Masonry Infilled Steel Frames Research Articles

Distinct Element Modeling of Masonry-Infilled Steel Frames with Openings

Numerical analysis of masonry-infilled steel frames (MISFs) is one of the greatest challenges faced by struc- tural engineers. This difficulty results from the presence of joints as the source of discontinuities and nonlinearities as well as the interaction of frame-infill panel. In spite of many studies performed on numerical modeling of solid MISFs, there are few studies on MISFs with openings. A 2D numerical model using the specialized distinct element software UDEC (2004) for the pushover analysis of MISFs with openings is developed. In this model, large displacements and rotations between masonry bricks are taken into account. A comparison between the results of distinct element modeling and the experimental results available in the literature showed a good correlation between them. Furthermore, It was found that the model has the capability to predict lateral load capacity, joint cracking patterns and explore the possible failure modes of MISFs with openings. Steel framed buildings are usually infilled with masonry panels as partition and surrounding walls. The composite steel-masonry framed building is called masonry-infilled steel frame (MISF) which has high lateral stiffness and load capacity. Under severe lateral forces, the surrounding frame interacts with the infill masonry panel increasing lateral stiffness and load capacity of the MISF. This is because, the frame and masonry infill panel deform in a bending and shear modes, respectively. In spite of the frame-infill panel interaction, the unexpected effects of infill panels are not usually taken into account in the analysis and design of such frames. Ignoring the structural effects of infill panels may results in wrong estimation of lateral stiffness, capacity and ductility of these frames. Since 1950's, many numerical and experimental re-

Performance Based Analysis of a Historic High Rise Building

The authors employed high-fidelity computer modeling to analyze the probable seismic performance of an ex- isting high-rise, steel frame building with unreinforced masonry infill walls in downtown San Francisco. The Pacific Telephone and Telegraph Co. building at 138 New Montgomery is a 26-story, historic office building. Constructed in 1926 this building was the tallest building in the western United States for a long period of time. The building's structural system comprises perimeter unreinforced brick masonry walls infilled within and supported by a steel frame. We con- ducted our analysis in support of the building's conversion to residential occupancy. As a result of the occupancy conver- sion, along with associated architectural modifications throughout the building, Section 3403 of the San Francisco Build- ing Code (SFBC) requires a seismic upgrade such that the building has a code-compliant lateral-force resisting system with no less than 75% of the strength specified by the code for new buildings of similar occupancy and structural system. Since the existing building does not have a lateral force-resisting system recognized by current U.S. codes, compliance with the prescriptive requirements would have required expensive retrofits. Instead, the authors employed a performance- based approach using the existing masonry infilled steel frame for a substantive portion of the building's seismic resis- tance, together with a new supplemental interior reinforced concrete shear wall. Rather than design to achieve code- specified strength limits, we used nonlinear response history analysis to demonstrate acceptable behavior under Maximum Considered Earthquake (MCE) shaking. Detailed modeling of the interaction between the masonry infill and steel frame is a key component of this approach.

Experimental study of concrete masonry infills bounded by steel frames

An experimental program was conducted to investigate the behavior and capacity of concrete masonry infills bounded by steel frames. Ten concrete masonry infilled steel frame specimens as well as one bare frame specimen were tested to failure under an in-plane lateral loading applied at the frame top beam level. The parameters considered in this paper included the aspect ratio, extent of grouting, opening of the infill and frame-to-infill stiffness ratio as reflected by varying the orientation of the frame column. The effect of each parameter on the failure mode, ultimate load, and stiffness of specimens is presented and discussed. Test results were then used to assess the efficacy of equations for the design of masonry infills suggested in the current design standards of both Canada and United States. The results show that the current Canadian design guidelines provide a markedly conservative design of masonry infills whereas the American design standard gives an improved estimate of infill stiffness and ...

Investigation on the behavior of brick-infilled steel frames with openings, experimental and analytical approaches

This article deals with an experimental program to investigate the in-plane seismic behavior of steel frames with clay brick masonry infills having openings. Six large-scale, single-story, single-bay frame specimens were tested under in-plane cyclic loading applied at roof level. The infill panel specimens included masonry infills having central openings of various dimensions. The experimental results indicate that infill panels with and without openings can improve the seismic performance of steel frames and the amount of cumulative dissipated energy of the infill panels with openings, at ultimate state are almost identical. Furthermore, contrary to the literature, the results indicate that infilled frames with openings are not always more ductile than the ones with solid infill. It seems that the ductility of such frames depends on the failure mode of infill piers. This experimental investigation shows that infilled frames with openings experienced pier diagonal tension or toe crushing failure and have smaller ductility factors than those frames with solid infill. Furthermore, a simple analytical method is proposed to estimate the maximum shear capacity of masonry infilled steel frames with window and door openings.

