Steel Structure Lecture on Bolts and Connections

1. 5/20/2022
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STEEL STRUCTURES
BOLTED CONNECTIONS
Dr Sarmad Shakeel
sshakil@nice.nust.edu.pk
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AISI/SAE STEELS
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• First digit
• The second digit of the series indicates the
concentration of the major element in
percentiles (1 equals 1%).
• The last two digits of the series indicate the
carbon concentration to 0.01%.
AISI/SAE STEELS
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AISI/SAE STEELS
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AISI/SAE STEELS
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TYPE OF BOLTS
Un finished bolts (ordinary or common bolts)
• A307 steel same as A36.
• Diameter: ½ to 1 ½ inches (increments of 1/8)
• Light structures and simple applications like purlins,
bracings,…)
High strength bolts
• A325 or A490 (Diameter: <=1 ½ inches)
• A449 bolts or A354 threaded rods
• Anchor rods F1554
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Rivet or bolts
• Cost (equipment, high strength)
• Seismic performance
• Labour (number and skills)
• Fire performance
• Dissemblance
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• Snug tight bolts
• Pre-tensioned bolts (70% of the yielding stress)-Seismic, fatigue loadings
• Slip critical bolts (same as pre tensioned except treatment of contact or fraying
surfaces) -only required when you have shear or combine shear or tension
Section J of AISC commentary guides you when you have to do the pre tensioning
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HIGH STRENGTH BOLTS
AISC Specification Section J
Methods for full pre tensioning (70% of tensile yielding stress)
1. Turn of the nut method (one third to one full turn following snug tight
condition)
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HIGH STRENGTH BOLTS
AISC Manual 16.2 Section 8
Methods for full pre tensioning (70% of tensile yielding stress)
2. Calibrated wrench method
3. Direct tension indicator
4.Twist off bolts
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HIGH STRENGTH BOLTS
Size of bolt holes
• Standard holes: 1/16 greater than the bolt dia.
• Oversized hole: greater construction tolerances. Not permitted for bearing type
connections
• Short and long slotted holes
• Section J3.2 of specification guides on which hole to use.
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HIGH STRENGTH BOLTS
AISC Specification Section J
Forces passing through the centre of gravity
Single shear or bearing connections (Forces overcoming the slip resistance)
Lap Joint (Centre of gravity of forces are not aligned resulting in couple which can
cause plates to bend)
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BOLTED JOINTS SUBJECTED TO AXIAL FORCES
Forces passing through the centre of gravity
Double shear or bearing connections (Forces overcoming the slip resistance)
Butt Joint (More capacity due to two shear planes, more symmetrical loading)
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BOLTED JOINTS SUBJECTED TO AXIAL FORCES
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Forces passing through the centre of gravity
Single shear or bearing connections (Forces overcoming the slip resistance)
Double plane connections (No bending moments)
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BOLTED JOINTS SUBJECTED TO AXIAL FORCES
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FAILURE OF BOLTED JOINTS
AISC Specification Section J3.3
To ensure bearing strength
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SPACING AND EDGE DISTANCE REQUIREMENTS
AISC Specification Section J3.4
To avoid damage during hole punching and end tearing
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SPACING AND EDGE DISTANCE REQUIREMENTS
• The distance from the center of an oversized or slotted hole to an edge of a
connected part shall be not less than that required for a standard hole to an edge of
a connected part plus the applicable increment, C2, from Table J3.5 or Table
J3.5M.
AISC Specification Section J3.4
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SPACING AND EDGE DISTANCE REQUIREMENTS
AISC Specification Section J3.5
To prevent moisture from entering joint locations
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SPACING AND EDGE DISTANCE REQUIREMENTS
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Assumptions: Loads passing through C. O. G (Centre of Gravity) exceeding the slip
resistance between the plates shear and bearing at bolts
Shear Strength
AISC Specification Section J3.6
For double shear strength is twice
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BEARING TYPE CONNECTIONS-LOAD VIA C.O.G
Shear Strength
AISC Specification Section J3.6
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BEARING TYPE CONNECTIONS-LOAD VIA C.O.G
Bearing Strength
AISC Specification Section J3.10
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BEARING TYPE CONNECTIONS-LOAD VIA C.O.G
Shear Strength
AISC Specification Section J3.6
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BEARING TYPE CONNECTIONS-LOAD VIA C.O.G
0.25 in def.
