Connections and Bracing Configurations

Connections and Bracing Configurations

اسلاید 1: 1ConnectionsandBracing Configurations

اسلاید 2: 2IntroductionThis presentation was developed as a teaching aid with the support of the American Institute of Steel Construction. Its objective is to provide technical background and information for connections and bracing configurations. The information provided is based on common design and construction practices for structures of twelve stories or less.The AISC Digital Library case study presentations document the construction of a steel frame for an office building. The case study includes photographs that were taken throughout the construction of the structural steel frame including detailing, fabrication, and erection. Project data including plans, schedules, specifications and other details are also included. The case study presentations are available in the Learning Opportunities section at www.aisc.org.This presentation goes a step further in detail in the areas of connections and bracing configurations. A more in-depth background is provided and details of common connections and bracing configurations are presented.The information is presented with concerns of a construction manager or general contractor in mind.

اسلاید 3: 3What Will You Gain From This Presentation?General knowledge of structural steelKnowledge of the types of steel frame connections defined in the American Institute of Steel Construction design specificationAn understanding of different types of connections used in structural steel framesInsight into the impacts of using certain connection typesFamiliarity with common bracing systems used in structural steel frames

اسلاید 4: 4Benefits of Structural SteelSome benefits associated with use of structural steel for owners are:Steel allows for reduced frame construction time and the ability to construct in all seasonsSteel makes large spans and bay sizes possible, providing more flexibility for ownersSteel is easier to modify and reinforce if architectural changes are made to a facility over its lifeSteel is lightweight and can reduce foundation costsSteel is durable, long-lasting and recyclable (AISC 1999)

اسلاید 5: 5Unique Aspects of Steel ConstructionProcurement and management of structural steel is similar to other materials, but there are some unique aspects to steel construction:Steel is fabricated off-site (above left)On-site erection is a rapid process (above right)This gives use of structural steel some scheduling advantagesCoordination of all parties is essential for achieving potential advantages(AISC 1999)

اسلاید 6: 6Forces On StructuresForces from gravity, wind, and seismic events are imposed on all structuresForces that act vertically are gravity loadsForces that act horizontally, such as stability, wind and seismic events (the focus of this discussion) require lateral load resisting systems to be built into structures As lateral loads are applied to a structure, horizontal diaphragms (floors and roofs) transfer the load to the lateral load resisting system(AISC 2002)Structural Steel Frame Elevation

اسلاید 7: 7Initial System PlanningThe type of lateral load resisting system to be used in a structure should be considered early in the planning stageLateral stability as well as architectural needs must be metThe three common lateral load resisting systems are:Braced FramesRigid FramesShear Walls(Adapted from AISC 2002)2113Shear WallRigid FrameChevron BracedX BracedRigid Horiz. Diaphragm (Floor or Roof)

اسلاید 8: 8Braced Frames and Rigid FramesThis presentation focuses on braced frames (left) and rigid frames (right)

اسلاید 9: 9Steel Frame Connection TypesThe Specification for Structural Steel Buildings (AISC 2005) defines two types of connections:Simple Connections (above left)Moment Connections (above right)Fully-Restrained and Partially-Restrained

اسلاید 10: 10All connections have a certain amount of rigiditySimple connections (A above) have some rigidity, but are assumed to be free to rotatePartially-Restrained moment connections (B and C above) are designed to be semi-rigidFully-Restrained moment connections (D and E above) are designed to be fully rigidSteel Frame Connection Types(AISC)

اسلاید 11: 11Simple ConnectionsDesigned as flexible connectionsConnections are assumed to be free to rotateVertical shear forces are the primary forces transferred by the connectionRequire a separate bracing system for lateral stabilityThe following few slides show some common simple framing connections

اسلاید 12: 12 Common Simple ConnectionsSingle Plate Connection (Shear Tab)A plate is welded to the supporting member and bolted to the web of the supported beamDouble Angle ConnectionThe in-plane pair of legs are attached to the web of the supported beam and the out-of-plane pair of legs to the flange or web of the supporting member(Green, Sputo, and Veltri)

