Deflection calculation on bar bundles when lifting 2

[MechEng..]

HI,

need some help to calculate the deflection curve.

18 M in length each bar is 24 dia bar bundle has 31 bars,weights 2T metric, has 9 -equally placed straps-how to calculate the deflection when the bar bundle is been lifted by a 10T crane or by a forklift.

Strap strength is 17KN per strap.

Need some help in calculating this.

 

[WARose]

It's going to vary based on location and how it is lifted. Obviously the deflection is going to look quite different with a forklift lifting from underneath vs. a hoist lifting it from (on top) @ the ends.

 

[WARose]

By the way, when you say "24 dia bar" (32 of them)....what does that mean? 24 mm diameter bar? And you say the full length is 18 meters and weighs 2 metric tons total?

Sorry for the questions.....but I am not use to working in metric.

 

[MechEng..]

what it is,

a 24 Dia bar @18 M Length with 32 no's of bars weights 2T (standard)

when the bundle is lifted it should have minimum deflection which doesn't affect the quality of the bar.

 

[WARose]

a 24 Dia bar

Again: what does that mean? 24 mm diameter? I need a dimension here.

Speaking of that, what are the lengths of your straps?

 

[MechEng..]

Each bar in the bundle is 24 mm in diameter.

the strap Width is 32MM, Strength is 17 KN

 

[WARose]

the strap Width is 32MM,

I asked for its length.

 

[MechEng..]

Sketch for what I am looking for

 

[IDS]

32 bars of 24 mm diameter and 18 m length have a mass just over 2 tonnes, so I think we can assume that's what is meant.

Assuming support points 0.5 m either side of the centre, and simply supported beam calculation, the end deflection would be:

Assuming the bars are melted down to form a solid cylinder of 136 mm diameter: 27 mm
Assuming 24 mm diameter bars free to slip with no friction: 8600 mm

So the actual deflection should be somewhere in that range.

Assuming the straps were done up tight I'd guess towards the lower end of the range, but try it and see (or ask someone who works with lifting 18 m long bars) would seem the most reliable way to check.

Apart from the deflections, moving a 2 tonne mass of 18 metre length with a fork lift sounds risky to me.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[MechEng..]

how about the bending moment and shear force diagram,any idea? When it lifted by a 10T crane.

Some sites still use forklift may be 2 to move the bundles,but not a standard practice.

 

[SlideRuleEra]

For minimum moment of a two-point pickup of a uniform distributed load on a uniform crossection (the rebar bundle qualifies) the answer is always the same. Magnitude of the uniform load (rebar weight) does not matter.
Total length does not matter.
The answer... two pickup points, each 0.207 x total length from the end. That is, each pickup point is 3.73 meters from the end of the 18 meter long bundle.

Minimum moment is probably a better critera than minimum deflection, but the answer is probably about the same.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[WARose]

He's talking 9 pick up points....not two. I asked for strap length because if there is any slack....the (controlling) deflection could be from the bundle conforming to the lengths. That's partly a field QC issue.

I did a forklift calc (with 2 pick up points near the middle a couple of feet apart) and came up with ridiculously high deflections. I'd forget about that.

 

[SlideRuleEra]

Thanks, WA. I missed the 9 pick up points. Agree to forget that plan. IMHO, the chances of the load being anywhere close to evenly distributed on 9 points is nil. Calculations on that subject are just an academic exercise, not a practical answer.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[IDS]

He's talking 9 pick up points....not two

I take those 9 points to be tie points, not pick up points. If the bundle acts reasonably close to a composite section and is lifted somewhere near the points indicated by slide rule era, then deflections would not be a problem.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[MechEng..]

Length of the strap is approx 700mm

the 9 points are tie points not pick points.

 

[WARose]

If the bundle acts reasonably close to a composite section and is lifted somewhere near the points indicated by slide rule era, then deflections would not be a problem.

Agreed. (That is, if he can tolerate about 13 inches of deflection.)

 

[MechEng..]

How many straps does it need to keep the deflection minimum?

Can anyone share cals done?

 

[CANPRO]

I think it would help a lot of you showed a sketch of your lifting arrangment. I assume you’re using a lifting beam for this, and probably have multiple fixed lifting points.

 

[SlideRuleEra]

MechEng - Why the focus on limiting defection during rebar handling?
As a former bridge contractor handling long rebar individually and in bundles with cranes, keeping the bending stress in the rebar below the yield strength is what is important. If bending stress is satisfactory, deflection is NOT important. Long bars can bend (deflect) a ridiculous amount without damage.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[IFRs]

Why does it matter how much the bundle deflects as long as the bars stay in their elastic region?