For all four type of seismic zones least total weight braced frames ebf for all three types of storey level frames. Comparing the results of braced frame bf1 and unbraced frame ubf1 shows a considerable improvement in the stiffness of dual system. 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. Inverted y shape eccentric braces have vertical steel shear link. Eccentric braced frame system performance structures congress.
Performance of each frame had been studied using nonlinear static analysis and nonlinear time history analysis for various parameters such as displacement and stiffness. Seismic design of steel special concentrically braced frame systems. Eccentric braced frame and scbfs special concentric braced frame reduced by increasing in pga values. Study of eccentrically braced outrigger frame under. An alternative system for eccentrically braced frames resisting. Structural behavior of steel building with concentric and. Development and research of eccentrically braced frames with. X bracing is more effective than other bracing, base shear. Although eccentrically braced frames ebfs have a wellestablished reputation as highductility systems and have the potential to offer.
Since 1993, asce 7 has recognized ebfs as high ductility systems, assigning them. 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. Members in a braced frame are designed to work in tension and compression, similar to a truss. The elastic seismic response of an eccentrically braced frame is similar to that of a couple shear wall. The other members of the frame show high axial forces, smaller shear and smaller moment relative to internal link forces. 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. 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. 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. Improvement of the seismic performance of the resistant. 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. The key components of the ebf system are shown in figure 1. Performance based seismic design of braced composite multi. Braced frames are almost always composed of steel members. Introduction steel structure can be designed using many methods.
Braced frames are a very common form of construction, being economic to construct and simple to analyse. A frame whose centerline braces are offset from the intersection of the centerlines of the columns and beams explanation of eccentricbraced frame. 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. Although eccentrically braced frames ebfs have a wellestablished reputation as highductility systems and have the potential to offer costeffective solutions.
Design and analysis of eccentrically braced steel frames. Braced frame systems are broadly classified in two categories. The structural analysis program sap2000 is a software package from computers and structures, which is based on the. A bracing system improves the seismic performance of the frame by increasing its lateral stiffness and capacity. Knee braced steel frame had excellent ductility and lateral stiffness. Evaluating seismic efficiency of combination of bracing for. Behavior of shear link of wf section with diagonal web. Introduction steel braced frame is one of the structural systems used to resist lateral loads in multistoried. Eccentricbraced frame article about eccentricbraced. Note that aisc requires ebf columns to remain elastic. Structural behavior of steel building with concentric and eccentric bracing. The bracing system consists of vertical, horizontal, and diagonal tubular members connected to jacket legs forming a stiff truss system. Study of eccentrically braced outrigger frame under seismic. The system essentially combines the features of a moment frame and a concentrically braced frame, while minimising the disadvantages of.
T he bucklingrestrained bracedframe brbf is a relatively new type of concentrically braced frame system. It is also evaluate the frame performance with two different heights and with different shear link lengths by. Performance of high rise steel frame with different type of bracing and without bracing waghmare a. 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. Design of bucklingrestrained braced frames by rafael sabelli, s.
Design of bracing connections in concentrically braced frames. The system essentially combines the features of a moment frame and a concentrically braced frame, while minimising the disadvantages of each system. 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. A study on dynamic analysis of steel structure with eccentric. Nist policy is to use the international system of units metric units in all its publications. Comparison of moment resisting, concentrically braced. Foundation in january 2009, tierney geotechnical engineering, pc tge provided a subsurface exploration and. 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.
The behavior of eccentric braced frame ebf is compared with conventional rc frame and inverted v bracing. Eccentric braced frame and scbfs special concentric braced frame reduced by increasing in. By providing eccentrically braced system in outrigger frame by varying the size of links and analyzing it. 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. Seismic behavior of reinforced concrete frame with. To estimate the performance of frames and the formation quality of plastic hinges, life safety acceptance criteria was selected.
Interaction between bracing system and moment resisting frame. Inelastic behavior of eccentric braces in steel structure. Braced frames are a common seismic lateral force resisting system used in steel. Assessment of first generation performance based seismic design methods for new steel buildings. 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. The lateral system consists of concentrically braced frames in both directions. 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. Hooshangi faculty of civil and environmental engineering, shiraz university of technology, shiraz, p. Pdf eccentric braced frame design for moderate seismic regions. Eccentric braced frame design for moderate seismic regions author.
A braced frame is a structural system designed 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. Bucklingrestrained braced frame under construction. This braced tube can also use for retrofitting of old r. The overall displacement and inter storey drift of the structure can effectively controlled by adopting braced frame models. This system transfers the horizontal load acting on the platforms to the piles. A study on dynamic analysis of steel structure with. 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. Comparative study and seismic analysis of a multistorey steel. It is found from the analysis in software, the type of bracing, location of bracing, bracing stiffness and bracing. Comparative study and seismic analysis of a multistorey. For 3 and 6 storey frame concentrically braced frames cbf shows maximum weight and for 9 storey frame moment resisting frames mrf.
For 3 and 6 storey frame concentrically braced frames cbf shows maximum weight and for 9. Performance of each frame is carried out and studied the comparatively through time history analysis. Performance analysis of different concentric braced frame. Inelastic response of ductile eccentrically braced frames. In this software, a plastic flexural hinge is modeled as a zerolength. Since the branding of eccentric bracing as a highseismic, highductility system in. Interaction between bracing system and moment resisting. The purpose of this study is to evaluate the performance of the structure with the. Comparison of the behavior of steel structures with concentric and. Eccentric brace frame, concentric brace frame, linear dynamic analysis. Eccentric bracings reduce the lateral stiffness of the. Bracing, which provides stability and resists lateral loads, may be from diagonal steel members or, from a concrete core.
