Top mounted timber joist hangers
Top mounted timber joist hangers
(OP)
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?






RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
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
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
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
RE: Top mounted timber joist hangers
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?
RE: Top mounted timber joist hangers
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.
RE: Top mounted timber joist hangers
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?
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
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
RE: Top mounted timber joist hangers
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.
RE: Top mounted timber joist hangers
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
RE: Top mounted timber joist hangers
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.
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers
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)
RE: Top mounted timber joist hangers
Mike McCann
MMC Engineering
RE: Top mounted timber joist hangers
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
RE: Top mounted timber joist hangers
If powder actuated fasteners are a problem, use Teks screws (self-drilling, self-tapping).
At the terminous where you do not have a corresponding hanger on the opposite side of the beam, just use a plate and put fasteners on both sides.
I believe these hangers are designed to develop some moment due to deflection of the joist, so the resulting force couple translates to shear in the fasteners. With the fasteners I have noted, that should not be a problem.
RE: Top mounted timber joist hangers
RE: Top mounted timber joist hangers