Lifting long girders

[wtshtf]

Can anyone recommend a source of info or literature on the lifting of girders?

My specific question has to do with how to determine the unbraced length of the girder. Since the pick points will either be with slings or some other type of cabled support, the points of support cannot be considered "brace points".
So, my immediate dumb question is: what do I consider the unbraced length? The total length of the girder? I wouldn't think so, because even if I lift if from the extreme ends, the compression flange is not braced anywhere along the girder.

If I determine that the compression flange needs to be braced, I would assume some type of stiffening beam or truss needs to be attached to the flange. How would I determine what this needs to be?

Thanks for any response.

 

[civilperson]

Lifting points need to be above the center of mass and a spreader beam of sufficient length needs to be used, (3/5 of L is a standard length). Get knowledgeable person to review the PICK Plan for angle of boom and clearance issues as well as jack foot loads and dunnage required.

 

[jorton]

I was recently responsible for evaluating the stability of long precast-prestressed girders during transportation and picking. The resources I found are as follows:

Chapter 8 of PCI Bridge Design Manual
"Handling and Shipping of Long Span Bridge Beams" by George Laszlo
"Buckling of Suspended Cambered Girders" by Walter L. Peart & Others
"Lateral Instability of Long-Span Prestressed Concrete Beams on Flexible Bearings" by Burgoyne & Stratford
"Lateral Stability of Long Precast Concrete Beams" by Stratford & Burgoyne
"Stability Design of Long Precast Concrete Beams" by Stratford & Others
"The Toppling of Hanging Beams" by Stratford & Burgoyne

I evaluated the girders using both the older Laszlo method and the PCI method. Both methods give you a factor of safety against cracking in the extreme tensile fiber (usually the top corner of the top flange for prestressed concrete girders). The PCI method seems to give a more conservative factor of safety. I had to iterate several times using the PCI method when accounting for P delta effects (the contractor was using a single crane pick with no spreader beam).

 

[wtshtf]

Thanks for the response. It looks like some of those publications will apply to steel stringers as well. I guess I should have noted that in my first post.

 

[DWHA]

I prepare many erection plans for contractors. I found a study done by a college in canada about the picking of steel beams. I ended up creating a spreadsheet to check the stability of the member. Give it a look.

http://www.civil.ualberta.ca/structures/reports/SER185EssaandKennedy.pdf

 

[wtshtf]

That's just what I was looking for. As soon as I find my way through the paper I'll create my own spreadsheet

 

[Qshake]

You can also consult the book of rigging, which may be dated but helpful. Or other references such as the Manitowac Crane manual....

Spreader beams are a must.



Regards,
Qshake

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