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Quantifying aleatory and epistemic uncertainty in nonlinear structural response simulation is key to robust performance-based seismic assessments. This paper focuses on the modeling parameters that are used to describe the nonlinear force-deformation response of the equivalent infill struts used in models of reinforced concrete frames with infills. The variability in several parameters is characterized by developing empirical and theoretical multivariate probability distributions based on the deduced-to-predicted ratios derived using data from 113 physical experiments. The effect of the uncertainty in the infill strut modeling parameters on maximum story drift ratios and associated limit state fragility functions is investigated for a 3-story reinforced concrete frame building with infills. Multiple stripe analysis is performed using hazard-consistent ground motions. Relative to when only record-to-record variability is considered, modeling parameter uncertainty has a non-negligible effect on the dispersion of the maximum story drift ratios, and affects both the median and dispersion of the limit state fragilities. [ABSTRACT FROM AUTHOR]

Lightweight masonry blocks (LMBs) are more environmentally favorable than solid clay bricks, and have gradually become the main material for the infill walls of modern buildings. It is of great importance for proposing a suitable hysterical model of LMBs infill walls to accurately predict the seismic responses of modern buildings. However, cyclic loading tests of LMB infill walls demonstrate that the existing formulas of equivalent strut models significantly overestimate the stiffness and underestimate the peak strength. To this end, the force-displacement curves of 24 cyclic loading tests of LMB infill walls sourced from existing literature are statistically analyzed. The modification coefficients of stiffness and peak strength are put forward, and other parameter values such as yield strength coefficient, unloading stiffness coefficient and pinching effect coefficient are also recommended. Then a full-scale cyclic loading test of an LMB infill wall is designed and conducted to verify the accuracy of the modified model. In addition, the applicability of the modified model is also verified by two infill wall tests from existing literature. The results indicate the modified model can accurately simulate the global hysteretic response of LMB infill walls, and the simulation accuracy of the peak strength is increased to more than 90%. This model provides a useful tool for the accurate evaluation of the seismic performance of modern buildings infilled with LMBs. [ABSTRACT FROM AUTHOR]

This study introduces the application of parallel arrangement of multiple axial springs in a nonlinear macromodel to capture the in-plane rotational behavior and predict shared axial forces between column and wall of an infilled frame under rotation. In addition, multiple failure mode of both boundary frame and infill can be simulated using the developed macromodel. A systematic arrangement of two types of elements, each with one shear spring and one axial spring, is used to replace the masonry infill panels in the numerical modeling of infilled frames. The constitutive models of the axial and shear springs are derived using the geometric properties of the infilled frame and the results of simple material tests such as tension tests of rebar and compression tests of masonry prisms and concrete cylinders. A brief summary of the experimental study and numerical simulation of a 1/2.5-scale 2-story 2-bay unreinforced brick masonry infilled frame specimen (the BF + MIW specimen) is presented, focusing on the behavior of existing vulnerable buildings in developing countries (e.g., Bangladesh). A distinct type of failure mode was observed in the BF + MIW specimen: snap-through shear failure of the column on the lateral loading side with simultaneous sliding at the beam-wall interface. The developed macromodel considers this failure mode. Another reinforced concrete frame specimen with unreinforced concrete block masonry infill is analyzed using the macromodel. Analysis results effectively approximate the overall behavior of the infilled frames and predict axial forces on columns under rotation. [ABSTRACT FROM AUTHOR]

In this paper, the influence of brick masonry infill walls on the seismic performance of reinforced concrete (RC) frames is investigated. The presence and the location of a door opening are considered as test variables. Four RC frames were tested: a control specimen (RC bare frame), an infilled RC frame, an infilled RC frame with door opening at the loading end, and an infilled RC frame with door opening in the center. The test specimens were full scale representatives of typical RC frames with brick masonry infill walls. The data from the testing was interpreted in terms of failure modes, hysteresis curves, energy dissipation characteristics, stiffness degradation, and performance levels as established by standards. It was observed that the infill walls improve the RC frame performance in term of strength and stiffness, whereas the addition of a door opening reduces this performance improvement. Shifting the door opening from the side to the center improved the RC frame performance in term of strength and stiffness. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A weak connection between the infill wall and the frame increases the probability of premature collapse during an earthquake, which can cause the loss of many lives. In this paper, the results of an experimental study consisting of the testing of three single-story, single-bay steel frames (a frame without an infill wall, a steel frame with masonry infill wall and no lateral anchorage, and a steel frame with masonry infill wall and the ADAS yielding damper) are presented. Then, ABAQUS was used to verify the numerical models and the parameters influencing the behavior of the frame incorporating ADAS yielding dampers were probed. The effects of these parameters on different aspects of the frames such as stress distribution, failure modes of the wall, stiffness, strength, ductility, and energy dissipation were investigated. The results show that using ADAS yielding dampers in the area where the frame and the infill are connected decreases the damage inflicted on both the infill and the frame, prevents the premature collapse of the infill, and enhances the frame's ductility. It is worth mentioning that altering the parameters affecting the performance of the frame and the infill wall can lead to the identification of their ideal behaviors. [ABSTRACT FROM AUTHOR]

