Bracing – What Is Piping

Bracing Connections involves the bolting of flat, angle, channel, I-section, and hollow section members to to a gusset plate to support the column or other members. The bracing member in a bracing connection can work in tension alone, or in both tension and compression and stabilize the main components by distributing the loads. In this article, we will explore the basics of bracing connections Benefits of Structural Steel Some benefits associated with the 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 Unique Aspects of Steel Construction Procurement and management of structural steel is similar to other materials, but there are some unique aspects to steel construction: Steel is fabricated off-siteOn-site erection is a rapid processThis gives users of structural steel some scheduling advantagesCoordination of all parties is essential for achieving potential advantages Forces on Structures (Fig. 1) Forces 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 structuresAs lateral loads are applied to a structure, horizontal diaphragms (floors and roofs) transfer the load to the lateral load resisting system Fig.1: Forces acting on structures The type of lateral load resisting system to be used in a structure should be considered early in the planning stageLateral stability and architectural needs must be met The three common lateral load resisting systems are: Braced Frames (Fig. 2)Rigid Frames (Fig. 2)Shear Walls Fig. 2: Braced and Rigid Frames Steel Frame Connection Types Simple ConnectionsMoment Connections: Fully-Restrained and Partially-RestrainedAll 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 rigid Fig. 3: Steel frame connection types Simple Connections Designed 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 Moment Connections Designed as rigid connections that allow little or no rotation, Used in rigid frames.Moment and vertical shear forces are transferred through the connection.Two types of moment connections are permitted: Fully-Restrained and Partially-Restrained (Fig. 4). Fig. 4: Moment Connections Rigid Frames Rigid 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 Braced Frames Diagonal bracing creates stable triangular configurations within the steel building frame“Braced frames are often the most economical method of resisting wind loads in multi-story buildings.”Some structures, like the one pictured above, are designed with a combination braced and rigid frame to take advantage of the benefits of both Temporary Bracing Structural steel frames require temporary bracing during constructionTemporary bracing is placed before plumbing up the structural frameThis gives the structure temporary lateral stabilityTemporary bracing is removed by the erectorIn 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 complete Concentric Braced Frames Bracing is concentric when the center lines of the bracing members intersect Common concentric braced frames used in buildings today include: Cross braceTwo-story X’sChevronSingle diagonals Cross bracing design is possibly the most common type of bracing. Bracing can allow a building to have access through the brace line depending on the configuration Cross Bracing Design Example The diagonal members of Cross bracing go into tension and compression similar to a truss.The 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 projectConnections for X bracing are located at the 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 Fig. 5: Different types of Bracing Chevron Bracing The 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 structureChevron 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 Eccentrically Braced Frames Eccentric 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 deformationEccentrically braced frames look similar to frames with Chevron bracingA similar V-shaped bracing configuration is used Combination Frames Fig. 6: Figure showing Combination Frames As shown in Fig. 6 (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 Few more useful resources for you.. 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