Infilled Steel Frames Research Articles

Experimental and analytical studies of infill wall with sliding joints considering a door opening

AbstractSemi‐rigid steel frame stands out due to its remarkable deformation capability under seismic loading, while the introduction of partitioned walls would disturb the expected seismic behavior of the infilled steel frames. Furthermore, the presence of door openings might exacerbate these negative effects. To mitigate the detrimental multiple‐diagonal strut effect of traditional infill walls around the door opening, an innovative low‐damage wall panels system: prefabricated infill wall panels with a door opening and sliding joints are presented for semi‐rigid steel frames. For testifying the effectiveness of the proposed structure, a quasi‐static test was carried out on three half‐scaled steel frames: a bare frame, a frame infilled with conventional wall panels with a door opening, and a frame infilled with the novel wall panel system with a door opening. Experimental results reveal that the developed innovative wall panels with a door opening could avoid unfavorable crack developments and opening deformation around the door area. It is mainly attributed to the releasement of the adverse multiple‐diagonal strut mechanism of traditional wall panels with door openings. Thus, the presented infilled frame showcases seismic performance similar to the bare steel frame, while having a higher energy dissipation capacity. Moreover, the developed analytical prediction method based on the superposition principle could accurately estimate the lateral load‐carrying capacity of the structures. Due to negligible deformation of the both bottom infill wall panel and the door opening, the innovative infill wall only contributes about 10% lateral load‐carrying capability to the infilled frame.

Analysis of infilled steel frames subjected to lateral loading

In Recent days Earthquake resistant design of structure has earned a lot of scope as Earthquake has become more common. Lateral loading behaviour and energy absorption capacity of monolithic Steel framed structures is significantly affected by Presence of infill which adds to the bracing of the structure, Researchers developed new methods of seismic analysis to analyse the behaviour of structure during occurrence of an Earthquake. Performance based seismic design gives methodology for accessing the performance of structure occupancy, life safety or Collapse prevention level. A non-linear static pushover analysis can be used to analyse the inelastic response of structure to lateral load or displacement. In the present research a 3D model of G + 8 story steel framed building is considered for seismic design and performance evaluation. The model was analysed using ETABS software by response spectrum method for zone V according to IS 1893–2016. The performance is accessed by Capacity Spectrum Method using non-linear pushover analysis. The result of all models are analysed and compared in terms of base shear, story displacement, pushover curve, spectrum curve, performance point of the structure. Overall performance of the structure is found in safer limits.

Seismic responses of infill walls with sliding joints and openings in semi-rigid steel frame

Forming door and window openings in partition infill walls is a frequent activity in engineering practices, while the complexity of the mechanical behavior of such infill systems with openings due to the destructive damage to the infill walls has not been thoroughly considered. To protect the vulnerable door and window openings and mitigate the detrimental multiple diagonal struts effect of infill around the opening, the paper presents two novel precast infill walls with sliding joints and door and window openings for semi-rigid steel frames. The quasi-static cyclic tests are performed on three specimens: a reference bare steel frame and two infilled steel frames with door or window opening. Test results confirm that the developed infill systems effectively prevent potential cracking or deformation of the openings and release the adverse multiple diagonal struts effect of infill with a door or window opening. Because of the working mechanism of the developed infills, the two infilled steel frames behave with similar seismic responses to the bare steel frame, while the novel infills are significantly undamaged and no detectable opening deformation is observed even at the inter-story drift ratio of 3.33%. Furthermore, both experimental and numerical responses of the developed innovative infill systems confirm the effectiveness of the infill systems without any additional fixtures to protect the fragile door and window openings.