Design
consideration
Shear Strength
AISC Specification Section J3.6
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BEARING TYPE CONNECTIONS-LOAD VIA C.O.G
• Slip critical connections are only used in case when slip could cause significant
deformations or instability in the structure
• Common application of slip critical connections- connections with over sized
holes or slotted holes
• How to make slip critical connections- use pre tensioned or slip critical bolts
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SLIP CRITICAL CONNECTIONS-LOAD VIA C.O.G
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Slip resistance
AISC Specification Section J3.8
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SLIP CRITICAL CONNECTIONS-LOAD VIA C.O.G
Slip resistance
AISC Specification Section J3.8
Fraying surfaces defined in Section 3 part 16.2 of AISC
Manual
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SLIP CRITICAL CONNECTIONS-LOAD VIA C.O.G
Slip resistance
AISC Specification Section J3.8
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SLIP CRITICAL CONNECTIONS-LOAD VIA C.O.G
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EXAMPLES
Checks to be performed
• Gross section yielding of the plates
• Tensile rupture strength of the plates
• Bearing strength of the plates
• Shearing strength of the bolts
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EXAMPLES
• Column cover plates need to resist longitudinal shear
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EXAMPLES
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EXAMPLES
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EXAMPLES
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EXAMPLES
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EXAMPLES
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EXAMPLES
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EXAMPLES
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EXAMPLES
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Subjected to shear and bending moments
Centre of gravity of loads not aligned with C.O.G of the bolts
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Subjected to shear and bending moments
AISC Specification does not give the procedure for their analysis.Three methods
are available in general for their analysis
• Elastic method (Most conservative)
• Reduced or effective eccentricity methods
• Instantaneous centre of rotation method
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Elastic analysis
Friction or slip resistance between connected parts is neglected.
Bolts are taken as elastic while connected parts are taken as rigid
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Elastic analysis
Magnitude of forces in bolts due to moment Pe
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Elastic analysis
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Elastic analysis
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Elastic analysis
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EXAMPLE
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EXAMPLE
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EXAMPLE
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EXAMPLE
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Reduced eccentricity method
Takes into account the affect of slip resistance of fraying or contacting surfaces using
modified eccentricity for elastic analysis
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Instantons centre of rotation method (Used by AISC manual)
Takes into account the affect of inelastic behaviour of bolts
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Instantons centre of rotation method (Used by AISC manual)
• Point O, Sum of horizontal components of R must be zero and the moments
caused by these horizontal components about point O should be zero
• Moment of eccentric load about point O should be equal to sum of moments of
Resisting forces R about point O.
• For correct O, sum of vertical components of R must be equal to Pu
∆ is the total deformation of the bolt and
its maximum value for A325 bolt is 0.34
in
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EXAMPLE
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EXAMPLE
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EXAMPLE
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BOLTS SUBJECTED TO ECCENTRIC SHEAR
Instantons centre of rotation method (Used by AISC manual)
Applying hit and trial process for inclined loads and unsymmetrical bolt arrangements
would even be more difficult by hand
If situation does not fit in the table presented in part 7 of the manual, use elastic analysis
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EXAMPLE
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EXAMPLE
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EXAMPLE
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EXAMPLE
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EXAMPLE
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BOLTS SUBJECTED TO SHEAR AND TENSION
Elliptical interaction curve
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BOLTS SUBJECTED TO SHEAR AND TENSION
AISC A360 Section J3.7
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BOLTS SUBJECTED TO SHEAR AND TENSION
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EXAMPLE
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EXAMPLE
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EXAMPLE
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BOLTS SUBJECTED TO SHEAR AND TENSION (SLIP CRITICAL
CONNECTIONS
AISC A360 Section J3.9
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TENSION LOADS ON BOLTED JOINT
Effect of pre tensioning??
AISC A360 Section J3.6
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TENSION LOADS ON BOLTED JOINT
Prying action
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TENSION LOADS ON BOLTED JOINT
Prying action
AISC Manual Table 7-15
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TENSION LOADS ON BOLTED JOINT
Prying action
AISC Manual Chapter 9
THANK YOU
Dr Sarmad Shakeel
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