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RE: 1930's Poured in Place Concrete Building

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Dennis:

 

FYI, there are provisions in the IEBC regarding wall anchorage for reinforced concrete buildings with flexible diaphragms (chapter A1) which would give you yet another basis for “reduction of hazards”. While it doesn’t treat the entire building, it does promote public safety and welfare. I believe you can download a older draft copy from the ICC website to get a sense of what it has to offer.

 

I would agree with the use of FEMA 356 as a reputable guideline for making recommendations on this type of building. At the very least, the professional obligation is to advise the client that means exist to seismically rehabilitate existing buildings. Too often these discussions about possible alternatives and risk reduction are bandied about by engineers and never make it to the clients table. I say this not as any criticism of what you’ve done so far, but as a general rule, engineers tend to internalize this decision making process when if fact we should find ways to engage the client more frequently in risk decision-making.

 

Of course, this all takes time and some are better than others in offering solutions, but nonetheless we can’t ignore the fact that our knowledge is what we are selling. We should also be prepared to admit that earthquake engineering is a long way from the exact numbers game we like to play, and recognize it may put some of us in an uncomfortable zone which we have to learn to live with.

 

 

 

Barry H. Welliver

barrywelliver2(--nospam--at)earthlink.net

 

-----Original Message-----
From: Dennis Wish [mailto:dennis.wish(--nospam--at)verizon.net]
Sent: Thursday, November 20, 2003 2:43 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: 1930's Poured in Place Concrete Building

 

Jake,

Thanks for the advice – I did think about this. If the City who owns the building allows me to treat it like a URM, then I would be able to design the moment frame to the capacity of the diaphragm rather than potentially higher loads from the second story structure above. In other words, as UCBC Appendix Chapter One works, the building will fail at the weakest shear transfer material. Normally it is a roof structure of 1x straight or diagonal sheathing, however, this building had been upgraded sometime after the early 30’s. The diaphragm might have been improved (see Roger Turks comments) and this needs to be evaluated.

I think that the City might consider the building to be a potential Hazard and allow me to design to provide sufficient secondary support and shear at the soft story (and maybe interior cross-walls if necessary) to protect the occupants until they can safely leave the building.

The problem is that this building is within 2 Km of the San Andreas Fault and we do need to consider that this area has been determined by Cal-Tech to be 50-years beyond a major seismic event.

 

I have a copy of FEMA 356 and will look though it as you suggest.

 

Thanks

Dennis

 

-----Original Message-----
From: Jake Watson [mailto:jwatson(--nospam--at)utahisp.com]
Sent: Thursday, November 20, 2003 4:37 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: 1930's Poured in Place Concrete Building

 

Dennis,

    Remember to consider relative rigidities of materials.  If you put a moment frame on the front, how far will it move before it does resists much force?  Will the masonry along that line fail before the frame takes over?  If the masonry fails in shear, will it still carry gravity loads or is there an alternate gravity load path?

    Also, I second Gerard's comments about change in occupancy.  I would review the new occupancy with the municipality before proceeding too far.  If you are increasing the "public hazard" significantly, you may need to be fully code compliant.

    As for the concrete, you might look a FEMA 356.  It might give you a better procedure to deal with the concrete.

 

Best of luck,

Jake Watson, P.E.
Salt Lake City, UT

 

-----Original Message-----
From: Dennis Wish [mailto:dennis.wish(--nospam--at)verizon.net]
Sent: Wednesday, November 19, 2003 11:52 PM
To: seaint(--nospam--at)seaint.org
Subject: 1930's Poured in Place Concrete Building

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.