Using existing building steel for piping supports 3

[curtis2004]

Hi everyone,

During maintenance projects which involve replacement or a new piping projects very often existing building steel is used to support a new or replacement system. Usually big building steel beams and columns are used to support pipe, if pipe loads are small.

However, is there any rule or criteria based on closer look would be warranted with structural engineer involvement? In what situation would you have concern about putting too much load to existing building steel? I understand that "big" and "small" is relative categories here.

I myself very often talk to our structural guys if necessary. What would rise alarm bells for you?

Thanks for your input,
Kurt

 

[MikeHalloran]

I wouldn't hang a pencil sharpener on a PEMB without somebody else betting his house that it won't bring the building down.


Mike Halloran
Pembroke Pines, FL, USA

 

[curtis2004]

Even if you have 3 ft high I-beam and 2" line with rod hanger load of 100 lbs?

 

[MikeHalloran]

My point was that PEMBs are engineered with a safety factor of 1.00000, or maybe a little less, >for all the loads that are specified when the building is ordered, and not one ounce more.<

Other industrial buildings are probably not designed to such razor thin margins in price and in strength, but you should check any nontrivial load that you propose to add.

I would call a 100 lb hanger load nontrivial, mostly because a 250 lb pipefitter may stand on the support while it's bearing the design load. Your experience may cause you to think differently and apply a different set of 'unspecified constraints' to any given problem.

Knowing an I-beam's depth alone will not tell you enough about its strength; I am amazed at the thinness of some of the rolled sections I have seen under travel/office trailers.



Mike Halloran
Pembroke Pines, FL, USA

 

[curtis2004]

I didn't meant Pro-Engineered steel building. They are "different species". I was talking about Industrial Building built from standard structural I-beams, HSS and C-channels.

As far as I know those are designed to limit deflections, not allowable stress. Usually Miscellaneous steel where pipe supports are attached either bolted or welded into columns or I-beams.

I know that this is structural engineer's responsibilities. However, is there any rough rules of thumb that will screen out situations for further study for structural engineer?

Thanks,

 

[MJCronin]

This is a question that has been around for a long time

Way back when......In the past, for many non-PEMB projects, the structural design of the building would typically include a 3 to 5kip load in the center of all significant spans.

This load was shown on the steel drawings. From there, it was easy to summarize the supported span loads for cable tray, piping, etc and compare the total against the margin.

About 20 years ago "Value Engineering" came to town...

Hell-bent on savings, psychotic value engineers attacked many projects..... they certainly may have been MBAs in disguise.

"Value Engineers" removed most maintenance space, removed the margin allowed for miscellaneous loads, declared a victory and demanded a bonus for all of the "money saved"....

Because they had no alternative, reasonable and prudent mechanical/piping engineers designed pipe racks within the PEMBs..... at additional project cost.

The Value engineers were all promoted and the piping engineers punished for going over budget because of the "new pipe rack"

Anyway..... that's the way I remember it

MJCronin
Sr. Process Engineer

 

[curtis2004]

MJCronin,

Thank your for your insight. It is one of complex issues piping engineer facing everyday. Sometimes, this issue is more challenging than pipe stress issues.

In our company 2.5 kip is borderline for referring the issue to structural engineer. Of course, you have to understand and check what is existing steel look like, and its condition.

When I am ordering pre-engineered buildings, I always include miscellaneous load of 5,000# in the centre of spans, when I do not have any data about piping layout. However, I always have something like preliminary layout. Sometimes, I include additional beam members between columns for piping support, cable trays, lights, fire suppression etc.

In case of having preiminary layouts, I would include something suitable, depending size, quantity of piping, fluid inside pipes, and pipe support spans. On top of this, I also include loads for possible alternative routing.

Of course in case of additional loads and members building cost will increase. However, this cost is marginal cost of building separate pipe rack or structure. Really it is cost of additional steel building supplier would add.

Regards,

 

[curtis2004]

MJCronin,

I've never seen structural design miscellaneous loads in steel drawings. Can you post here some example if you have?

Thank you,

 

[pdprao]

Usually it is a very common problem which has no simple solution . It is very important to consider the degree of pipe line loads, size of the structural members and original contemplated loads on the structural members.Many times the design & drawings will not be readily available for old building and therefore only technical experience of structural engineer matters based on his experience.
Heavy pipe loads shall not be loaded on structural member flanges such as I beams, c- sections which will lead to local distortion and member failure unless the structure is suitably designed.
Usually welding is not permitted on building steel beams which are carrying heavy loads .
Even the metallurgical properties of structural steel , hardening properties , direction of support loading are important parameters.
In important structures ,it is advisable to study the interaction of new loads on the structure by competent Structural Engineer where such changes are to be carried-out.

