Sloped deck on a level roof joist

[Loui1]

Longspan roof deck on longspan roof joists. The profile of the roof required the deck to slope perpindicular to the joist.

Is the deck required to sit flat on the joist? All i see is a 1 1/2" bearing length requirement just to prevent slip off.

Should the joist be rotated about it's long axis or instead some sort of shim welded to the top chord to provide a sloped bearing surface?

 

[dik]

Long span joists typically have a bearing greater than 1-1/2" and a joist seat of 5" deep and depending on the jurisdiction may require bolting.

Generally, the most economic method of obtaining the slope is by varying the joist bearing elevation. The insulation thickness can be varied to achieve the slope. To weld angles to the top chord to achieve the slope is very labour intensive and costly.

dik

 

[civilperson]

Joists must be vertical or engineered for the angle of variation from the vertical. A welded shim on the low edge is usually sufficient for the bearing seat connection adjustment for the joist on girder. Check with deck manufacturer for allowability of point bearing on joist.

 

[Loui1]

dik,
Not sure you understand the problem. Due to the configuration of the roof, the slope runs PERPINDICULAR to the long dimension of the joist. Therefore, along the entire length of the joist, the deck will only hit one of the oustanding angle legs of the top chord.

 

[twinnell]

Why wouldn't your change the framing so that the roof slope is parallel to the joists? You have to be able to get a fastener from the deck to the joist (puddle weld or Screw). I have seen stepped joists but it isn't recommended. The step joists that I have seen had a bent plate welded to the top chord and oriented such that the roof deck had full bearing on the bent plate. Similar to what you would do for a hip beam that supported bar joists.

 

[Loui1]

Because this is an architectural building, not a nice rectangular box.

Most of the roof does slope parallel with the longspan joists, but at one end where transitions into another element of the building I have this situation.

 

[haynewp]

I would look into rotating the joist so the deck bears across the entire top chord. The joist mfr. will have to design the seats for this angle. You may want to also discuss this with your local joist manufacturer to ensure that this is feasible for your loads and angle. Also, until your diaphragm is completed and connected to the LFRS, your joist top chord will be experiencing out of plane bending, unless another load path is created during erection to account for this. Call Vulcraft.


When things are steep, remember to stay level-headed.

 

[jike]

The method required depends upon the slope of the roof. If the roof slopes 1/8" per foot, you generally can weld directly to the joist. If greater slope, use a bent plate on the joist. It becomes trickier if the slope is changing along the length of the joist.

I recommend that you get additiona info. by discussing this with an erector, deck suppier and fabricator.

 

[nutte]

Even if your slope is 1/2" per foot, you're only sloping an extra 1/16" over 1.5". I wouldn't think twice about it. Let the fat guy stand on it and weld it down.