Masonry Infilled Steel Frames Research Articles

A multi-strut model for the hysteresis behavior and strength assessment of masonry-infilled steel frames with openings under in-plane lateral loading

The analysis of masonry-infilled frames (MIFs) with openings is a complex problem in structural engineering. Previous studies have shown that when an infill panel has an opening, it behaves as four separate subpanels around the opening. Therefore, it can be conceived that a perforated masonry infill panel behaves as four inclined compression-only equivalent struts in each direction. This paper presents a multi-strut model (MSM) using the equivalent strut concept for the nonlinear analysis of masonry-infilled steel frames (MISFs) with openings. The MSM consists of two inelastic side pier struts connected to the surrounding frame joints using rigid trusses representing the subpanels above and below the opening. The model incorporates an envelope curve and a hysteretic law to define the initial stiffness, peak strength, and post-peak strength behavior of the inclined struts under reversal loads. The MSM was used to analyze the lateral load behavior of tested MISFs with openings found in the literature. It was shown that the proposed model is efficient and can predict the stiffness and capacity of MISFs with openings under both monotonic and cyclic lateral loadings.

Simplified modelling of masonry-infilled steel frames under cyclic loading

Simplified modelling of masonry-infilled steel frames under cyclic loading

Correlation of Ground Motion Intensity Measures and Seismic Damage Indices of Masonry-Infilled Steel Frames

The main aim of this study was to analyze the response of structures with masonry infill walls to the intensity measure (IMs) parameters. Hence, two sets of earthquake ground motions, ordinary seismic records (OSR) and pulse-like seismic records (PLSR), were used for the nonlinear dynamic analysis of multi-story steel structures with masonry infill walls. Seismic performance was evaluated using the general indicators of damage (modified Park–Ang index), maximum inter-story drift ratio (MIDR) and roof drift ratio (RDR). The correlation between the multiple IM parameters with and without pulse-like ground motion and the damage indices of steel moment frames with and without masonry-infilled walls was determined using the Spearman correlation coefficient. Moreover, the correlation between the damage criteria and IMs was investigated. The results revealed that the spectral acceleration and velocity at the primary period of the structure and seismic parameters which are related to velocity have a strong relationship with MIDR and RDR. However, the correlations for PLSR and OSR were differed. The results indicated that the analysis of IMs with ground motion could help predict the parameters for building failure in various systems. The presence of masonry-infilled walls has changed the correlation coefficient for a fully infilled frame when compared with a bare frame.

The Theoretical Prediction of Collapse Mechanisms for Masonry-Infilled Steel Frames

The masonry infills in infilled steel frames are generally considered non-structural elements and are neglected in design by different codes. In fact, the presence of these infills should have a decisive influence on the mechanical properties such as lateral stiffness and ultimate strength. In the present work, a new macro-model has been proposed to model the masonry infill by two equivalent pin-jointed diagonal struts connecting the beams and the columns, respectively. To show the infill effect, the theory of plastic hinges has been adopted as an appropriate approach. In this parametric study, the prediction of the nature of failure mechanisms of structures subjected to a combined loading system has been presented, including their collapse loads with information about the location and order of plastic hinges. The model has been validated by theoretical and experimental predictions. In addition, interaction diagrams, \(\lambda V{-}\lambda H\), were constructed. From the result, the factors that have a direct influence are the infill thickness and the values of \(\alpha \). By comparing the collapse loads for the infilled frames to their corresponding open frames, it was found that the lateral stiffness and the vertical strength were considerably increased. It can be said that the two-strut model proposed can realistically capture the collapse mechanisms of infilled frames and can more accurately estimate the local effects due to the infill–frame interaction. Finally, important conclusions about the failure modes of the infilled frames and their corresponding collapse loads were drawn from this work.

