Infilled Frames Research Articles

Simplified pushover-based seismic risk assessment methodology for existing infilled frame structures

Simplified pushover-based seismic risk assessment methodology for existing infilled frame structures

Analytical study on behaviour and performance of infilled frame structure with reinforced eccentric opening

This numerical analysis has discussed the behaviour of the frame structure with eccentric infill wall opening modelled with shell and strut elements. In the beginning, validation models were created by following the laboratory tests results. Then, a simple one-storey infill frame structure with an opening was modelled with varying ratios by taking the strut angle formed to obtain an equation for the strut width that corresponds to the behaviour of shell element model with strut angles variation. The strut width equation was then applied to the 3-storey infill frame structures. The behaviour comparison between the strut and shell element model was then investigated by linear and nonlinear static analysis. The strut width equation for infill wall frame with eccentric openings (Weo) is determined by modifying the stiffness coefficient (Ce) based on the opening ratio. The application of the Weo equation to the infill frame model showed that the strut model had a comparable behaviour to the shell element model. The drift ratio comparison showed that the smaller the strut angle, the greater the structure stiffness. The pushover analysis shows the infilled frame model was able to withstand a larger base shear force than the open frame model.

A Review on Infilled frame Structure with respective of various Interface Materials

During major earthquakes, existing buildings have collapsed or suffered serious damage, resulting in number of losses, severe injuries, and deaths. Based on literature, the influence of this work reviewed the effects of interface with different materials and also to find how infilled frames behave in framed structure. This study's primary goal is to strengthen RC-framed structures and increase the ductility of infilled frames by using interface materials. The research offers a full range and points relevant to ductile parameters for more results in the field of infilled frames using interface materials. In parametric investigation the interface material with interface thickness and the combination of interface material with a particular frame, from that optimum value to be identified. This research benefits researchers, professionals, and specialists the behaviour of various structural systems, as well as innovative mitigation techniques that have been used in the literature to build progressive collapse resistance experimentally.

Stick model for response prediction of as-built and retrofitted infilled RC frames

The Stick model is a Multi-degree of Freedom system consisting of a series of story-level lumped masses connected in series by non-linear shear springs suitably calibrated to simulate the interstory behavior. The Stick model has been recently introduced to predict the seismic performances of existing buildings in terms of engineering demand parameters, such as interstory drift ratios and peak floor accelerations, both at the building and at the large-scale level. This model has been demonstrated to predict the damage concentration and distribution with sufficient accuracy still preserving computational time with respect to refined finite element models. Previous works proposed a calibrated model to represent the behavior of existing gravity load-designed infilled building typologies. Recent advancements suggest the adoption of simplified procedures to generate interstory shear spring backbones allowing the extension of the model to different building typologies also accounting for possible retrofit interventions.In this paper, a simplified procedure is proposed to generate interstory shear spring backbones. The procedure allows generating interstory backbones accounting for typical features characterizing existing buildings, explicitly simulating typical failure modes of non-conforming RC elements, infill-induced brittle failures, and introducing the effect of possible retrofit interventions to increase both the building structural capacity and the stiffness.

Numerical thermal performance analysis of light steel insulated walls under fire

Light-gauge steel-framed (LSF) walls are being adopted by the Algerian construction industry as a new alternative to the traditional infilled frames due to the advantages they provide. The strength-to-weight ratio of Cold Formed Section (CFS) leads to lighter structures and a decrease in the building cost. However, in the case of fire, the high shape factor combined with the loss of material properties of the unprotected, slender CFS can result in structural failure. Because of their conductivity, elevated temperatures have an effect on the thermal performance of panels, necessitating the use of appropriate insulation. The purpose of this paper is to perform a numerical analysis of the thermal behavior of LSF walls protected by plasterboard or magnesium oxide board, as well as cavity insulations. Numerical models are developed, using ANSYS software to simulate the thermal performance of LSF walls under ISO 834 fire. Thermal simulations are done to predict temperature profiles, maximum temperatures, and the estimated fire resistance level (FRL). This research has produced results to better evaluate the influence of different systems of protection and insulation used for the CFS under fire.

