Connection and Bracing

1. CONNECTIONS AND BRACINGS By / Muhammad Azeem

2. Outline Introduction Steps for Design Geometry Modeling Loading Design Parameters Analysis & Design Connections & Bracing Pipe Rack Design Flow Chart From Previous Presentation

3. Outline Benefits of Steel Structure Load Resisting Systems Frame Types Concentric / Eccentric Braced Frame Steel Frame Connection Types Simple Connection Moment Connection EM Connection Capacity Design Flow Chart

4. Benefits of Structural Steel Reduced construction time & no seasonal effect. Light weight and reduced foundation cost. Durable , Long Lasting and Recyclable. Easier to modify and reinforce if required.

5. Benefits of Structural Steel Fabrication off-site possible (right). On site erection is a time saving process (left). Schedule advantage.

6. Forces on Structure Forces from Gravity ,wind and seismic is imposed on all structures. Applied vertical forces are gravity loads. Forces that act horizontally such as wind, seismic require a lateral load resisting system to be built in structure. When lateral loads are applied to a structure, horizontal diaphragm transfer the load to the lateral load resisting system. Structural steel frame elevation

7. The type of lateral load (Seismic, Wind, Friction, Thermal ) resisting system to be used in a Structure Should be taken care in the Earlier Planning Stage. Common lateral load resisting systems Braced Frame Rigid Frame Initial Stage System Planning

8. Rigid frame, utilize the moment connection and this type is preferred where diagonal or x- bracing should avoid due to access requirement. Draw back of rigid frame is more cost than braced frame. Rigid Frame

9. Braced Frame Braced frame is the economical method of resisting wind load in multi storey structural frame. Bracing creates triangular configuration in the structures. Some structures like below picture take the advantage of both rigid and braced at the same time.

10. Bracings Member or system that provides stiffness and strength to limit the out of plan movement of another member at the braced point. (AISC Spec2010) Two types of bracing is defined in AISC (1997) seismic provision in steel structural building. Concentric Bracing Eccentric Bracing

11. A- Concentric Brace Concentrically braced frame are those in which the centerlines of members that meet at a joint intersect at a same work point to form a vertical truss system that resist lateral forces.

12. Commonly used bracing system in steel structure is X- bracing ( above left) Chevron (above right) A- Concentric Brace

13. X-Bracing Connection for X- bracing are located at beam to column joint. Bracing connection may require large gusset plate at the beam to column joint.

14. Chevron Bracing The members used in chevron bracing are designed for both compression and tension Chevron bracings allows for doorways or corridors through the bracing lines in a structure. “CHEVRON” “V” “DIAGONAL” ELEVATION WITH SEVERAL BRACING CONFIGURATION

15. Chevron Bracing Chevron bracing members use two types of connections. The Floor level connection may use a gusset plate as like in x-braced frame. The bracing members are connected to the beam/girder at the top and converge to a common point. When gusset plate is used, it in important to consider their size when laying out any mechanical equipment pass through braced bays.

16. B- Eccentrically Braced Frame Eccentric brace is commonly used in seismic regions and allow corridors and walkway through bay frame. In an eccentrically braced frames, bracing connect to a separate work point on beam/girder. The beam/girder segment or “link” between them absorbs energy from seismic activity through plastic deformation. Link E/B with typical brace to beam connection Eccentric Brace Gusset Plate Beam or Girder Stiffeners

17. B- Eccentrically Braced Frame Adopted AISC 327-05

18. B- Eccentrically Braced Frame Eccentrically braced frame looks very similar to chevron bracing.

19. B- Eccentrically Braced Frame Eccentric single diagonal brace can also be use to brace a frame.

20. Steel Frame Connection Type The specification of structural steel building (AISC 2010) defines two types of frame connections. Simple Connection (below left) Moment Connection (below right) Moment connection are of two types: FR & PR

21. Steel Frame Connection Type Simple Connection: Connection that transmit negligible amount of bending moment between connected members. Moment Connection: Connection that transmit bending moment between connected members. Fully restrained moment connection FR : transfer moments with a negligible amount of rotation between connected members. Partially restrained moment connection PR : transfer moments, but rotation between connected members is not negligible. AISC Spec.- 2010

22. Steel Frame Connection Types Simple connection (A) have rigidity but is assumed to rotate free. Connection (B & C) are examples of partially restrained moment connections. Connection (D & E) are examples of fully restrained moment. Adopted from Vol -II Connection .

23. Simple Connection Connection is assumed to be rotation free. Vertical forces are primary forces transferred by the connection. For this Connection a separate resisting system is required to design.

24. Single plate Connection ( Shear Tab) A plate is welded to the supporting member and bolted to the web of the supported beam. Double Angle Connection The in plane pair of legs are attached to the web of the supported member and out of plane pair of legs attached to the supporting beam web or flange. Commonly Used Simple Connection

25. Commonly Used Simple Connection Shear end plate connection A plate is welded perpendicular to the end of supported web and bolted to supporting beam. Seated connection An angle is mounted with one leg vertical against the supporting column & the other leg provides a “seat” upon which the beam is mounted ,a stabilizer connection is provided at top of the web.

