Vertical earthquake component

[Hrc]

Hello,
Im trying to model a vertical earthquake component on a girder. I would like to know is it necessary to multiply my Time-history curve with the Curve Multiplier equal to 9.81 m/sec2 in Applied loading or not. Values of the acceleration in Time-history curve are in m/sec2.
Thank you!

[seismosoft]

If you are introducing your accelerogram in m/s2, you obviously need not to multiply it by 9.81.

Seismosoft Support

[lcasprini]

I have a question about vertical earthquake component.

I have realized that in seismostruct you can not insert more than one response spectrum.
Is that correct?

So the only way to assess the vertical component is to enter the "vertical acceleration factor" inside the combination of calculation?
So the vertical response spectrum is not indipendent but depends on the horizontal response spectrum by a coefficient.

Thank you.

[huffte]

Hi lcasprini. Your interpretation is the same as mine. The default value of 0.7 on the vertical component basically matches the traditional assumption that the vertical spectrum is approximately 2/3 of the horizontal spectrum. This is likely an area where significant research will be needed. Some studies have shown that this ration may be greater than 1 for some earthquake ground motions. For now, it seems that the 2/3-method is the most rational approach to take until codes, standards, and research can identify the circumstances for which the assumption is not valid.