Simplest Double Angle Truss Connection?

[bookowski]

I have a double angle truss and I am looking for the simplest connection from web to chord. All members are double 3x3 and I need to get about 25k in the web at the ends (much less towards mid).

The building is located in a somewhat undeveloped area and the materials are limited and simplicity is key since this will be field constructed by local laborers. Material is their biggest expense, labor is cheap so I am trying to eliminate material from the connection.

Some info:
-Truss spans ~ 75+ ft.
-Hurricane Winds and partially open building so bott chords have a decent amount of compression (~50k), I have braced the bottom chords.
-Chords are 3x3x5/16 (they do not have access to larger than 3x3), web is also made of 3x3 angles
- They do have qualified welders (or so I am told).

I would like to avoid using a gusset at each node and welding everything up, however there is not enough weld length available if I try to just overlap the web angles to the chord angles. Using gussets at each node is a lot of plate material and fabrication, I am looking for a way to simplify this but still get a web to chord connection able to develop 25+ kips. Anyone have any ideas?

 

[Ron]

You're going to have unskilled labor build 75-foot span trusses on site? Not a great idea.

A gusset plate to pick up all the angles is the simplest connection. It can be bolted or welded, preferably welded.

 

[dik]

If labour skills are questionable, I might lean towards bolted connections with slip critical bolting, although they can mess this up, too... Structureal drawings should detail all connections.

Dik

 

[abusementpark]

Try using a WT for the top and bottom chords. That should give you more length to make the direct weld connection to the stem of the WT.

Are you going to be able to impose weld testing?

 

[bookowski]

I understand everyone's concern. However this is a situation where the resources are limited and there are limits to what we can do. As I originally posted, I am told that they will hire a couple of skilled welders, however the majority of cutting and fit up will be by unskilled laborers under the direction of one supervisor. Welds will only be visually inspected (and I am doubling the length of all welds compared to calcs).

Abusementpark - I thought of the WT's, those are not readily available and I'm trying to avoid it. I would have preferred the T's.

I'm skeptical of using bolts, I don't think they have the equipment/ability to fabricate with those kind of tolerances if at all.

What I was wondering was if anyone had a detail that avoided gussets. For example - has anyone ever turned the web angles 90 degress and then thread them through the chord angles welding the overlapping faces. I would then need a lot of stitch plates to tie everything together but this still seems simpler than all the larger gusset plates at each node....

Any other ideas to simplify the connection? The goal is to keep this simple in hopes that it can be built easily and correctly.

 

[OHIOMatt]

Are the webs double angle or single angle?

What is the depth of the truss?

 

[bookowski]

Webs and chords are all double 3x3, at least that's what I am currently showing. The double 3x3's are really only required for the web towards the ends but I kept it all uniform for simplicity. Due to the high wind loads all web members experience compression and tension depending on the case (gravity vs wind). The truss itself is like a scissor truss but the ends don't come to a point... not sure of the proper name. The depth is just over 2' at the ends and a little over 4' at the middle - it's vaulted.

 

[OHIOMatt]

I think that if you miter the webs and hold them just short of the 'k' of the angle, you should be able to get 2" on each side and 3"+ across the top of the top. If you do this on both sides, you should have plenty of capacity for 25kips.

Just put of curiosity, how are you adressing the horizontal thrust?

 

[bookowski]

Thanks OHIOMatt. I was thinking of doing this, I'm just not sure how well they will get that miter but it would definitely save a lot of plate material. The miter angle changes because the truss chords are not parallel. Seems like it may be the best option though.

Trusses sit on cantilevered concrete columns, the columns have been designed to take the thrust and they are fairly robust. They are actually restrained... hard to describe but there's sort of a mid-height slab tied into them. I also checked the truss with a roller in case the columns do not actually provide much resistance.

 

[OHIOMatt]

Just be sure to not the importance of maintianing work points. With this type of truss, you have a lot of likelyhood that the webs will be held apart. With angle chords, you want to limit the bending in the chords to as close to 0 as possible.

 

[bookowski]

Yeah, I have noted the work points on the drawings and tried to show graphically what that means (in case they are not familiar) so hopefully they get it close.

 

[bookowski]

OHIOMatt - I took a look and I don't think you can get enough weld length in there by mitering the web angles. You could get it for one leg of the web but there would be nothing left for the second leg, there's not enough room to fit both on a 3x3. Not if you need them to intersect at the WP. Looks like I'll have to stick with gusset plates.

 

[OHIOMatt]

What size filets are you using?

You would need 5" or so of weld on each side of the chord if you use 3/16" filet welds.

 

[bookowski]

Yeah it's not that a lot of weld is required, there's just not much room for both web angles to come together at that node and fit on the outstanding leg of a 3x3 (minus thickness and k). To intersect at the WP they are too close and there's not enough area to fit them. Once you start to draw it out it doesn't look so good. I don't trust little spits of weld even if calcs show that it's ok, I prefer to get at least a 2" run to trust it, I also want the welds somewhat balanced.