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

A local empowerment zone redevelopment agency is leasing a 1930’s concrete wall building from a local city. The building was a high bay fire station and since the original construction, a second story wood frame structure has been added. The walls were cored and while the cores were tested for compression, the reinforcement was found to be the old square rebar used in that period of time.

A firm from outside the area was brought in by an Architectural firm representing a bank that wishes to sub-lease the building. I was recommended by the local testing agency as a second opinion based on my knowledge of old Unreinforced Masonry buildings.

 

Even if there is minimum rebar, the walls that pose the least threat are the side walls which are long and solid. The shear transferred from the wood frame addition above is not a threat to these walls. There ends of the building pose another problem. The front is where two large doors were placed to allow fire trucks in and out. The rear wall is inaccessible at the time the testing lab inspected the building, but I would assume that the wall which the Architect shows on his plan is concrete, but too short and possibly too weak to be used as an appropriate shearwall – especially due to the shear from the second story wood frame addition. This rear wall is concealed by a wood one story addition added sometime after the building was constructed. This portion of the building will be removed by the bank and a new structure will be built in its place.

 

For those in California, here are my questions:

 

1. I don’t know of any Hazard Mitigation program in California that would require retrofit of the existing roof (floor of the second story) to the concrete walls. UCBC Appendix Chapter One does not address reinforced concrete buildings. Is this building exempt from retrofit rules in California?
2. The concrete is not the best – some good cores, others that have too much aggregate and local desert sand in the mix. Still, the length of the walls and the minimum reinforcement would resist lateral loads. I would plan on a steel moment frame in the front of the building connected by welding to the steel lintel above the doors. The new design pops the front out two or three feet which makes the frame an ideal solution as there is enough room for the grade beam and erection pads in proximity to the property line. The rear wall can be strengthened with Gunnite for shear and additional foundations added or replaced as needed. What choices do I have to reduce further deterioration of the concrete on the exterior face of the sides (long sides) of the building?
3. A mezzanine is to be added by the bank. I believe this mezzanine (which will induce additional shear) can be supported on a wood stud wall and the floor joists (TJI) supported by these walls. The mezzanine can be used to brace the walls from buckling, The bearing stud walls below can also be used to run utilities with minimum loss to leasable space. Does this sound like a reasonable plan?

 

The tough part is that the Empowerment zone has limited funds and I have no idea how to calculate the retrofit or upgrade portion of the project. If the mezzanine is used to brace the walls then the cost is absorbed by the bank as an improvement and does not come from the Empowerment Zone. This leaves me only the moment frame, a Gunnite wall at the rear and any coating or covering of the concrete that can improve or reduce further deterioration of the walls. The building is probably about 2000 square feet and the walls are 8-inch thick with joints at 8-feet horizontal as the this was the height of the lifts.

 

Another firm figured the reconstruction to bring the building into a safe zone would be close to $90,000.00 which seems very high to me. It is a prevailing wage project but I would think that at the worst case scenario, we would be talking between $50K and $60K.

 

I could use some advice as how I might approach this type of structure. My experience, besides wood, is URM and Structural Clay (Unreinforced). I’ve also done some Adobe but have not worked on this type of Concrete structure. Finally, the building is not on a state historic registry and not protected except by the allowances of the city Building And Safety division.

 

Please let me know what you think.

 

TIA

Dennis S. Wish, PE

 

PS. We have not done a Pachometer test yet and I am waiting for options before recommending spending any more of their money on this building. I was not involved in the original testing or preliminary plan development – I was brought in to offer a second opinion to another engineers report. While his report appears valid, his approach to solving the problem is to attempt to bring the building up to compliance. My approach would be similar to URM buildings – identifying their weakness and designing to the failure of the weakest element but providing sufficient secondary support to get people out of the building. After that there would be no guarantees.