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# Shear force on a bolt

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## Shear force on a bolt

(OP)
What are the shear forces on a bolt connecting a strut to a concrete floor? The strut is supporting a flight header for a stair platform and another strut supports the platform header.

### RE: Shear force on a bolt

If you take a long bolt horizontally with both hands and attempt to move the left hand upwards, you are subjecting the force you exert divided by the section of the bolt. Apply the concept to your case, seeking where such kind of force appears.

### RE: Shear force on a bolt

Not familiar with that structure, but in general, assuming the strut essentially does not carry moment at it ends (as the name "strut" implies), and neglecting friction, and assuming the strut has no other member connected to it between its two ends, then total shear force V on strut bolt(s) at floor would typically be V = P cos(theta), where P = strut axial force and theta = angle between strut axial centerline and floor.

But if the strut has any other members connected to it internally, between its two ends, the strut would also be a beam, having internal, beam shear forces, and the answer would be more complicated than the above.

### RE: Shear force on a bolt

errata:

...you are subjecting your bolt to shear, which is the force you exert ...

### RE: Shear force on a bolt

Isn't the Shear Stress value of a fastener generally given as a percent of its tensile strength per unit area?

Keep the wheels on the ground
Bob
showshine@aol.com

### RE: Shear force on a bolt

sprintcar,

The shear strength of a fastener may be given as a percent (e.g. shear strength = 60% of tensile strength), but the question relates to applied shear stress.  It makes no sense to relate this to the fastener's tensile strength.

### RE: Shear force on a bolt

If the strut is truely vertical, and only subject to axial loads, then the shear force on the bolt at the base is zero, and you could leave it out! However, there will always be some inclination, and some lateral loads, so a pair of bolts at the base is a good idea. Typically, a force of 2.5% of the axial load is used where a nominal connection is required.

Where a strut goes down to a ground-floor slab, consideration should be given to the possibility of an impact from a passing vehicle. Depending on the use of the building, there is a possibility of corrosion as dust collects round the base of the column. I would always have 2/M16 or 5/8" bolts.

Russell Keays

### RE: Shear force on a bolt

Insure you keep the shear plane out to the threaded area.

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