op mounted timber joist hangers

huangyhg

top mounted timber joist hangers
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?
why not ask simpson?
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
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
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   
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
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?

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.

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?
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.
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