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BOLTED CONNECTIONS

BOLTED CONNECTIONS. CONTENTS. Introduction Bolted Connections Bolts and Bolting Force Transfer Mechanism Failure of Connections In shear In tension Combined shear and tension Block shear. INTRODUCTION. Designed more conservatively than members because they are more

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BOLTED CONNECTIONS

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  1. BOLTED CONNECTIONS

  2. CONTENTS • Introduction • Bolted Connections • Bolts and Bolting • Force Transfer Mechanism • Failure of Connections • In shear • In tension • Combined shear and tension • Block shear

  3. INTRODUCTION • Designed more conservatively than members because they are more • complex to analyse and discrepancy between analysis and design is • large • In case of overloading, failure in member is preferred to failure in • connection • Connections account for more than half the cost of structural steel • work • Connection design has influence over member design • Similar to members, connections are also classified as idealised types • Effected through rivets, bolts or weld • Codal Provisions

  4. a) Lap Connection b) Butt Connection support (b) (a) TYPES OF CONNECTIONS -! Classification based on type of force in the bolts Single shear Double shear Shear Connections Tension Connection and Tension plus Shear Connection

  5. BOLTS AND BOLTING Bolt Grade:Grade 4.6 :- fu = 400 N/mm2 and fy = 0.6*400 = 240 N/mm2 Bolt Types: Black, Turned & Fitted, High Strength Friction Grip Black Bolts: usually Gr.4.6, made snug tight, ductile and cheap, only static loads Turned & Fitted; Gr.4.6 to 8.8, Close tolerance drilled holes, 0.2% proof stress HSFG Bolts: Gr.8.8 to 10.9, less ductile, excellent under dynamic/fatigue loads

  6. FORCE TRANSFER MECHANISM (a) Bearing Connection T Bearing stresses T (b) Friction Connection T Tension in bolt Frictional Force T Clamping Force, PO T Clamping Force, PO Bolt Shear Transfer – Free Body Diagram

  7. (a) Standard (b) Oversized (c )Short Slot (d) Long slot TIGHTENING OF HSFG BOLTS 1) Turn-of-nut Tightening 2) Calibrated Wrench Tightening 3) Alternate Design Bolt Installation 4) Direct Tension Indicator Method Hole types for HSFG bolts

  8. Zone of plastification FAILURE OF CONNECTIONS Shear Connections with Bearing Bolts (a) Shearing of Bolts Ps = ps As where As = 0.78A (b) Bearing on Bolts Pbb = pbb d t (c) Bearing on Plates Pbs = pbs d t  ½ e tpbs

  9. Bearing Type Bolts IS 800:2007 Shear capacity of bolt Reduction factor in shear for Long Joints Reduction factor in shear for Large Grip Lengths lg = 8 d /(3 d+lg) Reduction factor for Packing Plates pk = (1 - 0.0125 tpk)

  10. Bearing Type Bolts Bearing Capacity of bolt on any ply Tension Capacity Bolt subjected to combined shear and tension Vsb = (2.5 d t fu)/ γmb Tb =(0.90 fub An)/ γmb < (fyb Asb(γm1 / γm0))/ γmb

  11. FAILURE OF CONNECTIONS-1 Shear Connections with HSFG Bolts (a) Slip Resistance Vsf = (µf ne Kh Fo)/ γmf Kh =1.0 (clearance hole)  = 0.45 (untreated surfaces) Fo= proof load (b) Bearing on Plates Vbf = (2.2 d t fup ) / γmf< (3 d t fyp)/ / γmf

  12. Friction Grip Type Bolting Vsf = (µf ne Kh Fo)/ γmf Where, µf = coeff. of friction (slip factor) as in Table 10.2 (µf< 0.55) ne = number of effective interfaces offering frictional resistance to slip Kh = 1.0 for fasteners in clearance holes = 0.85 for fasteners in oversized and short slotted holes = 0.7 for fasteners in long slotted holes loaded parallel to the slot. γmf = 1.10 (if slip resistance is designed at service load) γmf = 1.25 (if slip resistance is designed at ultimate load) Fo = minimum bolt tension (proof load) at installation ( 0.8 Asb fo) Asb = shank area of the bolt fo= proof stress (= 0.70 fub) Note: Vns may be evaluated at a service load or ultimate load using appropriate partial safety factors, depending upon whether slip resistance is required at service load or ultimate load. Slip resistance

