Shear Stud Failures

[DHKpeWI]

We are in the construction phase of a low rise building where the above grade floors are composite steel beams. During a recent visit to a job site, I tested a sample of the shear studs by hitting them with a hammer until they were bent to 30 degrees from vertical per AWS D1.1 chapter 7. I found a failure rate on the welds of 20 - 25%. The contractor had an idependent agency test 200 studs and 15% (31) failed the bend test of AWS. What is an acceptable failure rate?

The failed welds that I observed had many holes or pours. The contractor believes that moisture is causing the porosity in the welds and thus the failures. It is my understandting that this kind of porosity can be caused by low weld energy.

As I read it, AWS D1.1 chapter 7 does not provide specific guidance about failures of installed welds.

The contractor went ahead and bend tested all the studs. I was thinking we should make them straighten the bent welds. Section 7.8 specifies that bent welds can be left in place, but I am not sure the intent is to have all the studs bent.

What are your thoughts?

 

[ishvaaag]

That at 30deg bent, the shear "cone" is moderately affected, hence the ability to anchor the shear the stress to the slab is also moderately affected. Say affection is proportonal to the base area of the cone shear, so (cos(30))^2/1^2=0.75%

25% reduction of the expected anchoring capacity is not much if on a small percentage of the studs, but on all, it is. Reduction can be even bigger seeing the more imperfect topping of the cone shear by the introduced inclination; so I would investigate how the beams fare with anchor capacities at 60 or 66% of what when straight expected, and would reinforce for the difference where required with complementary studs.

 

[ishvaaag]

Of course the % in the first paragraph above is errata.