Snow Damage Overstressed Rafters??

[exmechanic]

Can anyone tell me how an engineer determines if a rafter has been overstressed and thus collapse under less than design loads? I need an objective viewpoint.

My 75 year old house was damaged in a record snowfall. It has a 4 sided hip roof. Many roofs in the neighborhood with similar designs collapsed. Mine did not because of a bearing wall I added on one end some time ago. My engineer calculated that the load was 67% above design. The rafters on my house had a deflection under load of at least 1" (13' 5/12 pitch). The ridge board is unsupported. My insurance company's engineer's position is that the rafters and roof structure are not damaged and minor work is required on the walls.

The walls are 2 course masonry, fired brick exterior, unfired interior. The sill plates moved out 1" on each wall. Large cracks in exterior brick show where anchor bolts moved. 1" crack between plaster layer and interior brick wythe. Many large cracks in the interior plaster.

 

[ERV]

It is difficult to appraise the structural damage to the building without visiting the site. If the sill plates have moved out 1" on each wall, then the ridge has also dropped approximately 7/8".
I suggest getting a local contractor specializing in this type of work to asses the situation, in conjuction with your engineer, and get estimates of the costs to repair the damage. Submit them to your insurance company. Insurance companies try to get out by paying claims for as little as possible (they are going to give some sort of settlement based on their findings). Stick to your guns; they have to pay the actual cost of repairs. Most policies contain clauses for code upgrades. That is to say that once damage occurs of a structural nature they will pay for code upgrades (bring the structure to current codes).
Document every correspondence and be ready to hire an attorney if you get stonewalled.
It sounds to me that your house is going to need major structural work. Be persistent.

Good Luck.

 

[Focht3]

One additional suggestion: go ahead and interview attorneys now. You may not be in a proper frame of mind later. And be sure that your current consultants are all willing to serve as your experts before you pay them any more of your hard-earned money. Run their names by the attorney you select to be sure that you haven't hired a "problem."



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[exmechanic]

Thx for the quick responses.

I did have two contractors look at the house prior to Insurance company's engineer involvement.

They produced estimates based on the results of my engineer's report. The insurance company balked at this and then hired an engineer to dispute.

Ins. Co. Engineer's report says that the rafters were not overstressed and thus do not need to be replaced. My engineer disagreed.

Your calc on how far the ridge dropped is very close. I had put a line level on it and it has dropped.

The big disagreement is whether the rafters have been overstressed. The insur. co. engineer has not produced calcs and my engineer has not yet produced. I know there are calcs for steel beams ect that show max deflection before failure. Would like to know where to look for calculating the same for timber. The rafters were bowed at least 1" before unloading the snow.

At some point of increased uniform loading the rafter (beam) supported on an angle will fail. If the load was just up to the point of failure, there must be checks and splits to the wood fibers that will reduce the effective future load limits.

My framing book shows calcs for slope over 3/12,no finished ceiling,30 psf LL, 15 psf DL

It states in the note that the bold print values are limited by the extreme fiber stress in bending of the grade.

Any ideas on how do I determine what Grade of lumber was used in 1926 Denver house building? I know it is good lumber as I have removed some walls in the house and they are nothing like today's 2x4's

Is it possible to calculate the following:
1) 1.15xFb, Extreme fiber stress has been exceeded
2) deflection of 2x6 rafter 13' long @ 5/12 loaded with 50 psf live load 20 psf dead load.
3) Based on the above, can it be determined that the rafter was overstressed.

What are the actual formula's used to produce the rafter design tables seen in many framing books.

I would like to calculate myself (trained engineer always wants that regardless of discipline) prior to going to an attorney.

Thx

 

[Focht3]

Hang in there -

You might check with your State Board to see:[ol][li]If any complaints have been filed against the insurance company's expert, and[li]Informally discuss the situation with one of the Board's investigators.[/ol]You may find that your experience isn't unique -



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[pablo02]

Another quick item -- verify (w/ your State Board) if the Insurance's engineer is licensed in your State -- probably is, so follow-up w/ Focht3's comments -- if not, you should be home free (no pun intended)...

 

[ERV]

exmechanic,
Based on the information you provided:
Lumber common for that area and period would most likely have been douglass fir, probably 1 3/4" X 5 3/4" (dressed size may have been full 2"X6" green).
Fb = 1805 psi (adjusted)
E = 1,500,00 psi
Fv = 86 psi (adjusted)
live load deflection 0.40" (L/393)
toal load deflection 0.63" (L/246)

here is a link that may help:

http://www.cwc.ca

I think the biggest problem is going to pull the sill plates back into position for proper roof alignment.

 

[Focht3]

[blue]pablo02[/blue]'s comment is right on target; I encountered an out-of-state engineering firm on a litigation assignment about 6 years ago. The facility was more than 20,000 sf and their fee was in excess of $70k. You should have seen the attorney's face when - at the start of my videotaped deposition - I informed him that not only had the three individuals that signed the report practiced engineering without a valid license, they had committed a felony because of both the size of their firm's fee and the size of the building...

It was a real "Kodak moment" - too bad the camcorder wasn't pointed at him!



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.