Long span joist - Deck connection to exterior wall detail

[RFreund]

Which is "better" for the situation where you have a long span joist (in my current case 130') parallel to a rigid wall (i.e. masonry or precast):

Space the joist farther from the wall and have the deck bear on the wall?
- Cons - difficult to manage the camber and deflection of the joist relative to the stiff angle support.
or
Place a joist say 6" away from the wall and use a vertically slotted angle?
- Cons - Too much deflection for roofing membrane or something similar? Extra cost of extra joist?

EIT

http://www.HowToEngineer.com

 

[KootK]

I normally see this handled as follows:

1) Angle with no slots at the wall. You're right, baring special details, the roofing hates the movement.
2) Increase the stiffness of the first joist from the wall so that the transition is more gradual.

I'm not sure how practical this method would be for your situation though. It might be tough to double the stiffness of a 130' joist without out just flat out doubling up the joists.

At L/360, the center of your joist might deflect as much as 4" under snow load. If you go with the extra joist beside the wall, that connection might warrant some serious study to ensure that it can realistically sustain that degree of movement without locking up.

I wonder if one could make the deck adjacent to the wall a non-continuous single span to alleviate the deck moments? The rotation of that single span deck sheet ought to be on the order of three or four degrees.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[Brad805]

The extra joist will be a premium in this case unless you are using that as your chord element. If you would like to deal with the concern highlighted by Koot, you could use an extra joist in combination with a slotted JVI connector embedded in the wall. These connectors will restraint the joist laterally, but it will allow the joist to free-float vertically up to 3". We use these in precast quite frequently where we have long span joists parallel to our panels. I am not sure how well they would embed into a masonry wall given their size and shape, but it might be possible.

The easiest method would be to use flush embed in the wall. Typically the steel erector will best fit an angle to the pre-camber using straight segments as they weld the chord element to the embed plates. They can full pen the angle joints fairly easily if the angle thickness is reasonable. I doubt they will send the angle out to be rolled to the shape unless there is a lot of angle required. You will have to decide how to deal with the impact of the joist deflection in the last deck span.

 

[jike]

Place the 1st joist at either 1/2 joist space or full space from the wall. Rigidly fasten an angle on the wall to support the deck. If using the angle as the diaphragm chord then make sure you have a detail to provide continuity between segments of the angle. Alternately, use the 1st joist as the diaphragm chord.

The slope of the deck may require the last deck span to be single span (so it can flex). You may specify less camber for the last joist if you think that this will help.

 

[jike]

The profile of the angle fastened to the wall can either match the profile of the 1st joist or be level or anything in between depending on whether the top of the wall is a parapet or a gravel stop at the deck.

If you expect a lot of flex in the deck (at the first joist), you might consider a cover plate connecting the two decks together.

I hope these ideas help!

 

[RFreund]

This helps, Thanks!

EIT

http://www.HowToEngineer.com