Selection of a max acceleration load for binding application 7

[tnteng]

I am trying to select a reasonable g force to use in the design of a binding on a set of pipes. I have 9 pieces of pipe at 76' long. They are stacked in 2 "U" shaped frames which are spaced 40' apart. The pipes are stacked three rows by three columns. There is wood between the pipes and the whole assembly is secured with tie rods that are torqued to a specified torque. To determine the torque to use, I need to assume a max acceleration force along the axis of the pipe and then from that I will calculate the friction force between the wood and the pipe and then the required normal force to apply at the tie rod nuts.

This assembly will be traveling by sea and by truck. Does anyone have any idea if there is a standard g force that would be assumed for an applicaiton such as this one. I am also assuming that the transportaion by truck would be the worst case with regards to acceleration loading.

Thanks in advance for any help on this problem.

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[desertfox]

Hi tnteng

I don't know a standard figure for 'g' in your situation, however would it be possible to work the other way if you have sizes of your tie rod and nuts plus material properties
you could use the maximum torque for the nut and work backwards to find the maximum axial force allowable in the plane of the pipes.
I presume these tie rods are positioned vertical alongside
the pipes so I assume that the clamping force for the second and third row of pipes as to pass through the first row am i correct?. Secondly calculating torque figures is not that accurate when it comes to getting the required clamping force, how accurate do you need to be or are you takingg measurements on tie bar extension during tightening ?

regards desertfox

 

[tnteng]

Hey Desertfox,

Thanks for the help. If I was to work backwards then the maximum torque would result in loads that are too large for the rest of the frame. I am trying to limit the loading on the frame but still achieve an adequated clamping force.

Yes your assumtion is correct with regards to the rods. The required clamping force will be based on what is needed on the top row of pipes. The second and third rows will see that clamping force plus the additional clamping forces due to the weights of the pipe above them.

The torques will be applied with a torque wrench. I am aware that this will not be precise but I figured that the selection of the "design g force" value would be only an educated guess as well.

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[desertfox]

Hi thteng

Just an idea I did a search for braking distances for waggons and came up with a list for various waggons with different weights ie;-Leyland drops 32 Tonnes ABS(1/4 laden) stops in 20.68m travelling 30mph or 26.19m travelling at 45mph.
assuming constant retardation of speed and using the formula
v2^2=v1^2+2*a*s the de-accel can be calculated.

where v1 & v2 are the velocities in m/s ie:- v2 in this case
would be zero and v1 either 30mph or 45mph converted to m/s

s= stopping distance

so for the above stopping from 30mph I calculate a 'g' of about 0.647

Do you know what waggon you will be using.

here is the link anyway :-

http://www.rospa.com/drivertraining/

factsheets/pdf/stopping.pdf

best regards desertfox

 

[Barry1961]

I am wondering if the strength of the wood might be the way to calculate the required or allowable torque.

.6 G is a quick stop, I am impressed.

Barry1961

 

[rmw]

Back in the days that I operated a trucking fleet of flatbed trailers, I remember that there was a specific requirement for the 'head ache rack' mounted on the cab frame, or the barrier mounted on the nose of the trailer with respect to stopping the maximum permissible load at some kind of impact, but I wouldn't know how to go about backtracking and finding that, without digging through some old boxes of information.

All that kind of stuff is available on the web now, and I think it can be found at the Federal Motor Carrier Safety Association (dot) gov site. Start at

http://www.fmcsa.dot.gov

and look in the "390's".

With wood as your dunnage, I would also consider the effects of ambient moisture, or lack there of, on the binding. If the wood swells, then that increases the forces, and if it is going to a dry climate, the wood might dry out, and shrink, and lessen the binding forces.

rmw

 

[tnteng]

rmw - thanks for the information. I looked on the FMCSA site but what do you mean by "look in the 390's"?

Thanks,

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[arto]

You might also want to look at the shock loads for railcar "humping" in the classification yards. I seem to recall 10g's????

