Seismic Retrofit

[ZTGR]

Hi,
Thank you in advance for your opinions and recommendations.
We need to perform a structural retrofit analysis for a 6 story building built in the 60s. We have as built/construction plans that shows the foundation system to be 24-inch diameter piers drilled to 35 and 40 feet. We need to perform a geotechnical investigation to check the adequacy of the design with resepect to the foundation and seismic considerations. We are thinking to drill and sample using hollow stem drill rigs and CPTs. This is enough in my opinion to gather data to perform the seismic design and seismic hazards calculations. When do you consider using a geophysical survey for a seismic retrofit?

 

[hokie66]

If you have the as built drawings, the original geotechnical investigation should be available as well. Wouldn't that give you the same information as you are proposing to gather?

 

[ZTGR]

As built drawings are available, but geotechnical investigation is not available, the building was built in late 60s. Even no geotechnical information available on the foundation plan.

 

[hokie66]

Geotechnical engineers are generally well organized when it comes to filing away investigation reports for future use. If you can find out who did the 1960's report (that's not very long ago) or who was the piling contractor, you should be able to trace the report, even if the companies have changed hands.

 

[ZTGR]

Hokie66,
I gave what we have in hand. Even the City does not have further info. Thanks for ur advise.

 

[TDAA]

You can just do a standard investigation that would give you the data you would normally use.

As far as geophysical, I would consider using that about the same time I would on new construction - when it makes a difference in the site class (if using IBC) and thus causes a significant change in structural costs.

 

[cvg]

since geophysical methods (I'm thinking seismic refraction) are relatively non-destructive it may be useful in areas next to or between structures where you can't or don't want to bring in a drill rig.