One-Way Slab (Suspended Slab) With Metal Deck Design under Wheel/Vehicle Loads

[Flexural23]

Are there any references I can follow to learn/design a slab under wheel loads?

In my case, I have a concrete slab with a metal deck supported by structural steel beams. This floor will see vehicle loads and I want to design the slab for moment & shear under a concentrated point load.

Any tips are greatly appreciated.

 

[precast78]

I would distribute your wheel load to e width according to AASHTO LRFD 4.6.2.10. On the side edge of the slab, you should reduce this e width. Dont forget to add impact to your factored load.

 

[Flexural23]

Where can I get the AASHTO LRFD standards?

 

[precast78]

Equation is just there so you do not have to use finite element analysis. Or just go ahead and use finite element analysis and apply the load per tire patch.

 

[Flexural23]

I rather use the effective width method but I do not have the reference you mentioned.

 

[PittEng88]

You can purchase the AASHTO LRFD specs right off their website:

https://bookstore.transportation.org/category_item.aspx?id=BR

Also, if you are looking for a design example I would recommend Design of Highway Bridges: An LRFD Approach by: Barker and Puckett. This is the book I used in grad school for my bridge engineering class. It has some pretty thorough examples for deck and beam design that follow the AASHTO specs.

http://www.amazon.com/Design-Highway-Bridges-LRFD-Approach/dp/0470900660

Hope this helps

 

[racookpe1978]

Are you sure you want, and are ready for, the responsibility for "designing" such a structure?

Your fundamental questions and your (lack of) apparent preparations (no references, requests for internet advice and basic loadings of a vehicle over a complex suspended platform in midair) do not present strong arguments that you are able to complete such a design safely for the public to walk under, work under, or park on such a cantilevered slab.

 

[KootK]

I've looked at this a bit in the context of forklift loads on deck slabs during construction.

Here's a Canam Example: Link

Attached is a thoroughly unvetted spreadsheet that a colleague produced for me.

Two things to watch out for:

1) SDI recommends against using the metal deck for dynamic loads such as traffic. That leaves you with just the concrete slab and any rebar/WWM to work with.

2) I personally have encountered a disastrous situation where I allowed forklift traffic on an exposed deck and it cracked all to hell over the supports. If the deck will be exposed in service, consider the use of meaningful amounts of top steel.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Flexural23]

I am dealing with two cases, one existing structure and another "new" ramp/structure. For the existing ramp, they want to use heavier vehicles than originally designed for + there is a lot of deterioration and damages.

I have followed USD (United Steel Deck) provisions in determining the effective width (one for shear and one for moment) and checked the one-way shear. However, since my truck loads are very high (~170kN with load/dynamic factors) even "d" away from the face of my beam I am having a lot of trouble. There is roughly a failure ratio of ~1.7.

Is there any specific areas in the Canadian Bridge Code (CSA-S6) that specifically deal with this case?

 

[mike20793]

What type of structure is this? The AASHTO loads may be too conservative if this is a parking type structure or access for emergency vehicles.

 

[Flexural23]

It is just an outdoor ramp and deck area for a steel factory. Basically structural steel framing with a concrete slab on top (with a metal deck as formwork). The vehicles go up the ramp and are usually parked at the deck area, the client has a list of vehicles that the structure/ramp may potentially see. But these loads are very high, the new portion of the ramp needs at least a 375mm thick slab to accommodate one way shear.

The existing portion is already damaged and has only a 200mm thick slab, and clearly will have issues.

I just want to confirm I have the right methodology going forward (using the effective width method).

 

[mike20793]

You could try stiffening the new slab with ribs. You can strengthen the existing slab using FRP. What kind of spans are you dealing with? It makes sense that the slab by itself would have a hard time with such heavy vehicle loads. When I used to load rate/design box culverts we got very thick top slabs (>12") once the spans got over 12 ft or so.

 

[Flexural23]

On the new ramp, the span is no more than 1.5m, the slab is not too bad for flexural, it is mainly the one-way shear that governs. I've seen a couple different sources specifying the effective width as:

1. E=(4/3)*X + d
2. E=bm + (1-X/L)*X (where bm = width of wheel + 2*concrete slab depth, X = location of load from edge of slab, L = span of beam)

I am not sure which is more appropriate, but the first gives a more conservative value.

 

[KootK]

It's an unfortunate theoretical quirk that your one-way shear goes off the charts as your concentrated load approaches the support. My company has a policy that fire truck accessible slabs need to be 9" min for this very reason. I doubt that things are really as dire as these equations would have us believe.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.