Davit Loads

[PEinVA]

I have a scenario where I have my safety life line attachments are attaching to my composite steel beams. Obviously in the direction of the beam, I'm not worried about the imposed load and moment. However, how do I check if the deck is strong enough? Would I just impose a compression force on the concrete and see if shear bond is an issue?

I've never designed for these systems before so any help is appreciated.

Thanks guys.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[Bagman2524]

What are you checking the deck for? Is for the mounting of the davit base? If so you need to convert the moment at the base into tension and compression loads and check the anchor bolts for the tension load and the concrete for the bearing/shear load.

 

[PEinVA]

Bagman2524,
The issue is, will the composite beam/deck be strong enough in the weak direction of the beam. I've read when designing these attachments that the load needs to be assumed in all directions. So I am looking at the moment in the direction perpendicular to the span of the beam. Do I just get the properties of the composite beam in the weak direction and do a stress check?
Hope that helps with clarifying the issue.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[Bagman2524]

Yes, I would think so. Just put the crane in the position where it causing maximum loading on the beam weak axis and check the beam for these loads.

 

[PEinVA]

My boss has asked me to check the deck with the moment from the life safety line applied to it.

This means I'm applying the moment to the concrete only and determining what amount of reinforcing I would need to provide.

The moment is = 90 k-in.

How do I compute the effective width that I can count on from the concrete to resist this moment? If I have 30" of effective width, using 4 #8, it works. But when I go to 24", it won't work. I'm assuming a d at the center of the concrete, in this case 3.25"/2 = 1.625".

What do you guys think?

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[csd72]

Can you spread out your base plate (and anchors) to a width that works?

 

[PEinVA]

csd72,
Sorry for not stating this, but I plan on welding to the composite beam below the deck, but that moment is going to be transferred into the slab. also, how do I determine the effective width of the concrete?
Thanks

Rick

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[Bagman2524]

Seems like it remember 15t is a good number for effective width.

 

[msquared48]

Rather than go thru all this, why not add a temporary steel beam (or two) under the slab and anchor to that. Then the slab is taken our of the picture. The steel beam(s) could always be removed later when not needed.

Mike McCann
McCann Engineering

 

[PEinVA]

msquared48,
These are going to be permanent life line anchors for window washing and personnel maintenance. There are approximately 45 anchors along the roof for safety line tie back and a horizontal tie system. We were trying to reduce the need for structural steel because of how many anchors there were. The arch. didn't have all this in the original scope, so we're afraid it would look like we just didn't do our job if it adds a crazy amount of steel. Bagman2524, I'm using a concrete slab on metal deck, not just a concrete slab. Is 15t a typical value used due to some guidance in any code?

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[Bagman2524]

I don't think its' in a code. I remember finding this in some reference material/book. I used this to check a 4"-6" slab on a metal deck. If I can find where it came from I'll post it.

 

[Bagman2524]

ACI-318-05 Figure R13.2.4 (pg220) shows 8 x slab thickness as effective width to be used with a slab and beam acting together.

 

[Bagman2524]

That's 8 x slab thickness on each side of the beam. The total effective width would therefore be 16 x slab thickness + beam width.

 

[PEinVA]

Bagman2524 - The beams I'm using are #1 - steel beams with metal deck, this doesn't seem to apply to this scenario, #2 - I think I would consider it more if my beams were fully composite instead of partially composite, #3 - the method used in the steel deck manual for distribution of point loads is different than for a typical concrete slab, so I don't feel comfortable using that information in that way.


Thanks for the help tho.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke