Specifying Weld at Angled Truss Connection?

[abusementpark]

I want to know how to specify a weld to get an effective throat equivalent to 3/16" fillet weld. See the attached sketch. Thanks!

 

[BAretired]

It is preferable to specify the load to be transferred from web to chord and let the shop figure out how to do it.

BA

 

[kingnero]

Why would you let the shop figure that out, when you do the design? A shop drawing should be read by a weldor, which means all relevant information should be on it. (correct? or are we talking about different situations?)
Specify the weld as you would for a "regular" (90°) fillet weld, but with the dimensions adjusted to your situation.

In the USA, I believe z-value is mostly used (leg length), in Europe we always specify a-value (throat depth).
Specify either one of those (according to your location) to your minimum requirements.

 

[BAretired]

It is more important for the design engineer to provide actual loads to be transferred rather than elaborate weld symbols. The specifics of the joint depend on the weld process to be used and on the weld position (flat, horizontal, vertical or overhead). It is common practice for the fabricator to provide weld joint cross sections on the shop drawings to complement the weld symbols if necessary to clarify weld details.

The above quote is from Article 8.2.6 of "Hollow Structural Section Connections and Trusses". As shown elsewhere in the book, the fabricator has more than one option to achieve the desired result.

BA

 

[hokie66]

I agree with kingnero that welds should be specified rather than left to fabricators. But this preference is geographically based, as in some areas of the world, fabricators apparently have the appropriate design capability. My approach to specifying the weld in the OP's sketch would depend on the load. A 1/4" fillet would likely suffice for this size member, but if heavily loaded or subject to fatigue, a complete penetration weld with backing bars may be required.

 

[abusementpark]

Seems like I should be able to just tell them the required effective throat dimension and let them figure out how to achieve it. Thoughts?

 

[hokie66]

I would size a weld to transfer the force you need on the two sides parallel to the members, then just use the same size all around. It won't look the same on the cross sides, but no matter.

 

[BAretired]

That works if the force to be transmitted is much less than the capacity of the HSS but it does not work if full strength development is required.

When full strength development is required, special measures are needed to develop the section where the wall is at an angle to the surface to which it is connected. These are outlined in the book I referenced earlier.

BA

 

[hokie66]

If full strength is required, the transverse part doesn't help much, and a doubler plate or a knife plate is probably required. I still think that decision should be made initially by the engineer, not the shop.

 

[wannabeSE]

The question, (how to specify a weld to get an effective throat equivalent to 3/16" fillet weld?) is not clear, I see three possible questions:
1. How is the effective weld size calculated for fillet welds at acute and obtuse angle?
2. How are (partial penetration) welds specified with an effective weld size equal to a 3/16" fillet?
3. Can the effective weld size be specified for fillet welds in lieu of the leg length?

 

[SteelPE]

If you are going to specify welds, you should have a copy of AWS D1.1 handy to answer any questions like this. I have never specified this type of connection however, I do have a copy of AWS, hopefully this will help answer some of your questions.

 

[BAretired]

The best way to make the toe weld equal to a 3/16" fillet weld is to miter the HSS toe wall to a vertical face, then use a 3/16" fillet weld.

Note that the vertical walls of the HSS are getting a greater length of weld because of the slope than they would if they met the chord at right angles. If the angle is 45^o, they are getting 1.41 times the length of weld which means the toe weld is not quite so critical.

BA

 

[SteelPE]

I just found this while looking for something else. Look on page 19 of the attached link.

http://e-book.lib.sjtu.edu.cn/nascc2004/data/contents/NASCC PDF files/Orthog-Skewed Shear.pdf