Thread: Trailer Safety Chains

Found this on Google, BUT it does not state HOW they must be attached, as they recommend a 800 MPA breaking strain chain on the trailer, I would weld a 10mm thick plate to the sides of the drawbar and drill a hole to suit the internal size of the chain link to bolt using largest diameter possible High Tensile bolts. I would set the chain so that it was flat against the plate with about 2 mm clearance for the link to move and drill the hole so that the chain won't come forward.
Kryn

Drawbars must be securely attached to a substantial portion of the trailer.
Drawbars must withstand the following forces applied at the centre of the intended coupling without detachment or any distortion or failure, which will affect the safe drawing of the towed trailer:

Longitudinal tension and compression (N)	1.5 x 9.81 x ATM (kg)
Transverse thrust (N)	0.5 x 9.81 x ATM (kg)
Vertical tension and compression for rigid drawbar trailer (N)	0.5 x 9.81 x ATM (kg)

(For further information, refer to ADR 62/01 clause 14)
16.2 Drawbar Safety Chains

All pig trailers with rigid drawbars (with or without breakaway brakes—but excluding converter dollies) and, any other trailer without breakaway brakes, must be fitted with safety chains that are marked in accordance with the relevant Australian Standard and (or cables as applicable) complying with the following:

• trailers that do not exceed 2.5 tonnes ATM must have at least one safety chain complying with Australian Standard AS 4177.4-1994 or Australian Standard AS 4177.4-2004 ‘Caravan and light trailer towing components —Part 4: Safety chains up to 3500kg capacity’, or be a safety cable with a certified load capacity of the same;
• trailers over 2.5 tonnes and not exceed 3.5 tonnes ATM must have two safety chains of designation of 3500 kg complying with Australian Standard AS 4177.4-1994 or Australian Standard AS 4177.42004;
• trailers over 3.5 tonnes ATM must have two safety chains made from steel of a minimum 800 MPa breaking stress that conforms to the mechanical properties of Grade T chain as specified in Australian Standard AS 2321-1979 ‘Short Link Chain for Lifting Purposes (non calibrated)’ or Australian Standard AS 2321-2006 ‘Short Link Chain for Lifting Purposes.’ Each chain must be sized such that the minimum breaking load exceeds the ATM.

Originally Posted by seanjfitz

Hi all,
I'm halfway through building my flat top trailer, 4mx2.2m deck rated at 3 tonne. I know I can weld or bolt the safety chain to the drawbar, but I'm not happy about the strength that will provide.
How are chains usually connected for trailers up to 4.5 tonne? as that may be the style I'm after
Thanks all
Sean

Don't overcomplicate it, two lengths of 13mm AS4177 compliant and marked chains, mounted to an appropriately strong point on the drawbar and welded as per the recommendations really is adequate. I certainly would not follow KB's (well meaning, but simply wrong) advice.

If you are still unhappy, then on trailers over 3.5t, they mandate grade T chain which is not weldable. Go buy this, or the equivalent from your local truck and trailer suppliers place (Maxiparts, truckline etc) http://www.bartlett-equip.com.au/pdf/safetychains.pdf

The catch will be that your chain won't play well with shackles (eg. won't take well to shortening the chain by putting the shackle through a link other than the end link of the chain) and you'll have made something annoying and unpleasant all because you tried to reinvent the wheel.

Ended up just getting some chain from the trailer shop, will weld a plate to the drawbar and weld the chain to the plate. It's a nice long link so shackles will be easy.
Thanks guys
Sean

Be sure to take you welding certificate with you when you go to register, Last Friday my mate took his trailer to Regency Park (tihis where vehicle's are tested in SA) to have it checked so it could be registered, the towing hitch is welded to the drawbar as he did not have a certificate for the welding they would not pass it, the weldng now has to be either re-done and supplied with a certifcate or certified by a suitably qualified engineer

Originally Posted by KBs PensNmore

I would weld a 10mm thick plate to the sides of the drawbar and drill a hole to suit the internal size of the chain link to bolt using largest diameter possible High Tensile bolts. I would set the chain so that it was flat against the plate with about 2 mm clearance for the link to move and drill the hole so that the chain won't come forward.

bolting a chain to a plate is not a job for a high tensile bolt.

High tensile bolts are designed to CLAMP two plates together. The holding force comes from the friction between the two plates.
Tightening the bolt stretches the bolt which PULLS the two plates together.

For attaching a chain you need a plain (or galvanised) black bolt. The strength in this type of bolt is in the bolt's shank.

Originally Posted by China

Be sure to take you welding certificate with you when you go to register, Last Friday my mate took his trailer to Regency Park (tihis where vehicle's are tested in SA) to have it checked so it could be registered, the towing hitch is welded to the drawbar as he did not have a certificate for the welding they would not pass it, the weldng now has to be either re-done and supplied with a certifcate or certified by a suitably qualified engineer

Wow! Someone's power trip went too far that day. If you need a welding certificate to weld the coupling & chains on, then they might as well say you need one for the whole trailer. Not much point having a qualified welder do the chains if the drawbar or chassis isn't up to scratch.

