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Re: Seismic Retrofit of a Tilt Wall Building in Southern California

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Hi Bill:
 
Check with the City before you start the design.  Not all cities recognize the GSREB.  Voluntary rehab of Tilt-up is not being pushed by several cities in the so cal area and the building officials/owners have forgotten the impact these buildings had during the not so recent Northridge earthquake.
 
FEMA -276 published in 1999 is a better document which provides the typical deficiencies and cost based on the seimicity.  This answers all your questions but somehow the costs seem to be on the higher side.  If you want I can fax you a few relevant sheets.
 
The basic things - walls anchors, straps, blocking, cross ties across the diaphragm (which can be installed from the bottom) and steel jacking of pilasters (this will bump up the cost which happened on one project - to prevent rocking in wall panels).  Mostly the work can be done from underneath the roof by opening up the insulation.
 
On one of the projects  I had worked, joists were found to be damaged due to water intrusion.  This was found out later in the construction when the plywood was removed or even when the bottom insulation was removed.  This bumped up the cost of construction.
 
Engineering fees:  better to quote a per SF fees rather than engineering time involved.  Engineering time during construction - normally we specify the minimum number of time we will be out in the field - say about 4 and then spell out when the contractor needs to call us for observations.  Anything beyond that will be T&M.
 
Hope this helps
 
- Aswin
_____________________________
Aswin Rangaswamy, P.E.
Los Angeles, California
----- Original Message -----
Sent: Tuesday, September 21, 2004 8:23 AM
Subject: Seismic Retrofit of a Tilt Wall Building in Southern California

I am going to look at a prospective project, the seismic rehab of a 53,000 SF tilt-wall building. I think the building is about 30 years old. Original design drawings are available (according to the owner). The building is located in Pomona, CA.
 
Some quick questions:
  1. Does the retrofit primarily deal with the attachment of the wall to the roof diaphragm?
  2. What is the current "preferred" method to attach the wall to the diaphragm, Zone4 or ?
  3. What about the roof diaphragm itself? Owner says the existing roof is only about 4-5 years old, but they always tell me that.
  4. Are there any other component(s) to address?
  5. Is the governing document GSREB or ?
  6. I know this varies, but, roughly, what should the owner expect to pay for engineering fees through plan check approval?
  7. Same as #5 except: What should the owner budget for engineering time during the construction phase?
  8. Same as #5 except: What is a reasonable estimate of construction costs for the rehab?
  9. Is there anything else I need to consider?
TIA,
 
T. William (Bill) Allen, S.E. (CA #2607)
ALLEN DESIGNS
Consulting Structural Engineers
http://www.AllenDesigns.com
V (949) 248-8588 ? F (949) 209-2509