old beam strength
old beam strength
(OP)
i have an old steel building built in 1906 in New York City. I have to check the existing beams for some new loading. I have tested the beams and found that they are A36 steel. What allowable bending stress i am allowed to use? do i have to find the steel code of that era or can i use the .66Fy of the current code?






RE: old beam strength
tested and found it to conform to A36 steel, use the values for A36 steel.
For additional info, refer to AISC design guide #15, AISC Rehabilitation and Retrofit Guide. It includes the historic shapes and specifications.
RE: old beam strength
NYC 1948 lists allowable bending stress of structural rolled steel as 20ksi. I certainly wouldnt use anything more than that for your steel sections.
RE: old beam strength
1. I agree with CSEllc, it is VERY doubtful that the steel is A36, although it COULD meet A36 specifications - there is a difference. (A36 steel replaced the commonly used A7 steel back when the steel manual changed from the dark blue color to the light blue color - hows that for a scientific description?)
2. I would suggest finding a 1906 era structures text and reveiw design methods and values from that time to get a feel for what MIGHT have been done at that time for design and code issues. Computing those values will give you some good insights to the building structure.
3. Check the building against the current codes. The differeces from what you find in #2 will tell you where you may need to reinforce the structure.
4. A reference like "Structural Analysis of Historic Buildings" by J. Stanley Rabun, John Wiley & Sons, 2000, would also be a good buy.
Good luck!
RE: old beam strength
RE: old beam strength
When checking an old building, the current code is what governs. IBC even has an "existing buildings" chapter.
The current, "best" provisions of the adopted code are what apply to any building in a governing agency's area. That doesn't mean that you have to bring every element of the structure up to the code. Just that you have to use the current code for new work.
RE: old beam strength
RE: old beam strength
But if he gets 36 ksi for the yield, there is nothing inherently wrong with using 0.66Fy for that beam and material. The old 16ksi "allowable" limits were due to lack of knowledge back then - not a limit of the steel properties.
RE: old beam strength
RE: old beam strength
RE: old beam strength
I think you have to keep in mind, the quality control of the steel itself was likely not as good as current manufactured steel.
RE: old beam strength
P. 14 & 15
Working stress for tension members is usually placed at from 16,000 to 20,000 psi. "It should be understood that this discussion relates to ELASTIC strength and not ULTIMATE strength..."
P. 33
"In compression members the yield point (practically the ultimate strength)is reached with a load of 22,000 psi..."
From "Steel and Timber Structures" by Hool and Kinne, McGraw-Hill, 2nd Edition, 1942, Table 3 page 5:
Unit Stress Allowed on Steel by Various Cities (ksi)
Chicago Dallas Denver Detroit New York San Fran
Tension 18 18 18 18 18 20
Compres. 18 18 18 15 18 18
These valuses are from the noted cities building codes adopted between 1929-1941.
It is interesting to compare them to today's values and also interesting to see the values for San Franciso.
Just some more food for thought.