Braced frame systems are broadly classified in two categories. The john hancock center is a braced tube structure. A frame whose centerline braces are offset from the intersection of the centerlines of the columns and beams explanation of eccentricbraced frame. Design of bracing connections in concentrically braced frames. Performance of steel structure with eccentric bracing system are found in terms of later displacement, story. The behavior of eccentric braced frame ebf is compared with conventional rc frame and inverted v bracing. Comparison of moment resisting, concentrically braced.
The system essentially combines the features of a moment frame and a concentrically braced frame, while minimising the disadvantages of each system. Eccentric bracings reduce the lateral stiffness of the system and improve the energy dissipation capacity. Eccentric braced frame system performance structures congress. Inelastic behavior of eccentric braces in steel structure seyed mehrdad nourbakhsh submitted to the institute of graduate studies and research in partial fulfillment of the requirements for the degree of master of science in civil engineering eastern mediterranean university december 2011. Certain commercial software, equipment, instruments, or materials may have been used. Push over analysis is carried out by varying the link size using computer programs, sap 2007 to understand their seismic performance. Naveen kumar minajagi2 1pg student 2professor 1,2vnec, shorapur, karnataka, india abstractthe main objective of this thesis is to perform an attempt to extract the following results and compare these. Seismic design of steel special concentrically braced frame systems. Eccentric braced frame and scbfs special concentric braced frame reduced by increasing in. Eccentric braced frame design for moderate seismic regions. Nist policy is to use the international system of units metric units in all its publications. Seismic behavior of chevron concentrically braced frames with. By providing eccentrically braced system in outrigger frame by varying the size of links and analyzing it.
Eccentric braced frame systementails braces positioned in the plane of the frame where one or both ends of the brace beams does not connects at the end points of. There are variations in the platform bracing pattern. An alternative system for eccentrically braced frames resisting. Design and analysis of eccentrically braced steel frames. Design of special concentric braced frames, michael l. Interaction between bracing system and moment resisting frame. Since the branding of eccentric bracing as a highseismic, highductility system in. Inelastic behavior of eccentric braces in steel structure. It is also evaluate the frame performance with two different heights and with different shear link lengths by. A guide for practicing engineers, gcr 1591734, nehrp. Inverted y shape eccentric braces have vertical steel shear link. The system essentially combines the features of a moment frame and a concentrically braced frame, while minimising the disadvantages of. Seismic design of steel buckling restrained braced frames. A jacket structure is a welded tubular space frame consisting of vertical or battered legs supported by a lateral bracing system.
Members in a braced frame are not allowed to sway laterally which can be done using shear wall or a diagonal steel sections, similar to a truss. Eccentrically braced frames are a ductile, braced frame system that provides alternatives. During severe earthquakes, the inelastic action of the eccentrically braced frame ebf system is intended to be confined to the eccentric shear and momentlink elements. Jun 25, 2017 well, to start with, response reduction factors are not calculated parameters. To identify the behavior and performance of the eccentric bracing frame with the sma devices, the numerical models of the abovedescribed frames are analyzed by means of nonlinear static pushover analysis, timehistory dynamic analysis and seismic damage analysis, using the opensees program. T he bucklingrestrained bracedframe brbf is a relatively new type of concentrically braced frame system. Structural behavior of steel building with concentric and. Introduction steel braced frame is one of the structural systems used to resist lateral loads in multistoried. Knee braced steel frame had excellent ductility and lateral stiffness. Design and analysis of eccentrically braced steel frames with. The purpose of this study is to evaluate the performance of the structure with the. This braced tube can also use for retrofitting of old r. Performance of high rise steel frame with different type of bracing and without bracing waghmare a. A study on dynamic analysis of steel structure with eccentric bracing systems praveenkumar kattimani1 prof.
The structural analysis program sap2000 is a software package from computers and structures, which is based on the. Eccentrically braced steel frames are structures used to resist lateral loads as. Comparative study and seismic analysis of a multistorey. It is found from the analysis in software, the type of bracing, location of bracing, bracing stiffness and bracing.
Members in a braced frame are designed to work in tension and compression, similar to a truss. A study on dynamic analysis of steel structure with eccentric bracing. Three sets of ebf specimen were analysed by the merit of sap2000 v9. Eccentric brace frame, concentric brace frame, linear dynamic analysis. Braced frame models are efficient means to show ductile performance of the structure, and they provide effective means of lateral load resistance system. Certain commercial software, equipment, instruments, or materials may have been used in the preparation. For all four type of seismic zones least total weight braced frames ebf for all three types of storey level frames. Note that aisc requires ebf columns to remain elastic. Although eccentrically braced frames ebfs have a wellestablished reputation as highductility systems and have the potential to offer costeffective solutions. Although eccentrically braced frames ebfs have a wellestablished reputation as highductility systems and have the potential to offer costeffective solutions in moderate seismic regions, their. Steel bracings are lateral load resisting system used in seismic region. Each group consist of four types of steel eccentric braced frames such as inverted v braced frame, diagonally braced frame, chevron braced frame v braced frames, zipper type frame, one concentricallyx braced frame and one normal moment resisting frame.