  13. Clean mill scale Treatment of surface 0.33 Coefficient of friction (µf) Sand blasted surface 0.48 Red lead painted surface 0.1 TYPICAL AVERAGE VALUES FOR COEFFICIENT OF FRICTION (µf)

  14. 2T 2T Bearing type connection (b) HSFG Connection T T To To To+T To+T Bolt force B kN HSFG 2T Bearing type Proof Load Po B b n A Applied load 2T (kN) (d) Prying Effect ( c) External Tension versus boltforce Q Q T+Q T+Q BOLTS UNDER TENSION AND PRYING EFFECT

  15. Friction Grip Type Bolting Prying Force   = 2 for non-pretensioned and 1 for pretensioned  = 1.5 for LSM be = effective width of flange per pair of bolts

  16. Bolt strengths Steel grade ST42S Bolt grade Gr.43 Gr.50 Bearing bolts pbs 418 4.6 460 8.8 550 Shear strength ps HSFG bolts pbg 650 160 825 375 1065 Bearing strength pbb 435 970 Tension strength pt 195 450 DESIGN STRENGTHS FOR BOLTED CONNECTIONS Table 1 Bolt Strengths in Clearance Holes in MPa Table 2 Bearing Strengths of Connected Parts in MPa

  17. Stresses due to Individual forces Combination of stresses Fillet welds Combined bearing, bending and shear

  18. T V d V C e M = Td (a) (b) Standard Connections (a) moment connection (b) simple connection GENERAL ISSUES IN CONNECTION DESIGN Assumptions in traditional analysis • Connection elements are assumed to • be rigid compared to the connectors • Connector behaviour is assumed to • be linearly elastic • Distribution of forces arrived at by • assuming idealized load paths • Provide stiffness according to the • assumed behaviour • ensure adequate ductility and rotation • capacity • provide adequate margin of safety

  19. CONTENTS -1 • Analysis of Bolt Groups • Combined Shear and Moment in-Plane • Combined Shear and Moment out-of-plane • Beam and Column Splices • Beam to Column Connections • Beam to Beam Connections • Truss Connections • Fatigue Behaviour

  20. (a) (b) (b) (a) TYPES OF CONNECTIONS Classification based on type of resultant force transferred Concentric Connections Moment Connections

  21. BEAM AND COLUMN SPLICE Strength, stiffness and ease in erection Assumptions in Rolled-section & Plate Girders (a)Conventional Splice (b) End-Plate Splice Bolted Beam Splice Column Splices – bearing type or HSFG moment splices

  22. BEAM-TO-COLUMN CONNECTIONS (a) Simple – transfer only shear at nominal eccentricity Used in non-sway frames with bracings etc. Used in frames upto 5 storeys (b) Semi-rigid – model actual behaviour but make analysis difficult (linear springs or Adv.Analysis). However lead to economy in member designs. (c) Rigid – transfer significant end-moments undergoing negligible deformations. Used in sway frames for stability and contribute in resisting lateral loads and help control sway.

  23. BEAM-TO-COLUMN CONNECTIONS e (a) (b) (c) V Simple beam-to-column connections a) Clip and seating angle b) Web cleats c) Curtailed end plate • Economical when automatic saw and drill lines are available • Check end bearing and stiffness of seating angle • Clip angle used for torsional stability • If depth of cleats < 0.6d design bolts for shear only • Eliminates need to drill holes in the beam. Limit depth and thickness • t < /2 (Gr.8.8) and /3 (Gr.4.6)

  24. BEAM-TO-COLUMN CONNECTIONS column web stiffeners diagonal stiffener web plate (a) (b) (c) Rigid beam-to-column connections a) Short end plate b) Extended end plate c) Haunched

  25. Splice plate GussetPlate e GussetPlate support TRUSS CONNECTIONS (a) Apex Connection (b) Support connection Truss Connections

  26. Thank You

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