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

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Bill,
 
The GSREB is the usually-accepted standard for seismic retrofit of tilt-up buildings in S. CA. 
 
The retrofit will deal mainly with anchorage of the walls to the diaphragm [including anchorage at pilasters for tributary wall  mass], development of anchor loads into the diaphragm, and collectors at re-entrant wall corners.
 
Symmetry of the wall-anchor details is emphasized: one-sided PHD-anchors should not be used.  For a parallel-to-rafter anchor, I like to use a rafter-depth block between two rafters, the block backed with a 2x scab nailed to each rafter, with the wall-anchor rod centered on the length of the block, connected to the block with a Simpson BP plate-washer and nut.  For a perpendicular-to-rafter anchor, I would use an anchor rod centered between two sets of tightly-fit blocks that extend several rafter bays into the roof, connected to the remote rafter with a BP plate and nut.
 
Evaluation of the diaphragm is not included in the GSREB rules.
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net
 
 
 
 
----- 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