First Hi-Rise Fiberwrapped Seismic Upgrade in San Francisco 

The existing building could not be seismically upgraded with steel reinforcement because of the substantial amount of steel imposed an unacceptable load on the existing foundation piles.
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Exterior Wall coverings - FRP option: Under the voluntary seismic upgrade plan, our engineers and the Building Department  have agreed to convene  a peer review panel to evaluate  the use of “Fibrwrap,” a  fiberglass reinforced polymer (epoxy resin) , or FRP, as the main component  for the proposed seismic retrofit of the residential towers. The material provides structural strengthening when it is adhered  or bonded to an existing wall surface, such as the CMU walls of the residential tower. The FRP application can then be finished with a basic paint, plaster or intumescent  paint coating. With a basic paint finish, the overall thickness of the FRP system is about 1/8”.  


Questions to be resolved with the Building Department: Although the FRP will be used for structural purposes and evaluated by a peer review group,  we are seeking Building Department  comments regarding other considerations  related to its use . Our residential towers are located next to an adjoining public way, Clara Street, whose centerline would be treated as an adjacent  property line that is less than 20 feet away, under UBC 503. The existing exterior walls are bearing walls, reinforced CMU, and based on location, meet 2 hr NC rating as required for an R-1 Occupancy  and Type 1 Construction -UBC Table 5a. (See Dwg A1.0 & A3.0)      FRP in its basic paint form does not have a flame/surface burning classification from ASTM E-136 test, however the manufacturer  has been in the process  of obtaining this testing (FRP has previously been tested in British  laboratory  for a rating of Class II). Before its Class II rating can be verified by the ASTM test, what will be required by  the Building Department  for FRP to be used  architecturally  as a covering on the exterior  walls?  After it receives its rating, assuming it meets Class II, would those requirements change?   As mentioned, FRP comes in a various finishes, including an intumescent  paint finish which  has been tested and documented by ASTM for a class 1 rating (see enclosure), or a plaster  finish covering.  If a plaster finish coat is used as an alternate to the basic paint finish, is there a minimum plaster thickness  that will be required?

Interior Wall coverings - FRP: Similarly the FRP is used to provide shear strengthening at the interior corridor walls that are composed of CMU and act as bearing walls. FRP is scheduled to be applied to these corridor walls  in conjunction with a cover layer of of 5/8” type X gypsum board on 7/8” metal furring. This assembly covering met the  interior flame spread  requirements required for “other exitways” per UBC Table 8B, and to satisfy the requirement of UBC403.19, that non-conforming finishes be surfaced with an approved fire-retardant coating.  Building Department confirmed this method of “coating,” and accepted  subsequent data from ASTM test  when the material UL tested met Class II rating.   Once tested, the addition of gypsum board covering would no longer be required. even if the rating had  come back as a Class III material , based on  reductions allowed  for tested materials under Appendix Chapter 3418.2 item 20?  (For R1 and A3 occupancies, Table 8B requires  a Class I flame spread on vertical exitway “surfaces and Class II in “other exitways,” with smoke density limits – with reductions  allowed under appendix 34,   Class II at Stair Towers and Class III at other “exit ways” would be allowed.) (See Dwg AC2.1, AC2.2 & AC2.3)
  


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