Elevated Water Tank - Catwalk Guardrail

[Tamu83]

I have been asked to look at repairs to a damaged ladder/cage system on an existing elevated water tank. As a part of the repair, the owner has asked that a portion of the existing guardrail be removed in order to allow a step-thru at the catwalk level. The guardrail is a continuous ring around the perimeter of the tank, with diagonal bracing to the toe-plate at the outer side of the catwalk. The catwalk is supported by brackets at each tank leg and is rivited to the tank wall at the inside edge of the walk. It appears the trussed guard rail provides support for the outer edge of the catwalk, and that breaking the rail system would result in compromising both the support for the outer edge of the catwalk and the lateral support capacity of the guardrail. This tank was built by Pittsburgh Des Moines. Not sure of the date of construction, but most of the connections are rivited and the nuts are square.

At this point I'm just looking for someone familiar with the general design approach who can confirm or deny my preliminary assumptions, and possibly a reference to some design procedure information or a firm familiar with this type construction.

 

[Ron]

A photo or sketch would be helpful.

 

[JStephen]

I don't think that's the case. If I remember right, PDM used diagonal guardrail posts for all of their water towers, and CBI used vertical posts on theirs, and that was just a style issue, not a structural issue. But the girder section should be supporting the guardrail, not the other way around. The toeplate may actually be the flange on the beam section, so I would not cut into it.

You might want to check the height of the guardrail and the geometry of the guardrail/ladder access as compared to current OSHA. If they don't currently comply with OSHA, it's someone else's problem, but if you go changing them and then they don't comply, it's your problem.

From a practical standpoint, the work required to modify some of this stuff to comply with current OSHA rules can generate more hazard than leaving it like it is.

 

[Tamu83]

I have been trying to post a photo but it won't upload for some reason. I'll keep trying Ron, but thanks for the info JS.

 

[Tamu83]

Hopefully this worked.

 

[racookpe1978]

Your problem will become more clear - actually, all three of your problem, potential pitfalls to your assumed answer to your problem, and alternatives solutions to the problem - will become more clear if you show us what your client wants, and how you intend to answer that desire.

Sounds to me like he wants to cut the existing steel and part of the existing railing attachments so he can walk through the railing, rather than climb over it, like they probable are doing now. Leaving it as-is because it is a challenge to meet OSHA spec's when you rebuild won't work.

So, how are you going to replace the lost strength, and where are you going to put the new steel so strength is maintained? Once you've answered that, then you need to step back, re-read the OSHA railings-ladders-climbing restraint rules, and rebuild the step off so it meets spec.

 

[msquared48]

Looks like someone put an antenna mounting pole that is mounted to the ladder rungs, right in the middle of the entrance to the catwalk. Good thinking - obviously someone who does not have to get to the catwalk. No wonder there is no room to get under the railing. Move the pole and mount it in a different location. Access should then be no problem and meet osha specs.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JStephen]

That is a cable-type safety climb. The pipe part supports that cable, and the climbers use a harness with sleeve/brake that goes over the cable. If the top rail wasn't there, you could squeeze around it okay standing upright, which is how it ought to work.