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BOLTED CONNECTIONS

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

In shearIn tensionCombined shear and tensionBlock shear

CONTENTS

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

BOLTS UNDER TENSION AND PRYING EFFECT

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

PRYING EFFECT AND END PLATE DESIGNMinimum prying force Q is given by The corresponding prying force can then be obtained as Q = Mp/n. If the total force in the bolt (T+Q) exceeds the tensile capacity of the bolt, then the thickness of the end plate will have to be increased. = 2 (non-preloaded) = 1.5 for limit state designw = width/pair of boltsPo= proof load in consistent unitsn is the minimum of end distance orthe minimum thickness of the plate is obtained as follows

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

FAILURE OF CONNECTIONS-1Shear Connections with HSFG Bolts(a) Slip Resistance(b) Bearing on PlatesPsl = 1.1 Ks poPbg = pbgd t 1/3 e t pbgKs =1.0 (clearance hole) = 0.45 (untreated surfaces)po= proof load

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

ft/Pt10.4Shear and Tension Interaction Curvefs/Ps10.4COMBINED SHEAR AND TENSION(a) Bearing Bolts(a) HSFG Bolts

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

Block ShearBLOCK SHEAR FAILURECapacity=Shear Capacity of AB + Tension Capacity of BCT = (0.62 Avg fy/M0 + Atn fu/M1)orT= (0.62 Avn fu/M1 + Atg fy/M0)

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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.

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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)

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

Thank You

Teaching Resources IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

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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