اسلاید 13: 13 Common Simple ConnectionsShear End Plate ConnectionA plate is welded perpendicular to the end of the supported web and attached to the supporting memberSingle Angle ConnectionOne leg is attached to the web of the supported beam and the other leg to the flange or web of the supporting member(Green, Sputo, and Veltri)

اسلاید 14: 14 Common Simple ConnectionsSeated ConnectionAn angle is mounted with one leg vertical against the supporting column, and the other leg provides a “seat” upon which the beam is mounted A stabilizer connection is also provided at the top of the webTee ConnectionThe stem of a WT section is connected to the supported member and the flange attached to the supporting member(Green, Sputo, and Veltri)

اسلاید 15: 15Moment ConnectionsDesigned as rigid connections which allow little or no rotation Used in rigid framesMoment and vertical shear forces are transferred through the connectionTwo types of moment connections are permitted:Fully-RestrainedPartially-Restrained

اسلاید 16: 16Moment Connections

اسلاید 17: 17 Common FR ConnectionsBolted Flange Plate ConnectionWelded Flange Plate ConnectionTop and bottom flange-plates connect the flanges of the supported member to the supporting columnA single plate connection is used to transfer vertical shear forces(Green, Sputo, and Veltri)

اسلاید 18: 18 Common FR ConnectionsBolted Extended End-Plate ConnectionA plate is welded to the flanges and web of the supported member and bolted with high-strength bolts to the supporting columnWelded Flange ConnectionComplete-joint-penetration groove welds directly connect the top and bottom flanges of the supported member to the supporting columnA shear connection on the web is used to transfer vertical shear forces(Green, Sputo, and Veltri)

اسلاید 19: 19 Common PR ConnectionsPR Moment Connection – Wind OnlyA double angle simple connection transfers vertical shear forces while top and bottom flange plates resist moment forces produced by windNote that the size of the flange plate is relatively small in comparison to the beam flangeTop and Bottom Angle with Shear End Plate ConnectionAngles are bolted or welded to the top and bottom flanges of the supported member and to the supporting columnA shear end plate on the web is used to transfer vertical shear forces

اسلاید 20: 20Rigid FramesRigid frames, utilizing moment connections, are well suited for specific types of buildings where diagonal bracing is not feasible or does not fit the architectural designRigid frames generally cost more than braced frames (AISC 2002)

اسلاید 21: 21Braced FramesDiagonal bracing creates stable triangular configurations within the steel building frame (AISC 2002)“Braced frames are often the most economical method of resisting wind loads in multi-story buildings (AISC 1991).”Some structures, like the one pictured above, are designed with a combination braced and rigid frame to take advantage of the benefits of both

اسلاید 22: 22Structural steel frames require temporary bracing during constructionTemporary bracing is placed before plumbing up the structural frameThis gives the structure temporary lateral stability Temporary bracing is removed by the erectorTemporary Bracing

اسلاید 23: 23In a braced frame, temporary bracing is removed after final bolt-up is complete and the permanent bracing system is in placeIn a rigid frame, temporary bracing is removed after final bolt-up is completeTemporary Bracing

اسلاید 24: 24Concentric Braced FramesBracing is concentric when the center lines of the bracing members intersectCommon concentric braced frames used in buildings today include:X brace (above left) Two story X’sX bracing is possibly the most common type of bracingBracing can allow a building to have access through the brace line depending on configuration (AISC 2002)Chevron (above right)Single diagonals

اسلاید 25: 25X BracingThe diagonal members of X bracing go into tension and compression similar to a trussThe multi-floor building frame elevation shown above has just one braced bay, but it may be necessary to brace many bays along a column lineWith this in mind it is important to determine the locations of the braced bays in a structure early in a project(AISC 2002)X-braced building elevationX BracingTypical floor plan with X bracing1st FloorFloorFloorRoof