This paper presents an overview of the experimental results obtained by combined in-plane/out-of-plane (IP/OOP) tests carried out on reinforced concrete (RC) frames infilled with thin clay masonry walls. After preliminary characterization tests on building materials, combined IP/OOP tests on eight full-scale, one-bay, one-story infilled RC frames were carried out. Three external strengthening solutions were investigated considering three types of lime-based plasters, reinforced by means of dispersed fibers and/or bidirectional basalt meshes, applied on both sides of each wall. The experimental results of the tested frames are presented, discussed, and compared to evaluate the performance and the effectiveness of each strengthening solution. [ABSTRACT FROM AUTHOR]

The seismic performance of US-code conforming moment frames constructed with regularly distributed masonry infills was evaluated. Nonlinear dynamic analysis was performed considering cases with and without infills. Upon comparing these cases, it was revealed that the presence of infills causes two opposing effects on the original system-level behavior including system deformability reduction and roof drift demand reduction. When the former prevails, infilled frames were found to exhibit inferior performance relative to their bare frame counterpart, and vice versa. This leads to a conclusion that it is not always conservative to disregard influence of infills, even when they are regularly distributed. [ABSTRACT FROM AUTHOR]

This paper proposes a simplified approach to analyze the seismic performance of masonry infills with sliding joints in moment-resisting frame structures. The proposed methodology uses the equivalent strut approach, calibrated on the results of a novel analytical formulation, which considers the basic geometrical and mechanical properties of the infill. The method is validated through the comparison of the estimated infill resistance and shear demand on the column with those obtained from an extensive experimental and numerical study using refined finite element models. For the case studies considered, the simplified model offers a reliable estimate of the global and local response. [ABSTRACT FROM AUTHOR]

The fundamental period of vibration appears to be one of the most critical parameters for the seismic design and assessment of structures. In the present paper, the results of a large-scale analytical investigation on the parameters that affect the fundamental period of reinforced concrete structures are presented. The influence of the number of storeys, the number of spans, the span length, the infill wall panel stiffness and the percentage of openings within the infill panel on the fundamental period of infilled RC frames was investigated. Based on these results, a regression analysis is applied in order to propose a new empirical equation for the estimation of the fundamental period. The derived equation is shown to have better predictive power compared with equations available in the literature. [ABSTRACT FROM AUTHOR]

This research study investigates the change in dynamic characteristics of reinforced concrete moment-resisting frame buildings without and with fully infill walls. In addition, building models with partially infill walls have also been investigated. A set of different building models have been developed to perform the analysis as (1) bare frame (without infill walls), (2) frame with fully infill walls, (3) frame models with infill panels and soft storey located at base level, 3rd storey level, 6th storey level, 9th storey level, and 12th storey level. The equivalent diagonal strut method has been utilized in order to account for the stiffness and structural action of the masonry infill panels. Dynamic time history, using two ground motion records from near and far-fault regions, has been used to perform the seismic analysis of the considered model configurations. The selected two ground motion records have been scaled to meet the expected peak ground acceleration in Cairo zone. The two ground excitations are applied separately in two orthogonal directions. The structural software package ETABS has been used in developing the building models and performing the simulation analysis. Some selected numerical simulation results in terms of storey shear forces, lateral deflections, interstory drift ratios and overturning moments at each storey level are obtained for all the considered configurations and presented in comparative way. Based on the obtained time-history results, it has been found that the dynamic storey responses for bare frame model significantly differ from the responses obtained for both fully infill and partially infill frame models. [ABSTRACT FROM AUTHOR]

Partition walls are often made of masonry in Romania. Although they are usually considered non-structural elements in the case of reinforced concrete framed structures, the infill panels contribute significantly to the seismic behaviour of the building. Their impact is difficult to assess, mainly because the interaction between the bounding frame and the infill is an intricate issue. This paper analyses the structural behaviour of a masonry infilled reinforced concrete frame system subjected to in - plane loading. Three numerical models are proposed and their results are compared in terms of stiffness and strength of the structure. The role of the openings in the infill panel on the behaviour is analysed and discussed. The effect of gaps between the frame and the infill on the structural behaviour is also investigated. Comparisons are made with the in-force Romanian and European regulations provisions. [ABSTRACT FROM AUTHOR]

This paper discusses the performance of a structural fuse concept developed for use as a seismic isolation system in the design and retrofit of masonry infill walls. An experimental program was developed and executed to study the behavior of the structural fuse system under cyclic loads, and to evaluate the performance of the system with various masonry materials. Cyclic tests were performed by applying displacement controlled loads at the first, second, and third stories of a two-bay, three-story steel test frame with brick infill walls; using a quasi-static loading protocol to create a first mode response in the structural system. A parametric study was also completed by replacing the brick infill panels with infill walls constructed of concrete masonry units and autoclaved aerated concrete blocks, and applying monotonically increasing, displacement controlled loads at the top story of the test frame. [ABSTRACT FROM AUTHOR]