Eccentric braced frame and scbfs special concentric braced frame reduced by increasing in pga values. Comparison of the behavior of steel structures with concentric and. Structural behavior of steel building with concentric and eccentric bracing. Hooshangi faculty of civil and environmental engineering, shiraz university of technology, shiraz, p. Evaluating seismic efficiency of combination of bracing for. In eccentrically braced frames, a distance is either created.
The system, which on the whole performed very well during the 20102011 christchurch earthquake series, relies on yielding at the link beam between braces to dissipate seismic energy. Pdf eccentric braced frame design for moderate seismic regions. The key components of the ebf system are shown in figure 1. A guide for practicing engineers concentrically braced frames cbfs are a class of structures resisting lateral loads through a vertical concentric truss system, the axes of the members aligning concentrically at the joints.
So for a new design you would not have a defined rfactor value and would have to provide analytical and test data to substantiate the system s performance. Eccentricbraced frame article about eccentricbraced. Seismic behavior of chevron concentrically braced frames with weak beams s. The other members of the frame show high axial forces, smaller shear and smaller moment relative to internal link forces. To estimate the performance of frames and the formation quality of plastic hinges, life safety acceptance criteria was selected. Fig 3 general arrangement drawing for a typical floor for the shear wall system dual frame wall system it is a structural system which provides support for gravity loads, and resistance to lateral loads is provided by a specially detailed momentresisting frame and shear walls or braced frames in the dual system, both frames. Why does an eccentric braced frame system have a higher. Seismic behavior of reinforced concrete frame with. Performance of each frame is carried out and studied the comparatively through time history analysis. Concentric bracings, invertedv braces, pushover analysis, steel frame, x braces. For 3 and 6 storey frame concentrically braced frames cbf shows maximum weight and for 9 storey frame moment resisting frames mrf.
If you are using eccentric braced frames where the brace work point does not line up with both the column and beam centerlines, then you have to determine the displacement of the frame to be able to determine whether it is considered braced or not. Pdf eccentric braced frame system performance researchgate. Eccentrically braced frames ebfs are known for their attractive combination of high elastic stiffness and superior inelastic performance characteristics aisc 2005. Design of bucklingrestrained braced frames by rafael sabelli, s. These analytical studies have been performed by sap2000v14. There are three types of bracing system 1 concentric bracing system 2 eccentric bracing system. Performance of each frame had been studied using nonlinear static analysis and nonlinear time history analysis for various parameters such as displacement and stiffness. Effect of link on eccentrically braced frames 37 also figures 2,4 show that links generally exhibit very high shear, which is constant along the link length, and very large bending moments at the link ends. Introduction recent discussions related to the seismic performance of lowductility steel systems designed for moderate seismic regions have generated new interest in the costeffective design of ductile systems for such regions.
Advantage of eccentric bracing over concentric bracing. Sep 06, 2016 members in a braced frame are designed to work in tension and compression, similar to a truss. The eccentrically braced frame ebf system has not been optimized. Comparing the results of braced frame bf1 and unbraced frame ubf1 shows a considerable improvement in the stiffness of dual system. The lateral system consists of concentrically braced frames in both directions. Advantage of eccentric bracing over concentric bracing eccentrically braced frames can provide two distinct benefits. Since 1993, asce 7 has recognized ebfs as high ductility systems, assigning them. A bracing system improves the seismic performance of the frame by increasing its lateral stiffness and capacity. Assessment of first generation performance based seismic design methods for new steel buildings.
Braced frames are a common seismic lateral force resisting system used in steel. Although eccentrically braced frames ebfs have a wellestablished reputation as highductility systems and have the potential to offer. Seismic behavior of reinforced concrete frame with eccentric. Study of eccentrically braced outrigger frame under. This system transfers the horizontal load acting on the platforms to the piles. The ductile behavior of eccentrically braced frame is highly desirable for structures. The lateral stiffness of the system depends upon the flexural stiffness property o the beams and columns, thus reducing the lateral stiffness of the frame.
Bucklingrestrained braced frame under construction. Improvement of the seismic performance of the resistant. Bracing system a braced frame is a structural system which is designed primarily to resist wind and earthquake forces. It is inferred that the effect of a provision of bracing will increase the strength of the steel frames and roof displacement undergone by the frame gets reduced considerably in braced frame.
Interaction between bracing system and moment resisting. To oppose seismic loads, supported steel frames have numerous propping frameworks, for example, concentric bracing system, eccentric bracing system, knee bracing system and mega bracing. Braced frames are almost always composed of steel members. The overall displacement and inter storey drift of the structure can effectively controlled by adopting braced frame models. Evaluating seismic efficiency of combination of bracing. Development and research of eccentrically braced frames. Braced frames are a very common form of construction, being economic to construct and simple to analyse.
Performance analysis of different concentric braced frame. Comparative study and seismic analysis of a multistorey steel. Bracing system, concentric and eccentric bracing, lateral storey displacement, storey drift. A study on dynamic analysis of steel structure with eccentric. If you are using full concentric diagonal bracing, then yes you have braced frames.
