Top mounted timber joist hangers 5

[valeriepsuae85]

I have a project where the contractor did not install the 2x wood on top of a W8 girder, he used 3/4" plywood on top of the steel girder. The nails in the top of the hanger were placed in the predrilled holes but on an angle (like a toenail). I know Simpson has tested their top mounted timber joist hangers to be supported by a 2x on top of a steel member but I think the plywood can also hold the hanger in place. Is it reasonable to accept this type of installation?

 

[civilperson]

Why not ask Simpson?

 

[valeriepsuae85]

I asked my local Simpson Rep. He says that they can only recommend the 2x on top of the steel girder because that is the only assembly they have tested. They are won't offer help of alternatives to this situation. They are looking to a professional structural engineer (me) to determine if the attachment is acceptable

 

[BAretired]

valeriepsuae85,

Toenails in 3/4" plywood have less lateral resistance than vertical nails in shear. Thus, the connection is not equal to the Simpson detail. You have no valid criteria by which to judge the contractor's detail. If you are wrong, the responsibility will be yours and yours alone. If you are right, you will gain little.

My advice is to leave it alone.



Best regards,

BA

 

[valeriepsuae85]

The joist hangers are not used to transfer shear in this case. The top mounted hanger is in bearing and the top nailing is to provide a positive attachment to the supporting member. Once the floor sheathing is in place the shear is transferrred through the sheathing nails, this is why we have the option to use face mounted hangers in some cases.

 

[BAretired]

I was not suggesting that the joist hangers are required to transfer shear. But in order to carry the full listed gravity load, the nails in a top mounted hanger need to develop horizontal shear and some tension on top of the beam. Otherwise, the light gage plate would simply bend, allowing the joist to fail under a lesser load.

Also, the horizontal nails shown in the attached diagram would contribute more strength in a 2x6 than the edge of a piece of 3/4" plywood.

Best regards,

BA

 

[Ron]

What series of Simpson device was used?

I agree with BARetired. 3/4 inch plywood has little edge nail retention capability and the top toe-nailing will result in a much reduced capacity depending on the angle of the nail and the quality of the plywood. Are you sure you have 3/4 inch plywood? It might even be less than that.

You also have a 3/4-inch elevation bust if the design was original for 2x material. Has this been considered?

 

[valeriepsuae85]

If Simpson requires the top nails to have shear capacity, they should also specify a minimum shear stress for the wood nailer. They do not, they simply say it needs to be a 2x.

Certainly they have to assume some minimum, there would be a reduction in capacity if I installed Hem Fir as opposed to Doug Fir since Doug Fir is about 20% stronger in shear. Even worse would be using some crappy Canadian Lumber.

Also, Simpson does not have a guideline for minimum attachment of the nailer to the girder. They leave that up to the designer. Most engineers will provide some arbitrary bolt spacing that is not based on required capacity. Architects rarely show anything for the nailer attachment. There's no code minimum either.

I'm not saying that this is a good thing or even close to the right thing to do, I'm just stating that if shear was required to develop at the top nail, Simpson or code should address a minimum nailer attachment for top mounted hangers to function properly. The top hanger seat will definitely deform under load but will not lose it's bearing because the floor sheathing is attached and will not move relative to the joist.

 

[valeriepsuae85]

Ron,
Simpson LB210 hangers were used. The reason the 3/4" plywood was used is beacause there was a problem with matching existing floor elevation so the contractor installed the 3/4" plywood to lower the new floor elevation.

I went to the site and measured the plywood myself. It's definitely 3/4" plywood.

The capacity of the hanger will be reduced, I agree, but no one can say if it is reduced significantly.

Why does Simpson use the 2x nailer anyway? Is it because they are easy to install, readily available, you can counter sink the attachment bolts, they like using 1 1/2" nails, or some other arbitrary non stress related reason? Do they even know?

 

[kslee1000]

Can the simpson hanger be welded? If so, have you thought to provided a 3/4" plate/bar locally to build up the required strength.

 

[BAretired]

valeriepsuae85,

I'm not sure what "crappy Canadian lumber" you were thinking about, but in Alberta, the most common lumber in the construction industry today is SPF (Spruce/Pine/Fir). It is softer than Douglas Fir and considerably easier to work with.

The reaction at the corner of the nailer is not vertical. Neglecting friction and strap stiffness, it would be at 45 degrees to vertical and the horizontal leg would carry the same tension as the vertical leg. Because of friction and strap stiffness, it is much closer to vertical but unless the horizontal leg is capable of carrying the entire reaction in bending, there will be a horizontal component which must be resisted by nails.

The shear in the two nails is equal and opposite to the horizontal component at the corner of the nailer. It does not need to be transferred to the flange of the steel beam. Thus a nominal connection of nailer to steel is acceptable.

If the horizontal leg of the hanger is capable of carrying the entire joist reaction in bending, without reliance on tension, then perhaps it is adequate as built.



Best regards,

BA

 

[valeriepsuae85]

Simpson hangers can be welded and a 3/4" plate/shim may be used theoretically; however, all framing is completed already and the top flange is not accessible without major demolition. Also, it would be dangerous to weld within the proximity of the installed wood framing without major demo.

Are the top nails in the hanger useless after installation of the floor sheathing? Are they there for erection purposes? If they are there to resist some force, what magnitude is the force? I need a number.

I need a little more than rhetoric if I'm to make the call to demolish and re-install these hangers.

 

[valeriepsuae85]

I just realized that in the process of trying to be succinct, my tone may read as a little harsh. And admittedly I a little pissed at Simpson for lack of support on this topic. My apologies.

Thank you all for contributing your opinions and sharing your experience.

Please keep them coming, it's more food for thought, and I'm still thinking about this one.

Sincerely,
Valerie

 

[Ron]

The building code compliance of Simpson's hangers (and other manufacturers) is contingent upon strict adherence to the filed "evaluation report". In this case, ESR 2553 applies to the LB210 hanger. When the device is not installed in strict accordance with ESR 2553, then it does not have code approval.

In this case, the use of 3/4-inch plywood deviates from ESR 2553 (see paragraph 3.2.2), therefore, this installation does not comply with the building code.

 

[kslee1000]

Thanks for the star, but I don't really desrve it. Ron has set his footing on firm ground, I can only agree with admiration.

 

[Ron]

kslee1000...that's very kind of you..I've just been around quite a while!

 

[kslee1000]

It only take 30 seconds to appreciate a good piece of advice which may benefit many.

 

[lsmfse]

Agree with Ron
Could you possibly provide sections of "nested" nailer between the beam flanges and use face mount hgr?(3x hgr to fit over the 2x hgr)

 

[msquared48]

I agree with lsmfse. This is the best solution and I have used it in the past in similar situations.

Mike McCann
MMC Engineering

 

[valeriepsuae85]

I thought of the nested hanger idea which is a great idea. In this case, the contractor used the web area to run plumbing waste lines along the beam length on both sides of the beam. Doh!

Ron's input is true. The installation does not comply with testing standard. I agree and Simpson agrees also.

The testing standard gives us assurance that design professionals do not need to calculate hanger capacities, its so easy an architect can do it. It would be nice if we had enough information to engineer an alternative.

With other structural materials, we engineer connections that have never been tested all the time, it's part of our profession and expertise to do so. I just don't like having to settle for cook book engineering for timber framing.


please keep ideas flowing, thanks