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# Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

## Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

(OP)
Hi,

I'm designing a slab-on-grade subject to single-axle wheel load using ACI360 which refers to PCA 2001 Concrete floors on Ground for the attached chart.

Question.
What if design inputs are beyond the range of the chart? Stress per 1000 LB axle load < 3, Effective contact > 200 and wheel spacing > 120?
For your information, the slab is for mining dump truck with axle load of 550kN (124 kips) approximately.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

Design your slab on grade as a pavement section using PCA method or AASHTO method.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

(OP)
Thanks Ron,

I appreciate your comment and now Im using Chgapter 7 of ACI 360 Chapter based on Westergaard theory.

However for the chart solution, just wondered if we could extrapolate the curves for effective contact area and wheel spacing as attached.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

For something like that I'd be tempted to use a FEM concrete design software such as Ram Concept. Get the geotech to provide the subgrade modulus.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

Any chance of reinforcing the slab and perhaps allowing a thinner section. I'd suspect performance like a super highway is not needed permitting some lessening of the requirements for a lot of traffic.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

#### Quote (Baek)

Im using Chapter 7 of ACI 360 Chapter based on Westergard theory.
However for the chart solution, just wondered if we could extrapolate the curves for effective contact area and wheel spacing as attached.

I've used various (paper/pencil) graphical solutions (successfully) for a long time. IMHO, for this problem a qualified yes. See my comments on your sketch:

Consideration (sensitivity analysis) has to be considered on where to draw added contours. Even so, their location is an educated guess.
Cumulative errors on extrapolations could cause a fairly significant error on the final answer (pavement thickness). In other words, be conservative.
Bottom line... use a better method.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

(OP)
Thanks all, SlideRuleEra atrizzy oldestguy.

Basically I cleared my doubt on the extraploating method and its reliability. I didnt use it as we mentioned its not a good engineering practice for chart method as the author limited the range so we should be within.
I used following point load method as spacing between the two wheels is far thus no combined effect due to the two wheels.

Thanks again all.

### RE: Slab-on-grade Design Chart for Axles with Single Wheels ACI 360 PCA 2001 “Concrete Floors on Ground”

On my web site (http://rmniall.com) you will find two spreadsheets that perform rigorous analysis of arbitrarily-shaped pressure load(s) on an elastic slab on an elastic foundation.  One spreadsheet handles the case where the loading is on a fully infinite slab.  The other handles the case where the loading is close to the single edge of a semi-infinite slab.

These might be of some use to you, either in absolute terms or for a sensitivity comparison.

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