Modifying wide flange steel beams
Modifying wide flange steel beams
(OP)
I am working on an existing building with wide flange steel beam joists at the roof (simple span configuration). They are adding a significant amount of load to the roof. To increase the capacity of the beams, I am adding a steel plate (flat) to the bottom of the beams. Using Enercalc to find the properties of the modified beam I get two values for the section modulus (S). Speaking with another engineer I was told to use the higher value as the added steel will increase the tension capacity of the beam. Looking at my old text book it says that 'c' is the distance from the neutral surface to the extreme fiber and thus would always result in the lower value of 'S'. Please verify which of these is correct and if the second is correct is there ever a situation where you would use the higher value of 'S'.





RE: Modifying wide flange steel beams
And you can have any Stop and an Sbottom, usually the "c" used is where yield will first occur.
Also, adding the flange plate will not help with deflection unless the beams are jacked up first. It does not matter for strength.
Also, the code has has a section for singly symmetric shapes bent about their major axis - F4 in AISC 360-05
RE: Modifying wide flange steel beams
Deflection does not seem to be an issue, but I will double check this.
I will certainly utilize section F-4. It is interesting that in that section it utilizes Sxc for compression and Sxt for tension.
RE: Modifying wide flange steel beams
On page 327 of my 5th Edition (Ninth Printing) of the AISC code, under section 9(a) for tensile properties, it shows the minimum yield point to be not less than 33 ksi.
I think I would be conservative here, unless 36ksi is specifically stated on the drawings you have, and use 33 ksi material.
Mike McCann
MMC Engineering
RE: Modifying wide flange steel beams
The drawings specify the fourth printing, but I doubt that makes any difference. I will use 33 ksi for the existing steel. Is the 33 ksi minimum for steel angles as well as steel beams? I ask as there are some steel angles that I need to review as well.
Thanks,
Sam
RE: Modifying wide flange steel beams
So, I would say that angles are included too.
In all likelihood, you are dealing with a minimum of A7 steel.
Mike McCann
MMC Engineering
RE: Modifying wide flange steel beams