Site Period
Site Period
(OP)
Over the years I have frequently seen this formula used to figure the period of a site (in seconds): T=4H/Vs
Where:
T= period
H= layer thickness
Vs= shear wave velocity
Does anyone know if this is accurate if you were considering just the upper layers of the soil? In other words, if I wanted to determine the period for (say) the top 3 meters......is that what I would plug in for "H"?
Thanks in advance.
Where:
T= period
H= layer thickness
Vs= shear wave velocity
Does anyone know if this is accurate if you were considering just the upper layers of the soil? In other words, if I wanted to determine the period for (say) the top 3 meters......is that what I would plug in for "H"?
Thanks in advance.






RE: Site Period
RE: Site Period
RE: Site Period
Otherwise if a firm answer from a geotech isn't forthcoming I'd bound the problem by assessing the impact on foundation size for different site periods (perhaps plus/minus some percentage either side of your interpretation of the site period as will vary in reality). May not even be an issue depending on the foundation mass for other design checks if there is a large difference between the forcing frequency and your ground harmonic frequencies.
Resonance could occur over a very short frequency range, so you need to assess a wide range of likely frequencies at relatively small increments to assess if their are likely to be any vibration/resonance l issues. Simply choosing one frequency to check is potentially ignoring resonance occurring just to one side of the chosen site frequency/period.
RE: Site Period
You are likely thinking of a surface plate test or cross-hole shooting. I would do it here.....but I don't have the time.
In any case, digging through more of my resources, I have a bit more confidence (at this point) in letting "H" be the depth that the Rayleigh wave is active in.