Accounting for earthquake‐induced ground‐motion duration in building‐portfolio loss assessment

AbstractEarthquake‐induced ground‐motion duration can have a non‐negligible impact on the nonlinear seismic performance of structures. However, in current seismic risk assessment practice, hazard and vulnerability analyses generally only consider ground motion's amplitude and frequency‐content features, often relegating duration to implicit considerations. This study introduces a simulation‐based framework to explicitly quantify the impact of ground‐motion duration on building‐portfolio direct economic losses. Case‐study synthetic building portfolios located at different distances from a case‐study seismic source (i.e., fault) are assembled considering – individually and in combination – three building typologies representing distinct vulnerability classes in Southern Italy. Such typologies correspond to non‐ductile moment‐resisting reinforced concrete (RC) infilled frames designed to only sustain gravity loads (i.e.,pre‐codeinfilled frames), and ductile moment‐resisting RC infilled and bare frames designed considering seismic provisions for high‐ductility capacity (i.e.,special‐codeinfilled and bare frames). Event‐based probabilistic seismic hazard analysis is performed explicitly simulating duration jointly with spectral‐shape‐related intensity measures (IMs), accounting for their spatial and cross‐correlation. Sets of ground‐motion records are selected to conduct cloud‐based nonlinear time‐history analyses (NLTHAs) and derive fragility models for each considered building typology through archetype structures, simulating their structural response using computational models that account for stiffness and strength cyclic and in‐cycle deterioration as well as destabilising effects. Fragility models are derived using average pseudo‐spectral acceleration (in a range of periods of interest) as the primary IM and alternatively: (1) the dissipated hysteretic energy as an engineering demand parameter (EDP), implicitly accounting for duration given the cumulative nature of such an EDP and the adopted nonlinear modelling strategy, in a scalar format; (2) the dissipated hysteretic energy as an EDP, as before, explicitly considering duration as an IM together with spectral shape, in a vector‐valued format. Vulnerability models are then derived using the fragility models and appropriate building‐level damage‐to‐loss models. The portfolio loss exceedance curves and expected annual losses computed for each combination of exposure, hazard, and vulnerability models are critically assessed and discussed. Depending on the portfolio's size, exposure composition, location relative to the fault, site conditions and the seismic source model, the impact of duration on the loss estimates can be significant. For the considered settings, relative variations up to 200% between the scalar‐ and vector‐valued‐based portfolios expected annual losses are observed, attaining the highest discrepancies as the fault‐to‐portfolio distance increases.

Influence of MIWs on the seismic responses of moment resisting RCFs: A practical method

This study investigates the influence of masonry infill walls (MIWs) on the response modification factor of moment-resisting reinforced concrete frames (RCFs). To this end, several moment-resisting RCFs with a wide range of stories and bays are considered, and their base-shear versus roof-displacement curves are derived using incremental dynamic analysis. The frames are examined first with sixteen earthquake excitations, including the impact of masonry infill walls, and then without this effect. Four classes of clay brick masonry properties are utilized to cover a diverse range of masonry walls. Two cases are examined for infilled frames: in the first, all bays are infilled, and in the second, some bays in each story are infilled. The response modification factors of these frames are subsequently compared. The results indicate that MIWs significantly increase the secant stiffness and the strength of moment-resisting RCFs. The response modification factors of the infilled moment-resisting RCFs are found to be higher than those of bare frames. In addition, for most RCFs, the values of the response modification factor achieved for infilled moment-resisting RCFs are greater than the Iranian seismic code's prescribed value, whereas, for some bare frames, the code's recommended value is not met. Furthermore, several relations are developed to predict the response modification factors of infilled moment-resisting RCFs based on the bare frames' fundamental period and response modification factor. Four new frames subjected to seismic ground motions distinct from the primary earthquake excitations used to derive these relations and an experimental case are used to confirm their validity. Moreover, several graphs for the response modification factor of infilled frames with various clay brick masonry walls were developed. Using these graphs, building designers can determine the prism strength of MIWs required to meet the seismic code's prescribed value based on the fundamental period and response modification factors of bare moment-resisting RCFs.

Seismic performance evaluation of masonry infill R.C. frame considering soil-structure interaction

The structural damage due to recent seismic events in Nepal has led to a dire need for studies considering soil-structure interaction (SSI) as the majority of designers still adopt conventional design principles. These damages may be the result of the conventional fixed base method’s failure to take into account the underlying soil properties. Post $$M_w$$ 7.8 Gorkha earthquake, revised Nepal National Building code NNBC 105:2020 has classified soil types based on the rigidity of the soil. A comparative analysis is carried out using linear-static and nonlinear static (Pushover) analysis considering the fixed and flexible base of a masonry infill RC frame. The seismic performance parameter evaluated for a target inelastic drift of 2% are in terms of their fundamental time period, peak floor displacement, inter-storey drift ratio (IDR), ultimate load carrying capacity and yield mechanism. The consideration of SSI drastically influenced the fundamental time period, peak floor displacement and IDR with decreasing rigidity of soil. The fixed base structure exhibited a higher ultimate load-carrying capacity than the flexible base structure for all soil types. The masonry infill dissipated the seismic energy by the failure of the majority of struts. Furthermore, the post-yield behaviour of all models highlighted that the damage level of RC frame and masonry infill elements were higher for fixed base.

