Slab-On-Grade For Cat D10

[LIGWY]

I am looking at designing a slab-on-grade crossing for a Cat D10. My calculations are showing a 30" Thick Pad with #8 Rebar Min 12" Top & Bottom. The Client would like to place old railroad rails upside down approx 24" apart for the equipment to go across so the top of the concrete does not get damaged from the tracks. Is there any information helping with the calculations when placing the railway beam in the top of the slab?

 

[msquared48]

Fine. Go to 36" and add the rails with the same rebar.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

I don't know what design method you're using, but 30" is WAY too much pavement section for a D10. Probably on the order of 3x.

More importantly, armor the joints and provide good load transfer. Thickness should be about 10 inches, tops. Reinforcing is probably not necessary at long as you have to control joints spaced properly.

I designed a pavement section for a CAT dealer about 30 years ago. Designed for D8's. Thickness was 8 inches, all joints were armored with 3"x3"x3/8" angle. Performed for over 25 years until they demolished the facility and built a new one. They used my design in the new one as well.

 

[dik]

Good sub-base... I did one about 30 years ago that's still intact and it was 12" thick; I don't recall the rebar, but it was likely #5@ at 12 top and bottom...

Dik

 

[dik]

Should have added that Cat tracks are intentionally designed to minimise the loading on what they are driving on... also, the slab being in good condition was likely overdesigned <G>.

Dik

 

[hokie66]

12" sounds about right to me, based on workshop slabs for repair of D10's, D11's, and drag line buckets. But we always use steel fibre concrete to make the surface tough. The loads are well spread, but the tracks still give the surface a hard time. That is the reason the client wants to use rails, but my coal mine clients never liked that approach. They told of rails being pulled out, and I believed them.

 

[Zambo]

At 24" spacing how high does the top of the rail track sections have to be above the top of the concrete slab?

But once you have these track sections there the appearance isn't going to be so good anyway, and a trip hazard. So I would have thought better to use the steel fibres and to accept some damage from the grouser plates.

 

[dik]

I've not used rail, but ones that I've seen, the rail is approx 1/4" or so proud of the concrete surface, and a concrete 'edger' has been used to round the concrete adjacent to the steel rail. Until this discussion, I had no idea of what this was really for... I had always thought for 'skidding' objects... not wear resistance...

Dik

 

[LIGWY]

I re-evaluated my calcs and do get at 12" thick pad. I have #8 at 12" o.c.
There are issues with the rails coming out of the concrete overtime. They have an exisiting crossing where one of the rails did come loose and was removed.

 

[Ron]

Agree with hokie66...steel fiber in the concrete offers a great deal of toughness.

The rails are problematic for several reasons. First, they will increase the potential for cracking in the concrete. Further, there is no guarantee that the tracks will alway ride on the rails, so the potential for spalling and rail pull out from tracks getting caught in the spalled edges is high.

I have had very good results with steel fiber enhanced slabs (don't waste your time with polypropylene or glass fibers).

 

[Zambo]

A detail I have often used is to cast 20mm steel plate flush with the top of the slab. This is good for providing anchor points in fab shops etc.

So in this case 20mm plates say 200mm wide with fixing tangs at the back could be cast-in flush. The advantage is that the plates will have no effect on the slab rebar design or position.

Then fix "something" to the plates to give the clearance (Dik suggests 1/4" proud). The "something" could be a 50mm wide plate tacked in place or a good quality plywood clamped down (this would be replaceable).

 

[dik]

I've used cast in inserts to secure switchgear to. The equipment is actually welded down. I thought the plates that Siemens spec'd were pretty massive for the equipment until I felt the breaker work... wow! Shook the buiding slab... fortunately these don't operate often. Acceleration in the order of 250g to 300g. They have to open within 1-1/2 cycles to prevent an arc. Yup... you should be able to secure something to cast in plates <G>.

Dik

 

[msquared48]

Wyy not secure the rail by drilling 3/4" holes at 24" oc, or some other spacing, installing #5 bar, bent down and hooked at the ends as in a modified hairpin. A continuous bar could be threaded through the hooks for better continuity.

The spacings could be altered from rail to rail to avoid interference.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[cvg]

cat tracks are designed to minimize pressure when resting on earth. However, when resting on hard surfaces such as concrete, all the weight is on the cleats of each shoe. The shoes are 24" long x 44" wide and there would be one cleat on each end of each shoe. Total track length is about 8 feet so there are 4 shoes on each side contacting the ground. At any one time you would have about 8 cleats(on each side) resting on the slab. Total weight is nearly 150,000 pounds. So the load on each cleat is about 10 kips. The majority of the force necessary to move this behemoth is transferred through these cleats to the steel rails. And if at a slight angle, these may be point loads. I would think long and hard about how you will anchor these rails down so they will not fail.

 

[dik]

cvg... it's not the cleats that I've seen problems with, but the turning operations that tend to 'tear up' the surface.

Your point about high local stresses from the 'sharp' parts of the track as well as the difference in hardness of the two materials (steel and concrete) is well taken.

Dik

 

[Zambo]

I would call the cleats "grouser plates" - hope this is correct. The point is that tracks for a crawler crane, for example are flat, and without these plates do less damage to a concrete surface. Earthworks plant such as dozers and backhoes have these plates which do the damage, especially when turning.