Modelling of masonry infills in existing steel moment-resisting frames: Nonlinear force-displacement relationship

The study described and summarised in this paper was aimed at developing a framework for the definition of force-displacement relationships for single-strut models for masonry infill walls within steel moment-resisting frames. The methodology is based on a genetic algorithm optimisation and can be used for the calibration of force–displacement curves based on databases from either experiments or numerical simulation. A case study is also tested to demonstrate the framework in detail. Due to limited available experimental data on the seismic response of existing steel frames with masonry infills, a set of comprehensive finite element micro-models developed in Abaqus are used to generate a database. The optimal values of the parameters to feed a force–displacement relationship of the single-strut model of the masonry infills are obtained for each micro-model by solving optimisation problems with a genetic algorithm. The optimisation problem involves the minimisation of the discrepancies between the global responses from the database and their corresponding single-strut models through least square minimisation. With the optimal values as the input variables, a generalised quadrilinear model of the masonry strut is obtained through regression analysis and is validated against additional micro-models of infilled steel frames.

Seismic behavior of hollow-core infilled steel frames; an experimental and numerical study

This study describes an experimental program designed to investigate the influence of the presence and orientation of hollow-core wall panels as well as beam to column connection rigidity on the seismic performance of steel frames infilled with hollow-core wall units. For this purpose, four half-scale, single-story, and single-bay specimens, including three infilled steel frames and one bare moment frame, were subjected to cyclic lateral loading. The bare steel frame and two infill specimens had rigid connections, while the last one had pinned connections. One of rigid connections specimen was constructed with hollow-core wall panels placed vertically, whereas the other was fabricated with wall panels with the horizontal core. The experimental results indicated that the vertical placement of hollow-core wall units controlled structural damage and improved the seismic performance through the rocking mechanism within the steel frame. In addition, the strength, stiffness, and energy dissipation capacity of the infilled pinned connections frame were less than those in rigid connections specimen. In another part of this study, a parametric study was conducted with finite element method using ABAQUS software. The parametric nonlinear analyses study revealed that the infilled frames with hollow-core wall panels placed vertically had less initial stiffness and more strength than those with horizontal core panels. On the other hand, the initial stiffness and strength of the infilled steel frame, bare steel frame, and infill contribution were reduced by the decrease in the rigidity of the steel frame connections, regardless of infill aspect ratio and the relative stiffness of the hollow-core panels to the surrounding steel frame.

Cyclic behavior of semi-rigid steel frame infilled with damping wall panels

Semi-rigid connected steel frame is characterized by excellent displacement ductility and energy dissipation capacity, while detrimental infill-frame interaction from the traditional infill would be a key role in seismic behaviors for such steel frames and may damage both infill and steel frame. In this study, the solution to partition the infill with low-strength mortar sliding joints and uncouple the infill from the surrounding frame by flexible connections for the semi-rigid steel frames is presented. Three specimens designed in this context were examined experimentally and numerically. The test results show that the frame with low-strength sliding joints and flexible connections behaves similarly to the bare steel frame, and improves the energy dissipation capacity by about 19.83%. Unlike the semi-rigid steel frame with traditional infill, significant crack of the infill or local stress concentration on the columns is undetected even at a drift ratio of 3.33% in the proposed infilled steel frame. Parametric analysis results confirm that the friction factor of the low-strength sliding joints is the key parameter to improve the lateral bearing capacity of the infill system.

Investigation of different infill wall effects on performance of steel frames with shear beam-column connections under progressive collapse

This article examined steel frames with shear beam-column connections to determine the effectiveness of different masonry infill walls under progressive collapse. This research concentrated on the shear connection, which is the most common type of steel beam-column connection in steel buildings. Furthermore, this work experimentally evaluated one-third-scale steel-framed configurations with a single shear beam-column connection and another infilled steel frame wall configuration from the literature to verify the validity of 3D finite element models developed using the program ABAQUS. Finite element models were then used to investigate 16 different kinds of steel frames with infill masonry as well as the influence of multiple frames and the number of stories. In addition, the effects of a fully infilled frame and those of a bare frame and an infilled frame with openings were compared in flexural and catenary action phases. Results revealed that the steel building’s structural strength and energy dissipation against progressive collapse are significantly improved by infill walls.