Epistemic uncertainty in poorly detailed existing frames accounting for masonry infill variability and RC shear failure

AbstractRobust performance‐based earthquake assessment should consider the effects of both aleatory and epistemic uncertainty on seismic response parameters. While the effects of modelling uncertainty on specific engineering demand parameters and collapse fragility curves have been widely investigated to date on bare frame structural typologies, little attention has been paid to the impact of masonry infill properties variability on the uncertainty estimation in existing infilled RC frames. Previous studies available in the literature are mainly related to seismically designed RC buildings and the suggestions provided in international guidelines cannot be reasonably adopted for poorly detailed RC existing frames. As regards the uncertainty in existing RC frames, the role of masonry infills was often neglected or their interaction with the surrounding frames was not rigorously accounted for in the uncertainty estimation. With such limitations in mind, the aim of this study is to provide more realistic modelling uncertainty quantities to be adopted in seismic assessment of existing infilled RC frames, including, in a thorough manner, the impact of the variability of the masonry infill typologies and the occurrence of RC frame shear failure. Both the aleatory and epistemic uncertainties are estimated, in terms of the overall dispersion on specific engineering demand parameters and collapse fragility curves. Finally, the impact of such uncertainties on seismic risk estimates, quantified through expected annual losses, is also thoroughly investigated. The inclusion of additional random variables, not considered so far, in the uncertainty estimation framework, led to importantly higher modelling uncertainty quantities than those currently available from previous studies.

Influence of Masonry Infill Wall Position and Openings in the Seismic Response of Reinforced Concrete Frames

It is now widely recognized that the masonry infill frame used in reinforced concrete structures (RC) greatly enhances both the rigidity and strength of the surrounding frame. The lateral loading behavior of this RC frame is different from the frame without infill, although the structural contribution of infill walls is discarded in many countries, including Algeria. This paper aims to focus on the effect of openings and the effect of changing the distribution of masonry panels on the global behavior of buildings. For this, a pushover analysis is carried out to evaluate the seismic performance and assess the behavior of infilled RC, and to study the results related to capacity curve, inter-story drift and energy. The results obtained show that the effect of the openings and changing of the distribution of masonry panels can drastically change the overall behavior of the structures regarding enhancing strength capacities and energy absorption. Noticeable remarks in terms of distributing masonry panels within a frame are observed and several recommendations concerning the present practice might be important to be considered.

Numerical analysis of the in-plane behaviour of decoupled masonry infilled RC frames

Damage of reinforced concrete (RC) frames with masonry infill walls has been observed after many earthquakes. Brittle behaviour of the masonry infills in combination with the ductile behaviour of the RC frames makes infill walls prone to damage during earthquakes. Interstory deformations lead to an interaction between the infill and the RC frame, which affects the structural response. The result of this interaction is significant damage to the infill wall and sometimes to the surrounding structural system too. In most design codes, infill walls are considered as non-structural elements and neglected in the design process, because taking into account the infills and considering the interaction between frame and infill in software packages can be complicated and impractical. A good way to avoid negative aspects arising from this behavior is to ensure no or low-interaction of the frame and infill wall, for instance by decoupling the infill from the frame. This paper presents the numerical study performed to investigate new connection system called INODIS (Innovative Decoupled Infill System) for decoupling infill walls from surrounding frame with the aim to postpone infill activation to high interstory drifts thus reducing infill/frame interaction and minimizing damage to both infills and frames. The experimental results are first used for calibration and validation of the numerical model, which is then employed for investigating the influence of the material parameters as well as infill’s and frame’s geometry on the in-plane behaviour of the infilled frames with the INODIS system. For all the investigated situations, simulation results show significant improvements in behaviour for decoupled infilled RC frames in comparison to the traditionally infilled frames.