You don't have to go to Regency to get a trailer inspected for rego anyway. Just about every trailer manufacturer is accredited to inspect and register your trailer which is what I did. Best to avoid Regency for the above reason I reckon.

By the way, my chain is welded on as are 90% of the light trailers I've seen. The only other way I would consider is welding plates to the drawbar that protrude past the front of the drawbar, drill through the plates and use hammerlocks to connect the chains.

Originally Posted by ian

bolting a chain to a plate is not a job for a high tensile bolt.

High tensile bolts are designed to CLAMP two plates together. The holding force comes from the friction between the two plates.
Tightening the bolt stretches the bolt which PULLS the two plates together.

For attaching a chain you need a plain (or galvanised) black bolt. The strength in this type of bolt is in the bolt's shank.

Yes high tensile bolts are designed for more for tension, but they also have a lot more shear strength than a black bolt in the same clamping configuration .

I overcome the decent strength small chain inside dia by using double shackles thus using the pins through the chain. In Qld the traffic guys are having a blitz on shackles, you must have the rated ones (yellow pins) but the don'e seem to worry about the chains

from http://www.blacksfasteners.co.nz/ass...olts_45-48.pdf


Table27 Design Shear and Tension Capacities – Strength Limit State Commercial Bolts4.6/S Bolting Category (fuf = 400 MPa) Grade 4.6
Bolt Size -- M16
Shear Values (SingleShear) - Threads excluded from Shear plane -- 39.9 kN

Table32 Design Shear Capacity – Serviceability Limit State - High Strength Structural Bolts 8.8/TF BoltingCategory
(µ =0.35 , nei = 1 , ø = 0.7) Grade 8.8
Bolt size -- M16
DesignCapacity in Shearfor (øVsf)for kh = 1 -- 23.3 kN

Originally Posted by ian

from http://www.blacksfasteners.co.nz/ass...olts_45-48.pdf


Table27 Design Shear and Tension Capacities – Strength Limit State Commercial Bolts4.6/S Bolting Category (fuf = 400 MPa) Grade 4.6
Bolt Size -- M16
Shear Values (SingleShear) - Threads excluded from Shear plane -- 39.9 kN

Table32 Design Shear Capacity – Serviceability Limit State - High Strength Structural Bolts 8.8/TF BoltingCategory
(µ =0.35 , nei = 1 , ø = 0.7) Grade 8.8
Bolt size -- M16
DesignCapacity in Shearfor (øVsf)for kh = 1 -- 23.3 kN

How about comparing apples with apples, after all I did say for the same clamping configuration, so if you are going to use Table 27 for grade 4.6s, use table 28 for 8.8s, ie 82.7 kN.

I never did learn how to do limit state steel design.
I trained under the working strength (now called servicability?) design criteria.

From what I recall,
Black bolts fail when the shank bends (or the plate tears).
High tensile bolts fail when the two plates joined by the bolt move relative to each other. I can't remember if you also had to check the shank in shear.

LOL so did I Ian, but you should have also done Ultimate and Plastic design, LSD is just a new way of looking at them all. But all this is really irrelevant as I wouldn't recommend bolts at all in this application anyway.

If it was me I'd weld a decent plate on with an appropriate hole, then connect the chain with shackles so that the pin is through the chain (ie the same way they are connected to tow bar). I was waiting for a professional trailer maker to chime in on what they normally do.

I recall doing some form of ultimate design -- as in when the steel (or joint) fails how badly bent will it be ...
but the teaching emphasis was on this being a survivability check -- as in the bridge is stuffed and has to be closed but at least it hasn't fallen in the river.


to change the subject -- how is your shoulder?

Last time I had anything to do with building trailers was 2005, and the chains were welded on, the links were about 12 mm diameter and about 50 mm long. Back in 1985 or there about's, I was manager for a trailer hire yard, I got a phone call to come and collect the trailer, long story short, the trailer complete with the full tow-bar, became disconnected from the car. So in reality chains DO NOT prevent accidents!!!
We always checked the assembly before hiring after that!!!!!!
If in doubt weld 2 X 10 mm plates on the sides of the drawbar with a 15 mm hole in each (18 mm centre in from the edges), and use the rated D shackles.
Kryn

Yep, rated "D"shackles or preferably Hammerlocks are the best for attaching safety chains to trailers.
To digress a little, I came in contact with a trailer a couple of weeks back. 4500 Kg ATM, single axle on 17.5" dual wheels, full air brakes with a front mount telescopic tipper. Nice trailer you might say, but it was built and registered with a single pole drawbar - which broke on the second load, the axle was 50mm FORWARD of center, the hitch was attached with mild steel bolts, as was the hoist and it had two pissy little 8mm safety chains.
I really do wonder about the people that build and register trailers some times.
Construct your trailer to be failure free in critical areas, (axle, suspension, drawbar, brakes safety chains and hitch), then add a bit more to be sure.