Verification Example - Slab on Ground - Post Loading (PCA method)
Description
This verification example utilizes Tekla Tedds to check a slab on ground with a grid of post loads such as from rack storage supports. This example is based on Design Example A1.3 of the ACI 360R-10 Guide to Design of Slabs-on-Ground (page 59). Comparisons and contrasts are tabularized and discussed regarding the results from Tedds and the ACI Design Example. The Tedds file used in this example is provided in the Tedds “Select Calculation” window, under Verification Examples.
Problem statement
Determine the slab thickness due to loading by a grid of posts.
References
ACI 360R-10 Guide to Design of Slabs-on-Ground
Concrete Floors on Ground (2001) by PCA
Example information
The post configuration and loads can be seen in Figure A1.4 of ACI 360R-10.
Loading: Post Load = 15.5 kips
Plate contact area for each post = 36 in2
Long spacing, y = 100 in.
Short spacing, x = 40 in.
Concrete compressive strength, f’c = 4,000 psi
Modulus of rupture = 9√f’c = 570 psi
Subgrade modulus, k = 100 lb/in3
Factor of safety = 1.4 (determined from ACI 360R-10 Table 5.2)
Notes
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The procedure to determine slab on ground thickness for post loads utilizes design charts published by Portland Cement Association (PCA) in Concrete Floors on Ground (2001)
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Both Tedds and the ACI design example utilize the PCA design charts found in ACI 360R-10 (Figures A1.5, A1.6, and A1.7)
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The thickness is based on limiting the tension on the bottom of the concrete slab
Comparison of Results between Tedds and ACI 360R-10 Design Example A1.3 | |||
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Component | Tedds Result | ACI Design Example 1.3 | % Difference |
Allowable stress | 406.6 psi | 407 psi | 0.1% |
Stress per 1,000 lb of post load | 26.2 | 26.3 (value of 26 was used) | 0.4% |
Required slab thickness | 8.08” | 8.25” | 2.0% |
Conclusion
Upon reviewing the results above, the determination of slab on ground thickness due to post loads by Tekla Tedds matches ACI 360R-10 design example A1.3. Differences between Tedds and the example can be attributed to rounding of values in the ACI design example.