Semi trailer chassis stiffness

[Juan.BC]

Hi everybody,

I have a question about designing a semi-trailer chassis, the current design that I'm working on checked fine for bending stress, but we need to verify torsional stiffness. I've been searching on the internet for information of admissible torsion angle with no luck. Does anybody know anything about it that could help? Any help would be welcome!

Thank you!

Best regards,

Juan.

 

[FACS]

https://trid.trb.org/view.aspx?id=210784

Maybe something is in here

 

[LittleInch]

Hmmm,

There doesn't seem to be a requirement for torsional stiffness and I guess it varies depending on the type of trailer and the load / weight/ speed etc.

A simple flat bed or curtain side may be able to flex a lot without issue, but maybe a container lorry needs to be stiffer to prevent the locks coming off.

Whats the back ground here?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BrianPetersen]

It needs to not come apart.

Flat-bed trailers have heavy-duty frame rails that are often intentionally arched so that when loaded to capacity, it doesn't bow downward. The rails are usually channel or perhaps I-beam construction the industry-standard roughly 34 inches apart. They're not designed to be torsionally stiff.

Box trailers have flimsy, light construction with a floor just strong enough so that the intended point loads inside it don't punch through. The doors need to be able to open and close.

Bear in mind that the connection at the 5th wheel is not capable of transmitting a torque load. All roll stiffness is via the axles sitting on the ground. Most suspension designs for such trailers essentially don't allow independent left and right motion in roll (very high roll stiffness).

 

[drawoh]

Juan.BC,

Have you checked for regulations in your jurisdiction on truck trailers?

--
JHG

 

[Juan.BC]

Hello! And thank you for your quick response.

@FACS: Thanks for the link mate, seems to have useful information.

@LittleInch: Thanks for your answer, it's a 54ft long flat-bed trailer arched 2in as counter deflection, curtains on both sides. Load capacity 35Ton and chassis weight 2.3Ton.

@BrianPetersen: Thanks! I completely forget about the stiffness provided by the floor and suspension, I was focused on reducing some weight through reducing the number and resizing the bridges (in this case metal plates that connect the two rails). That's the main reason that I was looking for checking the stiffness of the chassis.

Best regards,

Juan.

 

[LittleInch]

Well maybe you need to analyse an existing model and use that for comparison.

I doubt you'll get a number but if your new lightweight model is say 40% less torsionally rigid, you might get complaints when they start using it and it could affect the road holding or "driveability"

Having said that when you look at extendable trailers, especially things like oversize pipe carriers, they only seem to have a single tube or box section so the flex on that must be quite something.

Maybe a DOT has something?

What other codes or regs do you have to design this to? Anything in there?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.