Lateral Stability of PPC Beams 1

[DWHA]

I am currently working on the design of a lifting system to lift PPC I Beams. These beams are going to be lifted by a crane. I am worried that the compression induced by the crane lifting the beams (due to the cables being at a 60 degree angle) may cause a buckling failure in the PPC I beam. I was wondering if there was anything (preferably in ASSHTO LRFD) that talks about this situation, and how to analyze this situation.
Thanks.

 

[DWHA]

Well thanks everyone. I asked a question and I have only one good suggestion for a method to seek the answer that I am trying to reach (thanks Denial). TampaBridgeDesign does make a good point, but I know if the beams are okay for lifting then they will be okay setting on the abutment/piers(at this point the compressive force will be released).

ANY OTHER SUGGESTIONS? PLEASE NO MORE TALK ABOUT SPREADER BEAMS, I KNOW OF THIS OPTION.

Qshake
The contractor asked me if the pcc beam could be lifted with out a spreader beam. Therefore I am going to do everything I can to answer that question. However if I cannot tell him a definate yes or no, then I will tell him that I was not able to determine that. Who ever said that I told the contractor that it could be done? I never said that. He asked me if I could do that, and I said that I would do some research and see what I could find. And yes spreader beams have worked in the pass and will continue to in the future, however there is nothing wrong with thinking outside the box and trying something new, is there? If ppc beams can be lifted without spreader beams in some cases and can save someone some money, why not do it?

 

[civilperson]

Spreaders and tension cables attached to the compression flange such as a mast of a sailing ship will produce a system capable of compression with out buckling.

 

[Qshake]

Since your referencing AASHTO in the original post I'll assume this is a bridge job.

I have designed girders for spans of 120' using 72" bulb tees and have seen them successfully erected with no spreader beams. In that particular case, the beams were lifted by two crawler cranes one at each lift point and walked in and set down. It was a very effective and efficient operation given that there were six beams in cross section and 10 spans. It did take time for site preparation and coordination was a must.

The lift was only about 50tons and something well within range of the crawler cranes. Yet the big issue was handling....if we would have used a single crane and if we would have spliced a spreader beam to facilitate lifting, what control would we have over the beam pivoting about the load line? Little to no control at all. Even if you ganged up on the beam's taglines with several workers it would be like the tail wagging the dog.

So if your spreader beam is too large from a practical standpoint perhaps you should be thinking outside a bigger box.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[DWHA]

Qshake
Using 2 cranes has been considered and is going be done (for part of the length that the beam is going to be moved). However there is a point where they want to handle the beam with 1 crane.
I appreciate the other suggestions, but that is not the info that I am looking for.
From now on, please only post messages that answer the initial question.
Thanks

 

[JEmH]

When you say that the cable is at 60 degrees, what do you mean? Is it 60 from horizontal or 60 from vertical. Either way, how far to the good or bad are you if you just look at this in a quick and dirty way? That is, if you just put the 1st order F and M from the self weight and the cable reactions on your most typical transformed section and see what stresses are at the center and ends, what happens. What I'm saying is, if at first blush it looks way cool or (more importantly) way bad, you might just tell the contractor that it's not worth the time to get into detail.

 

[Qshake]

It seems the answer you're looking for is how to work a stability problem (think euler beam-column with an imperfection - the imperfection being the camber). This procedure you can find in most stability texts; Timoshenko has a good treatment.

Unless of course, you'd like for someone to give you the formulas and answers lock stock and barrel. Otherwise put the pen to paper and to quote "I am going to figure out how and do this for them. "


Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.