اسلاید 26: 26X BracingConnections for X bracing are located at beam to column jointsBracing connections may require relatively large gusset plates at the beam to column jointThe restriction of space in these areas may have an impact on the mechanical and plumbing systems as well as some architectural features(AISC 2002)

اسلاید 27: 27Chevron BracingThe members used in Chevron bracing are designed for both tension and compression forcesChevron bracing allows for doorways or corridors through the bracing lines in a structureA multi-floor frame elevation using Chevron bracing is shown above(AISC 2002)Chevron BracingTypical floor plan with Chevron bracingElevation with several bracing configurationsRoof1st FloorFloorFloorChevron“V”“K”

اسلاید 28: 28Chevron bracing members use two types of connectionsThe floor level connection may use a gusset plate much like the connection on X braced framesThe bracing members are connected to the beam/girder at the top and converge to a common pointIf gusset plates are used, it is important to consider their size when laying-out mechanical and plumbing systems that pass through braced bays (AISC 2002)Chevron Bracing

اسلاید 29: 29Eccentrically Braced FramesEccentric bracing is commonly used in seismic regions and allows for doorways and corridors in the braced baysThe difference between Chevron bracing and eccentric bracing is the space between the bracing members at the top gusset connectionIn an eccentrically braced frame bracing members connect to separate points on the beam/girderThe beam/girder segment or “link” between the bracing members absorbs energy from seismic activity through plastic deformation (AISC 2002)Eccentric BraceLinkGussetEccentric brace with typical brace to beam connection(Adapted from AISC 2002)Beam or GirderStiffeners

اسلاید 30: 30Eccentrically Braced FramesEccentrically braced frames look similar to frames with Chevron bracingA similar V shaped bracing configuration is used(AISC 2002)

اسلاید 31: 31Eccentrically Braced FramesEccentric single diagonals may also be used to brace a frame(EERC 1997)

اسلاید 32: 32Combination FramesAs shown above (left) a braced frame deflects like a cantilever beam while a moment resisting frame deflects more or less consistently from top to bottomBy combining the two systems, reduced deflections can be realizedThe combination frame is shown above right(AISC 1991)Chevron bracedMoment resistingCombination FrameBracingMoment frame

اسلاید 33: 33Combination FramesThe plot shows the moment resisting frame alone, the braced frame alone, and the combined frameThe same wind load was used for each frame model (AISC 1991)(AISC 1991)O = Combined FramesX = Chevron or “K” Bracing = Moment Resisting

اسلاید 34: 34Structural Steel: The Material of Choice

اسلاید 35: 35ReferencesAISC. (n.d.). Steel Connections: Behavior and Practice [35mm Slide Show with Script]. American Institute of Steel Construction, Inc. Chicago, IL.AISC. (1989). Specification for Structural Steel Buildings, Allowable Stress Design and Plastic Design, 9th ed. American Institute of Steel Construction, Inc. Chicago, IL.AISC. (1991). Design Guide for Low- and Medium-Rise Steel Buildings. American Institute of Steel Construction, Inc. Chicago, IL.AISC. (1999). Load and Resistance Factor Design Specification For Structural Steel Buildings. American Institute of Steel Construction, Inc. Chicago, IL.AISC. (2002). Designing With Structural Steel – A guide For Architects. American Institute of Steel Construction, Inc. Chicago, IL . Earthquake Engineering Research Center, (EERC). (1997). W. G. Godden Structural Engineering Slide Library. Godden J119. Available at: http://nisee.berkeley.edu/bertero/html/recent_developments_in_seismic_design_and_construction.html. Viewed August, 2004.Green, P. S., Sputo, T., and Veltri, P. (n.d.). Connections Teaching Toolkit – A Teaching Guide for Structural Steel Connections. American Institute of Steel Construction, Inc. Chicago, IL.