Seismic performance and fragility analysis of infilled steel frame structures using a new multi-strut model

Whether UnReinforced Masonry (URM) infills should be employed as structural members in frame structures is a debatable subject in performance-based earthquake engineering. This paper presents a detailed assessment of the seismic response of infilled moment-resisting steel frames. A recently proposed multi-strut model is applied here to consider both the local and global effects of URM infills. The capability of the employed model in predicting the local and global effects of URM panels has previously been verified by the authors of this study. Two structures, a four-story building and a two-story building, were designed using seismic design codes, and one of the outer frames of each structure was selected for the numerical models. Based on the conventional layouts of URM panels in buildings, three different configurations are considered: the bare frame (model in which the URM panels are isolated from the surrounding frame), the infilled frame, and the soft-first story frame. Fifteen ground motion records have been used to perform nonlinear Incremental Dynamic Analyses (IDA), which were then employed to derive the fragility curves of the studied structures for the Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) limit states. The results show that in lower limit states, the masonry infill leads to some beneficial effects. However, at more severe limit states, these beneficial effects diminish and at some point, revert to adverse effects. This is evident in the CP limit state, wherein the masonry infill weakens the seismic performance of the structure.

Mechanical Behavior of CCA Wall Infilled Steel Frames with Preset Vertical Slits

In view of the unfavorable interaction between the steel frame and cellulose fiber cement sheets autoclaved (CCA) wall, preset vertical slits are adopted on the wallboard. Four 1:2-scale, single-bay, and single-storey steel frames, one bare steel frame, one CCA wall infilled steel frame without any measures, and two CCA wall infilled steel frames with different patterns of a slit, were tested under low cyclic load. The failure mode and additional stiffness of the CCA wall were obtained from the test. Besides, the effects of the vertical slits on hysteretic performance, bearing capacity, and the stiffness degradation of specimens were also studied. It was found that the preset vertical slits were effective in delaying the cracking of the CCA wall, and in reducing the additional stiffness of the CCA wall for the steel frame structures. To further study the failure characteristics of CCA wall, the finite element models of the CCA wall infilled steel frames were established and verified against the test results. The findings in this paper will have a certain reference value for the future research and engineering applications of similar steel frames with infill walls.

Seismic performance of semi-rigid steel frame infilled with prefabricated damping wall panels

In this research, two innovative semi-rigid steel frames infilled with prefabricated damping wall panels in different types of connection are proposed. Working principles and main features of the developed infill system with both uncoupling mechanism and sliding joints are defined. A quasi-static test was conducted to explore the seismic response of the two systems, as compared with a bare steel frame. Test results confirm that the detrimental infill-frame interaction is prevented by the proposed wall panels. Both specimens infilled with prefabricated damping wall panels characterize a considerably large deformation capacity up to 3.33% drift, while significant crack or corner crushing in the wall panels is not observed, contributed to the configurations of the prefabricated damping wall panels. The infilled steel frames have stable seismic behavior similar to the bare steel frame without infill, indicating that the prefabricated damping wall panels can be designated as an additional safety stock with damping for the steel frame rather than the major component of strength, stiffness, and brittleness. Specifically, thanks to satisfactory energy dissipation capacity of the damping layers, dissipated energy of steel frame infilled with the prefabricated damping wall panels is about 23.3% larger than the bare steel frame after yielding. Moreover, it would be a more effective and controllable configuration that the lateral displacement of the upper wall panel is directly enforced by the top beam.

