Hole Size and Strength

[dragoneggs]

Every structural bolt that I have installed on a bridge is tighten so that there is no movement between plates.
Bolted Bridge connections are designed based on clamping force not shear of the bolt. Riveted structures used the shear strength of the rivet body at the connections

To op , why not use bigger bolt. What exactly are you building.

I looked at snow plows on the job today. They all had slotted holes for adjustment with bolt size 5/8 or larger. They had washers on both nut and bolt side.

I'm not a bridge guy... aircraft more my specialty but generally one should design for a bearing failure rather than shear. This tends to minimize chances of catastrophic failure. Thus the thickness of the structure as well as the diameter of the bolt should be considered. But sometimes shear pins are purposely used to force failure at a location and reduce chances of damage to structure. Lots to consider when you really get into it... if it matters.

 

[dragoneggs]

Dragon
Why would you recommend reaming a drilled hole.
I agree that proper location ,(edge distance), spacing and tightening are important for proper performance of the connections
Irregularities (notches, cracks etc) are stress risers and can lead to failure.
Smooth Holes on the other hand are only a problems for the material is not enough section to handle the stress. Drilled holes are a standard method to repair cracks in bridges

I wasn't 'recommending' in fact I said a "way overboard" step would be to ream meaning that you get the hole size just right and surface finish finer than typical. This is of course overkill here but I was trying to edgemacate those who might be interested in a little more depth. Sorry about that!

 

[Streetcar]

Thanks for clearing the misunderstanding dragoneggs

 

[SPYDERLK]

There is a standard for bolt hole clearances. Typically a close fit and a free fit.
Standard Tap Drill / Clearance Holes Table - Engineer's Handbook -

Great chart! ... Wouldnt print well for me, but my wife worked on it and got it to come out with the full contrast. Now theres a copy in my shop.

,,,I go for the close fit area when parts are to see high or cyclic stress. High strength fasteners, when used for their capability will distort the head, shank, and the hole when significantly off center. This is hard on the hole and the fastener. Theres no way a washer can make up for it.
larry

 

[Streetcar]

When high strength bolts are used near their capacity , they distort and should not be reused in any hole

 

[SPYDERLK]

When high strength bolts are used near their capacity , they distort and should not be reused in any hole

Their true capacity however is quite a bit above size/grade torque specs. ... ~ 30%. I have tightened a plated and oiled Gr8 7/16x20 to 90ft lb. No plastic strain. I was surprised.