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rigging from existing roof beam

rigging from existing roof beam

rigging from existing roof beam

(OP)
Does anyone know an applicable standard for using an existing roof member to support rigging for a tank? The owner wants to use a beam clamp and hoist off the bottom flange of an existing beam, and asked me to evaluate if it is possible. At first I thought to use CMAA 74, but it may not be fully appropriate, and I cannot find anything within OSHA of ASME - maybe I am not looking in the right place?

RE: rigging from existing roof beam

structSU10,

I would try and evaluate it using ASME BTH-1 provisions (unsure of what year it's on now, I have a copy of the 2008 edition, but I'm fairly certain there is a newer edition).

Note that you should probably pick up a copy of ASME B30 to go along with the BTH-1.

RE: rigging from existing roof beam

Agreed, BTH for everything added to the existing structure.

To evaluate the structure itself, I'd imagine you'd use the relevant permanent design code.. but I'm the wrong person for that question.

RE: rigging from existing roof beam

I did a lot of this type analysis for my employer, an electric utility. Don't believe there is a standard. Use engineering principles. The old saying "the devil is in the details" applies.

1. Verify the precise beam size, span, and support. Make field measurements if reliable drawings are not available.

2. Make conservative, informed assumptions of the existing loads the beam carries.

3. Get the specs for the lifting clamp/hoist and determine exactly where it will be attached to the existing beam.

4. Determine information on the load to be lifted (weight, etc.) and what will be done with it once it is suspended (e.g. Lowered directly on a truck. Pulled, while suspended, to one side. Etc.)

5. If possible, be present during the lift and don't hesitate to speak up if conditions are different from what you were told.

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RE: rigging from existing roof beam

StructSU10:
My goodness, do we need a specific code or std. section/paragraph for every (and any) imaginable situation and condition in the whole universe, before we can do anything in the Structural Engineering realm today? What ever happened to good sound engineering experience and judgement in making some of these determinations? What ever happened to the good old code verbiage... ‘means and methods of construction shall be based on a rational analysis in accordance with well established principles of mechanics.’ This verbiage used to cover a multitude of conditions, and we ran with it. It used to be that clients or employers hired real Structural Engineers because the real ones had this experience and judgement and could make rational decisions about how to carry a project forward, or they knew when to draw a limiting line which should not be crossed. Our engineering today is actually being hampered by our absolute slavery to the codes and the need for a code section with the formula to point to, or we are paralyzed. If this is an in-plant maintenance operation what do codes and stds. or an AHJ have to do with it, other than using good sound engineering judgement?

I agree with the advice that SRE gave you completely, and would just flesh them out a bit, and add a few other ideas.
1. Make some determination on the steel grade. Find the original bldg. plans and specs. if you can. It always has amazed me that someone will spend millions of dollars on a bldg. project, and then, not save a set of plans and specs. for future use. What is the beam’s max. cap’y. given these conditions, how does this compare with the loads actually on the beam, so you know the beam’s reserve cap’y. for your use?
2. What are the actual loads on the beam? No design snow load in summer, no heavy storage which was designed for, lighter equip. above the beam than the original design, etc. What can you do to unload or support/brace your beam to give you the cap’y. you need? RE: load path, it is reasonable to assume that beam reaction points, columns, walls, ftgs. were designed for the max. design loads per code and shown on the drawings. But, the old saw..., trust, but verify still applies, do some basic verification, without redesigning every bldg. element.
3. What could you do to reinforce the bot. flg. or spread the loading a bit on the beam/flg. length to make things work? Get the clamp load up into the beam web as efficiently as you can. Could you put a new/temp. beam btwn. two existing bldg. beams to make things work, or to trolley the lifted load laterally.
5. Check the existing deflection of the beam (string line, laser level, etc.) and compare with a calced. value for your assumed loads. Does this reasonably verify your loads? What is the calc’ed. deflection for your max. cap’y. load? Pick some safety factor, and have some/the deflection during lifting be a stop action limit during the lift.

RE: rigging from existing roof beam

Is this using a beam in an existing building to lift a tank? Or using a beam in a tank to lift something else?
I would say ASME BTH is not applicable there, it's for BELOW The Hook, not above. But it is based on similar AISC building codes, and those would be the preferred standards.
A couple of notes in addition to the above. One, if the condition of the beam is in any way questionable, that needs to be taken into account as well. Secondly, beams that have been there a good many years may not correspond to any of the modern beams in the tables- it may take some research if it's a defunct beam.

RE: rigging from existing roof beam

(OP)
Thanks for the advice.

This is an existing roof beam being used to hoist a tank into position.

Calculations are required to be submitted, and a code reference is nice for something like that, especially with vertical impact and incidental lateral loading requirements and such.

RE: rigging from existing roof beam

For load criteria applied to the beam, look at the ASCE 7 provisions for cranes. End of chapter 4, I believe.

RE: rigging from existing roof beam

Unless the tank is centered directly below the roof beam, there will probably be some torsion and/or lateral load on the beam when the tank is lifted. I would bet that such loads were not used in the original design of the beam. Also, take a look at what is supporting the roof beam and the connections. That may be your weakest link.

RE: rigging from existing roof beam

Agree with all advice above, this is a common practice in industrial applications such as nuclear power plants. Not typically a code evaluation, but do use equations as a basis for acceptance. When I prepare these "Rigging Plans", things I consider include:

Available Margin: If rigging from roof or overhead floor system will other design loads be present during the evolution? Most often not. Will the roof have its design snow load on it during the lift? Will the floor above be carrying its design live load at the time of the lift? Will my single hoist load (really bending moment) be less than the aggregate live/snow load.

Dynamic Loading: Consider dynamic impact from rigging (probably 10% increase (Quasi-static) if chainfall or other manual hoist is used. Additional guidance in ASCE 7.

Load Soak: Always perform a load soak before continuing

Secondary Effects: Need to assess the impact of a single point load on the beam (vs original line load). Will your beam be controlled by lack of bracing points for lateral torsional buckling (LTB). I may specify additional bracing to prevent LTB.

Path of Hoist: DRIFTING LOADS from beam to beam can quickly produce large non-vertical forces in beams. AVOID this at all costs. If I need to laterally shift loads from one point to another, I use a trolley beam (rigging beam) and trolley block suspended from the structural steel. This evaluated load path ensures that the load on the structural steel is always vertical.




Jeff
Pipe Stress/Structural Engineer
www.xceed-eng.com

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