1890 FLOOR JOISTS

[EngineerAll]

I am working on duplex units that were built in 1890 The floors are constructed out of 2x10 actual size floor joists but I can not tell what type of wood was used hence I do not know what allowable values to use. The joists span 21.5 feet and are randomly spaced anywhere between 16 to 24 inches on center. Does anyone know the today's equivalent of 1890 2x10's (actual size) floor joists.
The fun part is the roof is made of 2x6 joists directly over 2x8 (actual sizes) too spanning 21.5 feet. It's an interesting design to analyze. Any help will be appreciated as usual.

Merry Christmas and Happy Holidays!

 

[boo1]

I would consider using a pocket knife, removing a sliver to try to determine the species. Typically SYP was the dominant joist material at that time in Eastern USA. The turpine smell of the old growth SYP is easy to pick out. What area of the country are you located?

 

[EngineerAll]

I am in Denver, Colorado.

Thank you very much!

 

[JAE]

Even if you found the species, you might still have trouble nailing down the appropriate allowable, or maximum, stresses to use in design. There's no standard anywhere that can give you the correct values to use, - sometimes we assume a DF No. 2 if the wood appears to meet the quality, visual grading requirements, etc. as this is usually conservative because much of the older wood used in buildings back then were denser and had better properties than today's lumber.

Another thing you can do is to take some samples and test for their maximum tensile stress in a lab - using a beam break method and then associating the results with current NDS graded lumbers.

Or a load test on the floor if you really want to know what you got.

 

[EngineerAll]

Thank you JAE and boo1 your input is greatly appreciated. I am leaning more on just checking it as DF #2 and since it's that old deterioration would be a factor I need to account for also so I think tha would be conservative to use DF 2

Thank you all

 

[boo1]

Old does not imply deterioration, visual and proding with a knife should prove that. Since it is old growth West coast timber DF#2 should be conservative.

 

[samdamon]

Engineerall- Contemporary (1890's) allowable stresses and load tables for various types of wood used as beams were published in the "Carnegie Companion" or in "Trautwine's Pocket Book". Both these manuals were published in many editions over decades. Editions of both can still be found on ebay and antique book websites.

A Carnegie Companion I have from 1897 says conventional rectangular 2x spruce and pine beams had an allowable "extreme fibre stress" of 750 psi, oak 998 psi, southern yellow pine 1245 psi. (Please verify those numbers with your own research!) For the first two species these old allowables don't appear that far from modern values for the better grades.

Anyway, you can identify the species that you have by cutting a small sample and sending it for analysis by the USDA forest products lab. Believe there was a post about that process here a while ago, try a search in eng-tips.

Good luck.

 

[Ron]

EngineerAll...one other thing, in addition to the good advice you've received so far, is to remember a structural basic....look at the connections. While age doesn't necessarily mean deterioration, it does often mean creep. Fairly often the connections will be loose or in poor contact, so check those out well. Further, check your fire codes....sometimes old lumber is rated differently because of the sap bleeding that can occur.

Also, you should use a manual wood coring tool to core completely through the wood at several locations. This will allow you to look at the center of the wood as this is a location often susceptible to attack by "wood destroying organisms (WDO)". Further, it will give you sufficient sample to get a species identification done. You can probably get that from your local agricultural extension station affiliated with your state universities. Most of them have arborists/foresters on staff or accessible for such things.

 

[boo1]

We did a 1870s era renovation, where the 12x12 columns were old growth heart SYP. The wood was so dense all fasteners had to have a pilot hole drilled.

An additional issue of renovation to consider was the joists are often notched from electrical and pluming upgrades.