how to calculate compression spring constant for modeling 1

[glad8tor]

ok the soils report indicates allowable soils bearing to be 2500 psf and recommended settlement to be 1 inch... i'm trying to model a mat footing and using spring constants (k/in)...how do i go ahead and calculate it?

Thanks

 

[fattdad]

You can't do it from the data provided. Bearing pressure (and settlement) has to do with soil stresses with depth below the foundation. Subgrade modulus has much more to do with the character of the soil in the near surface. You should ask the geotechnical engineer to provide an appropriate subgrade modulus for your slab-on-grade design. This will have to do with the soil type and density (whether natural density or compacted density of structural fill). I would anticipate a value of 100 to 200 pci, which you can somewhat enhance by thickening the base aggregate, per ACI 360.

Hope this helps.

f-d

¡papá gordo ain’t no madre flaca!

 

[onyeuko]

There are so many approaches to it but lets look at 2 of them:
1-proportion your foundation members such as the floor beams, the footing(strip or pad)etc. so that the bearing pressure is within 2500 psf. If you keep within this limit, the settlement should be with that allowed. You can calculate that using the standard foundation settlement equation. If it falls outside that recommended, then apply a safety factor of about 1.5-2.0 and re-proportion your footing.
2-Use the finite element modelling soft ware for foundation modelling to model your foundation(if you do not know of any good one, post again and ask me of one),then go further to check if the settlement calculated from the model is within that allowed for your structure. Check with the codes to be sure that you are obeying the norms as stipulated.
Good luck.
Teddy

 

[Ingseven]

I have noticed that there is a good approach utilizing the Dixon formula which use the E-modul and poissons ratio.

 

[oneintheeye]

isnt the modulus a function of the load required to cause settlement? Why then cant you divide one by the other, apply it to the raft? If using FEA why cant you using the area of the elements work out the spring stiffness at each node? I'm not advocating this approach here, just suggesting to gauge opinions.