In eccentrically braced frames, a distance is either created. Seismic design of steel special concentrically braced frame. Pdf recent discussions related to the seismic performance of lowductility steel. Seismic performance assessment of different types of. 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. Evaluating seismic efficiency of combination of bracing. Advantage of eccentric bracing over concentric bracing. Performance of high rise steel frame with different type. Design and analysis of eccentrically braced steel frames with.
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. Steel bracing was an effective and economical solution for resisting lateral forces in a framed structure. Introduction bracing is an effective upgrading strategy to enhance the global stiffness and strength of steel frames. Nist technical note 18633 assessment of first generation. Assessment of first generation performancebased seismic design methods for new steel buildings. If you are using full concentric diagonal bracing, then yes you have braced frames. 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. Concentric bracings, invertedv braces, pushover analysis, steel frame, x braces. Both ends of the brace beams connects at the end points of other framing members to form a truss, creating a stir frame. 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. Three sets of ebf specimen were analysed by the merit of sap2000 v9. 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.
Advantage of eccentric bracing over concentric bracing eccentrically braced frames can provide two distinct benefits. 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. 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. Steel bracing is economical, easy to erect, occupies less space and has flexibility to. For this reason design and performance analyses were carried out on 4. Braced frame models are efficient means to show ductile performance of the structure, and they provide effective means of lateral load resistance system.
Implementation of performancebased seismic design nist 2009a. Seismic behavior of chevron concentrically braced frames with. Design of special concentric braced frames, michael l. The performance of rc frame with inverted eccentric bracing is evaluated in terms of energy absorption capacity, stiffness of frame and ductility. By increasing the pgas the maximum base shear increases too. Assess the performance of different types of eccentrically braced frames by performing seismic analysis over the structure. Sep 28, 2015 by providing eccentrically braced system in outrigger frame by varying the size of links and analyzing it. Bracing system, concentric and eccentric bracing, lateral storey displacement, storey drift. A guide for practicing engineers, gcr 1591734, nehrp. 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.
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. Seismic design of steel special concentrically braced. Performance of steel structure with eccentric bracing system are found in terms of later displacement, story. And they do not qualify as eccentric braced frames either because the ebf links are defined as portions of the beams. Brbf use the ductility of steel more effectively than conventional braced frames, such as special concentrically braced frames scbf or. Push over analysis is carried out by varying the link size using computer programs, sap. They are unique to every building just like damping and the codes only provide with conservative upper limit estimates.
Eccentric braced frame system performance structures. Steel bracings are lateral load resisting system used in seismic region. To estimate the performance of frames and the formation quality of plastic. 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 variation of performance with change in link length, height of the building was also considered in this study. This series of powerpoint presentations covers the fundamentals of the design of seismicresistant steel building structures. Certain commercial software, equipment, instruments, or materials may have been used. A braced frame is a structural system which is designed primarily to resist wind and earthquake forces.
Bracing system a braced frame is a structural system which is designed primarily to resist wind and earthquake forces. Eccentrically braced frames are a ductile, braced frame system that provides alternatives. Performance of high rise steel frame with different type of. 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. A study on dynamic analysis of steel structure with eccentric bracing systems praveenkumar kattimani1 prof. Seismic design of steel buckling restrained braced frames. Eccentric bracings reduce the lateral stiffness of the system and improve the energy dissipation capacity. System performance staad is basic software for analysis. A jacket structure is a welded tubular space frame consisting of vertical or battered legs supported by a lateral bracing system. Why does an eccentric braced frame system have a higher. Jun 25, 2017 well, to start with, response reduction factors are not calculated parameters. Pdf eccentric braced frame system performance researchgate. Seismic behavior of chevron concentrically braced frames with weak beams s. Eccentric braced frame design for moderate seismic regions.
Adding bracings is associated with increasing the stiffness, but some of this increasing stiffness can be caused by. Concentric braced system cbfs eccentric braced frame ebfs a moment resisting frames mrfs. Well, to start with, response reduction factors are not calculated parameters. Concentric braced frame systems entails bracing members positioned in the plane of the frame. 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. Optimum performancebased design of eccentrically braced frames. The john hancock center is a braced tube structure. 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. The eccentrically braced frame ebf system has not been optimized. Push over analysis is carried out by varying the link size using computer programs, sap 2007 to understand their seismic performance. 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. Sep 06, 2016 members in a braced frame are designed to work in tension and compression, similar to a truss. Seismic behavior of reinforced concrete frame with eccentric.
Effect of concentric and eccentric type of bracings on. Development and research of eccentrically braced frames. Economy comes from the inexpensive, nominally pinned connections between beams and columns. Seismic design of steel bucklingrestrained braced frames. A study on dynamic analysis of steel structure with eccentric bracing. These analytical studies have been performed by sap2000v14. There are variations in the platform bracing pattern.
Seismic behavior of chevron concentrically braced frames. Certain commercial software, equipment, instruments, or materials may have been used in the preparation. There are three types of bracing system 1 concentric bracing system 2 eccentric bracing system. Pro is the most popular structural engineering software product for 3d model generation, analysis and multimaterial design. Eccentrically braced steel frames are structures used to resist lateral loads as. Eccentrically braced frames ebfs are known for their attractive combination of high elastic stiffness and superior inelastic performance characteristics aisc 2005.
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