Force of Falling Tree on House

[mferg318]

I'm inspecting the foundation of a home that was damaged by (2) oak trees that fell on it during a hurricane last year. The roof and walls were significantly damaged. I am trying to determine if any of the cracking and settlement of the slab are a direct result of the falling trees. The insurance company has agreed to pay for all damage except for the foundation, because they claim the foundation issues pre-existed the storm damage. One idea I have is to calculate the force of the falling trees and determine if that force is indeed large enough to induce shear failure in a slab-on-grade. Anyone have experience with this type of situation or with this particular calculation?

 

[Ron247]

Some advice on terminology. If the cause of the downward foundation movement is tree impact, it is not settlement. It was driven into the ground. Insurance companies prefer you call it settlement. Many have clauses about settlement not being covered. If I say normal settlement, I generally mean you built a structure on some ground that is somewhat compressible. When it moves down under its own weight and live load it "could" be called settlement. If it moves down from forces outside of reasonable design loads, it is not settlement.

Below are 2 pictures someone sent me showing baseball bat tree damage. You can see the tree is not far from the house in the first picture.

As others noted, your later post about new concrete cracks provide more proof it could be from the tree. In the pictures below, one of the exterior walls tried to move outwards at the bottom due to the tree. The wall did kick out at the base. This is not a slab house, but if it was and had the wall been anchor bolted better, I could easily see it causing a tension crack in a slab. The crack could be close to the wall or far away. Depends on the slab stresses. To me the slab is a brittle component since I will bet that any WWF is against the ground. Brittle components that are about to fail tend to look just like brittle components in good condition.

 

[3DDave]

It's a very hard problem. At the top is that it's an energy dissipation problem - how much kinetic energy was available in the mass of the tree and then where did it all go?

To move the foundation one needs a good understanding of how much energy would be required to displace the ground under/around it as well as to fracture it.

Sight unseen it's tough to decide. A google search for trees falling on houses show many with considerable above-ground structure damage, but it doesn't usually seem to distort all the way to the basement/foundation, but there is this one -

https://www.post-gazette.com/local/...rapping-man-westmoreland/stories/201907310199

which looks to have had enough energy to essentially cut the house in two. If the slab on that home isn't fractured I'd be surprised. Another extreme case:

https://decaturite.files.wordpress.com/2009/04/mak-home-tree-destroyed.png,

but it doesn't look to have damaged the underlying masonry.

The reasonable thing is a 50/50 split on the foundation work as neither side can possibly provide sufficient analysis based on gathered data from the time of the event to clearly demonstrate cause/lack of cause. It is unreasonable to expect that the home owner was counting on a tree falling to get the foundation paid for, but it's possible the tree falling exposed some otherwise concealed unexpected damage, say from settlement or washout, but that would not be considered normal maintenance.

However, reasonable is often tossed out when dealing with insurance. Example: if all your possessions are destroyed by heavy rain falling after wind blows the roof off, insurance companies have argued their liability is limited to replacing the roof and that the rest is flood damage on the grounds that water entering the house is flooding. Or, in the case put forward by Louis Rossmann, who had an amount of retail stock damaged by water filling his basement from a firefighting effort on a neighboring structure - yeah, that was classified as flood damage and not claimable.

 

[mferg318]

Some really good stuff here, and a lot of it. Let me take some time to digest and I will try to address all of it.