Bolted Connection Design Question Regarding Bending Moment and Tension

[AMM1086]

Hello all, I am designing a bolted connection for a table extension (steel) and have some concerns about the integrity of the structure. I am using 4x(3/8in) grade 8 bolts through 1/8in steel square brackets into a solid structure, and the extension is to stick out 20 inches, flush to the top of the table. The bolts are about 2in lower than the top of the table and my concern is the possible tensile stress and moment bending if larger forces are applied to the end of the table and potential failures of the system. Any advice on ways to analyze the tensile and sheer forces in the bolt would be a great help, thanks.

Alex

 

[drawoh]

This is a good question to ask on day[ ]one of an engineering course. Work out what loads the table must support. Draw a free body diagram of your legs. Work out the forces.

--
JHG

 

[desertfox]

Hi AMM1086

Try this site and scroll down till you see bolts withstanding bending forces.

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[AMM1086]

The design does not include legs to try to use minimal material and cut cost, it's for a drill bench extension to incorporate longer pieces on a machine with an inadequate work area. The image attached it a draw up of the extension, the shaded area being existing machine and the inner square is the location of the square tube frame. The math seems to suggest the design will hold for large loads (in the 6 to 10 ksi range), but just want to check the tensile forces in the bolts.

 

[Tmoose]

I need more pictures to understand what you are doing.
Is 6 ksi the tensile stress you have calculated in the bolt?

From what you supplied, it sounds like the bolts are down low, toward the bottom of the existing table, with little of the new table extension below the bolt centerlines .
So first, the bolts' location subjects them to pretty large tensile loads as a result ot the prying action at the new frame/table interface.
Additionally I would not expect anything made of 1/8 inch steel plate secured by 3/8" bolts to be a satisfactorily stiff flange, unless some strategically placed full height gussets are added quite close to the fasteners to provide a good load path.
When anchor bolts etc are farther than about 2 diameters from ribs, gussets, main tensile members, etc the flange thickness must be immense to prevent significant bending.

http://cr4.globalspec.com/PostImages/201111/22221_CA7157B9-AD6F-3C7A-E5F0004ACBBF6BFA.jpg

 

[desertfox]

Hi AMM1086

We could do with more detail but I think that the bolts/screws need to be as close as possible to the top of the table, in other words those blocks need to be turned through 180 degrees.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein