9 Replies Latest reply on Feb 19, 2014 12:00 AM by Jared Conway

    Bolted cantilever beam problem

    Damon Frashure

      Ok, so I know I did stuff like this back in school, but I'm getting nonsense answers now.

       

      I have a beam with one end bolted to a wall and one end supported on a roller.  I can get the total bolt shear load easy enough and the roller reaction.  I need to know what axial forces will be induced in the bolts by the bending stress in the beam though.  I know that it will net zero, but I also know it's not so simple beacuse I get crazy big numbers.

       

      Thanks in advance.

        • Re: Bolted cantilever beam problem
          Justin Strempke

          If one end is bolted and the other is roller-supported, it's not cantilever then, more like a fixed-roller supported beam - correct?  The bolt stress will depend on a ton of things and assumptions, like the orientation of the bolt fixture (flat or sideways to a wall), number of bolts, bolt pattern, plate geometry and thickness.

           

          One approach would be to use the fixed beam end and find your reaction moment, and work with you bolting pattern and flange from there.  You could always refer to say AISC codes which have provisions for bolt sizing.  If you do need the axial forces, you could assume your flange as as rigid plate and use leverage formulas with the found moment.

           

          Just tossing some thoughts around, if you could give a screen shot or a sketch of your setup it may be more helpful.

            • Re: Bolted cantilever beam problem
              Damon Frashure

              The top of the beam has a 3500lb load distributed on it, and the end has 4 bolts in it.  The 4 bolts are on a 100mm x 300mm pattern.

               

              I'll look at the AISC and see if we own copies of the codes, but It's also an oddball situation where I'm having to use Siegmund connecting bolts to hold together this welding fixture.

                • Re: Bolted cantilever beam problem
                  Justin Strempke

                  That is one amazing octagonal flange plate!  As for your beam flanges, if one oct plate is fixed and the other on roller, it appears your beam flanges are fixed-fixed, though I suppose translation is allowed on the end...  Most of your bolt stress will be shear unless you have substantial beam deflection to warrant prying.

                   

                  Out of curiosity, what bolt loads are you showing?  Any preload, tight-fit, etc?

                    • Re: Bolted cantilever beam problem
                      Damon Frashure

                      The Siegmund welding fixtures we use are beasts, that's for sure.

                       

                      When I do a hand calc on the beam assuming moments about the nuetral axis, I get a bolt tension of 12,000 pounds (ish) and shear of ~550lb.  After 8 hours of running an FEA over night on it, all of my pinned joints are less than a few thousand pounds axial, but several thousand pounds shears.

                       

                      The beam has a slip joint on one end, so I was assuming that only the pin was taking the load (seemed more conservative than assuming fixed-fixed).

                       

                      I'm not feeling so nervous about these joints failing any more and crushing one of my welders, but we'll see when I get back allowable connecing bolt numbers.

                • Re: Bolted cantilever beam problem
                  Jared Conway

                  What values are crazy big? (Haven't run your model)

                   

                  The solve time may be expected with bolts and no penetration. Did you try running as all bonded just to see if it runs to completion? There may be another setup problem that is causing the run time issue.