Effect of Bracing Systems on Fire-Induced Progressive Collapse of Steel Structures Using OpenSees (original) (raw)
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The collapse behaviour of braced steel frames exposed to fire
2011
Progressive collapse mechanisms of braced two-dimensional steel-framed structures, subjected to fire heating, are investigated using a robust static-dynamic procedure developed by the authors. 20 cases have been analysed to provide a comprehensive view of the mechanisms of progressive collapse for these frames, with different bracing systems under different fire conditions. The influences of stiffness and strength of the bracing systems are also analysed. The results indicate that the pull-in of columns is one of the main factors which generate progressive collapse. Horizontal "hat truss" bracing systems have limited capacity to avoid pull-in of columns supporting the heated floor, although they can directly redistribute the vertical load lost by buckling columns to adjacent columns. On the other hand, vertical bracing systems have the effect, not only of increasing the lateral restraint of the frame, which reduces the pull-in of the columns, but also of effectively preventing the collapse progressing from local to global. Stronger vertical bracing systems can redistribute load from a buckled column to its surrounding structural members. Frames with a combined hat and vertical bracing system can be designed to enhance the capability of the frame as much as possible to prevent progressive collapse when a heated column buckles.
Civil and Environmental Engineering Reports
The progressive collapse phenomenon refers to a chain of damages in a structure where all or a large part of the structure is destroyed by an initial local collapse in it, which can lead to very disastrous results. Therefore, the prevention of progressive collapse has become a necessary action in the design and analysis of buildings and it is vital to investigate this topic more accurately. This study aims to present a proposed pattern in the configuration of braces at the height of a high-rise steel building for reducing the probability of progressive collapse. In this regard, the vertical displacement of 18-story structure with four scenarios of column removal and five concentric bracing patterns including V, Inverted V, X, discontinuous X-bracing at height, and a combination of Xbracing in the side spans and discontinuous X-bracing at height in the middle spans are investigated and compared. In this study, the Alternative Path Method (APM) is used based on the GSA guideline for t...
Effect of Steel Bracing in Progressive Collapse of Multi Storey RC Buildings
International Journal of Recent Technology and Engineering (IJRTE), 2019
Rapid increase in manmade and natural disasters can lead to structural instability which triggers the partial or complete collapse of the building. These manmade disasters include gas cylinder explosion or terrorist attack or instant removal of the primary structural element which leads to the progressive collapse of the building. To avoid the progressive collapse of building due to man-made disasters, incorporate the mechanism which resists the man-made disaster while the design for existing or newly constructing building. In this paper, an attempt is made to understand the effect of with and without providing steel bracing at various positions column removal in multi-storey building one at a time as per General Service Administration and Unified facilities criteria codes. The propagation of progressive collapse with and without the effect of steel bracing is studied in this paper. A seven-storey RC building is modelled and analysed for various column removal scenarios in SAP 2000 ...
Progressive Collapse Mechanisms of Steel Frames Exposed to Fire
Advances in Structural Engineering, 2014
OpenSees is an open-source object-oriented software framework developed at UC Berekeley. The OpenSees framework has been recently extended to deal with structural behavior under fire conditions. This paper summaries the key work done for this extension and focuses on the application of the developed OpenSees to study the fire-induced progressive collapse mechanisms of steel structures. The implicit dynamic analysis method (Newmark method) is applied and the influences of the load ratios, beam sizes and fire scenarios on the collapse behavior of frames are investigated. Single-compartment fire scenarios in the central bay and edge bay are considered, respectively. A total of four collapse mechanisms of steel frames are proposed by varying the three influencing factors. Most of the collapse of steel frames is triggered by the buckling of the heated columns. The thermal expansion of heated beams at early heating stage and their catenary action at high temperature have great influences ...
Progressive Collapse Prevention of Steel Frames with Shear Connections
This Steel Technical Information and Product Services (Steel TIPS) report provides information and technologies that can be used to protect steel building structures against progressive collapse in the event of removal of a column. Chapter 1 provides general information on progressive collapse of steel building structures. Chapter 2 provides information on progressive collapse behavior of steel frames with shear connections. Design guidelines are provided, and a numerical example demonstrates application of the guideline. Chapter 3 discusses the tests performed on the exterior frame of a full-size test structure where the beam-to-column connections were bolted seat angles with an additional bolted single angle connecting the web of the girders to the columns. The tests consisted of removing the middle column of the exterior frame and pushing the joint at the top of the removed column down 19, 24, and 35 inches to measure the strength, stiffness, and ductility of the structure as well as the connections. The steel frame with shear connections showed considerable resistance to progressive collapse after removal of a column. This was primarily due to the development of catenary force in the beams that were connected to the top of the removed column and to a lesser extent to membrane (catenary) action of the steel deck of the floors adjacent to the area of collapse. Chapter 4 discusses the research project conducted to investigate the use of steel cables to prevent progressive collapse of new steel building structures and develop design recommendations. The tests showed that the use of cables would increase progressive collapse resistance of the steel structures significantly. Chapter 5 focuses on the results of progressive collapse tests done on the exterior frame of the test structure where the beam-to-column connections were typical shear tab (single plate) shear connections. The tests were repeated adding steel cables to the structure to investigate the feasibility of using steel cables as a retrofit measure to prevent progressive collapse of the existing steel building structures with only shear connections. These tests found that the specimen with shear- tab connections alone (without the cables) had considerable strength after removal of the column and was able to resist design gravity loads primarily because of the catenary tension force developed in the girders that were connected to the removed column as well as due to the additional catenary (membrane) force developed in the steel deck of the floor. The addition of the cable, as a retrofit measure, was also very efficient in adding strength to the progressive collapse resistance of the existing structure.
IJERT-A Study On Bracing Systems On High Rise Steel Structures
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/a-study-on-bracing-systems-on-high-rise-steel-structures https://www.ijert.org/research/a-study-on-bracing-systems-on-high-rise-steel-structures-IJERTV2IS70765.pdf The major concern in the design of multi-storeyed steel building is to have good lateral load resisting system along with gravity load system because it also governs the design. This paper is presented to show the effect of different types of bracing systems in multi storied steel buildings. For this purpose the G+15 stories steel building models is used with same configuration and different bracing systems such as Single-Diagonal, X bracing, Double X bracing, K bracing, V bracing is used. A commercial software package STAAD.Pro V8i is used for the analysis of steel buildings and different parameters are compared. The property of the section is used as per IS 800:2007 which incorporates Limit State Design philosophy.
Effect of Initial Local Failure Type on Steel Braced Frame Buildings against Progressive Collapse
International Journal of Engineering
In many studies, the alternative load path method (APM) has been used for progressive collapse analysis. In this method, one or several columns of the building are removed and the building response is investigated. This method ignores the initial local failure cause of building and this can affect the structural response. Investigation of ignoring the initial local failure cause of steel braced frames is the main purpose of this research. The variables include the type of progressive collapse investigation (ignoring the initial cause of failure or APM, considering blast loading and the heat caused by the fire as the initial causes of failure) and the location of the initial local failure in plan (outer and inner frame) and in floors (1st, 2nd and 3rd). 4-story braced steel buildings were simulated using ABAQUS software and the responses were compared using different methods. The most important results showed that the axial forces are very noticeable in the columns around the damaged site if the initial local failure caused by explosive loading; while these forces are ignored when APM is used. Therefore, due to this significant difference, if the design of a steel building is to be considered against progressive collapse, it is recommended to consider the initial local failure in order to make the appropriate design in accordance with it. Therefore, the initial loading type has a very significant effect on the structure response, and ignoring the initial local failure can lead to incorrect predictions of the structure response.
International Journal of Engineering
Ignoring the primary damage to structural components due to blast load or fire is the alternate load path (APM) method's weakness in progressive failure analysis. The new technique used in this study examines the structure's more realistic responses by considering the initial cause of the failure. Also, buckling-restrained braces (BRBs) are applied to diminish the potential for progressive failure in braced steel buildings. Variables include the type of primary local loading (APM, blast loading, and heat caused by fire), the position of column removal in the plan (inner and outer frame), the type of brace (BRB and CB), and the number of stories (3, 5, and 8 stories). The buildings were simulated using ABAQUS. The results showed that BRBs in steel buildings under blast load, compared to conventional braces, reduce the potential of progressive failure. The use of BRBs provides much more energy absorption than conventional bracing systems due to brace buckling prevention.
Behaviour of Concentrically Braced Steel Frames under Fire Loading
Scientia Iranica, 2021
Knowing how a steel structure behaves under fire loading is of vital importance, given a large number of events in recent years have proved the vulnerability of steel structures under this type of hazard. Older concentrically braced frames have been widely used in buildings, which had been formerly designed without observing seismic provisions and details. Although the vulnerability of this type of structural systems, here referred to as non-seismic braced frames, has been studied under earthquake loading before, its behaviour under fire loading has not been investigated yet. This paper investigated the behaviour of global and local responses of the mentioned structural system under various uniform fire scenarios. The heating and cooling phases of fire were taken into account for different building stories using the finite element method. The results of analyses showed that the braces buckled at high temperatures due to the large compressive axial forces and expansion of lateral constraints. This phenomenon led to the early loss of lateral resistance of stories, which, in turn, resulted in the failure of columns. Consequently, the underlying floor collapsed under fire. The analysis results contribute to a better understanding of the behaviour of steel braced frames under fire conditions.
Effects of Steel Braces on Robustness of Steel Frames against Progressive Collapse
Journal of Structural Engineering, 2021
External installation of steel braces is one of the effective approaches to increase the lateral load resistance of the steel moment-resisting frames. However, the effects of existence of steel braces on the robustness of steel moment-resisting frames to resist progressive collapse is still not clear as little study has been carried out. To fill this gap, in this paper, six multi-story steel moment-resisting subframes (three bare frames and three braced frames) were fabricated and tested. Test results indicated that the specimen with reduced beam section in the connection zone performed best among three types of connections, due to the guaranteed formation of plastic hinges at the location of reduced section and avoiding brittle fracture of weld at the connection. Experimental results proved that steel braces could increase the load resisting capacity by 45.1% and 83.9% of the frame with weld connection and end plate connection, respectively. As the gusset plate restricted the rotation of the plastic hinges in the second story of the braced frames with V-shaped bracing, which decreased its deformation capacity and degraded its catenary action capacity. Actually, the ultimate load of the braced frames with Vshaped bracing is only 87.5% of that of the counterpart without any braces. As the compressive braces were severe buckled before the displacement reached 0.4% of the beam span, it has little effects on yield load but increases the initial stiffness of the bare frames. Thus, majority of the benefits of the bracing system were attributed into the tensile braces. Moreover, the analytical results evaluated the differences in load resistance and development of load resisting mechanisms in different stories. Furthermore, the contribution of compressive and tensile braces was decomposed individually by analytical analysis.