The design examples are arranged with lrfd and asd designs presented side by side, for consistency with the. Seismic design special concentrically braced frames. A balanced design procedure for special concentrically braced. The structural design of tall and special buildings, 2218, 14221438. Seismic design of steel special concentrically braced frame. Tr maximum required tensile strength for connection design given in section of the aisc seismic provisions aisc 2005c, as the lesser of the following. The emphasis is detailing for seismic design categories sdc of d and higher which require special steel moment frames smf and special concentric braced frames scbf.
Seismic performance of concentric braced steel frames from pushover analysis madhusudan g. Special concentrically braced frames scbfs are among the most common steel. This study explores the possibility of improving the seismic response of concentrically braced frames cbfs by including friction connections at the end of the bracing members. Moghaddassi3 abstract this paper provides a designers view on asymmetric friction connections afc, its advantages and disadvantages, and how to consider its application in concentrically braced frames cbf. Special concentricallybraced frame scbf systems are a type.
Decades of research on the seismic behavior of braced frames has resulted in comprehensive design requirements. Two bracing configurations, chevron and xbracing over two stories, are considered for each braced frame. The eccentric connection to the frame means an eccentric brace transfers lateral forces via shear either to another brace or to a vertical column. But from these three mechanisms, optimum case for various. Seismic design of steel bucklingrestrained braced frames a guide for practicing engineers this guide addresses the seismic design of steel brbfs in typical building applications within regions of moderate to high seismic hazard, corresponding to seismic design categories sdc c through f as defined in asce 7. The comparison is based on the frame design for a two story office building located in henderson, nv.
Seismic performance of special concentrically braced. Analysis and design of chevron brace connections with flat. Seismic detailing of gusset plates for special concentrically braced. Element software has been used and the comparison between the performances of 1 bay x and inverted. Jun 19, 2016 about this lecture will cover the basics of the design of concentrically braced steel frames following u. Frames smf and special concentric braced frames scbf.
The connection design must account for these different. Typical shearmoment interaction diagram for wide flange sections. For 3 and 6 storey frame concentrically braced frames cbf shows maximum weight and for 9 storey frame moment resisting frames mrf. Moghadam and armin aziminejad, quantification of seismic performance factors for self. Lehman department of civil and environmental engineering, university of washington, seattle, wa 981952700, united states. Chapter 7 special concentric brace frame connection design.
In this paper, the role of exural capacity of beam in carrying this unbalanced force and consequently, seismic behavior of braced frame were investigated by nite element analysis. We used to estimate 10% of the total weight for connection material. A balanced design procedure for special concentrically braced frame connections charles w. Seismic performance of special concentric steel braced frames. In special concentrically braced frames scbfs the brace provides. When properly proportioned, eccentric braced frames may exhibit a more ductile characteristic and greater energy dissipation capabilities than a concentric braced frame in the same material. Special concentrically braced frames cbfs are widely used as efficient lateralload resisting systems in seismic regions. Seismic design of a concentrically braced frame civil. A stepbystep outline of the seismic design process, as well as the relevant capacity design principles, is presented.
Change the frame type to eccentrically brace frame. Despite the advantages of using concentrically braced frames, they may not perform satisfactorily in a severe seismic event. Hss connection solutions under seismic loading for. Seismic design parameters equivalent lateral force analysis threedimensional analysis drift check. Special concentrically braced frames scbfs, all the acronyms and symbols used in this paper are listed in the appendix table a. Balanced design procedure for special concentrically braced.
National earthquake hazards reduction program nehrp technical. Now you can export vertical diagonal brace connections and vertical chevron brace connections from risa3d into risaconnection as either ordinary concentric braced frames ocbf or special concentric braced frames scbf. Structural behavior of steel building with concentric and eccentric bracing. Cbfs are a common structural steel or composite system in areas of any seismicity. Advances in design requirements for buckling restrained. Design of bracing connections in concentrically braced frames. See post for information on how to model a seismic vertical brace connection in the stand alone version of risaconnection. This gives eor the benefit of using a value of 7 for response modification factor r7.
