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Parking Garage Retrofit

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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?