Wednesday, August 31, 2011

RE: Joplin, MO - St. Mary's Cross - Tornado survivor???

I had a very similar experience with columns corroding at the concrete interface some years ago at an old automobile plant. 
I would doubt that there is a weep hole to allow interior moisture to escape for the hollow shape.  So the corrosion that is evidenced from the outside is also probably present on the inside.  You can measure the section loss on the outside of the tube steel and have a reasonable expectation that the same loss is present on the interior. 
An ultrasonic test can confirm the loss of section, and determine the thickness of the wall at various points.  It is not very expensive if you have an NDT ultrasonic weld inspector in the area.   Whether or not you confirm the section loss with NDT, you should at least make some determination of the loss of section.  You can determine the current section modulus and the cross section area.  Then you can compute the stresses in the remaining steel and determine its adequacy. 
Taking the cross down will give you the time to make a more definitive determination of section loss.  Then you can form a plan of action to repair the cross. 
I designed a cluster of 10 crosses for a church back in the 1970's.  We just used base plates and anchor rods to support the crosses.  We used a good coating system to preclude corrosion.   They are still there.  Wow! that was about 36 years ago. 
A hollow shape should have a weep hole to allow moisture to escape.  That is something you may want to consider.  If you want to have a bit more assurance, you can plate the exterior to reinforce the walls.  Just make sure that you weld the reinforcing plates to seal moisture from the interior (except for that weep hole).  If you weld reinforcing plates on the walls, you can take all of the stresses in the reinforcing plates and assume 100% section loss.  This is conservative, but you will save the cost of the NDT.  You can spray the interior of the shape through the weep hole with a corrosion inhibiting coating. 
1.  Take the cross down.
2.  Cut off the cross at the base.
3.  Patch the concrete.
4.  Weld reinforcing plates on the wall of the cross.  Provide a generous corrosion allowance. 
5.  Weld a base plate to the reinforced base.
6.  Coat with a good corrosion inhibiting coating system
7.  Install the cross with anchor rods (I like the DUC post installed anchors)
8.  Drill in ports and inject epoxy into the interstitial space around the anchors to preclude corrosion and freeze thaw problems
9.  Grout the base plate
Regards, Harold Sprague
> Date: Fri, 26 Aug 2011 09:46:18 -0500
> Subject: Joplin, MO - St. Mary's Cross - Tornado survivor???
> From:
> To:
> Hi to everyone!
> I was asked by one of our managers (who used to attend St. Mary's) to
> inspect the Cross at St. Mary's church. The cross has some fame,
> being as it was the only part of the church that survived the May 22
> tornado.
> The demolition contractor had talked to the Father (Priest?) of the
> parish, telling him that he thought that the buckling had gotten worse
> after a recent thunderstorm.
> The site is clear of debris and is easily accessed (now) on foot.
> The cross was at one time in a fountain, so there was extensive
> corrosion on all four sides right above the slab.
> Based on anecdotal evidence, the base of the cross is 12 feet below
> the slab (there was a basement behind the cross).
> It doesn't appear to me that the building which was around the cross
> was actually connected to the cross, at the very least just the
> flashing.
> It appeared to me that the buckling and tearing took place due to the
> thinned walls (from the corrosion) and that even without the storm,
> the cross was going to require corrective action due to the corrosion.
> I'm recommending that the slab be removed around the base of the cross
> in order to ascertain the extents of the corrosion. I'm also
> recommending that the cross be braced before the slab removal.
> Comments or feedback would be greatly appreciated.
> Mike Jones
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