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DEPARTMENT OF CIVIL ENGINEERING

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SEMESTER- 5^TH

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SUBJECT- STRUCTURAL DESIGN – ii

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TOPIC – BOLTED CONNECTIONS

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BY- ER. ABHISEK MOHANTY

(Lect In Civil Engineering Department)

AY:2021-2022

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BOLTED CONNECTIONS

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

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In shear

In tension

Combined shear and tension

Block shear

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CONTENTS

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INTRODUCTION

• Designed more conservatively than members because they are more

complex to analyse and discrepancy between analysis and design is

large

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• In case of overloading, failure in member is preferred to failure in

connection

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• Connections account for more than half the cost of structural steel

work

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• Connection design has influence over member design

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• Similar to members, connections are also classified as idealised types

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Effected through rivets, bolts or weld

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• Codal Provisions

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Shear Connections

Tension Connection and Tension plus Shear Connection

TYPES OF CONNECTIONS -!

Single

shear

Double shear

Classification based on type of force in the bolts

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BOLTS AND BOLTING

Bolt Grade: Grade 4.6 :- f_u = 400 N/mm² and f_y = 0.6*400 = 240 N/mm²

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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

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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

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FAILURE OF CONNECTIONS

(a) Shearing of Bolts

(b) Bearing on Bolts

(c) Bearing on Plates

Shear Connections with Bearing Bolts

P_s = p_s A_s where A_s = 0.78A

P_bb = p_bb d t

P_bs = p_bs d t ≤ ½ e t p_bs

Bearing Type Bolts

Shear capacity of bolt

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Reduction factor in shear for Long Joints

Reduction factor in shear for Large Grip Lengths

β_lg = 8 d /(3 d+l_g)

Reduction factor for Packing Plates

β_pk = (1 - 0.0125 t_pk)

Bearing Type Bolts

Bearing Capacity of bolt on any ply

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Tension Capacity

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Bolt subjected to combined shear and tension

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V_sb = (2.5 d t f_u )/ γ_mb

T_b =(0.90 f_ub A_n)/ γ_mb < (f_yb A_sb (γ_m1 / γ_m0))/ γ_mb

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FAILURE OF CONNECTIONS-1

Shear Connections with HSFG Bolts

(a) Slip Resistance

(b) Bearing on Plates

K_h =1.0 (clearance hole)

μ = 0.45 (untreated surfaces)

F_o= proof load

V_sf = (µ_f n_e K_h F_o)/ γ_mf

V_bf = (2.2 d t f_up ) / γ_mf < (3 d t f_yp)/ / γ_mf

Friction Grip Type Bolting

Slip resistance

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Where,

µ_f = coeff. of friction (slip factor) as in Table 10.2 (µ_f < 0.55)

n_e = number of effective interfaces offering frictional resistance to slip

K_h = 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.

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γ_mf = 1.10 (if slip resistance is designed at service load)

γ_mf = 1.25 (if slip resistance is designed at ultimate load)

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F_o = minimum bolt tension (proof load) at installation ( 0.8 A_sb f_o)

A_sb = shank area of the bolt

f_o = proof stress (= 0.70 f_ub)

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Note: V_ns 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.

V_sf = (µ_f n_e K_h F_o)/ γ_mf

TYPICAL AVERAGE VALUES FOR COEFFICIENT OF FRICTION (µ_f)

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BOLTS UNDER TENSION AND PRYING EFFECT

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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

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Concentric Connections

Moment Connections

TYPES OF CONNECTIONS

Classification based on type of resultant force transferred

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BEAM AND COLUMN SPLICE

Bolted Beam Splice

(a)Conventional

Splice

(b) End-Plate

Splice

Strength, stiffness and ease in erection

Assumptions in

Rolled-section

& Plate Girders

Column Splices – bearing type or HSFG moment splices

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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

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(b) Semi-rigid – model actual behaviour but make analysis

difficult (linear springs or Adv.Analysis). However lead

to economy in member designs.

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(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.

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BEAM-TO-COLUMN CONNECTIONS

Simple beam-to-column connections a) Clip and seating angle

b) Web cleats c) Curtailed end plate

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(a)

(b)

(c)

1. Economical when automatic saw and drill lines are available

Check end bearing and stiffness of seating angle

Clip angle used for torsional stability

2. If depth of cleats < 0.6d design bolts for shear only
3. Eliminates need to drill holes in the beam. Limit depth and thickness

t < φ/2 (Gr.8.8) and φ/3 (Gr.4.6)

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BEAM-TO-COLUMN CONNECTIONS

Rigid beam-to-column connections a) Short end plate

b) Extended end plate c) Haunched

column web

stiffeners

diagonal

stiffener

web plate

(a)

(b)

(c)

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TRUSS CONNECTIONS

(a) Apex Connection

Truss Connections

(b) Support connection

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Thank You