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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 - PowerPoint PPT Presentation

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  • BOLTED CONNECTIONS

  • Introduction Bolted Connections Bolts and Bolting Force Transfer Mechanism Failure of Connections

    In shearIn tensionCombined shear and tensionBlock shear

    CONTENTS

  • 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

  • Shear ConnectionsTension Connection and Tension plus Shear ConnectionTYPES OF CONNECTIONS -!SingleshearDouble shearClassification based on type of force in the bolts

  • BOLTS AND BOLTINGBolt 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 loadsTurned & Fitted; Gr.4.6 to 8.8, Close tolerance drilled holes, 0.2% proof stressHSFG Bolts: Gr.8.8 to 10.9, less ductile, excellent under dynamic/fatigue loads

  • TIGHTENING OF HSFG BOLTS1) Turn-of-nut Tightening2) Calibrated Wrench Tightening3) Alternate Design Bolt Installation4) Direct Tension Indicator MethodHole types for HSFG bolts

  • FAILURE OF CONNECTIONS(a) Shearing of Bolts(b) Bearing on Bolts(c) Bearing on PlatesFig. 9Shear Connections with Bearing BoltsPs = ps As where As = 0.8APbb = pbb d tPbs = pbs d t e t pbs

  • 10.3 Bearing Type Bolts10.3.2 Shear capacity of bolt

    10.3.1.1 Reduction factor in shear for Long Joints10.3.1.2 Reduction factor in shear for Large Grip Lengthslg = 8 d /(3 d+lg)10.3.2.3 Reduction factor for Packing Platespk = (1 - 0.0125 tpk)

  • 10.3 Bearing Type Bolts10.3.3 Bearing Capacity of bolt on any ply

    10.3.4 Tension Capacity

    10.3.5Bolt subjected to combined shear and tension

    Vsb = (2.5 d t fu )/ mbTb =(0.90 fub An)/ mb < (fyb Asb (m1 / m0))/ mb

  • FAILURE OF CONNECTIONS-1Shear Connections with HSFG Bolts(a) Slip Resistance(b) Bearing on PlatesKh =1.0 (clearance hole) = 0.45 (untreated surfaces)Fo= proof loadVsf = (f ne Kh Fo)/ mfVbf = (2.2 d t fup ) / mf < (3 d t fyp)/ / mf

  • 10.4Friction Grip Type Bolting10.4.1 Slip resistanceWhere, f = coeff. of friction (slip factor) as in Table 10.2 (f < 0.55) ne = number of effective interfaces offering frictional resistance to slipKh = 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.

    mf = 1.10 (if slip resistance is designed at service load)mf = 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. Vsf = (f ne Kh Fo)/ mf

  • TABLE 10.2 TYPICAL AVERAGE VALUES FOR COEFFICIENT OF FRICTION (f)

  • 10.4Friction Grip Type Bolting10.4.2 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 ) / mf < (3 d t fyp)/ / mfTf = (0.9 fu A)/ / mf

  • BOLTS UNDER TENSION AND PRYING EFFECT

  • 10.4Friction Grip Type Bolting10.4.5 Prying Force

    = 2 for non-pretensioned and 1 for pretensioned = 1.5 for LSMbe = effective width of flange per pair of bolts(Conti.)

  • Table 1 Bolt Strengths in Clearance Holes in MPa Table 2 Bearing Strengths of Connected Parts in MPa DESIGN STRENGTHS FOR BOLTED CONNECTIONS

  • 10.5.9 Stresses due to Individual forces

    10.5.10 Combination of stresses10.5.10.1 Fillet welds

    Combined bearing, bending and shear (Conti.)

  • 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 Distances minimum 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 Fasteners spacing 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

  • GENERAL ISSUES IN CONNECTION DESIGNAssumptions 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

  • 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

    CONTENTS -1

  • Concentric ConnectionsMoment ConnectionsTYPES OF CONNECTIONSClassification based on type of resultant force transferred

  • COMBINED SHEAR AND MOMENT IN PLANE Bolt group eccentrically loaded in shear 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 Combined shear

  • COMBINED SHEAR AND MOMENT OUT-OF-PLANEBolt group resisting out-of-plane momentTi = 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

  • BEAM AND COLUMN SPLICEBolted Beam Splice(a)Conventional Splice(b) End-Plate SpliceStrength, stiffness and ease in erectionAssumptions in Rolled-section& Plate Girders Column Splices bearing type or HSFG moment splices

  • 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.

  • VBEAM-TO-COLUMN CONNECTIONS Simple beam-to-column connections a) Clip and seating angle b) Web cleats c) Curtailed end platee(a)(b)(c)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 onlyEliminates need to drill holes in the beam. Limit depth and thickness t < /2 (Gr.8.8) and /3 (Gr.4.6)

  • BEAM-TO-COLUMN CONNECTIONSRigid beam-to-column connections a) Short end plateb) Extended end plate c) Haunchedcolumn webstiffenersdiagonalstiffenerweb plate(a)(b)(c)

  • BEAM-TO-BEAM AND TRUSS CONNECTIONS(a) Apex ConnectionTruss Connections(b) Support connection Beam-beam connections similar to beam-column connectionsMoment continuity may be obtained between secondary beamsCheck for torsion in primary beams

  • FATIGUE BEHAVIOURFatigue leads to initiation and growth of cracks under fluctuating stresseseven below the yield stress of the material (High-cycle fatigue)

    Fatigue cracks grow from points of stress concentrationsTo 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 scaleComponents are designed below the endurance limit

    www.steel-insdag.org Thank You

    Teaching Resources for Steel Structures IIT Madras, SERC Madras, Anna Univ., INSDAG CalcuttaTeaching Resources for Steel Structures IIT Madras, SERC Madras, Anna Univ., INSDAG CalcuttaTeaching Resources for Steel Structures IIT Madras, SERC Madras, Anna Univ., INSDAG CalcuttaTeaching Resources for Steel Structures IIT Madras, SERC Madras, Anna Univ., INSDAG CalcuttaTeaching Resources for Steel Structures IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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