Evaluating simplified macromodeling approaches of simulating infilled reinforced concrete frames with openings

AbstractSimulating the contribution of masonry infills on the reaction of reinforced concrete (RC) frames have been the concentration point of numerous numerical studies. However, the effects of openings are often neglected by technical codes, which may lead to sensible errors in predicting the seismic behavior of masonry infilled frames. In this study, the simplified macromodeling approaches of equivalent diagonal strut model (EDSM) and two‐dimensional discrete macroelement model (DMEM) compared to a finite element model (FEM) and the influence of the modeling approach on the lateral response of infilled frames, with different percentages of openings, was investigated. A nonlinear static pushover analysis for conveying the terms of the monotonic loading procedure of the benchmark experimental program has been employed. Concerning the results, the stiffness of the masonry infilled frames by increasing the amount of opening was decreasing. The outcomes of this study may increase the knowledge of comparing the possible methods for modeling masonry infilled frames with openings.

The Over-Strength Coefficient of Masonry-Infilled RC Frame Structures under Bidirectional Ground Motions

The over-strength coefficient is one of the key factors for the seismic safety of a structure. For RC frames, the infill wall may improve the lateral bearing capacity, while the seismic demand increases as well, which leads to the unexpected seismic performance of an infilled RC frame in past earthquakes. Therefore, it is necessary to systematically study the over-strength effect of the infilled RC frames from the point of seismic capacity and demand. In this paper, 36 RC frame structures with/without infill walls are designed, and the corresponding finite element modelings, considering the in-plane and out-of-plane performance coupling effect of infill walls, are established to conduct incremental dynamic analyses (IDA). The seismic capacity values of over-strength coefficients are calculated, utilizing the IDA results under bidirectional ground motions. The effects of seismic precautionary intensity and number of stories on the over-strength coefficient of the RC frame with/without infill walls are discussed. The over-strength coefficient capacity value of the infilled frame is apparently higher than that of the bare frame, due to the contribution of infill walls. However, the seismic demand analysis of the over-strength coefficient shows that the capacity–demand ratio of masonry-infilled RC frame structures is greatly reduced, especially for the bottom soft-story infilled frame.

Seismic collapse assessment of reinforced concrete frames infilled with hollow concrete bricks

Lessons from past earthquakes indicate that infill walls affect the seismic collapse resistance of the frame. However, research on quantifying the effect of infill walls on the frames’ seismic safety is limited. Therefore, this paper focuses on this issue. Firstly, the finite element models of reinforced concrete frame infilled with hollow concrete bricks (HCB) are developed and validated by a laboratory test of a one-span one-story infilled frame. Then, the earthquake-induced collapses of infilled frames are simulated and discussed. The influence of the HCB infill wall arrangement on the seismic collapse resistance of frames with different heights is quantitatively studied. The results indicate that the HCB infill wall reduces the collapse resistance capacity by 24.5% for frames with an open ground floor. In contrast, the improvement in the collapse resistance by infill walls gradually decreases with the increase in structural height for frames with continuous HCB infill walls. The collapse resistance can even be reduced when the frame exceeds eight stories.

A macro‐model for describing the in‐plane seismic response of masonry‐infilled frames with sliding/flexible joints

AbstractMasonry infill walls are among the most vulnerable components of reinforced concrete (RC) frame structures. Recently, some techniques for enhancing the performance of the infills have been proposed, aiming at improving both the global and the local behaviour of the infilled frame structure. Among the most promising ones, there are those that aim to decouple or reduce the infill‐frame interaction by means of flexible or sliding joints, relying respectively on rubber or low‐friction materials at the interface between horizontal subpanels or between the panels and the frame. Numerous models have been developed in the last decades for describing the seismic response of masonry‐infilled RC frames, but these have focused mainly on the case of traditional infills. This study aims to fill this gap by proposing a two‐dimensional macro‐element model for describing the in‐plane behaviour of RC infilled frames with flexible or sliding joints. The proposed modelling approach, implemented in OpenSees, is an extension of a discrete macro‐element previously developed for the case of traditional infill panels. It is calibrated and validated in this study against quasi‐static tests from the literature, carried out on masonry‐infilled RC frames with sliding and rubber joints. The study results show the capabilities of the proposed modelling approach to evaluate the benefits of using flexible joints in terms of minimising the negative effects of the interaction between infill and RC frame and limiting the increase of global stiffness of the system with respect to the bare frame condition.