Nonlinear analysis of masonry-infilled steel frames with openings using discrete element method

Nonlinear numerical modeling of masonry-infilled frames is one of the most complicated problems in structural engineering field. This complexity is attributed to the existence of joints as the major source of weakness and material nonlinearities as well as the infill-frame interaction which cannot be properly modeled using the traditional finite element methods. Although there are many numerical studies available on solid masonry-infilled steel frames’ behavior, however, few researches have been conducted on infilled frames with openings. In this paper a two-dimensional numerical model using the specialized discrete element method (DEM) software UDEC (2004) is developed for the nonlinear static analysis of masonry-infilled steel frames with openings subjected to in-plane monotonic loading. In this model, large displacements and rotations between masonry blocks are taken into account. It was found that the model can be used confidently to predict collapse load, joint cracking patterns and explore the possible failure modes of masonry-infilled steel frames with a given location for openings and relative area. Results from the numerical modeling and previous experimental studies found in the literature are compared which indicate a good correlation between them. Furthermore, a nonlinear analysis was performed to investigate the effect of door frame on lateral load capacity and stiffness of infilled frames with a central opening.

Neural network based modeling of infilled steel frames

A neural network based model is developed for the structural analysis of masonry infilled steel frames, which can account for the non-linearities in the material properties and structural behaviour. Using the data available from the analytical methods, an ANN model with input parameters consisting of dimension of frame, size of infill, properties of steel and infill was developed. It was found to be acceptable in predicting the failure modes of infilled frames and corresponding failure load subject to limitations in the training data and the predicted results are tested using the available experimental results. The study shows the importance of validating the ANN models in simulating structural behaviour especially when the data are limited. The ANN model was also compared with the available experimental results and was found to perform well.

Hazard mitigation and strengthening of unreinforced masonry walls using composites

An experimental investigation was conducted to study the behavior of unreinforced masonry (URM) walls retrofitted with composite laminates. The first testing phase included testing 24 URM assemblages under different stress conditions present in masonry walls. Tests included prisms loaded in compression normal and parallel to bed joints, diagonal tension specimens, and specimens loaded under joint shear. In the second testing phase, five masonry-infilled steel frames were tested with and without retrofit. The composite laminates increased the stiffness and strength and enhanced the post-peak behavior by stabilizing the masonry walls and preventing their out-of-plane spalling. Tests reported in this paper demonstrate the efficiency of composite laminates in improving the deformation capacity of URM, containing the hazardous URM damage, preventing catastrophic failure and maintaining the wall integrity even after significant structural damage.

Analysis of masonry infilled steel frames with seismic isolator subframes

The Seismic Infill Wall Isolator Subframe (SIWIS) system is developed for use in building frames with masonry infill walls in order to prevent damage to columns or infill walls and minimize life-safety hazards during potentially damaging earthquakes. The SIWIS system, which consists of two vertical and one horizontal sandwiched light-gauge steel studs with “rigid-brittle” elements in the vertical members, is designed to allow infill wall–frame interaction under wind loading and minor-to-moderate earthquakes for reduced building drift but to disengage them under damaging events. The SIWIS system acts as a “sacrificial” element just like a “fuse” to save the infill wall and frame from failure. Nonlinear finite element models for two cases, a single-bay, single-story steel frame and a two-bay, three-story steel frame, in three forms including bare frame and infilled frame with and without SIWIS system were performed to develop an understanding of how the system responds to lateral loading. Analysis results show that the concept of SIWIS system works in providing initially high stiffness followed by an isolation of infill wall from interaction with the confining frame. Practical design guidelines are proposed and applied to an eight-story office building.

Seismic Retrofit of Concrete-Masonry-Infilled Steel Frames with Glass Fiber-Reinforced Polymer Laminates

An experimental investigation was conducted to study the effect of retrofitting unreinforced concrete masonry-infilled steel frame structures using glass fiber-reinforced polymer (GFRP) laminates. The study focuses on enhancing the in-plane seismic behavior of unreinforced masonry (URM) infill walls when subjected to displacement controlled cyclic loading. Six full-scale single-story single-bay steel frames with different infill configurations were tested. The retrofitting technique using GFRP laminates aimed at creating an engineered infill wall with a well defined failure mode and a stable postpeak behavior as well as containing the hazardous URM damage and preventing catastrophic failure. Results demonstrated the effectiveness of the GFRP laminates in preventing both shear and tension cracking by supplying the required tensile and shear strength. The GFRP laminates also increased the lateral load capacity and enhanced the postpeak behavior by stabilizing the masonry face shells and preventing their out-of-plane spalling. Supporting the face shells against out-of-plane spalling, allowed the wall to carry more in-plane loads and prevented sudden drop in the load carrying capacity.