Seismic design study of concentrically braced frames with and. This lecture covers the basics of the design of concentrically braced steel frames following u. Special design and detailing rules for connections, beams, and columns. This location was chosen because of its moderately high seismicity. Performancebased plastic design method for steel concentric. Structural behavior of steel building with concentric and. All models were analyzed using a generalpurpose finiteelement software. The brb brace is placed in a concentric braced frame and becomes a bucklingrestrained braced frame brbf system. Seismic design and hybrid tests of a fullscale three. Design with asd and lrfd are based on the same nominal strength for each element so that the. A technology introduced in the late 1990s, it has been codified in just over 5 years and has been incorporated into over 500 buildings to date. The vertical component of bracing force should almost cancel out.
National science foundation american iron and steel institute reproduced by, national technical information service u. Structural steel design 69 thus, the loss of resistance at both ends of a single beam only results in a 6 percent reduction in story strength. Seismic behavior of chevron concentrically braced frames. May 25, 2016 vertical diagonal brace connections and vertical chevron brace connections may be designed as special concentric braced frame scbf connections in risaconnection v6. For braces in special concentrically braced frame systems, the advantages of using an hss can be offset by the need to design the rest of the frame components based on the expected strength of the brace sabelli et al. Seismic design of industrial bolted concentric brace. Honeck 2 acknowledgments the publication of this steel tips was made possible by the support of the structural steel educational council ssec and by the financial support of the california iron workers administrative trust. Resist lateral earthquake forces by truss action special type of brace members used. Technical report 1 penn state college of engineering. Seismic design of steel special concentrically braced frame systems. A guide for practicing engineers, second edition, gcr 1691741, nehrp seismic design technical brief no.
A balanced design procedure for special concentrically braced frame connections. The knife plates and ip buckling braces sustained a peak 0. Seismic design procedures for concentrically braced frames. To check the member design against the special seismic provisions, you will follow the same steps as for standard. Eccentric braced frame design for moderate seismic regions author.
Special concentrically braced frames scbfs have become more popular as lateral load. The behavior of special concentrically braced frame scbf systems have been compared with eccentric braced frame ebf in 5, 10 and 15 stories buildings. In this manuscript, seismic behavior of these two kinds of bracing systems has been studied. To achieve the intended yield mechanism and behavior, plastic design is applied to detail the frame members. Seismic design of ductile special concentrically braced frames. Beams and columns with moment resisting connections. A balanced design procedure for special concentrically. Designs of special concentrically braced frame using aisc 341. Nbsd proprietary analysis and design software list. Apr 19, 2018 hi, is there any guidance or a preferred workflow for designing special concentric braced frames using rss. Effect of the gusset plates on the behavior of shear connections.
Gusset plate connections between the steel braces and the supporting frame members play an important role in the performance of special concentrically braced frames scbfs under earthquake. Retrofit of concentrically braced frames jeffrey berman, dawn lehman, and charles roederandrew sen uw ryan ballard kpff, dan. Risaconnection designs scbf per the provisions found in section f2 of the aisc seismic provisions for structural steel buildings aisc 3412010. Through the analysis of different connection types, their applicability to future projects can be evaluated. For concentrically braced frames, capacity design generally implies allowing buckling and yielding in the diagonal bracing members while avoiding this in other frame members and components. Concentrically braced frames cbfs are stiff, strong structures that are suitable for resisting large lateral loads. The use of special concentrically braced frame scbf design methods in other components, such as in a horizontal diaphragm. Software to calculate dimensions for gusset plates in special concentrically braced. The following features of seismic design of steel buildings are illustrated. Seismic design of steel special concentrically braced. Seismic design of ductile special concentrically braced frames duration.
Design of seismicresistant steel building structures. The braces are typically used for structures where seismic activity may be encountered, regardless of whether wind or seismic loads govern the design of the structure. For all four type of seismic zones least total weight braced frames ebf for all three types of storey level frames. Click fence and fence all of the steel members in the braced frame on grid a. Structural steel connection design software descon 8. Collapse mechanism for the simple eccentrically braced frame of fig. Structural engineering software, spreadsheets, for analysis and design, including wood, lateral analysis. Structural design software engineering international. It is assumed to be located on a soft soil site in vancouver, british columbia, representing severe seismic conditions.
