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Dynamic Shear Modulus vs. Static Shear Modulus

Dynamic Shear Modulus vs. Static Shear Modulus

I'm being asked to design a footing for a piece of vibrating equipment and the geotechnical report gives no dynamic soil properties. The goetechnical engineer completed their work over 3 years ago, long before my firm was even hired, and there's no way the client will pay for further geotechnical investigation at this stage.

Question #1: The geotechnical report does however give static soil properties. The area is primarily meta-sandstone. I'm looking for a formula that relates the dynamic shear modulus of rock (specifically sandstone) to the static shear modulus. Is there such a thing?

Question #2: The static shear modulus is given in the report as 80 MPa. Does that seem to be in the ballpark?

RE: Dynamic Shear Modulus vs. Static Shear Modulus

DCBII, do you have the results of any geophysical survey in the area? with a Vs (sher wave velosity) value? The 80 MPa value doesn't sound unreasonable, we usually define a Gmax or G0 which means G at small deformations (usually measured by geophysical means), then we should apply a degradation scheme which is different in dynamic and static conditions. So if your G is a G0 there might be no degradation depending on the machine, otherwise a totally approximate way to degrade is to apply a 0.5 factor, which is also applied to static degradation.

Bottom line, does the report specify Gmax or G0 or just G static? To be more precise, a static G should have an 'operational' label which means it has already been degraded

RE: Dynamic Shear Modulus vs. Static Shear Modulus

It calls it an "Estimated Static Elastic Shear Modulus". It does not specify whether or not it's been degraded. I do have a seismicity report, which gives a response spectrum for a shear wave velocity of 1800 m/s, but I don't think that's necessarily the shear wave velocity on site. Typically the response spectrum values are generic and need adjustment using coefficients to suit actual site conditions.

RE: Dynamic Shear Modulus vs. Static Shear Modulus

Hello, i am curious have you fixed the problem ?

RE: Dynamic Shear Modulus vs. Static Shear Modulus

Dear friends, u can use limit analysis for your work. in this method there is no need to use young modulus and shear modulus. u can download basic information from this link:

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