Seismic Acceleration

[pba]

I have a small steel structure to design. Late in the design I have been informed that I need to consider seismic action. I've previously used UBC 97 for this using the static force procedure. For this project however all I'm given is an acceleration value of 1.6m/s2.

Can anyone advise how I use this value to do a simple UBC style check?

For your information the project is in Northern France and my background reading does not indicate that seismic assessment is needed.

 

[Taro]

First you need to determine whether that acceleration value is a peak ground acceleration, short period spectral response acceleration, or something else. Is the UBC even the appropriate building code for this area?

 

[Bagman2524]

In simplfied terms:
You need to determine the fundamental frequency of the structure to determine if it's "rigid" or not. Usually a f > 16.67 Hz is considered rigid. I'm calculating your acceleration to be about .16g. Multiply .16 x your structure load to get a lateral force that needs to be applied at the base of your structure.

 

[Taro]

It may not be quite as simple as that. Depending upon what exactly that acceleration value represents, you may need to consider soil amplification, inelastic response modification, and other issues. A request for more information seems to be in order.

 

[pba]

Taro, Bagman2524,

Thank you for your responses. Rest assured, the request for more information was made before I posted here!

Bagman2524, How do you determine 0.16g from an acceleration of 1.6m/s2? is this simply 1.6m/s2 devided by acceleration due to gravity (9.81m/s2)?

The structure will be rigid - It's essentially a concrete box.

Ground conditions do concern me as this will be on aluvial material of significant depth. I'm currently thinking that this 1.6 figure is the ground acceleration at the site location and accounts for the ground conditions. - This site is in Northern France where seismic evaluation in not usually required.

Taro, You are right UBC is not the appropriate code. There may be a French code but we have not been able to track that down (yet). There is also a Eurocode available but the format is rather different to UBC and is of limited value without the National Annexe which should give the country specific data and this is not yet published!

UBC gives me Zone 0 for Paris and Zone 2A for Bordeaux. The site is closer to Paris. I think I'll attempt to do a UBC type approach with assumed soil properties and see how close I get to 0.16g...

 

[Bagman2524]

I typically deal in english units, so I converted to ft/s2
1.6m = 3.25 ft. 1.6 x 3.25 = 5.2 ft/s2. Accel of gravity (g) = 32.2 ft/s2. 5.2/32.2 = 0.16g