Pre Cast Roof - Point Loads from Hoist Rail

JoelTXCive · Feb 20, 2023

I have a small 1-story control building for a wastewater treatment plant that houses blowers and other mechanical equipment.

The 8" thick hollowcore roof of this structure supports a crane rail and a rolling 2-ton hoist. My employer has used this setup for many years, but I have never felt comfortable about the hoist setup; and have been able to avoid sealing the sheets for the 6 years I have been here. One of the older engineers in the office always sealed the sheet.

The older engineer is gone now and I'm stuck with the hoist detail on two current projects. See below:

There are no posts supporting the crane rail. The system relies upon composite action and sharing of load between pre-cast panels.

Questions:

Overall, question....What can I do to improve this setup?

[ul]
[li]~~I think that If I have a 2 ton hoist, then the normal OSHA/ASME rules would apply and the hoist's supporting structure needs to have a safety factor of 5? (Design point load of 20kips)~~ (edited)[/li]

[li]The pre-cast panels are a delegated design item. I could specify that the panels be designed for the 2-ton hoist and have it be part of the pre-casters' sealed submittal? I'm not confident at all that these hollow core panels can handle a 20kip point load though. (specifically the shear load)[/li]

[li]I could design a cast-in-place roof that I do have confidence works for the hoist; and then allow the contractor to submit sealed sheets for alternative designs if they have a better idea?[/li]
[/ul]

What do you think?

DaveAtkins · Feb 21, 2023

I faced this exact situation recently. We ended up with an S-beam which spanned across the entire building and did not fasten to the PCC planks.

DaveAtkins

JLNJ · Feb 21, 2023

I would not use a load factor of 5 on the forces from the rail to the precast. I would use "normal" hoist impact loading.

As for the load distribution to adjacent precast elements, that might need a call to a precast supplier. Two tons does not seem insurmountable.

I would probably start by modeling the system with the stiffness of the precast and the stiffness of the beam to see how the load path varies when you vary the location of the hoist along the length of the beam.

jayrod12 · Feb 21, 2023

I suggest reaching out to a local pre-caster that maybe you're friendly with. Ask him the reality of hollow-core supporting the 2 ton hoist. Doesn't seem unrealistic to me either.

JLNJ · Feb 21, 2023

You might want to look at your hanger rods. I don't think A325 is the proper spec.

JoelTXCive · Feb 21, 2023

Thank you JLNJ. I think you're correct. Those should be F1554.

I haven't done anything with the old detail yet other than print it out. It's left over from prior engineers in my office.

I'm going to reach out to a local pre-caster today and see how they feel about the hoist hanging from their roof.

Worst case, I think I can add some columns and have the crane rail be self supporting. Since I have two similar projects with the hoist, I should be able to split the design time between them.

KootK · Feb 21, 2023

1) I've done a bunch of these as the precaster's engineer. I'm usually fine with it for intermittent use / low fatigue situations.

2) I see no composite behavior unless there's a roof topping.

3) The precasters can do a lot with load distribution between planks to make a go of this kind of thing. See the PCI hollow core manual which can be downloaded various places for free.

4) I prefer the perpendicular to plank version of this. For the parallel to plank version, you can run out of effective shear width near the plank ends. One can, of course, grout cores etc to improve local shear capacity. I've always thought it might be nice to have the beam ends be wall supported but I've never actually executed on that.

JoelTXCive said:
I could design a cast-in-place roof that I do have confidence works for the hoist

Most of my concrete experience is with CIP and I started doing precast late in my career. Over time, I came to realize that many of the things that used to make me uncomfortable with plank really stemmed from issues that are also present in CIP but somehow wind up going largely unexamined in CIP where we somewhat blindly accept the dogma of what is and is not worthy of checking in that space.

In short, most EOR's considerably underestimate what can be done successfully with plank.

JoelTXCive · Feb 21, 2023

Good news.

I talked with a local pre-caster that does a large volume of hollow core panels.

They said the 2-ton hoist was no big deal and they will account for it in their design if it is on our plan sheets. For my 27' span, they suggested upping the section depth from 8" to 10" to be safe. Other than that, just make sure I call out the hoist in the delegated design text so that they are aware.

The connecting bearing plate to the panel will still be in my scope, but as long as get the load into the panel; they are good with it.

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Pre Cast Roof - Point Loads from Hoist Rail

JoelTXCive

Civil/Environmental

Recommended for you

DaveAtkins

Structural

JLNJ

Structural

jayrod12

Structural

JLNJ

Structural

JoelTXCive

Civil/Environmental

KootK

Structural

JoelTXCive

Civil/Environmental

Similar threads

Part and Inventory Search

Sponsor