Dynamic Analysis of Foundation
Dynamic Analysis of Foundation
(OP)
How do we calculate Dynamic Spring and Damping Constants for bedrock and soil, for the case given below.
Type of Structure : Steam Turbine Generator
Operation Speed : 3600 rpm
Foundation : Pedestal Type, 46'x106'x42'high
Existing Ground Elev. : 790.0'
Top of Rock Elev. : 786.0'
Footing bottom elev. : 778.0'
Shear wave velocity (soil): 211 m/sec
Shear wave velocity (rock): 1275 m/sec
VALUABLE GUIDANCE IS HIGHLY APPRECIATED. THANKS IN ADVANCE.
Type of Structure : Steam Turbine Generator
Operation Speed : 3600 rpm
Foundation : Pedestal Type, 46'x106'x42'high
Existing Ground Elev. : 790.0'
Top of Rock Elev. : 786.0'
Footing bottom elev. : 778.0'
Shear wave velocity (soil): 211 m/sec
Shear wave velocity (rock): 1275 m/sec
VALUABLE GUIDANCE IS HIGHLY APPRECIATED. THANKS IN ADVANCE.





RE: Dynamic Analysis of Foundation
Also Foundation Analysis and Design by Bowles probably has the equations your looking for spring constants.
references by Gazetas is also good.
I don't know about damping though.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Dynamic Analysis of Foundation
RE: Dynamic Analysis of Foundation
I have drilled every equation from Bowles and came up with some numbers. The numbers were unacceptable by our client and also the Ao factor in this case was 12.5, but bowles procedure was good for Ao<1.5
I tried Novak, but the procedure in his 1974 paper is applicable to concrete and wooden piles and can be stretched to H-piles in some given conditions.
Dobry and Gazetas procedure is the same thing given in Bowles.
I personally did not check Richart,Hall and Woods,but my co-worker did, only to be unsuccessfull.
Thank you.
RE: Dynamic Analysis of Foundation
Richart, Hall, and Woods is an old text (1969) but I thought it did give enough info to set up a dynamic model. I could be wrong however.
Another idea is some software I saw that looked interesting at cadreanalytic that is described as a "utility for determining the stiffness values for foundations and footings in order to consider ground/structural interactions." I have no experience with this program.
The program is Rescol seismic version 2.0
http://cadreanalytic.com/products.htm
Regards,
-Mike
RE: Dynamic Analysis of Foundation
RE: Dynamic Analysis of Foundation
A steam turbine/generator pedestal is "tuned" to cancel out vibrations from operations. The typical pedestal is a very large, isolated, reinforced concrete "table", probably with about 8 stout legs that sits on a thick reinforced concrete inertia block. An inertia block 12 feet (or so) thick is not unusual. The top of the pedestal (table top) may be a 4 to 6 feet thick. The legs may be 8 to 10 feet square (or rectangular) in cross-section. A total height of 42 ft. is typical.
During both start-up and shut-down of the turbine/generator the rotating speed goes thru several resonant vibration frequencies. There is even some vibration at synchronous speed (3600 rpm for a 2-pole, 60 Hz machine). The dampening effect of this entire, integrated mass (the inertial bock, pedestal itself & the turbine/generator) is critical to keep vibration of the accelerating/decelerating/operating unit within acceptable limits.
I have had to explain this principle on several occasions (as an electric utility engineer) for legal purposes - in a "nutshell" have referenced to this whole structure as a kind of "anti-tuning" fork.
Now, I'll get out of the way and try to learn something from you.
www.SlideRuleEra.net
RE: Dynamic Analysis of Foundation
RE: Dynamic Analysis of Foundation
I for one always like to hear your two cents. Based on what you say, this one is beyond me too.
-Mike
RE: Dynamic Analysis of Foundation
Right now we are trying to create a model in Dynamat, Ensoft Inc. software. Hopefully this will work.
I have come up with some numbers based on the "FHWA, Geotechnical Earthquake Engineering for Highways, Circular No. 3" as suggested by Qshake. The numbers were in the same range of that of Bowles, but there were no bottlenecks in the procedure.
Next step would be comparing those numbers with Dynamat results and go from there. All your suggestions are really helping and I will keep you posted as I tackle this Dynamic Analysis.
MORE SUGGESTIONS ARE WELCOMED AND HIGHLY APPRECIATED.