Fragility assessment of existing low-rise steel moment-resisting frames with masonry infills under mainshock-aftershock earthquake sequences

This paper presents the fragility assessment of non-seismically designed steel moment frames with masonry infills. The assessment considered the effects of multiple earthquakes on the damage accumulation of steel frames, which is an essential part of modern performance-based earthquake engineering. Effects of aftershocks are particularly important when examining damaged buildings and making post-quake decisions, such as tagging and retrofit strategy. The procedure proposed in the present work includes two phase assessment, which is based on incremental dynamic analyses of two refined numerical models of the case-study steel frame, i.e. with and without masonry infills, and utilises mainshock-aftershock sequences of natural earthquake records. The first phase focuses on the undamaged structure subjected to single and multiple earthquakes; the effects of masonry infills on the seismic vulnerability of the steel frame were also considered. In the second phase, aftershock fragility curves were derived to investigate the seismic vulnerability of infilled steel frames with post-mainshock damage caused by mainshocks. Comparative analyses were conducted among the mainshock-damaged structures considering three post-mainshock damage levels, including no damage. The impact of aftershocks was then discussed for each mainshock-damage level in terms of the breakpoint that marks the onset of exceeding post-mainshock damage level, as well as the probability of exceeding of superior damage level due to more significant aftershocks. The evaluation of the efficiency of commonly used intensity measures of aftershocks was also carried out as part of the second phase of assessment.

Experimental Investigation of Using Sandwich Panels as Infill Plate in a Steel Plate Shear Wall

A total of five steel frame specimens, one bare and four infilled, were designed with thin-walled steel sheets and corrugated sandwich infill panels in order to increase their load and energy dissipation capacity. For this experimental study, single-story, single-bay steel frames of nominally-pinned beam-to-column connections were prepared with a scale ratio of 1:3. A quasi-static cyclic loading pattern was applied to the control bare and infilled steel frames, and their behavior was investigated both experimentally and analytically using SAP2000 and ABAQUS finite element software. First, five identical bare steel frame specimens were prepared and one of them was tested as a control specimen, and its rigidity and cyclic behavior was determined experimentally. Then, two sandwich panel specimens were prepared by connecting sandwich panels in the second and third bare steel frames using appropriate connections. The fourth specimen had only a single steel plate infill. Finally, the fifth specimen was prepared by removing the polyurethane material from inside the sandwich panel and only steel plates were attached to both faces of the frame. This way, it was possible to compare the effect of the polyurethane material inside the sandwich panel and the corrugated steel plate on the overall system behavior. In all specimens, the infill plates were fastened to the frame connection profiles using self-drilling screws and the responses of the specimens were compared in terms of their maximum load capacity, initial stiffness, ductility and energy dissipation capacity values under cyclic loading. The experimental and analytical investigations showed that, similarly to steel plate infills, the specimens with sandwich panels also behaved in a ductile manner with relatively lower load and energy dissipation capacities. Results of the strip model and the finite element model analyses were then compared with the experimental results and they were both found to be in good agreement.

Effect of infill walls on mechanisms of steel frames against progressive collapse

In this study, the effect of masonry infill walls on the progressive collapse mechanisms of steel frames is investigated. Three two-story by four-bay steel frames are designed: a bare frame, frame with full-height infill walls, and frame with partial infill walls. The applied vertical load, horizontal displacement, failure modes, stress development, and load redistribution mechanisms are investigated under center column pushdown scenarios. The influences of critical material properties and opening dimensions of partial infill walls are also investigated in this study. The results indicate that masonry infill walls significantly enhance the maximum applied vertical load and initial stiffness; however, they decrease the ductility and can alter the failure modes of the steel frames. The outward movement of the steel frames is a result of the diagonal compressive actions of the infill walls, and the changes in the bending positions of beams are a result of the bracing effects of the infill walls. The mortar joints and opening dimensions significantly influence the progressive collapse performance of infilled steel frames. In addition, different modeling strategies for masonry infill walls are developed and compared. Finally, a preliminary design procedure adopting masonry infill walls to protect the steel frames against progressive collapse is proposed.