Design of special concentric braced frames, michael l. Special concentrically braced frames scbfs are stiff, strong structures that meet. Performance assessment of special concentricallybraced frames. The ufm is adapted to seismic applications by designing the connection to resist the. Seismic design of steel bucklingrestrained braced frames a guide. The 1997 ubc permits the use of nonconcentric bracing connections where the individual member centerlines do not all converge to one point at the connection. This dissertation describes a research program on special concentrically braced frame scbf and bucklingrestrained braced frame brbf systems. The design of ductile concentrically braced frames has evolved considerably over the past few revisions of aisc 341. Special concentric braced frames may be utilized in dual systems together with special moment frames in all seismic design categories with no limitation in the building height. Twostory and fourstory chevron braced frames were modeled in abaqus software and studied by means of nonlinear cyclic pushover and nonlinear. Pdf seismic performance of concentrically braced frames. Certainly, beam will still need to be designed for overall forces. The focus is on capacitydesigned connections in steel concentrically braced. Bracing, which provides stability and resists lateral loads, may be from diagonal steel members or, from a concrete core.
Buckling restrained braces standards developments and innovative applications kimberley robinson1 the buckling restrained braced frame brbf represents the stateoftheart in braced frame design. Hi, is there any guidance or a preferred workflow for designing special concentric braced frames using rss. Check of compactness and brace spacing for moment frame, 6. Stepbystep design procedures on typical scbfs are completed under aisc 34105 and aisc 34110.
Detailing methods presented in this paper for smf and scbf may still be applicable to the steel intermediate moment frame imf, steel ordinary moment frame omf, and steel ordinary concentric braced frames ocbf in lower sdc a, b and c. 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. Design tools ordinary concentric braced frame systems ocbf ocbf brace design hss aisc 34105 section 14 aisc 34105 example 3. In the ew direction, the ocbf system meets the prescriptive requirements of standard section 12. Ram frame steel seismic provisions tutorial ram staad. Created an etabs model for analysis and design of both admin building scbf and classroom building ocbf. Eccentric braced frame design for moderate seismic regions. Jul 21, 2015 this paper presents a performancebased plastic design pbpd methodology for the design of steel concentric braced frames. Dont create any special connections they drive up cost. Stepbystep design procedures on typical scbfs are completed under aisc. This is more of an issue for concentrically braced frames where the frame.
Vertical diagonal brace connections and vertical chevron brace connections may be designed as special concentric braced frame scbf connections in risaconnection v6. This report discusses and compares the designs of ordinary concentric brace frames ocbf and special concentric brace frames scbf. The design examples are arranged with lrfd and asd designs presented side by side, for consistency with the aisc manual. A stepbystep outline of the seismic design process, as well as the relevant capacity design principles will be presented. Special concentrically braced frames scbfs are commonly used lateralload resisting systems in seismic design. Instructional material complementing fema p751, design examples. This is a common type of connection for hss brace members. It is very powerful but our main benefit has been speed. Jan 29, 2016 seismic design of ductile special concentrically braced frames aisc education. Designs of special concentrically braced frame using aisc 34105. In scbfs, the braces are connected to the beams and columns by gusset plate.
Specific to brace connection design relative to vtype and. The module on special plate shear walls was prepared by rafael sabelli dasse design, san francisco. The beamtocolumn connection requires special consideration. The intention for seismic design of a ductile special concentri. Jun 28, 2016 now you can export vertical diagonal brace connections and vertical chevron brace connections from risa3d into risaconnection as either ordinary concentric braced frames ocbf or special concentric braced frames scbf. Economy comes from the inexpensive, nominally pinned connections between beams and columns.
Brbs yield both in tension and compression no buckling. Plastic moment distribution for example frame obtained by direct plastic design procedure. These connections will slip at a predetermined load level in order to absorb and dissipate by friction most of the energy input by earthquake ground motions, and then avoid yielding and buckling of the bracing members. The loads were calculated using the provisions of eurocode 8 en 19981 for dissipative behaviour q1.
