Repair by replacement

[eieio]

I am replacing two existing potable water steel tanks supported on reinforced concrete saddles with two new tanks (same size, same diameter, just about the same everything) due to the age of the tanks and suspected deterioration around the saddles.

The saddles are in good condition and may only require minimal rehab before installing the new tanks.

The location of the project is in a known seismically active area. I do not know for certain if the original saddles were designed for seismic, but I suspect not.

In reviewing the codes, it seems I am okay to reuse the saddles without having to make any upgrades to current seismic as long as the new tanks do not overstress the saddles by more than 10% [existing structure sections].

However, I am not sure how to approach the tanks themselves. Do they need to meet the current code?

 

[MiketheEngineer]

If you put your seal on it or not - I would review the WHOLE thing. Yes - they need to meet code....

That is your responsibilty as an engineer - Health and Welfare of the public - part of our Ethics code.

"Suspected deterioration around the saddles" - Sounds like they need work also??

Are these 500 gallon tanks or 500,000 gallon tanks. There is a great difference in the potential out come....

 

[eieio]

One tank is 25K gallons and the other is 5K gallons (hydro pneumatic).

The deterioration appears to be in the tanks, although it will not be clear until they are lifted out of the saddles. There was some weep-seep-reseal action going on previously, but it has stopped. There are no signs of any rebar expansion or corrosive action in the concrete at the interface. However, paint and caulking can hide things.

There was some discussion of repairing the 25K tank, but I am trying to determine just how long it can be out of service. Replacement is less risky to the timeline than repair.

Due to the welding requirement on the 5K pressure tank, replacement is the more cost-effective way to go in this case.

 

[H57]

I would think that the new tanks should meet the current code requirements. According to the IBC you can only add 5% to an existing structure and not have to verify compliance of the structure (3403.2)

The supports should not have to be replaced/modified if you are replacing a tank with another tank of the same size, imo.

 

[eieio]

H57

Even the IBC is confusing. IBC 2006 3403.2.3.2 allows for an increase not to exceed 10% cummulative increase or 5% decrease in support capacity.

Either way, with the tanks being basically the same all around, I do not expect any increase in stress to the supports. It appears little has changed to them since they were installed over 50 years ago.

 

[eieio]

Going back to the Saddles:

To answer MiketheEngineer, there are no signs of cracking, no signs of rebar expansion – one spot that is showing delaminating, but not on large scale and in a repairable location. Concrete does not fail silently - generally the signs are there well before it goes.

I know how they were constructed (size and layout of rebar), but nothing of the mix or water content (fresh vs. brackish from local source).

What kind of non-destructive testing could be done to determine the integrity of the rebar in the saddles? Possible identify areas that need to be repair (if small scale and in good location for a repair)? Determine if new saddles need to be provided?

Any suggestions would be appreciated.

 

[kslee1000]

If no cracks, no rust stain on concrete surfaces, the chaces are the rebar are in good shape, well bonded. I will hammer the surface to locate hollow spots (near the surface). If any, chip the concrete open (locally), inspect and repair.

 

[DonPhillips]

My opinion, if you were in one of my jurisdictions, would be the talks are being replaced and the replacement is significantly the same as what was there. I would call the local building official and here are the 2007 Ohio Building Code (based on the 2006 IBC) that may apply to you locally:

"3401.2 Maintenance. Buildings, structures, equipment and parts thereof, shall be maintained in a safe and sanitary condition and in accordance with the condition(s) established in current and any previous plan approvals and Certificates of Occupancy. Devices or safeguards which are required by this code shall be maintained in conformance with the code edition under which installed. The owner or the owner’s designated agent shall be responsible for the maintenance of buildings and structures. To determine compliance with this subsection, the building official shall have the authority to require a building or structure to be re-inspected. The requirements of this chapter shall not provide the basis for removal or abrogation of fire protection and safety systems and devices in existing structures without approval of the building official."

You would still be required to apply for an approval but this section says the existing can be maintained.

However, if I were the designer, I would review the current code requirements with the owner and recommend they upgrade the design to meet the current code. If the owner declines, get it in writing.


Don Phillips

http://worthingtonengineering.com