Truss column connections 1

[Bertil B]

Hello!

I am currently working on a truss to column connection. The truss and column is build up from RHS, and the column-truss connections is currently a end plate and 4 bolts. (see attached picture). I have assumed that only shear forces will act. But after further investigation, I believe that the connection must handle some axial force. I did an analysis with both ends fixed, but then I get a huge amount of axial force in the connection. Is there anyone here that might help me out?

 

[Bertil B]

Picture of the truss/roof system

 

[BAretired]

1. How can there be axial force if you are not connecting the bottom chord to the column?
2. Should you connect the bottom chord of the truss to the column for building stability?
3. Can ordinary bolts be installed in the HSS?
4. Should HSS columns be left open at the top during construction? Cap plates keep rain out.

BA

 

[klaus.]

What is the problem ?
This is everyday work for s structural engineer ....
If you are not familiar with steel structure it might be better you hire a structural engineer


best regards
Klaus

 

[dik]

Can you bear the two outside wall trusses and weld (with temp erection bolt) and the interior truss on the same cap/crown plate and bolt through?

Dik

 

[MotorCity]

First, do not model a truss with both ends fixed. A truss, by the classic definition, only has axial forces. Model one end pinned and the other as a roller support. When the truss deflects downward, it will generate a huge axial thrust if you try to resist that load (which is what you are seeing). Let the top chord move longitudinally when the truss deflects

 

[rb1957]

if you want "truth", well as much truth as FEA will give you, then you need to model the posts, the adjacent frames, etc.

fixing both ends of the beam is a classic example of over-constraint. better if you support both ends with a finite stiffness (I typically use three rods and constrain the far nodes) and of course constrain rigid body freedoms.

Your beams are good examples of "properly" pinned beams, with very little moment stiffness at the ends. There will be a small axial force on the ends, reacting the inclined member.

This looks to be a pretty simple truss, does it Need FEA ? (though maybe you only went there to answer the axial load question ?)

another day in paradise, or is paradise one day closer ?

 

[BAretired]

There will be a small axial force on the ends, reacting the inclined member.

Really? How could this be?

BA

 

[rb1957]

how else to you balance the inclined member ? There'e a vertical reaction (presumably).

another day in paradise, or is paradise one day closer ?

 

[BAretired]

The vertical reaction is balanced by a tensile force in the end diagonal and a compressive force in the top chord. There is no axial force transmitted to the column connection, only shear. If the bottom chord is attached to the column, it would be a different story.

If building stability relies on columns and trusses as opposed to shear walls or bracing, then bottom chords need to be connected to columns in which case axial forces will be present in top and bottom chords at the column. Then, columns and trusses will be frame members.

BA

 

[rb1957]

I was thinking more of the horizontal truss member than the support.

However, with the symmetry of the beam there could be a self-reacting tension reaction in the columns, driven by the stiffness/flexibility of the columns. Practically negligible.

another day in paradise, or is paradise one day closer ?