Dynamic Analysis of Foundation on soild rock 1

[dynamicd]

I would like to know if we are analysing and designing foundation of elevated centifugal machine supported on solid rock, (and no soil layer),
What are the soil spring constants to be used?

As rock is lava derived and foundation is kept after blasting, I presume there is no damping effect to be considered.

Secondly I think the soil spring cannot have tension but only can have enormous compression.

Do we have to anchor foundation in rock, --- hope not!!
The machine weight is aprroximately 900 kips and total foundation weight planned to be 4500 kips with approximately 4 ft thick mat.
We can use SAP 2000 non linear program to analyse.
Please suggest some ideas and if anyone has dealt this type of problem before then shed some more light how it was done.
Thanks.

 

[abhio]

The blasting is likely to shatter your rock and leave it in poor condition. So I would advise you to leave some thickness of rock to be cut out. As for spring constants, you are right in assuming that there would be no tension. You could carry out a plate load test to estimate the spring constants, as well as USPV (ultrasonic pulse velocity tests), as we have done for a particularly large reft foundation. There are some correlations between USPV and modulus of subgrade reaction available in standard litrature. Although Vesic's formula does not really appy for rock, it would be a good estimate.

 

[ronster]

For a structure of that size you should have a geotechnical engineer test and evaluate the bearing material and provide you with the design information. It seams inappropriate to ask this group if you have to anchor the foundation to the rock, as the structural engineer I assume you are performing a lateral load analysis and will determine if their are any tension forces at the base of the foundation.