shear strength of HS bolts 3

[Ash7633]

Hi everyone,

I need to carry an ultimate load of 31 kN on 2M20 - 8.8 bolts. the bolts are vertically inline and the load is eccentric to the centre line by 400 mm.

this results in 31 kN shear force vertical and mt=13 kN.m

the question is if I hang the load on the two bolts will the shear force distribute equally between the two bolts considering there is 800 mm distance between the two bolts?

 

[Lomarandil]

The shear will distribute evenly to the two bolts.

If your eccentricity is in the plane of the bolted connection, it will be resolved with additional shear, also evenly distributed (since you have only two bolts). See the elastic or instantaneous center methods.

If there eccentricity is out of the plane of the connection, that moment will be resolved with bolt tension, which will most commonly not be evenly distributed. (for gravity load, the top bolt controls).

----
just call me Lo.

 

[dik]

The load is small for the M20 fasteners... you might want to check to see if there are any code requirements for spacing of fasteners... 800mm seems like a fair distance.

Dik

 

[Ash7633]

Hi Lomarandil,

Thank you for your reply. that's correct.

Please, see attached image.

my concern is is there a possibility that the behaviour of the load pose more shear force on one of the bolts than the other. like for example the top one may carry extra shear than the bottom or worest take the full shear load in addition to the tension from the moment?

how to make sure that the bolts are fully engaged with the bracket and carry the load equally?

 

[dik]

Other than the eccentricity, a single M20 fastener should provide lots of shear capacity.

Dik

 

[Ash7633]

Hi dik,

Thank you for your answer,

as far as I remember from uni I was told that highstrength bolts do not have max. spacing reqruitement only min.

 

[Ash7633]

Hi dik,

you mean I compaire the 31 kN to 92.6 kN shear capacity for category /s and with 92.6 kN for TB bolts as bearing mode.

Is this right?

Thanks
Ashely

 

[dik]

something like that... I don't have the values in front of me, but I suspect a 12mm would also work...

Dik

 

[dik]

OP: "as far as I remember from uni I was told that highstrength bolts do not have max. spacing reqruitement only min."

Could be... just a caution... 800mm seems like a long distance between fasteners.

Dik

 

[r13]

my concern is is there a possibility that the behaviour of the load pose more shear force on one of the bolts than the other.

In my opinion, it can happen due to mishap in bolt installation. For example, the upper bolt is set exactly on center of the bolt hole, and the shank of the lower bolt is just in touch of the bottom of hole edge, for standard bolt hole with 1/16" larger than the bolt, while the upper bolt is engaged in bearing, there is still 1/16" gap above the lower bolt. However, I think the plate will give a little (when over stressed) to engage both bolts ultimately.

 

[dik]

I often rely on yielding of the material... been using plastic design for nearly 50 years...

Dik