Steel Web Joists & Girders
Steel Web Joists & Girders
(OP)
My client does not have blueprints for two commercial businesses he was retained to replace A/C units. Old units are approximately 2400 lbs and new units are 3000 lbs. Several field inspections were performed but no luck indetermining the type of steel joists used (J, H, LH, DLJ...etc). Field Measurements of the Top & Bottom Chords do not match some of the tables on-Line. My analysis of the joists revealed higher reactions and moments than shown on some of the tables that could or match the type of joists. I double checked my work. I do not want to take chances and assume. Any suggestions?
Any idea's?
Any idea's?






RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
If that doesn't work then you must completely measure the joists including all panel point locations and member sizes. Try to get the yield strength info. from the manufacturer. Note that the web strength might be different than the chords. Analyze the joist as a truss using the SJI specification for the year that the joists were manufactured.
One word of caution: Sometimes existing joists are overstressed in their current state so don't just say well we are only adding 600#......
I hope this helps!
Good luck!
RE: Steel Web Joists & Girders
Make sure that you personally verify the existing loads in the field both below the roof and above. Things often change from the design drawings. Roofs getted re-roofed (sometimes heavier, sometimes lighter). Owners add equipment. Ceilings change (sometimes lighter, sometimes heavier). Buildings get additions (sometimes creating drifted snow).
I think that you get the idea!
RE: Steel Web Joists & Girders
It is your professional responsibility to fully analyze the complete situation.
This has nothing to do being "stress free"......but that is a whole different subject!
RE: Steel Web Joists & Girders
I called Vulcraft, John Hancock Joists and their engineers, I must say, were very helpful. The concern was stress reversal due to the shift in the vertical shear.
I recommend that you get a copy of SJI’s 75 YEAR MANUAL 1928 - 2003. I won the previous edition. This is a valuable reference if you get involved in renovation work and need to evaluate capacities of steel joists. You can get a copy from their web site, for modest fee. Here is the web site: http://www.steeljoist.org/publications/
As a last resort, I would as-built the joist members and run a 2-D model using STAAD or similar software and had check the stresses using the joist specifications that are published by SJI. You may want to confirm the period that they were built. I would also search for the tags, as previously mentioned. The tags hold good information that may be of good help.
Lutfi
www.cdeco.com
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
If you do a computer model of the joist based on field measurements you can get a reasonable estimate for the member stresses. In order for the joist to be ok the stresses in the welds also have to be ok. I question if it is possible to accurately field measure the welds that tie the joist together.
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
I agree with the rooftop platform -- we do that often on existing buildings.
Also keep in mind that many older buildings proprietary (non-SJI) joists were popular -- Macomber Allspan and Kalmantruss are two that come to mind off the top of my head...
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders
RE: Steel Web Joists & Girders