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This paper addresses the sensitivity of the in-plane and out-of-plane behaviour of reinforced-concrete (RC) frames with masonry infill panels to a select number of material related parameters. Instead of general conclusions, the intention is to facilitate a deeper insight into the behaviour of infill-frames at a micro level over a wide range of drift values. A script, which has recently been developed, is used to generate the finite element (FE) models of an infill-frame with desired geometric and mechanical properties. Also, the same three-dimensional FE model is used for both in-plane and out-of-plane analyses of infill-frames. The sensitivity analyses are conducted in three sequential parts: the analyses of a masonry bare wall under one-way bending, the analyses of an infill-frame under out-of-plane loading and the sensitivity analyses of an infill-frame under in-plane loading. A simple method is delineated to overcome convergence issues which are related to the highly nonlinear finite element models to be solved using the Newton-Raphson algorithm. [ABSTRACT FROM AUTHOR]

An extensive statistical analysis is conducted on experimental data to achieve a formula for the strength and stiffness of masonry- infilled frames having central openings. For this, most of the available experimental data were collected and categorized based on their confining frames and opening types. The reliability of existing empirical relations was investigated, in which a reduction factor was suggested that shows the ratio of strength or stiffness of perforated infill to a similar solid one. The study shows that the relation recommended by the literature is the most accurate, among others, to estimate the lateral strength and stiffness of perforated infilled frames. Modified formulas derived from trend analysis of collected experimental data were proposed to determine the mechanical properties of perforated infilled frames. It is also shown that the reduction factor of the ultimate strength of infilled frames caused by the presence of openings depends highly on the material of the confining frames (steel or concrete), but the reduction factor of stiffness is not affected by the frame type. Therefore, different equations are proposed for the strength and stiffness of infills with openings. [ABSTRACT FROM AUTHOR]

The damage to non structural masonry infills in RC frame structures induced by earthquake ground motions represents a considerable source of economic losses and a serious threat to human lives. Although measures for the prevention of infill damage are to some extent included in modern seismic design codes, an effective design procedure has not yet been achieved. Hence, the objective of this research is to identify, through numerical investigations and a review of previous experimental findings, the performance of masonry infills in RC frame structures designed following European code provisions, with reference to different design parameters, including building height, level of design seismic loading, ductility class, masonry typology, and infill density. The introduction of possible improvements to the current design procedure is envisaged, with the aim of achieving enhanced infill damage control through the limitation of inter-story drifts. In particular, as the first part of a wider research program, the study is focused on the behavior of traditional unreinforced clay masonry infill typologies, with masonry panels constructed in complete contact with the surrounding RC frame, since such construction techniques are still being widely used in European seismic regions. [ABSTRACT FROM AUTHOR]

This paper presents research on the behavior of a type of building popular in high seismic zones with a lateral-load-resisting system consisting of masonry-infilled reinforced concrete (RC) frames. Older buildings of this type typically were designed for gravity loads in combination with insufficient or no lateral loads, therefore they do not meet current seismic code requirements. Also, the participation of infill panels in the lateral load resistance of RC frames was not recognized in the original design, often resulting in an overly conservative design. In an attempt to determine the seismic vulnerability of this type of structure, an experimental program was carried out to evaluate the behavior of five half-scale, single-story laboratory models with different numbers of bays. The results indicated that infilled RC frames exhibit significantly higher ultimate strength, residual strength, and initial stiffness than bare frames without compromising any ductility in the load-deflection response. Furthermore, the number of bays appears to be influential with respect to the peak and residual capacity, the failure mode, and the shear stress distribution. [ABSTRACT FROM AUTHOR]

Simple methods for determining the corner crushing strength and the in-plane stiffness of masonry infills are developed. The methods are applicable to structural clay tile, clay brick, and concrete masonry infills and to both steel and concrete bounding frames. The corner crushing strength is determined as a function of the infill thickness and the infill prism compressive strength. The stiffness is determined using a stepwise function of the displacement and is a function of the relative stiffness of the infill to the frame. The only infill material property required for the stiffness is the modulus of elasticity. The methods were developed by looking at a wide variety of tests as reported in the literature. [ABSTRACT FROM AUTHOR]

Buildings with masonry infill walls (MIWs) in reinforced concrete (RC) frames are commonly used all around the world. It is well known that infill walls may affect the strength, stiffness, and displacement ductility of the structural system. Different approaches have been adopted in different codes and guidelines to consider the stiffness and strength contribution of MIWs on RC frame behavior. This study compares the ability of the existing guidelines to estimate stiffness, strength, and deformability of RC frames with MIWs by using a compiled experimental database composed of 51 experiments from 24 different studies. Alternative expressions are proposed in this study to provide improved estimates of stiffness and deformability of infilled RC frames. [ABSTRACT FROM AUTHOR]