 

[DSB123]

I presume you have all heard of the straw that broke the camels back. In reality any additional loading applied to an existing structure should undergoe an assessment by a competent Structural Engineer. How do you know that the structure is not loaded to its full capacity without an assessment? Are you willing to add more load when you do not know the utilisation of the members? Sounds like another collapse waiting to happen. You have seen what overloading can cause - the indian workshop collapse a few years ago!!!!

 

[LittleInch]

IN terms of raising alarms I sometimes work on the FGT (the Fat Guy Test). Imagine one or more of your more stoutly built colleagues hanging, standing or even jumping up and down on said structural member and then figuring out if you would feel safe standing underneath them or if the roof might collapse....

For even larger loads work out how many normal cars it takes hanging off the point and do the same thing.

The biggest question though is whether any pipes that are already there were allowed for or have they already taken up any spare capacity the building had in the first place??



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

"sometimes work on the FGT (the Fat Guy Test)"
I am that fat guy, and tromping around on the steel tends to reveal if another 300-500# is a significant load. Wear boots with stiff heels [no kidding]

"How do you know that the structure is not loaded to its full capacity without an assessment?" The wonderful thing about steel is that it is elastic. Look for deflections - is the camber still up?. Perform the FGT. No Fat Guy? Use several regular ones, tromping in step with one another.

This will cover the piping up to about a single 6"NPS and waterfilled. Somewhere around that point, it is time to bring in a structural guy and start spending money. It just isn't prudent to reroute 10"NPS Chillwater supply & return pipes w/o an assessment of the loadbearing ability of the existing steel.

 

[curtis2004]

Duwe6,

When you have 8", 10" or bigger, you have much more budget to play with, and you are absolutely right that structural guy should take charge.

I was talking about small projects with 2"-4" lines involved, when you do not have much money to spend. And if you ask money for structural engineer assessment, most likely those projects will be cancelled.

Most importantly, engineering judgement should be exercised when taking on those jobs to make sure we do not really overstressing any structural steel.

Thanks,

Curtis

 

[dhengr]

Curtis2004:
2.5k gravity load is no insignificant pipe loading on a structural member in an existing structure, and your company should be very careful with that rule of thumb. No building designer in his right mind just arbitrarily designs all the beams for an extra concentrated load of 2.5k hanging off the bottom flange of all the beams, and you and the Industrial guys are want to put them anyplace. You asked for some rules of thumb and seem a little reluctant to involve a Structural Engineer. You should have a Structural Engineer on your team for just such discussions. You go ahead and tabulate the loads, and that includes all of them, not just the pipe weight. I’m always floored by the fact that people will pay millions of dollars for a bldg. and then not keep a few set of drwgs. and specs. so we have a vague idea what’s actually there. The gut check, the experience and judgement, the Structural Engineer has gained over twenty years of doing this work is well worth his involvement, and you’re obviously fishing in the dark at this stage of your development. He won’t necessarily redesign the whole bldg., but he will look at the general loads on the bldg. and on those beams (joists, purlins, etc.). He will give some consideration to how you are hanging those loads and distributing them, so as not to overload the beams at that location. Usually, by the time you get those loads to the columns and foundations, they are not a big percentage of the total, although that’s not always true either,and he’ll check that too, and make adjustments accordingly. There is no simple answer to this problem, expect for the 1" compressed air piping.

 

[Duwe6]

". . small projects with 2"-4" lines involved"

Fat Guy Test is just the ticket for determining if a small [< 500# per hanger] load can be added to a steel structure. It really does work - if there is little or no deflection, the steel is either moderately loaded or overloaded*. Just don't call it a FGT - you dynamically applied loading similar to the dead-load of the proposed piping and evaluated the response of the structure to that dynamic load.

*You should be able to tell which case it is by visual inspection. Don't forget to check for rooftop HVAC equipment.

 

[BigInch]

Buildings are normally designed for dead load (weight of beam and flooring system) + live loads X lbs/ft2. Process building live loads might be 50lbs/ft2, or 100lbs/ft2 or more, but absolutely nobody just puts 2000 lb loads in the center of a span, unless the design specs required them to do it.

The typical loadings are variable for each type of use, see attached

http://www.asce.org/uploadedFiles/sei/Books_and_Journals/Errata_1_ASCE_7-10_Table_4-1.pdf

So you can get an idea about what a new pipe load will do to it by equating this to the live load and calculating the beam's live bending moment; a simple pinned end span, would be M = (w * L^2)/8

for a point load at center of a simple pinned span M = P * L/4

Solve for P

That can also vary by type of beam end connections and wind loads, etc.

If your pipe load is greater than P / 2, seek professional advice. Some of you might want to do that anyway.


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