Pdf recent discussions related to the seismic performance of lowductility steel. Swetha sunil 16 2017 it focuses on seismic study of reinforced concrete building with different bracing system by changing the height of the system using response spectrum analysis. Eccentric braced frame design for moderate seismic regions author. Seismic design of steel special concentrically braced frame. Assess the performance of different types of eccentrically braced frames by performing seismic analysis over the structure. Honeck 5 notation definition overstrength and global ductility capacity of lateral force resisting system table 16n or 16p ubc, 1997 r f ratio of the expected steel tensile strength to the minimum specified tensile strength f. Effect of concentric and eccentric type of bracings on. Steel bracing was an effective and economical solution for resisting lateral forces in a framed structure. Seismic performance assessment of different types of. Performance of high rise steel frame with different type.
Sep 28, 2015 by providing eccentrically braced system in outrigger frame by varying the size of links and analyzing it. Both ends of the brace beams connects at the end points of other framing members to form a truss, creating a stir frame. Although eccentrically braced frames ebfs have a wellestablished reputation as highductility systems and have the potential to offer costeffective solutions in moderate seismic regions, their system performance has not been widely discussed. Bracing system, concentric and eccentric bracing, lateral storey displacement, storey drift 1 introduction steel braced frame is one of the structural systems used to resist lateral loads in multistoried buildings. Push over analysis is carried out by varying the link size using computer programs, sap. Eccentric braced frame system performance structures. A braced frame is a structural system designed to resist wind and earthquake forces. Assessment of first generation performancebased seismic design methods for new steel buildings. For this reason design and performance analyses were carried out on 4.
They are unique to every building just like damping and the codes only provide with conservative upper limit estimates. Eccentric bracings reduce the lateral stiffness of the. The function of the jacket is to support the topside facilities, provide supports for conductors, risers, and other appurtenances, and serve as a template for the foundation system. Inelastic response of ductile eccentrically braced frames. Foundation in january 2009, tierney geotechnical engineering, pc tge provided a subsurface exploration and. Implementation of performancebased seismic design nist 2009a. There are two types of bracing systems 1 concentric bracing system and 2 eccentric bracing system 1 concentrically braced frames cbfs are a class of structures resisting lateral loads through a vertical concentric truss system, the axes of the members aligning concentrically at the joints. By increasing the pgas the maximum base shear increases too. The variation of performance with change in link length, height of the building was also considered in this study. So for a new design you would not have a defined rfactor value and would have to provide analytical and test data to substantiate the systems performance.
A study on dynamic analysis of steel structure with. Pro is the most popular structural engineering software product for 3d model generation, analysis and multimaterial design. X bracing is more effective than other bracing, base shear. Eccentric bracing consists of diagonal braces located in the plane of the frame where one or both ends of the brace do not join at the end points of other framing members. Development and research of eccentrically braced frames with. Concentric braced system cbfs eccentric braced frame ebfs a moment resisting frames mrfs. Seismic behavior of chevron concentrically braced frames. Performance based seismic design of braced composite multi. Seismic design of steel special concentrically braced.
Introduction bracing is an effective upgrading strategy to enhance the global stiffness and strength of steel frames. Concentric braced frame systems entails bracing members positioned in the plane of the frame. The elastic seismic response of an eccentrically braced frame is similar to that of a couple shear wall. Nist technical note 18633 assessment of first generation. The maximum base shear is increasing in scbf systems with increase in braced spans and reduced in order in scbf systems with decreasing braced spans. Performance of high rise steel frame with different type of. The primary focus of the material is on ductile detailing of steel structures for seismic resistance, rather than on calculation of lateral forces, dynamic analysis, or. The bracing system consists of vertical, horizontal, and diagonal tubular members connected to jacket legs forming a stiff truss system. Brbf use the ductility of steel more effectively than conventional braced frames, such as special concentrically braced frames scbf or. In this software, a plastic flexural hinge is modeled as a zerolength. Adding bracings is associated with increasing the stiffness, but some of this increasing stiffness can be caused by. Optimum performancebased design of eccentrically braced frames. Adding bracings is associated with increasing the stiffness, but some of this increasing stiffness can be caused by interaction between the frame and bracing system. Behavior of shear link of wf section with diagonal web.
Seismic design of steel bucklingrestrained braced frames. System performance staad is basic software for analysis. Steel bracing is economical, easy to erect, occupies less space and has flexibility to. A braced frame is a structural system which is designed primarily to resist wind and earthquake forces. This series of powerpoint presentations covers the fundamentals of the design of seismicresistant steel building structures. Economy comes from the inexpensive, nominally pinned connections between beams and columns. For 3 and 6 storey frame concentrically braced frames cbf shows maximum weight and for 9. The performance of rc frame with inverted eccentric bracing is evaluated in terms of energy absorption capacity, stiffness of frame and ductility. And they do not qualify as eccentric braced frames either because the ebf links are defined as portions of the beams.
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