Lightning Damage to Slab-on-grade 1

[peterkosmoski]

Does anyone know of a case where a lightning strike caused cracking to form in a concrete slab-on-grade foundation?

I am evaluating a claim where there are extensive cracks in the slab of a house that was recently struck by lightning. The adjuster is unwilling to spend $$$ on concrete cores and petrographic examination, and to my eyes the cracks appear to be typical shrinkage cracks likely caused by too much water in the concrete mix. The residence has only a few damages to the cosmetic finish materials outside of the localized blast area, indicating a relatively low level of shock vibration to the structure from the blast.

Does anyone know of any papers or publications that address lightning damage to concrete structures?

 

[bjb]

Did the lightning strike the slab directly, or did it strike the house framing?

 

[peterkosmoski]

It appears to have struck the roof.

 

[bjb]

I'm not aware of a case where a lighning strike to a house caused damage to the concrete slab, and I find it difficult to imagine that a lightning strike to the roof could cause cracking in the slab. A far more likely cause for the cracking is that the concrete mix that was supplied probably prone to shrinkage-too much water, slump too high, improper jointing, maybe questionable finishing and installation, bad curing. Residential concrete is not known for its high quality.

If you do come across information about lightning strikes causing damage to concrete, please let me know.

 

[LPPE]

Electricity follows the path of least resistance. Highly unlikely it traveled through the slab on grade. Most likely cause is what bjb stated above.

And wouldnt a bolt of lightning tend to fuse the concrete and aggregates together, rather than crack them?

 

[SlideRuleEra]

peterkosmoski - Here are two references

ftp://imgs.ebuild.com/woc/C840413.pdf

ftp://imgs.ebuild.com/woc/C710218.pdf

 

[Ron]

peterkosmoski...in a word...NO.

The cracks are likely shrinkage cracks, caused by contractor procedures during construction.

Lightning damage to slabs is very localized and not in the form of cracks. Lightning causes spalling at the point of entry as it superheats the moisture in the concrete and it expands rapidly, causing localized spalling.

 

[peterkosmoski]

Thanks for the help everyone. I have a much better handle on this topic now.

 

[bridgebuster]

I agree with Ron. High voltage electricity causes spalling. A few years ago, I had to investigate a prestressed concrete box beam that was damaged this way. The contractor was grouting shear keys in a bridge that was over an electrified (catenary)railroad. The keys weren't sealed properly and some of the grout hit the catenary line. The result was a blowout (spall) in a beam and a portion of one backwall.

You would think they'd learn from the first mistake because a week later they did it again.