Special concentrically braced frames scbfs are a special class of cbf. Seismic design of ductile special concentrically braced. Detailed design examples for bracingtogusset plate connections in socalled ocbfs ordinary concentric braced frames or those designed for a higher seismic force level with very little inelastic deformation, scbfs special concentrically braced frames or those designed to a lower force level than ocbfs with detailing provisions to accommodate. Comparison of moment resisting, concentrically braced. Seismic performance of concentrically braced frames with and without. The design base shear is obtained based on energywork balance equation using preselected target drift and yield mechanism. Typical software utilizes a spectrum presented as a. The horizontal component of bracing force is adding up and will be used to check beam web local effect by converting the horizontal component to vertical force. Special concentrically braced frames scbfs are a special class of cbf that are proportioned and detailed to maximize inelastic drift capacity. Apr 06, 20 the following figure shows an idealised concentrically braced frame in which the masses are concentrated at the nodes and all the connections between the members are assumed to be pinned. Demand to capacity ratio dcr is varied in beam and columns 0. A model to simulate special concentrically braced frames. Seismic design of steel buckling restrained braced frames.
The frame seismic response is examined with and without application of the special seismic design requirements. Specifically i was wondering if ram has builtin functionality to check the effects of compression brace buckling, or if its preferred to export to a program like elements that can model springs or perform a pushover analysis. Considerations for use of hss in seismic frame systems. Design of scbfs using ram structural system ram staad. Seismic evaluation and retrofit of concentrically braced. Repeat for the braced frames on grid f except change the frame type to special concentric braced frame for the upper 2 bays, and scbf chevron for the lower bay. This example utilizes a transverse intermediate steel moment frame and a longitudinal ordinary concentric steel braced frame. Variation of frame stiffness for different aspect ratios. Seismic design special concentrically braced frames s. Special cbfs scbf are used for seismic design and are designed and detailed to sustain relatively large inelastic deformations without significant deterioration in resistance. The large r y values associated with hss increases the forces for which the other components need to be designed. Current seismic design requirements aisc 2005c for special concentrically braced frames permit braces that buckle out of the plane of the gusset to be designed with pinned ends if a detail can be provided that allows for the end rotation that is expected from the buckling of the brace. Bucklingrestrained braced frames brbfs type of concentrically braced frame beams, columns and braces arranged to form a vertical truss. The building was designed in 2004 and uses the 2003 edition of the international building code and asce 702 as a reference standard.
Balanced design procedure for special concentrically. This paper summarizes the seismic design of three scbfs with different heights, namely, 4, 10, and 20 stories, at different sites. Eric grusenmeyergrad report connecting repositories. But with descon software, we can do preliminary connection design so fast that we get a better estimate. Superior structural engineering software for analysis and design by risa tech, inc. A comparative study zasiah tafheem and shovona khusru international journal of civil and structural engineering volume 4 issue 1 20 moderate seismic region. This seminar is designed for practicing engineers and is dedicated to completing a multistory special steel concentrically braced frame example so that common concerns and application of requirements can be illustrated. The brace undergoes repeated yielding in tension and buckling in compres sion to concentrate the damage only to brace, thus ren dering the gravity system to remain safe and collapse free during. A cast modular bracing system for steel special concentrically braced frames. Foundation design for braced frames sandman21 structural dec 17 17.
We are a design build firm so we do estimates with a preliminary structure design. This seminar will present fundamentals on the seismic behavior of concentrically braced frames and the current aisc 34116 provisions for special concentrically braced frames that are intended to achieve ductile seismic response. Seismic ground motion from usgs sesimic hazard program. Design of links and beamtocolumn connections for eccentrically braced steel frames by egor p. Braced frames are a very common form of construction, being economic to construct and simple to analyse. Seismic design special concentrically braced frames youtube. This paper presents the seismic performance of regular 6, 9, 12 and 15 storey special concentric xbraced frames in which tension bracings are designed for the lateral load of 100%, 70% and 60% of base shear. Seismic behavior and design of friction concentrically. Seismic detailing of gusset plates for special concentrically braced frames.
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