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RE: Parking Garage Retrofit

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Search the archives for a summary of parking garage loading per code, it should be about 18 months ago.  I compared several different codes for garage live loads.  ASCE published an article 2 to 3 years ago specifically addressing parking garage loading.  That article was the impetus for the '03 code cycle loading requirements.  Get your hands on ASCE 7-02, I suspect there is commentary addressing this issue.

Secondly, pay attention to what LL section you use.  IIRC, You can use the older LL reduction methods (R=r(A-150)).  See IBC section 1607.9.2.  I don't recommend this; but hey, there it is.

The down side to Fiber Wrap is fire ratings.  Works great for seismic upgrades.  Generally the fire happens after the earthquake, not during.  Can be hard to make it work for gravity elements.

Best of luck,
Jake Watson, P.E.
Salt Lake City, UT


---------- Original Message ----------------------------------
From: "John C. Jones" <john(--nospam--at)struct-engr.com>
Reply-To: <seaint(--nospam--at)seaint.org>
Date:  Tue, 28 Sep 2004 11:39:59 -0500

>You might double check those LL reductions and how they relate to total LL.  I think the IBC only calls for 40psf LL for decks that are limited to cars (non Expedition type vehicles) where SBC was 50 psf.  That will help on the horizontal framing.
> 
>
>John C. Jones, PE 
>Barnett Associates 
>Pell City, AL 
>205-884-5334 
>205-884-0099 (fax) 
>
>-----Original Message-----
>From: Mike Zaitz [mailto:mzaitz(--nospam--at)hgbd.com]
>Sent: Tuesday, September 28, 2004 10:31 AM
>To: seaint(--nospam--at)seaint.org
>Subject: Parking Garage Retrofit
>
>
>Morning;
> 
>We are getting involved in a study for a vertical addition to a 2 story parking garage.  The original design is precast girders and double tees with cast in place fixed based columns on pile caps with piles. A note on the drawings indicates that the structure was designed for 1 future level for gravity only.  Any seismic and wind resistance for the future level would require additional bracing or shear walls.  Based on some preliminary research the following has been discovered:
> 
>·        The structure was designed under the 1994 Standard Building Code (1994 SBC) and the expansion will require design per the 2000 Standard Building Code (2000 SBC aka the IBC 2000).
>
>·        The seismic forces in the cantilevered columns have increased 82% with the current configuration and the new seismic loads.  The columns as currently reinforced are inadequate for these new forces and will require retrofitting.
>
>·        The 2000 SBC has changed the method of reducing Live Load for a passenger car parking garage.  It allows a 20% reduction in Live Load for members supporting 2 or more floors.  This would allow the reduction to be applied to the columns and the footings.  No reduction in Live Load is permitted for horizontal members.  The 1994 SBC allowed a reduction of up to 40% for horizontal members and 60% for vertical members based on the tributary area of the member.  The calculations for the precast members needs to be reviewed to determine the final impact of this.  I am waiting for these calculations to be sent to me but there is a distinct possibility that the existing precast members will require retrofitting.  This will also impact the foundations.  
>
>What I am trying to do now is to determine what methods of retrofitting the project are even in the realm of feasibility (throwing mud on the wall and seeing what sticks as my boss calls it).  I am looking at adding shear walls to take ALL of the lateral forces and then the existing columns will only be required to resist gravity loads (will make the tying of the existing diaphragm to the shear walls interesting).  Based on this I believe that wraps on the columns are a feasible approach for increasing the capacity of the columns.  Another idea is to jacket the columns with additional concrete and steel.  A possibility for retrofitting the double tees is to use the carbon fiber wraps on the stems and then pouring a 2" topping slab.  This will cause numerous problems with the added weight, etc.  No real ideas for reinforcing the girders.  
>
>With the budget set at about $10,700 per space I do not think there is any chance that retrofitting the garage is economically feasible.  I am guessing that it will be more in the range of $15,000+ per space.  It looks like our primary solution to the parking issue will be to build a new parking garage near the existing.
>
>Any comments or suggestions?
>
>
>
 

 
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