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Section 4.8
Bolt Summary
Last Revised:
06/16/2011
Strength Limit States:
All strength limit states take the form:
| LRFD |
ASD |
| Ru < ftRn |
Ra < Rn/Wt |
| Req'd Rn = Ru/ft
< Rn |
Req'd Rn = Ra
Wt < Rn |
| Ru / (ftRn)
< 1.00 |
Ra / (Rn/Wt)
< 1.00 |
Which is: FORCE on a bolt < STRENGTH of a bolt
The STRENGTH of a bolt is computed by:
Simple Tension or Shear
| Limit State |
Specification |
Nominal Capacity |
Typical Design Variables |
f |
W |
| Tensile Rupture |
J3.6 |
Single Bolt Capacity:
FntAb |
Bolt Material, Bolt Size |
0.75 |
2.00 |
| Shear Rupture |
J3.6 |
Single Shear Plane:
FnvAb |
Bolt Material, Bolt Size |
0.75 |
2.00 |
| Slip Capacity |
J3.8 |
Single Shear Plane:
mDuhscTb |
Bolt Material, Bolt Size |
0.75 |
2.00 |
Combined Shear and Tension:
Bearing Type Fasteners (-X or -N bolts):
- Modify the nominal tensile rupture capacity for the presence of shear (SCM
J3.7)
- Apply the shear rupture limit state without modification
| Limit State |
Specification |
Nominal Capacity, Rn |
Typical Design Variables |
f |
W |
| Tensile Rupture |
J3.7 |
Single Bolt Capacity:
F'ntAb |
Bolt Material, Bolt Size |
0.75 |
2.00 |
| Shear Rupture |
J3.6 |
Single Shear Plane:
FnvAb |
Bolt Material, Bolt Size |
0.75 |
2.00 |
Slip Critical Type Fasteners (-SC bolts):
- Modify the nominal slip capacity for the presence of tension (SCM
J3.9)
- Apply the tensile rupture limit state without modification
| Limit State |
Specification |
Nominal Capacity, Rn |
Typical Design Variables |
f |
W |
| Tensile Rupture |
J3.6 |
Single Bolt Capacity:
FntAb |
Bolt Material, Bolt Size |
0.75 |
2.00 |
| Slip Capacity |
J3.9 |
Single Shear Plane:
mDuhscTbks |
Bolt Material, Bolt Size |
0.75 |
2.00 |
The FORCE on a bolt is computed by:
Forces Concentric with the Bolt Group at the Faying Surface:
- All bolts are assumed to be equally stressed in
tension.
- All shear planes are assumed to be equally stressed in
shear.
Eccentricity in the Plane of the Faying Surface:
- Elastic Vector Method: See SCM pg 7-8. Computes shear in the
bolts. Direct method that is conservative and has an inconsistent
factor of safety.
- Instantaneous Center of Rotation Method: See SCM pg 7-6.
Computes the relationship between the applied load and the shear load in the
worst case bolt. Iterative method that is more consistent with test
results and not as conservative as the Elastic Method.
Eccentricity out of the Plane of the Faying Surface:
- Case I Method: See SCM pg 7-10. Basic mechanics (Mc/I) using
the compression contact area to find the tension in the worst case bolt.
Finding Ix
may be iterative. If the shear is concentric with the bolt group it is equally divided among the shear planes
otherwise use either the elastic vector or IC method to find the bolt shear
forces.
- Case II Method: See SCM pg 7-12. Uses basic statics (Applied
Moment = Pe = rat n' dm= Internal Moment) without
considering the contact area to find the tension in the worst case bolt. If
the shear is concentric with the bolt group it is equally divided among the shear planes
otherwise use either the elastic vector or IC method to find the bolt shear
forces.
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