry infilled RC frames. Based on the experimental study on the lateral load behaviour of GFRG infilled RC frames, it was understood that the GFRG panels enhance the structural performance of the RC framed structure. To delve further into this, numerical modelling of GFRG infilled RC frames with different fillings inside the cavities of the panel was performed using SAP2000. The GFRG panels were modelled using nonlinear layered shell elements, while the interface between the GFRG web and the infill material was represented using multilinear plastic link elements. The monotonic lateral load–deflection behaviour and the in-plane hysteresis response were simulated by performing monotonic and cyclic pushover analyses. The cyclic pushover analysis incorporated pivot hysteretic models for the materials, hinges and links. Validation of the proposed numerical models was carried out by comparing the results with those obtained from the experimental study. Key parameters such as peak load, initial stiffness, stiffness degradation, and energy dissipation were carefully compared to ensure the accuracy and reliability of the proposed model. It was observed that the proposed numerical model was able to capture the monotonic and cyclic load–deflection behaviour and other performance parameters. The numerical model accurately predicted the peak load in the positive direction but overestimated the corresponding value in the negative direction. Moreover, the overestimation observed in the cumulative energy dissipated for all the specimens is relatively minor and does not significantly affect the overall accuracy of the model.

Seismic performance of RC frames with masonry infills retrofitted by precast ultra-lightweight insulated cementitious composites plates

Seismic performance of RC frames with masonry infills retrofitted by precast ultra-lightweight insulated cementitious composites plates

Predicting natural vibration period of concrete frame structures having masonry infill using machine learning techniques

The natural period of vibration is one of the most significant factors used in the seismic design of buildings. Although the building design codes and previous studies provide some empirical methods to compute the natural period of vibration (T), their marginal accuracy and inability to incorporate the effect of masonry infill on vibration period significantly limits their use. Thus, researchers are constantly trying to find new and accurate methods to calculate T of concrete structures. To this end, this study presents the novel approach to predict T of reinforced concrete framed buildings (RC buildings) using Multi Expression Programming (MEP), Extreme Gradient Boosting (XGB), and Gene Expression Programming (GEP) machine learning algorithms. For this purpose, an extensive dataset of 569 points was gathered from previously published studies and split into training and testing sets for training and testing the algorithms respectively by using several error evaluation metrices like coefficient of determination (R2), Root Mean Squared Error (RMSE), and Objective Function (OF) etc. The results of error evaluation showed that XGB is the most accurate algorithm having the least OF value of 0.012 compared to 0.037 of MEP and 0.048 of GEP. Additionally, several explanatory analyses like sensitivity and shapley analysis were conducted on the XGB model which showed that number of storeys and opening ratio are the most contributing variables to prediction period of vibration. Thus, the models developed in this study can be practically utilized for determining natural vibration period of reinforced concrete frames with masonry infill.

Seismic Vulnerability Assessment of Self-Centering Prestressed Concrete Frames with and without Masonry Infill Walls: Experimental and Numerical Models

Seismic Vulnerability Assessment of Self-Centering Prestressed Concrete Frames with and without Masonry Infill Walls: Experimental and Numerical Models

Cyclic testing and diagonal strut modelling of different types of masonry infills in reinforced concrete frames designed for modern codes

This article presents an experimental study on cyclic testing of full-scale reinforced concrete (RC) frames designed for modern codes with three different masonry infills: burnt clay brick, fly ash brick, and autoclaved aerated concrete (AAC) block masonry. A digital image correlation (DIC) system was used to study, in detail, the failure pattern and the complex interaction between the infill and the surrounding frame. The experimental results were compared with the pre-existing analytical models for strength and stiffness to determine the best-fit model. The experimental results indicated that the masonry-infilled frames had higher strength, stiffness, and energy dissipation capacity compared to the bare frame, and brittle modes of failure were avoided due to the design for modern codes. The masonry infill altered the RC frame’s deformation pattern by constraining the end portions of the columns from moving laterally, resulting in widespread flexure cracks throughout the column’s height, unlike the bare frame, where cracking was limited to the end portions. The modification was minimal in the case of AAC block masonry infill. The AAC block infilled frame reached different damage states at lower drifts than the other two infill types. The strength and stiffness, separately, were found to be in good agreement with some of the existing models; however, none of the considered models could predict both stiffness and strength accurately.

Efficiency of FRPU strengthening of a damaged masonry infill wall under in-plane cyclic shear loading and elevated temperatures

This paper presents results of in-plane shear tests carried out at the ZAG laboratory in Ljubljana (Slovenia) on a RC frame with masonry infill made of clay blocks (KEBE OrthoBlock). The frame was loaded with constant vertical loads at the top of the columns and then by gradually increasing horizontal cyclic loads at the top beam level. Acquired forces and measured displacements allowed capturing hysteretic behavior for determination of dissipation energy. In addition, two Digital Image Correlation (DIC) systems, Aramis and the CivEng Vision, were used to visualize the behavior of the tested specimens, with an emphasis on computing locally required information about the behavior of highly deformable interfaces. Three types of specimens were tested in-plane: the reference specimen in form of plain RC frame, the reference specimen with constructed masonry infill without any strengthening and the specimen, previously damaged and then strengthened on both sides using glass mesh bonded to the infill and the RC frame using flexible adhesive made of polyurethane matrix (Glass Fiber Reinforced PolyUrethane - GFRPU system). The strengthening process, allowed the specimen to withstand additional cyclic loads, reaching a maximum drift of 3.6 % without serious damage disqualifying the structure from further exploitation. The GFRPU strengthening system was found to be highly effective in preventing infill collapse of damaged masonry infill wall during in-plane loading. Additionally, the results of extended thermal analysis of PU are presented as polymers are, in general, a material, poorly resistant to heat. However, the analyzed PU manifested stable properties up to 200 degrees Celsius, which makes this material promising in civil engineering applications at elevated temperatures.