26. Moment Connection Designed as rigid connection with little or no rotation. Moment and vertical shear forces are transferred through the connection. Two types of moment connection are allowed: Partially restrained moment connection. Fully restrained moment connection.

27. Moment Connection Fully restrained (FR)Connection Have sufficient strength to transfer moment with negligible rotation between connected members. Partially restrained (PR)Connection Have sufficient strength to transfer moments with rotation between connected members.

28. Commonly Used FR Connection Welded flange plate connection Bolted flange plate connection *With column web Top and bottom flange plates connect the flanges of supported member to the supporting column. A single plate is used to transfer the vertical shear force.

29. Commonly Used FR Connection Bolted extended end plate connection A plate is welded to the end of supported beam and bolted to the supporting column flange . Welded flange connection Complete joint penetration groove welds directly top and bottom flanges of the supported member to supporting column. A shear connection at web is used to transfer the vertical shear force. *With column flange

30. Commonly Used PR Connection PR moment connection A double angle simple connection transfers vertical shear forces while top and bottom flange plates resist moment forces produced by wind. Top and bottom angle with shear end plate connection Angles are bolted or welded to the top and bottom flanges of the supported member and to the supporting column. A shear end plate on the web is used to transfer vertical shear forces.

31. Calculations End Moment Connection (1) MEMBER Mm = 0.6Fy x Sx (kN-m) Vm = 0.4Fy x Awn (kN) Tm = 0.6Fy x 2Af (kN) Af = bfb x tfb (mm2) Awn = ( d1 - 2tfb ) x twb (mm2) (2) HIGH STRENGTH BOLT Mb = n1 x Qt x ( d1 - tfb ) (kN-m) Vb = n2 x Qs (kN) Tb = 2 x n1 x Qt (kN) n1= Number of tension bolts n2= Total Number of bolts (4) END PLATE Mp = Ff x ( d1 - tfb ) (kN-m) Tp = 2 x Ff (kN) Ff = 4 x Me / ( α m x Pe ) (kN) Me = bp x 0.75Fy x tp2 / 6 (kN-m) α m = Ca x Cb x (Af / Aw)1/3 x (Pe / db)1/4 Pe = Pf - (db / 4) - 0.707S1 (mm) Ca = 1.13 Cb = ( bfb / bp )1/2 db = (mm) Aw = twb x (d1 - 2tfb) (mm2) (5) STIFFENER DESIGN (5-1) COLUMN FLANGE BENDING STRENGTH Fcap = 4 x Me /( α m x Pe ) Me = bs x 0.75Fy x tfc2 / 6 (kN) bs= 2.5 x ( Pf + tfb + Pf ) (kN-m) Pe = g / 2 - db / 4 - k1 (mm) α m = Ca x Cb x ( Af / Aw )1/3 x ( Pe / db )1/4 (mm) Af / Aw = 1.0 min Mst = Ff x ( d1 - tfb ) (kN-m) Ff = Fcap + Fst (kN) min Tst = 2Ff (kN) (5-2) TENSION CAPACITY OF STIFFENER PLATE Fst = 0.6Fy x Ast (kN) Ast = ts x ( bfc - twc - 2 x 5 - 2 x 25 ) (mm2) (5-3) SHEAR CAPACITY OF STIFFENER PLATE Fst = 0.4Fy x Ast (kN) (5-4) STIFFENER WELD CAPACITY OF COLUMN FLANGE Fst = fw x Ast (kN) Ast = 0.707 x lw x Sflg (mm (5-5) STIFFENER WELD CAPACITY OF COLUMN WEB Fst = fw x Ast (kN) Ast = 0.707 x lw x Sweb (mm2) lw = 4 x (dc/2 - tfc - 25 - Sweb) : HALF lw = 4 x (dc - 2tfc - 2x25 - 2xSweb) : FULL (3) WELD Mw = Ff x ( d1 - tfb ) (kN-m) Ff = Fw x Awf (kN) Vw = Fw x Aww(kN) Tw = Fw x 2Awf Awf = 0.707 x S1 x (2bfb+2tfb-twb ) (mm2) Aww = 0.707 S2 x ( d1 / 2 - tfb ) x 2 (mm2) SAFE LOAD OF CONNECTION Ma =min.(Mm,Mw,Mb,Mp,Mst) (kN-m) Ta = min.(Tm,Tw,Tb,Tp,Tst) (kN) Va = min. (Vm,Vw,Vb) (kN)

32. References AISC VOLUME-II CONNECTION CONNECTION TEACHING TOOLKIT (AISC) AISC 327-05 SEISMIC DESIGN MANUAL AISC 2010 SPECIFICATION FOR STRUCTURAL STEEL BLDGS

33. Thank You