The seismic upgrade must follow the most recent California Building Code the CBC 2016 and the USGS guidelines. The USGS guidelines are contained in USGS, Earthquake Hazards Program, Seismic Design Maps and Tools for Buildings and Bridges http://earthquake.usgs.gov/research/hazmaps . The seismic factors obtained depend on the site Longitude and latitude as well the soil type extracted from a geotechnical investigation and a soil report.
A sample analysis calculation is given here:
The seismic lateral forces can be calculated utilizing the California Building Code CBC 2013/2016. Based on the latitude & longitude for site location and the site characteristics, for example, the seismic factors are determined as follows:
Latitude 37.8000 degree North, Longitude -122.000 degree West
Site Classification “D” stiff soil profile.
The soil factors including maximum accelerations and design accelerations are compiled as function of the spectral acceleration and for example they can be:
- Site Coefficients – Fa=1.0, Fv=1.5
- Spectral acceleration for 0.2 sec. period (short) – Ss=2.013g
- Spectral acceleration for 1 sec. period – S1=0.786g
- Maximum spectral response acceleration (short) – SMs=FaSs=2.013g
- Maximum spectral response acceleration – SM1=FvS1=1.18g
- Design spectral response acceleration (short) – SDs=2/3SMs=1.34g
- Design spectral response acceleration – SD1=2/3SM1=0.79g
The structural engineer designing the foundation and framing must follow the guidelines given above by the geotechnical engineer when performing his calculations for both seismic retrofitting for existing structures and newly designed structutes.