Quality indicators after discharge from the intensive care unit in 3 public hospitals

Although there are many researches on infilled steel frames with welded beam-to-column connections, however, few studies were undertaken to investigate the behaviour of these infilled structures but with other common connection types (extended endplate, flush endplate and header plate connections), particularly under combined vertical and horizontal loading. In this paper, firstly, a simplified numerical model of infilled steel frames under cyclic loading, considering the interactions between frames, infills and beam-to-column connections' components, was constructed. The model results were compared with experimental data for cyclically-loaded infilled frames, showing good agreement. Using the verified model, a parametric study on infilled steel frames with five different beam-to-column connection types, under vertical and cyclic horizontal loads, was performed. Several parameters, including vertical load level, infill thickness and vertical load application method, were investigated. The results showed that increasing the level of vertical load (uniformly distributed on the beam) minimised the difference in performance between the frames with welded connections and those with bolted connections. Under vertical loads of 0, 16% and 24% of the columns' axial capacity, the horizontal ultimate load of frames with header plate connections, was, respectively, 73%, 86% and 91% of that of frames with welded connections. Hence, when the infilled frames are subjected to relatively high levels of vertical load, utilising header plate connections may be a viable alternative to using welded connections. Furthermore, a simple analytical method for predicting the stiffness and load-carrying capacity of masonry-infilled steel frames (with different connection types) under vertical and horizontal loads, was proposed.

Numerical study on masonry-infilled steel frames under vertical and cyclic horizontal loads

Although there are many researches on infilled steel frames with welded beam-to-column connections, however, few studies were undertaken to investigate the behaviour of these infilled structures but with other common connection types (extended endplate, flush endplate and header plate connections), particularly under combined vertical and horizontal loading. In this paper, firstly, a simplified numerical model of infilled steel frames under cyclic loading, considering the interactions between frames, infills and beam-to-column connections' components, was constructed. The model results were compared with experimental data for cyclically-loaded infilled frames, showing good agreement. Using the verified model, a parametric study on infilled steel frames with five different beam-to-column connection types, under vertical and cyclic horizontal loads, was performed. Several parameters, including vertical load level, infill thickness and vertical load application method, were investigated. The results showed that increasing the level of vertical load (uniformly distributed on the beam) minimised the difference in performance between the frames with welded connections and those with bolted connections. Under vertical loads of 0, 16% and 24% of the columns' axial capacity, the horizontal ultimate load of frames with header plate connections, was, respectively, 73%, 86% and 91% of that of frames with welded connections. Hence, when the infilled frames are subjected to relatively high levels of vertical load, utilising header plate connections may be a viable alternative to using welded connections. Furthermore, a simple analytical method for predicting the stiffness and load-carrying capacity of masonry-infilled steel frames (with different connection types) under vertical and horizontal loads, was proposed.

Realistic behavior of infilled steel frames in seismic events: experimental and analytical study

An experimental and analytical study is carried out to investigate the effects of lateral loading type on the behavior of masonry infilled steel frames. During earthquake the lateral load is applied as distributed loading to the top beams and columns through rigid floors; however, in most available experimental studies the lateral loading is applied as concentrated loading. In this study, two identical specimens are tested and their behavior is compared under distributed and concentrated lateral loadings. Finite element models of the specimens are also developed and validated against the experimental results. To have a better view, the influence of loading type is studied on another experimental specimen having concentrated loading. A parametric study is also conducted on the influence of loading type in multi-span frames and infills with different aspect ratios. The obtained experimental results show that the distributed loading results in 18.5 and 29% increase in the strength and stiffness of Infilled frames, compared to the case with concentrated loading. Less strength and stiffness in specimens subjected to concentrated loading is a result of stress concentration at the infill corner near the loading point which leads to premature corner crushing. Therefore, it is believed that the codes’ formulas, mostly based on specimens with concentrated loading, are conservative, underestimating the real ultimate strength and stiffness of masonry infilled steel frames.

