Deck spanning wall to long span joist 2

[WWTEng]

Consider a long span roof joist; say 70’, parallel to a wall. The roof deck spans from a steel angle bolted/anchored to the wall over the roof joists. The bearing angle is obviously a rigid connection as it can’t deflect but the bar joist can deflect 2”-3” at the center under live load. I have seen this detail and used multiple times but I was wondering if excessive deflection (very long joist) could create any issue with the roof deck.

 

[Ron]

Not usually a big deal. If you want a bit more flexibility, cut a slot in the deck over the LSJ, just the top of the flutes, not the bottom. Be sure to attach the deck to the joist on both sides of the slot.

 

[SteelPE]

A bigger problem you may have is dealing with the camber of the joist. Your joist will have camber and the wall will not. Depending how close those two are together there may be an issue if not detailed properly. We usually end up with a bunch of large iron workers standing on the deck trying to get to down but for very long spans this will not work as the camber is just to much. Options you have to avoid this:

1)Compensate for the camber of the joist with the wall angle:
2)Specify the required camber for the end joist to be 1/2 the design camber.

This is similar to what Ron is referring to in his post above.

 

[WWTEng]

Ron,

Thanks for the idea. Could be useful in the future.

SteelPE,

Actually the side wall is a percast panel. Instead of embed angles I asked for embed plates and the angle is to be welded in the field so I think it would be easier to match the camber. Also, the joists are spaced closer next to the wall 2', 4' and then 5' c/c. So I think the LL deflection from angle to the first joist should be minimal (probably 1-1.5" or less).

 

[RFreund]

So you want the angle to be rigid? As opposed to putting a joist say 6" away from the wall and use a vertically slotted angle? would it be bad to do this, if so why? Cost? Too much deflection for roofing membrane if there is a parapet or something similiar?

Ron - I don't think I understand the slot concept. Could you maybe elaborate?

Thanks.

EIT