OWSJ Roof deflection 2

[palk7 EIT]

Hi,

There is an 80-foot span open web steel joist, and apart from the roof loading, it also picks up the floor walking track hung through the hangers. In this case how to go about the deflection limit, the Live load limit L/360 allows 2.67" and total L/240 allows 4". These look large value, considering it also carry floor as well, should the maximum total deflection limit be limited to 1.5" (L/640)? on the drawing? How to go about this?

Thank you

 

[jayrod12]

Vibration is going to be the largest concern for a running track. I'd do some digging into that side of things and then come back with questions. I anticipate needing likely stiffer than even what you're proposing to keep the vibration checks in place.

 

[palk7 EIT]

With vibration, checked for the floor framing system (metal deck with concrete), and the floor beam configuration was ok, but didn't link that to the OWSJ connection with hangers. One end of walkway is connected to regular beam/ column and other end to the hangers and to roof joist

 

[KootK]

It would be useful to see what this looks like on plan.

Where track runs perpendicular to joists, usually you are hung so close to the joist ends that deflection isn't a problem.

Where track runs parallel to joists, a good strategy can be to install bridging to force three joists to share the hangar load.

 

[palk7 EIT]

Attached roof plan and floor level plan

 

[palk7 EIT]

Thank you KootK, attached a plan view, could you provide a prudent option for this situation

 

[KootK]

I'm a little tight on time this morning but I'll give you a quick run down on what I know and try to return later:

1) Get rid of those braces on the interior of the walkway. Surely you can get that done on the outside of the building and clean it up.

2) When I've dealt with this before, the architects have had a standard for how sloped a running surface can be. And it was more liberal than I expected. People do, after all, run on crowned street pavement without their ankles snapping etc.

3) This is one of those situations where a perfectly conservative design will sink you. If the slope and bounciness of the track has to be imperceptible during a blizzard and while a Navy seal unit is running along it in lock step, you're toast. So explain this to your client and target good 99.5% of the time.

4) With my previous recommendation, you should be good to go for joist impact on vibration.

5) Use a hanger setup that allows for field adjustment. You want to dial everything out that is not snow/live load.

6) Per @jayrod12, stiffness is your friend here. Go for whatever you think you can get without killing the joist design. L/1200, double joist... whatever. That said, an 80' thing will move appreciably under full design load and there's not much getting around that. The only full antidote is posts below instead of hangers above.

7) Watch the transitions into the corners. There will be deck twisting there as you transition from the two different OWSJ deformation regimes. I've done this as, I hope, a matter of thoughtful detailing:

a) A fair bit of track slab reinforcing near the corners.

b) Movement joints in the guard rails before and after the corners.

 

[jerseyshore]

If the slope and bounciness of the track has to be imperceptible during a blizzard and while a Navy seal unit is running along it in lock step, you're toast.

This is amazing.