High Seismic Loads 1

[ash060]

Working on project in a very high seismic area, Ss = 1.863 and S1 = 0.866. When I run the ASCE equations, I get a Cs greater than 1, is this something that happens? I am just surprised that the acceleration is greater than "g". So just wondering if this is a real phenomena.

 

[driftLimiter]

Inspection of typical earthquake response spectra indicates that buildings can experience spectral acceleration that is well over the peak ground acceleration. So if the site has a high expected peak ground acceleration, and the building lateral system has a low ductility, then yes it's certainly possible.

Most of the time I see a lateral coefficient greater than one is for anchorage of non structural components. But its certainly possible on a building as well.

 

[WinelandV]

Are equations 12.8-3 or 12.8-4 (ASCE 7-16) not doing anything for you?

Please note that is a "v" (as in Violin) not a "y".

 

[HTURKAK]

This could be valid for SFRS ; rigid , plain concrete wall systems ,cantilever column systems etc.Pls look for R = response modification factor in Table 12.2-1.

Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[ash060]

I was just spitballing numbers and got the initial result with Cs greater than 1, I have to start digging into things and refining my numbers, but I wanted a gut check from other engineers to make sure I wasn't heading down a ridiculous path.

 

[driftLimiter]

Well ash060 it is somewhat unusual its a really high seismic load. As HTURKAK mentions the table 12.2-1 provides limitations on low ductility systems in high seismicity regions, generally this pushes us to use a higher R factor.

Also the structural period can have a large effect on Cs so take a close look at that. Some structures may vary significantly from the estimated periods, some engineers employ more rigorous techniques to determine the period and take it into the Cs equations.

Finally Section 12.8.1.3 offers a means of reducing Cs if certain requirements are met.