Experimental study on the seismic performance of RC frames considering the cast sequence of infilled walls and columns

The relative values of lateral stiffness and ultimate limit state of bearing capacity of vertical members are defining factors of the seismic failure or collapse mode of structures. This paper focuses on how the different construction sequences of infilled walls and frame columns influence the seismic performance of frame structures based on the low-cycle reciprocating loading tests of six single-layer two-span frame structure models with a ratio of 1:4, including two frame models without infilled walls (F model), two frame models with walls built later (LW model), and two frame models with walls built first (FW model).According to the test results, different construction sequences of infilled walls have a significant impact on the seismic performance of frame structures. The FW model introduces the process of “building the wall first and then casting the column” with the wall and the column highly combined with each other and the infilled wall involved in the internal force distribution of the frame structure, boasting the largest bearing capacity and initial stiffness; LW model is built by “pouring the column first and then building the wall” with a low combination between wall and column, its bearing capacity and initial stiffness second to FW model; F model has the smallest bearing capacity and initial stiffness. Shear failure and poor ductility are found in the FW model due to the restraint effect of the infilled wall; bending failure in the F model with a large displacement but good ductility; shear failure tends to appear in the LW model structure with the failure in bonding between reinforcement and concrete in the end and good ductility. The research results can provide a reference for the elastic–plastic seismic response analysis considering the interaction of infilled wall and frame.

Seismic Performance Target and Fragility of Masonry Infilled RC Frames under In-Plane Loading

Masonry infilled RC frames are one of the most common structural forms, the damage of which, in earthquake events, usually cause serious losses. The determination of the seismic performance target is the key foundation of performance-based seismic evaluation and design for masonry infilled RC frames. In this paper, an extensive database of experimental tests on infilled RC frames loaded in an in-plane direction is collated. According to the crack propagation and elastic-plastic characteristics of infilled RC frames, the damage process is divided into four stages, and then the criteria of the damage states (DS) are proposed. In addition, the seismic performance targets expressed as inter-story drift ratio (IDR) for the four stages are suggested, which would support the performance-based in-plane seismic analysis of infilled RC frames. Finally, the proposed in-plane seismic performance target is utilized to analyze the fragility of two masonry infilled RC frame structures.

Stick model for as-built and retrofitted infilled RC frames

The Stick model is a MDOF system composed of masses lumped at the story level, connected in series by nonlinear shear link elements suitably calibrated to simulate the interstory inelastic behavior. The model has been demonstrated to predict with sufficient accuracy the dynamic response of existing masonry-infilled RC structures in terms of damage concentration and evolution under specific ground motion records. Previous works proposed interstory backbones calibrated on the response of refined MDOF finite element models representative of gravity-load designed buildings. In this work, with the aim of extending the applicability of the Stick model to different building typologies, a simplified procedure is proposed to generate interstory backbones for the Stick model simulating the behavior of existing masonry-infilled RC structures in as-built and retrofitted configurations. The procedure allows generating Stick models accounting for different levels of design (gravity load, obsolete seismic codes), age of construction, number of storeys and in-plan shape and dimensions. Relevant features characterizing existing buildings are accounted for, explicitly simulating typical failure modes of non-conforming RC elements, brittle failures induced by local frame-infill interaction phenomena, and introducing typical building-level collapse modes for existing buildings. The proposed procedure is extended to account for the possible implementation of retrofit intervention at the building level to both increase the structural capacity and the stiffness of the building. The proposed procedure can be employed to generate typological Stick models to be adopted in large-scale loss assessment studies, also evidencing the beneficial effect of possible retrofit interventions.

Developments and research on fire-induced progressive collapse behaviour of reinforced concrete elements and frame - a review.

Many studies have been carried out for understanding the mechanism of failure of RC structural systems under varying temperature circumstances. Similarly, several methods have been developed for improving the fire resistance of concrete buildings, with respect to material selection and detailing aspects. However, only some of the researchers have concentrated on composite behavior of interaction between the structural elements and functional elements, like interaction between masonry infill walls and RC frame elements in the emergence of fire. Several numerical models have been developed for analysis of infilled frames. For simulating the action of fire on full-scale reinforced concrete buildings, three factors, namely, presence of loading, place of fire, its intensity, and duration, must be considered since the material behavior depends on the stress level, intensity and duration of fire and the sensitiveness of structural element to the location and application of fire. To consider the combined effect of load and high temperature, finite element analysis is used. For simulating the intensity and time factor for temperature rise, transient state studies must be done.

On the Seismic Behavior of Masonry Infilled Frame Structures

Infilled frames are usually modelled in the context of global building analysis using simplified procedures without considering the aspects resulting from the interaction between the panel and the frame. Other aspects, such as adequate design of the floor beams and the beam-columns’ joints, and control of potential sliding shear failure of the columns, that significantly affect the structural response, are also typically not accounted for. In the present work it is intended to look over the literature to evaluate the state of the art regarding the lessons learn from recent earthquakes, the evolution of the structural codes considering the infill masonry panels, and how this influences the evolution of the numerical models and the experimental works to overcome the existent gaps.