Lateral Load Behavior of Masonry Infilled Steel Frames with Repair and Retrofit

This paper introduces a new analytical approach for the evaluation of shear strength and cracking pattern of masonry infill panels. This method is based on minimizing the factor of safety with reference to the failure surfaces. This approach can also be used to determine the shear strength parameters and the modulus of elasticity of brickwork material. The paper also presents the results of experimental and analytical investigations on repaired and strengthened brick infilled steel frames. Two main repair techniques were examined in which the corner material is replaced with concrete or a concrete cover is placed on the panel. Both experiment and analysis have confirmed the efficiency and adequacy of these techniques.

Three-Strut Model for Concrete Masonry-Infilled Steel Frames

Masonry infill panels in framed structures have been long known to affect strength, stiffness, and ductility of the composite structure. In seismic areas, ignoring the composite action is not always on the safe side, since the interaction between the panel and the frame under lateral loads dramatically changes the stiffness and the dynamic characteristics of the composite structure, and hence, its response to seismic loads. This study presents a simple method of estimating the stiffness and the lateral load capacity of concrete masonry-infilled steel frames (CMISFs) failing in corner crushing mode, as well as the internal forces in the steel frame members. In this method, each masonry panel is replaced by three struts with force-deformation characteristics based on the orthotropic behavior of the masonry infill. A simplified steel frame model is also presented based on the documented modes of failure of the CMISF. The method can be easily computerized and included in nonlinear analysis and design of three...

A parametric study of masonry infilled steel frames

A previously developed computer model was used to investigate the effects of a wide range of parameters applicable to concrete block masonry infilled steel frames. Height to length panel aspect ratios were varied from 0.5 to 1.5 to reflect how other parameters were affected by these values. Eight different types of parameters were studied. The method of applying horizontal load was found to have little effect. Isolation gaps between panel and beam reduced both the stiffness and strength of the infilled frame. While panel-to-column ties generated an increase in peak load, local stress concentrations caused by the ties resulted in additional deterioration of the panel. Strength was found to vary with mortar joint bond strength, with the effects being more significant at higher aspect ratios. Increasing beam stiffness increased strength for low aspect ratio frames, and increasing column stiffness had a similar effect for high aspect ratio frames. Gravity loading was beneficial in increasing shear resistance up to a limit where it caused crushing of the masonry infill. The increases in strength of infilled frames were found to be disproportionate to increases in the strength of the masonry.Key words: masonry, steel, infill, frame, analytical, variables, shear, strength, deflection, interaction.

A parametric study of masonry infilled steel frames

A parametric study of masonry infilled steel frames

Masonry infilled steel frames subjected to dynamic load

Experimentally determined dynamic responses of ten scale models of masonry infilled steel frames were compared with the results of three simple analytical models. Effects investigated included stiffening and strengthening contribution of the masonry infill, degradation of the system, motion intensity, frame stiffness, and rotational joint rigidity at slab-to-column intersections. Tests on one-third scale models, subjected to sinusoidal motions, revealed that masonry infill markedly increases the dynamic strength and stiffness of the system. At weak-to-moderate motions (below 0.5 g), models exhibited a nonlinear response before the final failure, while strong motions accelerated the system degradation rate. Stiffer frames and rotationally rigid joints resulted in significantly increased system dynamic strength. A braced frame model wherein cross-bracing replaces the panel action adequately predicted linear and lower-region nonlinear responses of infilled frames with flexible column-to-slab rotational conditions. Satisfactory predictions of the linear response of framed walls with rigid column-to-slab rotational conditions were made with a single degree of freedom model. The third analytical model based on an equivalent strut technique was found to be unsatisfactory for predicting dynamic response of masonry infilled frames. Key words: masonry panel, steel frame, shear, dynamic, analytical, experimental.

Behaviour of masonry infilled steel frames

Masonry shear panels used as infilling in steel frames are investigated experimentally. Twenty-eight large-scale specimens were tested to ultimate panel strength under in-plane, horizontal loading applied at roof level. Of the parameters varied in the test series, interface conditions between panel edges and frame were found to significantly affect the strength and behaviour. Column-to-panel ties were found to be ineffective in increasing ultimate strength while initial stiffness was only marginally increased. A 20 mm gap between the upper edge of a panel and roof beam was particularly detrimental to the system shear capacity. While panel openings reduced initial major crack load, the same was not necessarily true for their effect on ultimate strength. Reinforced bond beams at one third and two thirds of the panel height forced initial major cracking to occur quite close to ultimate, which itself was only marginally increased. The lowest initial major cracking and ultimate loads were recorded for those specimens consisting of a panel in a hinge frame with a 20 mm gap between the upper edge of the panel and roof beam. Key words: masonry, infilled panel, steel frame, experimental, in-plane, behaviour, strength.