figuring out what wood was used in old construction? 1

[altswear]

Are there any general guidelines for determining the capacity of an old wooden beam built early-mid 1900s? I was going to back calculate the capacity but am unsure if I should use the allowable stresses of douglas-fir or go more conservative.

Thank you!

 

[SlideRuleEra]

In the US, start by finding out what type of wood:

USDA Forest Products Lab - Wood Identification Service

http://www.SlideRuleEra.net

 

[Ron247]

The appearance of the grain, color and some other general information may put you in the ballpark of the type of wood. No way to check density without damaging the beam to some degree. I read an article once about using blacklights to measure fluorescence to help identify some woods. I think the link below is the article I read.

https://www.wood-database.com/wood-articles/wood-identification-guide/

 

[WARose]

If I couldn't identify it by the methods described by other posters....a big thing for me would be: where is this? In the southeast (for example) I would be betting on Southern Pine #2. It's just going to vary by region/location.

 

[JAE]

One thing that can help - if you can swing it - is to arrange for an existing member of known dimensions and span to be loaded by a specific weight.

You can then measure the net deflection of it relative to its original position. This gives you an instantaneous deflection which allows you to back calculate a modulus of elasticity.
This at least might get you in the ballpark to compare with published wood species and grade with their E values.

Not an exact approach for sure but at least gets you an understanding of the member's material stiffness.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[msquared48]

Good luck in driving a nail in that stuff.

Old DF is rock hard and has a real stong memory.

Mike McCann, PE, SE (WA)

 

[NorthCivil]

Its all about where you're located. If you have enough local timber experience, you should be able to tell what type of wood it is quite readily.

If you don't have local timber experience, make a phone call to a local colleague who does.

If you dont have a local colleague to rely on, make a conservative assumption and design around that.

 

[JAE]

Just knowing the species doesn't help you all that much as the actual grade of lumber, or for very old wood, the true flexural capacity of the lumber is still very much an unknown.
Comparing very old wood to current "No. 1" or "No. 2" visual grades isn't much more accurate that just guessing a number.

A deflection test per above - or taking a sample or three and loading it to failure would get you a better idea.

But Mike is right - the older wood tended to be much more dense with pretty good flexural/shear/axial capacities compared to today's wood.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Canuck65]

There are labs around that you can send a match stick sized sample of the wood and they identify the species. As pointed out by others, this does not give you a grade for the lumber, but there are lumber graders around that will visit sites and provide a certification. Older wood tends to be stronger than newer woods. Local knowledge is very valuable.

 

[robyengIT]

in Italy we have Standard UNI 11035-1 ; 11035-2 and 11035-3 so called "Visual grading to determine the mechanical strength of structural wood". I don't know if there is any publication in english

 

[altswear]

Thanks everyone for the broad range of insightful comments. I will most likely choose a conservative estimate for the capacity of the wood and design around that as it seems to be the least invasive method.

For what it's worth, project is located in the northeast.

 

[SlideRuleEra]

...old wooden beam built early-mid 1900s
For what it's worth, project is located in the northeast.

Because of project location, pin down construction time frame as closely as possible.

In the early 1900's, it is highly possible that elm, chestnut, or old-growth long leaf pine, transported to the NE in large quantities from the southeast USA, was used for the beam.

By the mid 1900's (say, 1950s) all three of these woods were no longer commonly available because of disease and over harvesting. Ruling out those woods would be reasonable.

http://www.SlideRuleEra.net