Utility Pipe Trestle?

[dtse86]

My boss wants me to design a utility trestle that supports several large utility pipes in between buildings on site. I have no idea what typical design/build practices there are for this type of structure. He wants a modular design with 18' sections and catwalks on either side so that the workers can stand while joining the pipes. He also seems to think that the only way to get the pipes within the trestle, is to lift sections and slide them in through the side. Does this seem typical? I know I've seen trestles at facilities with triangular supports along the sides. How do they fit the pipes in? Also, a steel trestle made of 18' sections sounds pretty heavy. Does this design sound practical at all?

 

[Ron]

How much space is between the buildings? Could be some long spans. Design it with an open top so that the pipes can be dropped in from above...don't design for side entry.

You're essentially designing a pedestrian walkway with some heavy eccentric loads or you can do a symmetric double walkway with the pipes in the middle.

 

[hokie66]

What is the height of the catwalks above the ground?

 

[dtse86]

The run is about 80' North and then 140' East. It'll be about 20'-30' in the air carrying 4 pipes from 6"-8" and some cable tray for building controls and possibly a few 1/4" high purity gas lines.

 

[dik]

That 'dogleg' is going to be pretty difficult to accommodate, in particular with an open top <G>.

 

[dtse86]

Yea, I was wondering how they typically support something like that, with all that weight on there. And my boss wants to make it so that its easy to add more pipes after initial install if necessary. Because pipes get upsized and more pipes get added on this site quite often. It's pretty dynamic here and he just wants to make sure that if more utilities do need to be run, we have enough room in the trestle to do so.

 

[jike]

I suggest using a couple of LH joists spanning 35 to 40 feet, depending on where you can locate the supporting bents and what you have to span over. Tie the joists together at the top and bottom chords to make a box truss (trusses on 4 sides).

I am assuming the bents would have two legs X braced together. Foundations will depend on soil conditions. If piling or deep foundations are needed, you might want to span further to minimize the foundation cost.

Analyze the structure for lateral loads due to wind, seismic and ice. You might want to include provisions for future pipes, etc.

 

[hokie66]

I would tend to use A frames rather than braced frames for the bents. Make the legs of CHS or SHS sections, with a symmetrically cantilevering wide flange headstock on top. Then fabricate the pipe gallery/catwalk sections and drop them on top of the headstocks. I would use all wide flange or channel sections for the gallery, not steel joists. Use bar grating or expanded mesh for the catwalks. Agree with Ron, leave the top open for installation and maintenance of pipes.

 

[dtse86]

Thanks guys. Now to tell my boss his idea won't work...