Trailer Rollover

[JBJohn]

Can Trailer (towed by prime mover) prone to Rolling Over? We have instances that 3 similar trailers (Liquid Tankers) have rolled over at U turns at different locations over last 3 years! Is it possible to some how rule out design problem? If cannot, then what remedial actions should be taken for the similar Trailers for prevention? Are there Sway/ Roll Bar available (or that can be designed) for trailers?

 

[patprimmer]

How much liquid was in the tanks and how is it contained.

Regards
Pat
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[BrianPetersen]

Trailers towing liquids are *very* prone to rolling over, because of liquid sloshing around inside the tank. The liquid naturally goes towards the outside of the tank due to centrifugal action, and add that to its tendency to slosh back and forth, and it can very easily roll the trailer over.

Nothing you do with the suspension of the trailer can address this. Instead, you have to address the liquid's tendency to slosh back and forth. If the trailer is either completely full or completely empty, it cannot slosh. If the tank is "compartmentalized" with longitudinal baffles - which need to be hefty enough so that very little liquid can flow between compartments, only enough to allow the trailer to be filled and emptied properly - then there is less tendency to slosh.

 

[JBJohn]

As i understand from the suppliers, these are having baffles to avoid liquid sloshing.

Best Regards
Jojy

 

[LionelHutz]

Tell the drivers to slow down...

 

[patprimmer]

Are the baffles breaking free at the welds on the trailers that roll over.

I have to admit Lionel's response also occurred to me.

I don't know that it would be cost effective or not, but I would think a number of compartments fully sealed at all but the top edge with external lines connecting them. These connecting lines having some sort of interlock so they must be closed before the trailer can be moved.

I think these trailers probably have air over spring brakes. If there was an air leak introduced if the valves where open, that could easily immobilisers the trailer.

Regards
Pat
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[gt6racer2]

Trailer suspensions, at least here in the US, are most often sourced as a module by the trailer manufacturer. Whilst typically there is no traditional roll/sway bar on these modules, the suspension is designed to be inherently very stiff in roll by forcing flexure of the main trailing links/axle tube in the roll mode. At one time I did look at rollover impact of further stiffening the roll mode of the suspension on a class 8 trailer - but found very little benefit to be had. As noted by ealier postings, for a fluid carrying trailer, avoiding fluid movement is key. However, another idea would be to lower the CG of the load by using shapes other than the (cost driven )cylinders that we often see. I'd have thought using a triangular section (point up !)would lower the CG and reduce sloshing tendency at the same time. Vertically displaced or varied section, to lower the load height between the hitch and the rear axle would also be helpful.

 

[JBJohn]

Thanks Pat, Brian, Lionel & GT6 racer for your kind responses.

As a matter of fact the trailer was carrying cryogenic liquid. It is understood that it was full (permitted as capacity) at the time of rolling over. Further such trailers have in built baffles to avoid any liquid sloshing. Of course as suggested, the speed is the factor we are looking into. But what intrigues us is the fact that only these trailers are rolling over. Trailers from other manufacturers have not shown similar rolling on the same route/ same drivers!!

 

[BrianPetersen]

If the trailer was almost full, then sloshing is not an issue. Then it comes down to center of gravity height related to track width.

As noted above, trailer suspension normally has very high roll stiffness due to its design. What suspension was on the trailer - air suspension with trailing arms on each side to the axle (most common design nowadays)? If it's a reasonably new trailer, I doubt if it has leaf springs - those have high roll stiffness simply by being bloody stiff.

What's the weight distribution on the trailer? Only the rear wheels of the trailer are capable of providing roll stiffness. If the center of gravity height is above the ball coupler at the fifth wheel - which it usually will be, for a loaded trailer - then whatever weight is on the front of the trailer, is contributing roll-over moment as opposed to helping with stability.

 

[NormPeterson]

Is it perhaps a combination of braking while turning, with longitudinal slosh getting involved?


Norm

 

[bradleyelwood]

JB,
I designed air ride suspensions, spring suspensions, etc for a number of years and was chief engineer at a trailer manufacturer.

Not all suspensions are created equal. The roll stiffness of one air ride suspension may be much different than the next....the same is true of spring suspensions.

You have not really told us what the vehicle is...tractor-semi? Full truck & full trailer? Are the towing vehicles also tipping over? A tractor-trailer combination gets its stability from both the trailer suspension and the tractor suspension.

Are the towing vehicles IDENTICAL in your whole fleet? How big is the fleet? Have you talked to the drivers of the different types of vehicles?

There are ways to compare roll stability of two different vehicles experimentally without doing a lot of calculations.

You mention baffles...are there transverse baffles which prevent longitudinal sloshing? Are there longitudinal baffles which limit transverse sloshing? "Full to capacity" may still have air space or in this case vapor space above the liquid which would allow sloshing.

gt6racer2 had a good point...what is the height to the C of G of the tank and its contents, and how does this compare to the other trailers?

You mention that this happened at U turns... Were the accidents at low speed with a tractor which was at a sharp angle to the semi trailer? What was the terrain? Flat? Sloping? Cross slope?Tractor fifth wheels oscillate about a horizontal pivot and if the tractor turns 90 degrees, the tractor stability goes close to zero.

 

[sbozy25]

Find a company that can supply you an electronic height sensing air ride suspension. I think Link mfg, Kelderman, and Monroe have them available.

I worked at a company that designed one of these suspensions and had similar problems. We fixed it by changing ECU programing and putting a heavy duty sway bar on it.

Road Master in Portland Oregon has a wide selection of sway bars and can probably recommend one to try at a reasonable cost.

Cabbages, knickers, It hasn't got A BEAK!

 

[BrianE22]

Is wheel track narrower on these trailers (compared to the ones that don't tip over)?

 

[dfoxengr]

the stiffness of the suspension is almost a non-issue since lateral migration of the CG in roll is probably a very small component of the overturning moment on the trailer.

as someone said, if full or well baffled, calculate the (cg height)/(track width) as a non-dimensional number and compare the different trailers. possibly the height of the tongue in relation to the CG could also be a factor.

 

[bradleyelwood]

JBJohn,

We havent had any responce from you since 4 Feb. From this we can assume that you have solved the problem, is this right?

If you want wour suggestions, ideas etc, pleae give us feedback.

 

[JBJohn]

Nope!
I haven't come to a conclusion. I am sorry i didnot reply back to posts but we are still awaiting the trailer details.