Shake-table study of plaster effects on the behavior of masonry-infilled steel frames

The effects of plaster on the behavior of single-story single-bay masonry-infilled steel frames under in-plane base accelerations have been experimentally investigated by a shake-table. Tested structures were made in a 1/3 scale, with realistic material properties and construction methods. Steel frames with high and low flexural rigidity of beams and columns were considered. Each type of frame was tested with three variants of masonry: (i) non-plastered masonry; (ii) masonry infill with conventional plaster on both sides; and (iii) masonry infill with a polyvinyl chloride (PVC) net reinforced plaster on both sides. Masonry bricks were made of lightweight cellular concrete. Each frame was firstly successively exposed to horizontal base accelerations of an artificial accelerogram, and afterwards, to horizontal base accelerations of a real earthquake. Characteristic displacements, strains and cracks in the masonry were established for each applied excitation. It has been concluded that plaster strengthens the infill and prevents damages in it, which results in more favorable behavior and increased bearing capacity of plastered masonry-infilled frames compared to non-plastered masonry-infilled frames. The load-bearing contribution of the adopted PVC net in the plaster was not noticeable for the tested specimens, probably due to relative small cross section area of fibers in the net. Behavior of masonry-infilled steel frames significantly depends on frame stiffness. Strong frames have smaller displacements than weak frames, which reduces deformations and damages of an infill.

Seismic loss estimation of mid-rise masonry infilled steel frame structures through incremental dynamic analysis

The seismic loss estimation is greatly influenced by the structures' failure mechanism. In case of infilled structures, the resultant failure mechanism is difficult to predict, due to the composite behaviour of the frame and the infill panel, making the loss estimation a challenge. Moreover, as identical buildings are commonly constructed with different qualities, their structural response and subsequently the losses can vary within a building stock. In this study, by conducting a numerical investigation, the influence of construction quality and its induced structural damage on the economic losses will be measured. Considering a typical, mid-rise masonry infilled steel frame structure, a realistic simulation of construction details has been carried out in full-scale. The numerical models take into account the variation of material properties, different types of joints and a number of possible deficiencies. The results indicate that the construction quality has a conspicuous impact on the vulnerability of the structures.

Comparison of Developed Numerical Macro and Micro Masonry Models for Static and Dynamic Analysis of Masonry-infilled Steel Frames

First, the basic characteristics of macro and micro masonry models in numerical analyses of masonry structures are discussed. Afterwards, developed numerical macro and micro masonry models, intended for the nonlinear static and dynamic analysis of unreinforced and confined masonry walls, as well as of masonry-infilled frames, are briefly presented. The models are tested on previously performed experimental tests of masonry-infilled steel frame under horizontal static force and masonry-infilled steel frame on a shake-table. The precision of both models is compared. It is concluded that both numerical models can provide reliable results. However, the macro model has more advantages for wide practical application.

Kontrolirano seizmičko ponašanje čeličnih okvira sa zidanom ispunom

Whether used as a curtain/partition wall or a bearing part of the structure, masonry infill significantly affects structural behaviour of the primary structure. Two different types of masonry units (‘strong’ and ‘weak’), often used in Croatia as infill of steel frames, are initially considered in the paper. Based on experimental results obtained by testing behaviour of these two types of masonry units, a third type of infill is proposed, which is a specific combination of the initial two types, and enables realisation of controlled behaviour of masonry-infilled steel frames.

Influence of vertical load on in-plane behavior of masonry infilled steel frames

Results of an experimental program are presented in this paper for the influence of vertical load on the in-plane behavior of masonry infilled steel frames. Five half-scaled single-story, single-bay steel frame specimens were tested under cyclic lateral loading. The specimens included four infilled frames and one bare frame. Two similar specimens as well as the bare frame had moment-resisting steel frames, while the remaining two specimens had pinned steel frames. For each frame type, one specimen was tested under simultaneous vertical and lateral loading, whereas the other was subjected only to lateral loading. The experimental results show that the vertical load changes the cracking patterns and failure modes of the infill panels. It improves dissipated hysteresis energy and equivalent viscous damping. Global responses of specimens, including stiffness and maximum strength, do no change by vertical loading considerably. Regarding the ductility, the presence of vertical load is ignorable in the specimen with moment-resisting frame. However, it increases the ductility of the infilled pinned frame specimen, leading to an enhancement in the m-factor by at least 2.5 times. In summary, it is concluded that the influence of the vertical load on the lateral response of infilled frames can be conservatively ignored.

