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Heavy Wood Truss Information
3

Heavy Wood Truss Information

Heavy Wood Truss Information

(OP)
I am an engineer retained to investigate a failed wood truss building.  Three bottom chords on different trusses, different locations failed.  I am trying to find backup information on trusses.  I believe that this truss is pre 1956, probably WWII.  I have the ASCE document on upgrading wood structures.  Would like to find more information such as were reduced snow loads used and what was the life expectancy of these buildings vs others of their era. This is going into litigation and I would like to be as well armed with the facts as possible.  

RE: Heavy Wood Truss Information

These, I assume are large timber trusses.  You should complete a model of them for analysis. Try to determine the loads on them at the time of failure. Try to determine what failed and the sequence of failure (if it exists).  Try to determine what has happened to the trusses since they were fabricated.  Why did they fail now, after standing for 50 years?  What the existing design loading was.  Determine the materials of construction. Analyse the various connections. Any deterioration, fire, insects, rot... Just for a start... Whole bunch of things...

Dik

RE: Heavy Wood Truss Information

The local building official may be your best bet for determining what loads were applicable at the time.

For a failure in a building that old, it would be interesting to know the basis for litigation.

RE: Heavy Wood Truss Information

dik...you've covered it nicely, as usual.  The only thing I would add is to check changes in material properties with time and check creep.

RE: Heavy Wood Truss Information

What shape and type of trusses were they?  Bowstring?

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Heavy Wood Truss Information

What happened to the trusses since they were fabricated includes any new or recent alterations to the trusses or facility that would increase the loading.

Has there been any noticeable weather change... heavier snowfalls, colder, etc.

Has the building been 'sealed' during the last decade that might increase humidity and lead to 'dry-rot' (actually brown rot)  What is the moisture content of the structure? <18%-20%?

Dik

RE: Heavy Wood Truss Information

There may not have been a building code in effect at the time of construction. I have a copy of Canada's first... goes back to the late 1940's.  Many jurisdictions in the US didn't have a code until the last few decades.

Dik

RE: Heavy Wood Truss Information

(OP)
I have been looking into all of these issues.  What I need are some background documents.  Such as Army Corp or Navy docs discussing these issues. I have read "Evaluation, Maintenance and Upgrading of Wood Structures from ASCE" and it is a good start.  Thanks for all the input.

Jim

RE: Heavy Wood Truss Information

(OP)
Dik,

How can I get a copy of Canada's code?

Thanks

RE: Heavy Wood Truss Information

I'll see if I can scan it... it's in pretty poor condition... and really small...

Dik

RE: Heavy Wood Truss Information

What condition are the top chord and web members in?

Garth Dreger PE
AZ Phoenix area

RE: Heavy Wood Truss Information

You might want to have the lawyer look into Canadian case law regarding corrosion of early parkades and liability when construction was in keeping with practice at the time.

Dik

RE: Heavy Wood Truss Information

2
Failure mechanism to consider:

Splitting of Lower Chord along Bolt at Steel Splice Plates and Heel Plates

Tension Failure in Lower Chord

Cross grain shrinkage of timber attached with steel side plates with multiple rows of bolts often causes the initial splitting.
- Timber defects (Large knots)

Excess Loading
– Gravity
– Mechanical Equipment
– Multiple layers of roofing
- Interior pressure
- Physical damaged

Differences in timber design values from as built to today

Earthquake induced loads

Physical
- Rot
- Insects
- Water
- Fire

Attached is an article
 

RE: Heavy Wood Truss Information

How did this turn out?

Dik

RE: Heavy Wood Truss Information

Man, most truss people wouldn't want to touch this with a 10' pole. There are just so many factors......and history between the past and now it would be very hard to determine if any negligence took place unless you had a smoking gun.....ie a roofer sits 5000 pounds of shingles in a 6x6 area.  

RE: Heavy Wood Truss Information

Not sure of the exact type of constrcution - but many "pole" barns were built in this era.  Some actaully followed guidelines set up by the University Schools of Ag Engineering.

You might search some of these..

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