Using Strip Analysis to calculate Moment on a simply supported concrete slab bridge

[BGHamilton]

I am getting some crazy results on my strip analysis of a simply supported concrete slab bridge and I think I don't understand the application of the Live load.

AASHTO H20 Specify 32,00 pounds on the rear axle and 16,000 pounds on one wheel. The wheel foot print amounts to 10” x 20” which creates a load of 16,000/10/20 or 80 psi, (11,520 psf).

I have been assuming that since the strip analysis uses a 12” wide strip the length of the bridge span, this 11,520 psf should be used in the calculation of the Moment. But doing so results in the requirement of a 46 inch thick slab.

How does one apply the H20 loading in the strip analysis of a concrete slab bridge?

Thanks

 

[JoelTXCive]

What is your span?

Are you doing a uniform loading of 11,520? I think you need to do point loads.

Also, here is a link to TxDOT's standard details for pre-stressed slab beams. They come in 4ft and 5ft widths. You can compare your design loads to them to see if you are in the ball park.

Have a look at the 'Optional Design' section. There is an 'Ultimate Moment Capacity' for Strength 1.

For example, a 24ft wide roadway with SB15 (slab beam 15" thick) spanning 25ft has a capacity of 551 kip ft.

[link ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/standard/bridge/psbsts08-17.pdf]Link[/url]

ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/standard/bridge/psbsts08-17.pdf

 

[bridgebuster]

You cite H20, I'm assuming that you're following the standard specification. Look in Chapter 3, you can distribute the load over a wider section. Look for the distribution factor for slabs with main reinforcement parallel to traffic.

 

[BGHamilton]

JoelTXCive,

The Span is 18.5' the width is 20'.

The 18.5' includes the 2' wide abutments on each end. So the unsupported span is 14.5'

It is for a driveway entrance to an orchard. It crosses an irrigation canal, (12.5' wide)

Bridge Buster,

Thanks for the info. I will check that out.