Seismic response of masonry-infilled steel frames via multi-scale finite-element analyses

Effects of masonry infills on the seismic vulnerability of steel frames is studied through multi-scale numerical modelling. First, a micro-modelling approach is utilized to define a homogenized masonry material, calibrated on experimental tests, which is used for modelling the nonlinear response of a one-story, single span, masonry-infilled portal under horizontal loads. Based on results of the micro-model, the constitutive behavior of a diagonal strut macro-element equivalent to the infill panel is calibrated. Then, the diagonal strut is used to model infill panels in the macro-scale analysis of a multi-span multi-story infilled moment-resisting (MR) steel frame. The seismic vulnerability of the MR frame is evaluated through a nonlinear static procedure. Numerical analyses highlight that infills may radically modify the seismic response and the failure mechanism of the frame, hence the importance of the infill correct modelling.

Experimental study on the response of seismically isolated masonry infilled steel frames during the initial stages of a seismic movement

A novel seismic isolator is presented to detach the structural behavior from the infill effect during earth movements, with the aim of avoiding strong interactions. An experimental campaign was carried out to determine the influence of this isolator during the early stages of the seismic response of masonry-infilled steel frames, testing different configuration schemes to assess their effectiveness in terms of overall isolation, reduction of peak loads, strain levels and energy dissipation. The device was found to hinder the formation of the damaging diagonal compression struts by absorbing the relative displacements between frame and infill. The results achieved show that seismic interaction between infill panels and the structural skeleton can be faced from an isolation point of view.

The application of a reinforced plaster mortar for seismic strengthening of masonry structures

Abstract The effects of plaster mortar on the behaviour of 1/3 scaled, one storey, one bay masonry-infilled steel frames under horizontal in-plane static loading are experimentally investigated in this paper. Two types of steel frames are considered: one with high flexural rigidity of the beams and columns and another with low flexural rigidity of the beams and columns. Each frame was tested with three masonry variants: (i) bare masonry infill, (ii) masonry infill with pre-mixed plaster on both sides and (iii) masonry infill with pre-mixed plaster on both sides and reinforced with a polyvinyl chloride (PVC) net. All of the frames were loaded successively by a horizontal force in the beam direction until structural collapse. Afterward, the experimental results were compared to those from the presented numeric model for the nonlinear static analysis of planar structures made of concrete, steel and masonry. The model was upgraded by including the effect of plaster on the overall stiffness and strength of the masonry and verified using the experimental tests. This experimental investigation shows that plaster significantly contributes to the strength and load-bearing capacity of masonry and therefore to the strength and load-bearing capacity of masonry-infilled frames.

Analytical modelling of masonry-infilled steel frames

Masonry itself is a composite heterogeneous material whose structural behaviour is strongly affected by many influencing parameters with a wide range of possible values, construction procedures as well as care methods taken afterwards. When the masonry panel is added into the surrounding frame the complex interactive frame-infill system is established exhibiting highly nonlinear inelastic structural behaviour. Therefore, the analytical modelling of masonry-infilled frame structures is a very complex task that demands various data matching given in-situ conditions, otherwise applied methods and analytical models used have only a theoretical value. In this paper analytical modelling of infilled steel frame structures is based on previously experimentally calibrated data. The base for calibration of analytical models was experimental testing of one-bay, one-storey infilled steel frames conducted at the Faculty of Civil Engineering, Josip Juraj Strossmayer University of Osijek. Two series by three steel frames were infilled with perforated clay blocks (‘strong infill’) and autoclaved aerated concrete blocks (‘weak infill’) respectively. The significant difference in structural behaviour of these two kinds of masonry infill is observed and modelled. The macro-models (single-strut and three-strut model and infill-panel macro-model) and detailed 2D micro-models were applied. A total of eight analytical models were analysed with their relevant characteristics along with the quality of epresentation of the measured global and local results as well as their applicability.

Discrete Element Modelling of Masonry Infilled Steel Frames with Multiple Window Openings Subjected to Lateral Load Variations

Steel framed structures are routinely infilled with masonry or concrete walls. The infill offers in-plane shear resistance that adds to the one from the steel frame. However, the stiffness effect on the entire frame’s response is usually neglected. In recent years, researchers have recognised the lack of in-depth understanding on infilled steel frames; hence specialised computational tools have been developed to provide an easy way of assessing these interactive structural systems and aid practising engineers in evaluating the overall behaviour. A computational model to study the behaviour of masonry infilled steel frames for the non-standard case of variable potential positions of openings and their interaction, when subjected to in-plane monotonic loading, is herein developed. Using the Discrete Element Method (DEM) and the software UDEC, the masonry wall is modelled as an assemblage of distinct deformable blocks while the mortar joints as zero thickness interfaces. The numerical model validated against full scale experimental tests found in the literature and a good agreement obtained. In addition, a series of parametric studies were performed to draw the significance of the size and location of the openings on the lateral load capacity, as well as the stiffness and failure mechanisms of the infilled steel frames.􀀁From the results analyses, it was found that the inclusion of multiple openings significantly reduces the strength and stiffness of the system. In particular, placing an opening close to the point of application of the lateral load will result to further reduction of masonry infill’s stiffness.

On a numerical model for static and dynamic analysis of in‐plane masonry infilled steel frames

AbstractA numerical model is presented for both static and dynamic analysis of planar masonry‐infilled steel frames, which are loaded only in their plane. The model can simulate all main nonlinear effects of the frame‐infill‐foundation‐soil system. With this model, bare steel and concrete frame structures, masonry structures, as well as masonry‐infilled steel and concrete frame structures can be analysed. Verification of this model was performed on two experimental tests. In example 1 a masonry‐infilled steel frame under static cyclic load and in example 2 a masonry‐infilled steel frame under dynamic load were analysed. The obtained numerical results agree well with experimental results.

Concrete masonry infilled steel frames subjected to combined in-plane lateral and axial loading – An experimental study

An experimental program involving the testing of 14 specimens was conducted to investigate the behavior and capacity of concrete masonry infills bounded by steel frames. Five infill specimens as well as one bare frame specimen were subjected to an in-plane lateral load applied at the frame top beam level whereas the remaining 8 specimens were tested under combined in-plane axial and lateral loading. Specimens included non-grouted, partially grouted and fully grouted infills. The openings of infills were also considered. The presence of axial load resulted in a marked increase in the lateral resistance of the infills and the correlation between axial load and lateral resistance is discussed. In addition, grouting and opening on the failure mode, lateral ultimate load, and stiffness of specimens are presented. The comparison of the test results with values suggested by the current design standards of both Canada and United States shows that the Canadian standard provides a markedly conservative design of masonry infills whereas the American design standard gives an improved estimate of infill stiffness and strength.

Cyclic testing of single bay steel frames with various types of masonry infill

This paper presents results of a part of the Croatian project “Seismic design of infilled frames” and deals with masonry infilled steel frames. The behaviour of steel frames infilled with masonry, commonly used in Croatia, was experimentally investigated under quasi-static cyclic loading. Besides, a new structural solution is proposed. Nine one-bay, one-storey masonry-infilled steel frames with three different masonry infill types: perforated clay blocks (C), lightweight AAC blocks (A) and newly proposed combination of these materials (CA), were built and tested. Proposed combined masonry infill (CA) allowed partial separation of the masonry from the frame at certain drift levels and prevented the infill’s detrimental effects.