Multi-bay and pinned connection steel infilled frames; an experimental and numerical study

The equivalent diagonal strut is one of the most prevalent approaches to model the infill panels recommended by many seismic guidelines. Previous studies have revealed that the rigidity of frame connections affects the behavior of the infill frames, but this matter is not considered in the macro modeling of the infill panels. Further, use of the same equivalent struts in the multi-bay infilled frame is questionable, while, the previous researches have suggested that the strength and stiffness of double-bay infill panels are not twice as large as those of a single-bay one. Here, an experimental program has been conducted to explore the effect of connection rigidity and number of bays on the behavior of infilled steel frames. Five specimens including one bare frame, two infilled rigid connection frames, and two infilled pinned connection frames were tested under in-plane lateral loading excitation. Considering the results of experimental tests, a series of parametric analyses have been conducted on the finite element models. The results indicated that the strength and stiffness of the infill panel in the pinned connection frames were less than those in the rigid connection frames. Therefore, a new equivalent strut model was proposed to model the infills in the pinned connection frames. In addition, it was observed that the influence of infill panels in the multi-bay infill frames had a direct relationship with the number of bays. In other words, the properties of equivalent struts do not vary with the increase in the bay numbers in the infilled frames.

Estimating the local and global effects of infills on steel frames by an improved macro-model

Masonry infill panels change the seismic behavior and internal forces of surrounding frames and should be considered in analysis and design phases. Single equivalent strut model, the most common strut model, does not address the internal forces and therefore the multi-strut models are preferred. In this paper, the previously proposed three-strut model (model PD) has been improved to represent a more reliable prediction of both local and global infill effects. For this, an in-depth finite element sensitivity analysis is performed. It is shown that the new model estimates the bending moment and shear force distribution and predicts the stiffness and strength of the infilled steel frames more accurately than previously proposed models in the literature. Properties of the nonlinear hysteretic behavior of infilled frames including stiffness degradation and strength deterioration can also be determined precisely. Finally, the macro-model is further developed to capture the global seismic response and element force distribution of frames with a soft first story.

Cyclic behaviour of infilled steel frames with different beam-to-column connection types

Although numerous researchers demonstrated the significant difference in performance between the various beam-to-column connection types, most of the previous studies in the area of infilled steel frames focused on the behaviour of frames with welded connections. Therefore, there is a need for conducting studies on infilled steel frames with other common connection types (extended endplate with and without rib stiffeners, flush endplate and shear connections). In this paper, firstly, a two-dimensional finite-element model simulating the cyclic response of infilled steel frames was presented. The infill-frame interaction, as well as the interactions between connections' components, were properly modelled. Using the previously-validated model, a parametric study on infilled steel frames with five different beam-to-column connection types, under cyclic loading, was carried out. Several parameters, including infill material, fracture energy of masonry and infill thickness, were investigated. The results showed that the infilled frames with welded connections had the highest initial stiffness and load-carrying capacity. However, the infilled frames with extended endplate connections (without rib stiffeners) showed the greatest energy dissipation capacity and about 96% of the load-carrying capacity of frames with welded connections which indicates that this type of connection could have the best performance among the studied connection types. Finally, a simplified analytical model for estimating the stiffness and strength of infilled steel frames (with different beam-to-column connection types) subjected to lateral cyclic loading, was suggested.

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.

An Experimental Investigation on the Ultimate Strength of Partially Infilled: Braced Steel Frames

Infilled walls are usually, considered as non-structural elements. However, these walls are effective in carrying lateral loads. In this regard, an experimental investigation was planned and conducted to study the effect of braced and partially infilled steel frames with cement mortar and concrete in comparison to the bare frames. All these frames were tested up to collapse and subjected only to horizontal loads to obtain an effective and possible solution for soft storey which are generally not infilled. In comparison to bare steel frames, partially infilled frames have an increase of lateral load capacity by 45–60%. Central bracing is more effective than that of the corner bracing. For the same load partially infilled frames have significantly less deflection than that of the bare frames. A reduced load factor is suggested for the design of soft storey columns with the partial infills. A mathematical model has been proposed to calculate the theoretical ultimate load for the braced, cement mortar and concrete partial infilled frames.

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.