This document summarizes a study on bolt failures in a heavy steel lap shear joint. The goals were to evaluate grade 5 bolts currently in use, demonstrate sequential bolt failure, determine maximum load capacity, and calculate a safety factor for a heavy lift rigging fixture. Testing of an assembly with 8 bolts found failures at 2 bolts and 6000 lbs of load. Testing of an assembly with 6 bolts found failures at 4 bolts and 6000 lbs of load, indicating complete failure would occur at 3 tons of load. The document recommends stamping the plates with a maximum 1.5 ton load and changing to higher strength Grade 8 bolts to increase the bolt safety factor of 1.2 to an acceptable 1.5.

1. Bolt failure study in a heavy steel
plate lap shear joint
10/12/17 rev A
Don Blanchet
3B Associates
dwb3298@verizon.net
15” x 10” x 1” plates lap shear
¾ UNC-10 – 8 placesPrepared for
CBL construction
Vitoria , Brazil

2. Lift Rigging Safety

3. Goals
 Evaluate the grade 5 ¾ inch bolts that
are in use.
 Demonstrate sequential bolt failure.
 Set the maximum load capacity.
 Heavy lift rigging fixture application
factor of safety.

4. Bolt Torque

5. Results 8 bolts 2 failures

6. Results: 8 bolts 2 failures
Fixed end
welded
Load applied
6000 lbs

7. Results 6 bolts 4 failures

8. Results: 6 bolts 4 failures
Fixed end
welded
Load applied
6000 lbs
With a 3 ton load , the assembly will fail completely
In sequence 2-bolts, 4-bolts, 2-bolts

9. Bolt Safe loading – 1.5 Tons

10. Bolts factor of safety 1.2
or 20% margin of safety

11. Max stress in plates
factor of safety = 2.6

12. Recommendations
 Stamp plates with “max load 1.5 tons”
 Change from grade 5 to Grade 8 bolts