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Below Grade Connection - Epilogue

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Thanks to all for their input into my query. What I’ve decided to do is to specify coating the metallic surfaces with a coal tar epoxy, Rust-Oleum C9578. The contractor originally submitted a water based epoxy which is a terrible choice for two reasons. First of all, it is water based and therefore water is a solvent for this product. Doh! Secondly, this is not a cost effective product to install because not only does the surface needs to be primed before it can be coated but the unit cost of the water based product more expensive than the coal tar product. I think this is due to the fact that the water based product has additives to make the final surface look “pretty”, which is not necessary in my application.

 

The second measure I have taken is I’ve changed the weld specification. Based on loads, I needed a 3/16” fillet weld. I am changing that to 5/16” to provide a 1/8” sacrificial thickness without adding a great deal of cost to the job. After all, a 5/16” F.W. is still a one pass weld. I believe the only difference in cost between a 3/16” and 5/16” F.W. is the cost of the welding rod. I believe they both can be laid down at the same rate, but I’m not a welder so I’m not certain of that.

 

There are some reasons why I didn’t take some of the advice offered on the list.

 

I could have changed out the plates to stainless steel. Not only is the cost different not insignificant, but this option would have introduced a change in specification in the weld. More importantly, I believe it would have required special reinforcing in the wall panel. The plate embedded in the wall panel is welded to the vertical reinforcing in the wall. Sure, all of this could have been achieved but I can visualize the “rolling of the eyes” by the contractor as he reviews the revised detail(s) reflecting this approach. All of this is a “gray area” to me since I haven’t done much work with stainless steel (another reason I wanted to stay away from it).

 

I considered placing either a curb or lean concrete to try to seal the metal parts. One problem is that some of the walls occur on the property line and placing this material on the “other” side of the wall would be problematic. Further, I’m not convinced that this solution would have solved the problem. After all, the concrete would shrink away from the wall panel once cured and allow rainwater to run down the panel and reach the metal plates.

 

Regards,

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers