Two Way Truss System Conncection Detail

[norm2design]

I was wondering if any other member of this forum can help me out.

I am desiging a two way truss system and was thinking about how to make the connection at the junction of the two truss.

In such a case one truss will be continous and the other will frame into it. So the connection should be able to handle the force thru the top and bottom chord.

The truss span = 180 feet, 60 feet apart in both direction.
Top and Bottom Chord are W shapes.
Vertical are W shapes.
Diagonals are double angle.

Any suggestions or comments?

 

[structuresguy]

Hi

I recently designed a 200 ft X 250 ft span truss system, but my trusses were 25-30 apart c/c. I put the bottom chords layed horizontal (H instead of I). This way the webs were in line with each other. I then had one direction prefabed full length. The opposite direction was field fit (on the ground), shear clipped in place, and then full pen welded the flanges of the discontinuous piece to the continuous piece.

This was required to transfer the full design load, as the web alone was inadequate. You may or not require stiffener plates welded in to transfer loads across the continous chord. Also, obvisouly need to check any inadvertent moments due to fully welding the flanges. I found not problem for me, especially when you consider that there were large gusset plates for bracing welded in the vertical plane, so those would have restrained rotation anyway.

Hope this gives you some things to think about.

 

[trainguy]

You really should design your connections so you do not have to rely on a particular piece of plate (e.g. flange) working in 2 directions ( sigma x , sigma y )or else you'll have to check the combined stress (Huber-Mises) and this could unduly penalize your weight.

Check out Blodgett (Design of Welded Structures) pg. 2.11-5 and note that the tau-xy term should be squared, it is a typo.

Better yet, use separate tie plates above the flange you are intersecting.

tg

 

[dik]

I recently had an intersecting round HSS frame that requirred full penetration welds for both crossing tubes. This was achieved by turning a solid steel block and inserting it at the junction and welding the crossing tube to it.

 

[flamby]

How are you going to design it? The half-truss may transfer some lateral reaction to the full-truss at meeting point, so I would design the supports c & d of the half-truss as free to move.
|c
|o
a-------b
|
|d

The detail of support at c and d is more important than connection detail at o.

For detail at o, make sure you join the trusses at nodes only and not at midspan of any panel or member. You can weld gusset plates to the gusset plates of full-truss at right angles and use them. If you do this, the right angle T-gusset plate has to be stiffened suitably.