Pipe Support Beam - Analysis
Pipe Support Beam - Analysis
(OP)
I am designing a simple span steel I-beam to support future piping (quantities, sizes and support fastening conditions of the piping will vary and are unknown at this time) and my client advised me to assume 800 PLF uniform (piping DL + LL) load acting across the full length of the beam. They also want the beam and piperack bents installed now. What unbraced-length-of-compression-flange (Lb) should I assume in designing the beam? One source that I read advises to assume 1/3 of the full beam length while another one advises to assume the full beam length when the piping support conditions are unknown. Does anyone have any advice on this? I don't want to design an unsafe beam but I also do not want to be overconservative, since there will be several such beams on this project and the construction cost will be significant.






RE: Pipe Support Beam - Analysis
I would opt for the assumption that the beam is laterally unbraced over its full length unless you have good reason to assume otherwise.
BA
RE: Pipe Support Beam - Analysis
i usually use length though. the cost of your beam is minor compared to cost of the pipes and equipment.
RE: Pipe Support Beam - Analysis
Remember tht pipe locations can always be changed or removed too. So, even with definitive locations for the pipe, I would still use the full length.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Pipe Support Beam - Analysis
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Pipe Support Beam - Analysis
RE: Pipe Support Beam - Analysis
I asked you before but you have not responded, what is the span of the beam?
BA
RE: Pipe Support Beam - Analysis
There are several beams and bents involved in my project, all with different lengths but the same loading criteria. Some beams are approx 10 feet long, some are approx 20 feet long and some are approx 30 feet long, but I don't see how the length affects the "philosophy" that I am looking for. Thanks in advance for your explanation on this.
RE: Pipe Support Beam - Analysis
if you use 2/3L, what unity ratio will you use so you dont over/under design? is it 1.0 or 0.9? remember 800plf is just an assummed load based on 8" pipes.
the best it to coordinate with other structural engineers in your project so you are all in the same page.
RE: Pipe Support Beam - Analysis
RE: Pipe Support Beam - Analysis
Also, this is not the "philosophy" forum. And, “fictitous "brace" points” may cause real beam failures which is philosophically sometimes/usually/maybe not a good thing.
RE: Pipe Support Beam - Analysis
BA
RE: Pipe Support Beam - Analysis
I have an old (1993) copy of the Fluor guidelines which says the same thing. I believe these were based on the AISC 9th edition steel code. That was before AISC had specifically codified the fact that points of inflection cannot be considered to be bracing. Since AISC has clarified this, it is more difficult to justify that assumption (unbraced length = 1/3 of span) than it used to be.
Pipe racks do have a lot of redundancy in them. So, you could argue that the pipes which are supported by the beam will do a lot to brace the top flange of the beam. That should limit the type of lateral torsional beam buckling that we're concerned about. But, only for the top flange. It shouldn't help you much in the negative moment region where the bottom flange is in compression.
Personally, I would use the full length of beam, but with a larger Cb factor.