Seismic Loading using COM624
Seismic Loading using COM624
(OP)
I have a question about using COM624 with seismic loads.
There is an option for the loading to be "cyclical". I assume this is what I want for seismic loading. Is this a correct assumption?
If I check 'Y' then I am asked how many cycles? What would be an appropriate number?
Next question has to do with the soil modulus 'k'. Should this value be adjusted for seismic loading?
Then I have a question about the p-y curves. If the program is doing cyclic loading does it adjust the p-y curves accordingly. In some literature I read it tends to indicate it does.
Thanks.
There is an option for the loading to be "cyclical". I assume this is what I want for seismic loading. Is this a correct assumption?
If I check 'Y' then I am asked how many cycles? What would be an appropriate number?
Next question has to do with the soil modulus 'k'. Should this value be adjusted for seismic loading?
Then I have a question about the p-y curves. If the program is doing cyclic loading does it adjust the p-y curves accordingly. In some literature I read it tends to indicate it does.
Thanks.





RE: Seismic Loading using COM624
If you are using cyclic criteria, then the p-y curves for cyclic loading are different than static curves. But I can't tell you how, exactly, since each researcher used a slightly different approach. You will need to read the technical paper(s) that formed the basis for the p-y curve(s) you are using in your analyses.
A word of caution: under some circumstances, the cyclic curves originally recommended - and incorporated in COM624 - may not be conservative. For example, the soft clay criteria proposed by Matlock (1972) includes a cyclic reduction factor of 0.72 for peak lateral resistance. However, tests performed by Shell Oil at Harvey, La. clearly show that more severe degradation can occur - for that site, the reduction should have been 0.29! That's a ratio of about 2.5...
P-y curves are a sophisticated tool - and not really recommended for novices. If you have a seismic problem, you need to hire a geotechnical consultant that is conversant in both seismic design and p-y curves. Tread carefully.
RE: Seismic Loading using COM624
RE: Seismic Loading using COM624
You can run quasi-static analyses using COM624, but you have to be careful to use an "appropriate" number of load cycles at the current load level to get a reasonable response. COM624 is still a lot better at predicting the moment distribution than other approaches, such as elastic half-space modelling. But be careful with deflections - all of the currently available solution techniques do a relatively poor job of predicting deflections (including COM624 and LPILE - COM624's commercial successor.)
COM624 is better with wind loading than earthquake loading - load application is slower and more akin to the conditions assumed for "cyclic loading." It isn't a perfect modelling match, but it's pretty good. It's very similar to the wave loads that are experienced by offshore oil exploration platforms. Cyclic p-y curves were designed to model the soil response to repeated wave loads on pile foundations. COM624 resulted from decades of research sponsored by the oil industry - particularly Exxon and Shell.
I suggest that you purchase a copy of LPILE from Ensoft in Austin, Texas. Not only will you get a GUI interface, you will get technical support. If you aren't familiar with p-y curves, then the support alone is worth the price of the program. Talk to Bill Isenhower - a friend and classmate at The University of Texas. He's very knowledgeable in this subject area -