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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 Dr S R Satish Kumar, IIT Madras

  2. CONTENTS • Introduction • Bolted Connections • Bolts and Bolting • Force Transfer Mechanism • Failure of Connections • In shear • In tension • Combined shear and tension • Block shear Dr S R Satish Kumar, IIT Madras

  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 Dr S R Satish Kumar, IIT Madras

  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 Dr S R Satish Kumar, IIT Madras

  5. BOLTS AND BOLTING Bolt Grade:Grade 4.6 :- fu = 40 kgf/mm2 and fy = 0.6*40 = 24 kgf/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 Dr S R Satish Kumar, IIT Madras

  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 Dr S R Satish Kumar, IIT Madras

  7. ¾ turn position snug-tight position Tightening of HSFG bolts (a) Standard (b) Oversized Feeler gauge (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 Dr S R Satish Kumar, IIT Madras

  8. Zone of plastification FAILURE OF CONNECTIONS Shear Connections with Bearing Bolts Fig. 9 (a) Shearing of Bolts Ps = ps As where As = 0.8A (b) Bearing on Bolts Pbb = pbb d t (c) Bearing on Plates Pbs = pbs d t  ½ e tpbs Dr S R Satish Kumar, IIT Madras

  9. 10.3 Bearing Type Bolts IS 800:2007 10.3.2 Shear capacity of bolt 10.3.1.1 Reduction factor in shear for Long Joints 10.3.1.2 Reduction factor in shear for Large Grip Lengths lg = 8 d /(3 d+lg) 10.3.2.3 Reduction factor for Packing Plates pk = (1 - 0.0125 tpk) Dr S R Satish Kumar, IIT Madras

  10. 10.3 Bearing Type Bolts 10.3.3 Bearing Capacity of bolt on any ply 10.3.4 Tension Capacity 10.3.5 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 Dr S R Satish Kumar, IIT Madras

  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 Dr S R Satish Kumar, IIT Madras

  12. 10.4 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. 10.4.1 Slip resistance Dr S R Satish Kumar, IIT Madras

  13. Clean mill scale Treatment of surface 0.33 Coefficient of friction (µf) Sand blasted surface 0.48 Red lead painted surface 0.1 TABLE 10.2 TYPICAL AVERAGE VALUES FOR COEFFICIENT OF FRICTION (µf) Dr S R Satish Kumar, IIT Madras

  14. 10.4 Friction Grip Type Bolting 10.4.2 Bearing capacity 10.4.3 Tension capacity 10.4.4 Combined Shear and Tension Reduction factor in shear for Long Joints will apply here Vbf = (2.2 d t fup ) / γmf< (3 d t fyp)/ / γmf Tf = (0.9 fuA)/ / γmf Dr S R Satish Kumar, IIT Madras

  15. 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 Dr S R Satish Kumar, IIT Madras

  16. 10.4 Friction Grip Type Bolting 10.4.5 Prying Force   = 2 for non-pretensioned and 1 for pretensioned  = 1.5 for LSM be = effective width of flange per pair of bolts (Conti….) Dr S R Satish Kumar, IIT Madras

  17. Steel grade Bolt strengths 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 Dr S R Satish Kumar, IIT Madras

  18. 10.5.9 Stresses due to Individual forces 10.5.10 Combination of stresses 10.5.10.1 Fillet welds Combined bearing, bending and shear (Conti….) Dr S R Satish Kumar, IIT Madras

  19. 10.2 Fasteners spacing and edge distance 10.2.1 Minimum Spacing - 2.5 times the nominal diameter 10.2.2 Maximum Spacing - shall not exceed 32t or 300 mm, whichever is less, where t is thickness of the thinner plate 10.2.2.2 pitch shall not exceed 16t or 200 mm, in tension members and 12t or 200 mm, whichever is less, in compression members 10.2.3 Edge and End Distancesminimum edge shall be not less than that given in Table 10.1.maximum edge distance should not exceed 12 t, where  = (250/fy)1/2 10.2.4 Tacking Fastenersspacing in line not exceeding 32t or 300 mm If exposed to the weather, 16 t or 200 mm max. spacing in tension members 1000 mm max. spacing in compression members 600 mm Dr S R Satish Kumar, IIT Madras

  20. 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 Dr S R Satish Kumar, IIT Madras

  21. 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 Dr S R Satish Kumar, IIT Madras

  22. (a) (b) (b) (a) TYPES OF CONNECTIONS Classification based on type of resultant force transferred Concentric Connections Moment Connections Dr S R Satish Kumar, IIT Madras

  23. Rmi x’ ri y’ P  O COMBINED SHEAR AND MOMENT IN PLANE • Bolt shear due to Px and Py • Rxi = Px/n and Ryi = Py/n • M = Px y’ + Py x’ • Rmi = k ri • Mi = k ri2 • MR = k ri2 = k ri2 • Bolt shear due to M • Rmi=M ri/ ri2 Bolt group eccentrically loaded in shear Combined shear Dr S R Satish Kumar, IIT Madras

  24. Ti li Li d Li NA d/6 C (a) (b) (c) COMBINED SHEAR AND MOMENT OUT-OF-PLANE Bolt group resisting out-of-plane moment Ti = kli where k = constant M =  Ti Li = k  li Li Ti = Mli/ li Li Shear assumed to be shared equally and bolts checked for combined tension+(prying)+shear Dr S R Satish Kumar, IIT Madras

  25. 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 Dr S R Satish Kumar, IIT Madras

  26. 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. Dr S R Satish Kumar, IIT Madras

  27. 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) Dr S R Satish Kumar, IIT Madras

  28. 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 Dr S R Satish Kumar, IIT Madras

  29. Splice plate GussetPlate e GussetPlate support BEAM-TO-BEAM AND TRUSS CONNECTIONS Beam-beam connections similar to beam-column connections Moment continuity may be obtained between secondary beams Check for torsion in primary beams (a) Apex Connection (b) Support connection Truss Connections Dr S R Satish Kumar, IIT Madras

  30. FATIGUE BEHAVIOUR • Fatigue leads to initiation and growth of cracks under fluctuating stresses • even below the yield stress of the material (High-cycle fatigue) • Fatigue cracks grow from points of stress concentrations • To avoid stress concentrations in bolted connections • Use gusset plates of proper shape • Use match drilling • Use HSFG bolts • Fatigue also depends on range of stress fluctuations and reversal of stress • pre-tensioned HSFG avoid reversals but lead to fretting corrosion • Fatigue design carried out by means of an S-N curve on a log-log scale • Components are designed below the endurance limit www.steel-insdag.org Thank You Dr S R Satish Kumar, IIT Madras

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