The effects of brick wall and RC tie variables on the seismic performance of low-rise confined masonry buildings

An extensive parametric investigation is carried out to determine the effects of different RC tie system and brick wall variables on the performance of confined masonry walls and buildings. The variables considered include: the number of storeys and adjacent walls, the walls aspect ratio, thickness and compressive strength of masonry walls, presence of openings, the RC tie system dimensions, compressive strength and detailing of the longitudinal and transverse reinforcements. The main aim of the investigation is to verify the efficiency of some of the prescriptive code recommendations and to provide a basis for further descriptive guidelines for low-rise confined masonry buildings. Among the major conclusions, it is found that the main affecting parameters are those of the masonry walls themselves. When the walls have sufficient shear capacities, due to lower aspect ratio, higher compressive strength and wall thickness and lack of, or small openings, the flexural demand on the tie system is small and its elements act mainly as axially-loaded tie elements. Therefore, the least affecting parameters are those of the tie system's reinforcement detailing. However, when the masonry walls are weak in shear (low masonry strength and large openings), the demand on the tie system increases, to the point that instead of acting as an integral part of the wall, it acts similar to a weak, moment-resisting frame having infill masonry walls, for which it has not been designed. The scenarios that this will happen include: the wall aspect ratios AR > 2, the masonry compressive strength, f′m < 5.0 MPa and the ratio of length of opening to the length of the wall, Ol/Wl > 0.5. To avoid such behaviour, it is also suggested that the tensile stresses in the longitudinal bars of the RC tie elements be limited to 0.6fy.

The effect of openings in URM infills on the seismic resilience of a reinforced concrete building

ABSTRACT In high seismicity regions, the use of unreinforced masonry (URM) infills in reinforced concrete buildings is massive. In most of them, the openings in URM infills due to architectural requirements cause a variation in lateral stiffness which, in turn, alters the dynamic characteristics of the building. Although much research was developed about the effects of openings on the building performance, studies on assessing functionality reduction and resilience of a building in post-disaster scenarios are very few. This paper gives a contribution to that issue by performing and interpreting a parametric analysis which considers five models of a low-rise R.C. building with different percentages of infills openings. The results are expressed as extreme damage probability percentage, damage loss ratio and loss of resilience. The results show that the case with percentage of opening in in the outer and inner infill walls respectively (referred to as IF20–15%) corresponds to a damage loss ratio and a loss of resilience less than the other cases by 3%. IF20–15% model has the extreme damage probability of 5–7% less when compared with other opening cases. Based on this result, for the considered building the optimum infill opening of IF20–15% can be recommended.

Calibration of resistance factors for seismic design of masonry infilled frames using the random finite element method

This paper presents a reliability analysis of concrete masonry infill walls with an aim to examine the efficacy of the resistance factor specified in the infill design under seismic loading. A numerical model for masonry infilled reinforced concrete frames was developed and encoded in OpenSees for this study. The model was validated using experimental data. Two features were involved in this reliability study, including 1) that the effect of spatially varying masonry compressive strength f′m on the lateral resistance of masonry infills was considered using the Random Finite Element Method, and 2) that seismic load with different return periods was considered to provide a more complete treatment of a reliability analysis. The study selected six Canadian cities with varying levels of seismic intensity for this analysis. By calculating the probability of failure of infill frames subjected to earthquake loading at different locations, the paper showed that the current resistance factor of 0.6 in the infill design equation suggested by the Canadian masonry design standard is conservative. To achieve a reliability index of 3, this factor could be increased to 0.65 for all cities studied. For cities with low seismicity such as Toronto, the results suggest that an even higher resistance factor is justified.

Fragility and vulnerability models for poorly-detailed infilled buildings accounting for building-to-building and masonry infill variability

While in poorly-detailed masonry-infilled reinforced concrete (RC) buildings the significance of masonry infills is acknowledged, less attention has been paid to the variability surrounding their mechanical properties and its potential impact on fragility and, consequently, vulnerability models to be used in seismic risk estimation. This study addresses this gap by proposing updated fragility and vulnerability models of existing poorly-detailed masonry infilled and pilotis RC frames that consider the variability in building layout and infill properties. A large building portfolio, representative of those designed according to Italian codes between 1970 and 1980, is selected as case study, incorporating building-to-building variability through various geometrical configurations. Updated modelling uncertainty parameters, specifically derived for existing infilled RC frames, are used, including the variability surrounding the properties of different infill typologies and the occurrence of RC frame shear failure. The portfolio was analysed through multiple-stripe analyses, followed by the development of upgraded fragility models for buildings with different heights and geometrical configurations. Finally, the corresponding vulnerability models were derived using damage-to-loss models calibrated with post-earthquake observation damage data from the 2009 L'Aquila earthquake. The updated fragility and vulnerability curves can be used for more refined seismic risk estimates of large building portfolios, that account for building-to-building and infill-to-infill variability, revised modelling uncertainty estimates and a more robust intensity measure (AvgSa).