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["Dennis Wish" <dennis.wish(--nospam--at)verizon.net>]

I am involved in a project that will require the seismic retrofit of a 1920 reinforced concrete one story fire station. Since the building was constructed, a second story wood framed addition was added and this is to be saved with the concrete building below. The light framed addition was constructed above the concrete parapets.

There is a one story light-frame addition that is attached (not known how yet) to the rear of the building. The client wants to demolish this one story wood frame slab on grade. This will be reconstructed and we will provide a separation between the concrete structure and the wood framing to prevent pounding of the wood light framing against the concrete building

The concrete is in poor shape, but in the strong direction, the shear from the roof down is small and capacity of the walls to transfer this shear to the foundation is possible.

The front of the fire station is a soft story and I will provide a moment frame to resist the lateral loads. The connection of the frame might be tricky. There rear of the building is concrete and I will check the existing wall (we have not gotten this far yet) to see if the existing concrete has sufficient strength to resist the lateral load of the concrete structure with the wood second story.

 

What I need are demolition notes. I have most of my notes from URM buildings and have reviewed Chapter 13 of the 2003 Existing Building Code. Obviously I am preventing any type of impact tool including rotary hammers and drills. However, the architect is concerned because of the age of the building that we should provide some shoring for the second floor and wood framing above as they removed the fire station slab.

 

I also requested that they saw cut the connection between the wood structure at the rear and the concrete to cleanly remove the walls. However, they wanted to know if they could use jack hammers on the rear wood structure. I believe this would be okay as long as they kept the jack hammers at least three feet away from the concrete walls.

 

Does anyone have a set of specification for demolition that I might review and draw from to help keep the Existing Building safe while the work goes on. I don’t see the need to provide secondary support for the upper level since the wood framed structure is concentrically built up on the concrete parapet and the building has held together this long.

 

Finally, I would feel more confident if this were a URM building because I have a lot of experience with these. I’ve only done a few retrofits of reinforced concrete buildings but they were not as old and in very good shape.

 

Any advice or help would be greatly appreciated.

 

TIA

Dennis S. Wish, PE

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