 

[rmw]

tnteng,

When you get to the site, look under rules and regulations, and there are a long series of regs starting at part 390. The regulations that cover load securement are somewhere therein. I don't deal with flat beds any more, so I don't go there. I mainly deal with passenger carrying issues, so loads and binders don't apply.

Oh, well, I went and looked, and actually, it was hard to find. Go to;

http://www.fmcsa.dot.gov/rulesregs/fmcsr/regs/393.htm

and, now I will say look in the 393.100's.

Good luck.

Rmw

 

[notnats]

Arto is on the right track. The best coefficient of friction between bitumen and rubber tyres is less than 1, so you will never get braking forces > 1g. I would be more worried about clumsy crane drivers than normal road forces.

My observation of truck drivers tying down a load is that they prevent movement by applying massive vertical forces to the load via their chains. These forces may well exceed your tie bolt pre load, so it might pay to give them a tie down lug to use.

 

[Philrock]

If you want the pipes not to slip even in a crash, you might do well to use something like the 10 g figure that Arto mentioned.

Also, as rmw mentioned, the wood can swell and shrink, making the situation difficult if not impossible to control. What comes to mind to deal with the wood shrinkage is a stack of belleville washers on each tie rod - between the top piece of wood and the top tie rod nut. This would allow the wood to shrink and swell without changing the tie rod tension too much.

 

[tnteng]

Many thanks to all who have provided feedback on this problem. One thing that I have concerns over is that the maximum axial and lateral "g" force selected should be based on the worst case of transport by sea as well as by truck. The FMCSA site provides good numbers to use for loads to assume if transport is by truck. Can anyone point me to a resource that would give suggested acceleration loads for transport by boat/barge?

Thanks in advance for any help with this matter.

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[unclesyd]

I had to give rmw a star as he pointed out a very serious concern about the headache shields I have based on personal experiences and burying two friends.

One was killed by CI pipe and the other by of all things terra-cotta pipe in sudden stop accidents back when the trucks were relatively slow.

Check the design carefully.

 

[rmw]

Thanks unclesyd, I've seen a couple of those situations. Tragic.

Tnteng, Sorry, I don't have any sites to send you to for G forces for sea, but I ship stuff by sea from Europe all the time, and I have to deal with temperature changes. You may ship it from the sauna of the gulf coast, but it may end up passing through the north atlantic, which, on a hot summer day, is still colder than the gulf coast ever gets.

My stuff is steel machine parts, so I have seen it come in completely rusted when the anti-rust was not applied, due to the condensation at sea.

If you want to see what the sea can do to freight, go to

http://www.cargolaw.com,

and look around on the site. A real eye opener.

The people who operate that site might have somewhere to send you to for your queston.

rmw

 

[zeusfaber]

tnteng,

For road transport, the general rule seems to be 0.5g laterally and acceleration restraint, and 1g braking

Helpful references might be the UK Department of Transport "Safety of loads on vehicles - code of practice" at

http://www.dft.gov.uk/stellent/groups/dft_roads/documents/page/dft_roads_506864.pdf

or the (still draft) european standard EN 12195-1

For sea transport, you might like to take a look at UK Defence Standard 00 35-3. It's a biggish download from:

http://www.dstan.mod.uk/data/00/035/03000300.pdf

The following extract describes the sort of environment your load might encounter (without making allowances for safety factors)

2.3 Quasi-static environments
2.3.1 Inertial accelerations: During sea transportation inertial accelerations are experienced.
However, these accelerations are usually less than those experienced by materiel during other phases
of deployment. For general cargo the worst case values[2] are;
Upwards 2 g (excluding gravity)
Downwards 2 g (excluding gravity)
Lateral 0.8 g
Forward 2 g
Aft 1 g
2.3.2 Tilt: Payloads may be subjected to static tilt conditions of up to 30 degrees.

Hope this helps a bit.

A.