Steel Joists Bearing on Masonry Wall 2

[j19]

I'm looking at Section 5.3(a) in the SJI Standard Specifications and trying to wrap my head around the bearing requirements of steel joists on masonry walls. It says (in my words) that the joist shall extend not less than 4" over the masonry support and that the steel bearing plate can extend no more than 1/2" past the face of the wall. So, if I have an 7 5/8" wall thickness and allow the plate to overhang the wall 1/2" on each side, I can still get the minimum required 4" bearing length and allow for a small gap between joists (see attached sketch). Is that correct or am I misinterpreting the requirements?

 

[SteelPE]

You really think this is what you are going to get in the field? If you are worried about bearing, stagger the joists slightly and sleep well at night.

 

[manstrom]

yep. stagger the joists.

 

[jimstructures]

In my dealing with joist manufacturers they have been willing to treat those dimensions as nominal dimensions, so the block wall is 8" deep not 7 5/8" deep and the detailing correction of making the joist ~ 1/4" shorter on each end for erection ease is also ignored. So they accepted 3 11/16" of bearing on a steel angle acting as a bearing plate supported by a 8" CMU masonry wall. i.e. 3 11/16" + 1/4" detailing reduction = 3 15/16" bearing length.

Bottom line check with the specific joist manufacturer to find out what they accept.

Jim H

 

[BAretired]

I would not extend the plate beyond the face of the wall. I would use a plate with a dimension of 6" perpendicular to the wall. It would be centered on the wall and anchored in a concrete bond beam with re-bar or headed studs. The dimension parallel to the wall would provide ample tolerance for welding joist shoes and result in an acceptable bearing stress.

Each joist shoe would bear a minimum of 2 1/2" on the steel plate as provided in 5.3(a) of the SJI Standard.

BA

 

[msquared48]

I think you are reading this wrong BA, but please correct me if I am wrong here...

It seems to say in 5.3(a) that for the masonry wall bearing application, with the steel plates that 4" of bearing depth is required for "K" trusses, whereas, in 5.3(b), for bearing directly on the flanges of steel beams, only 2.5" of end bearing length is required for "K" trusses.

Two different situations here... I am looking on pages 239 and 240 in the specification section in my SJI 60 year manual...

Mike McCann, PE, SE (WA)

 

[BAretired]

Mike,
I attach a page from the SJI document.

The operative words in 5.3(a) are "unless it is deemed necessary to bear less than 4" (104 mm)". It is up to the specifying professional. If I were the specifying professional, I would deem it necessary to bear less than 4". Bearing on steel beams requires a minimum bearing length of 2 1/2". I see no reason why this situation is any different.

BA

 

[msquared48]

I will check on Monday, but I do not think that wording is in my manual.

Mike McCann, PE, SE (WA)

 

[BAretired]

Mike,

Whether a joist bears on a steel bearing plate or a steel beam flange, it is steel to steel contact. What is the justification for requiring a greater bearing length for a plate than a flange? (irrespective of what your manual says)

BA

 

[msquared48]

I had the same thought earlier,too,
regarding the steel plate. I am just saying what I think the spec says here.

Mike McCann, PE, SE (WA)

 

[msquared48]

IMy impression from reading the spec was that they were concerned with overstressing the masonry if the bearig width was less than 4". Why 4" is a magic number, I do not know. I was also wondering why they did not specify a minimum bearing plate thickness to decrease any deflection in the bearing plate that could produce steress concentrations on the masonry underneath. Seems like there would not be much, if any, anyway. Perhaps there is a commentary on the section?

Mike McCann, PE, SE (WA)

 

[msquared48]

BA:

I checked and my copy does not read that way at all. You must have a more recent version than mine -1985.

Mike McCann, PE, SE (WA)

 

[BAretired]

Mike,

I don't have a hard copy at all. I found a 2010 version of it on the internet:

http://www.newmill.com/pdfs/steeljoists-sec4.pdf

BA

 

[msquared48]

OK. Thanks BA. This is an obvious change in the design recommendations.

The bearing plate just has to be specially engineered if bearing less than 4" in depth on the masonry.

Mike McCann, PE, SE (WA)