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RE: Old Southern Pine Allowable Stresses

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Back then they called it Timber.  I have Milo Ketchum’s  “Structural Engineer’s Handbook”, 1918.  Page 298


Note above Table V – The working unit-stresses given in Table V are intended for railroad bridges and trestles.  For highway bridges and trestles the unit stresses may be increased twenty-five percent.  For buildings and similar structures, in which the timber is protected from the weather and practically free from impact, the unit stresses may be increased fifty percent.


He has a table that shows Longleaf Pine to have the following properties:

Average Ultimate Extreme Fiber Bending Stress – 6,500

Safe Bending Stress – 1,300

Modulus of Elasticity – 1,610,000

Shearing Parallel to Grain Average Ultimate – 720

Safe Shear Stress – 180

Longitudinal Shearing In Beams Average Ultimate – 300

Safe Longitudinal Stress – 120

Compression Perpendicular to Grain Elastic Limit – 520

Safe Stress – 260

Compression Parallel to Grain Average Ultimate – 3,800

Safe Compression Stress – 1,300

Compression For Columns Under 15 Diameter Safe Stress – 980

Formula For Safe Stress In Long Columns Over 15 Diameters –   1,300 * (I-L/(60*d))




Footnote to Table: These unit stresses are for green condition of timber and are to be used without increasing the live load stresses for impact.







From: Andrew Kester, PE [mailto:akester(--nospam--at)]
Sent: Tuesday, September 26, 2006 6:16 PM
To: seaint(--nospam--at)
Subject: Old Southern Pine Allowable Stresses


I have looked on the internet and came up very empty handed...


Does anyone have any idea of allowable stresses (mainly bending) to use for actual 2"x12" deep rafter beams, most likely S. Pine, approximately 100 years old, in the Central Florida area? The building is over 100 years old, I don't know if the rafter beams are original, but I would guess yes.


The beams are inside and high and dry, I believe in pretty good condition other then their age. No serviceablity problems. Now I know grading wasn't what it was, but these are likely virgin forest type lumber, especially in Central FL... So I am expecting an increase then from say good ole # 2 S Pine??


Please CC me directly if you have any info.


Andrew Kester, PE
ADK Structural Engineering, PLLC
Lake Mary, FL