Carabiner open/closed ratings

Climbing carabiners typically have a KN rating with the gate open that is *much* lower than the gate-closed rating. Fairly typical is 23kn closed, 7kn open. Even for wire-gate carabiners.

Does this mean that puny wire is capable of adding 16kn of tensile strength? Or is there some mechanics magic going on?

Here's why 'yes' is intuitive to me: assuming (I know, falsely) that the rated force is guaranteed to deform the carabiner every time, imagine slowly increasing the force on a carabiner: at 7kn, it bends enough to engage the wire gate, and as the force increases it's all taken up by the wire.

My guess is that once the wire engages the force is shared 50/50ish between the spine and the gate.

There indeed are additional mechanics going on. Loading w/the gate open causes bending on the spine in addition to tensile loading; this amplifies the stresses on the spine. The bending increases as the carabiner deforms and the load moves away from the spine.

So the wire alone doesn't add 16kN tensile strength; by maintaining the shape of the biner, it keeps the majority of the load on the spine.

DrRockso wrote:My guess is that once the wire engages the force is shared 50/50ish between the spine and the gate.

Probably not 50/50 on wiregate biners. Consider these two BD biners with similar material and gate design:

blackdiamondequipment.com/e…

blackdiamondequipment.com/e…

The oval, which will splits the load 50-50 between spine & gate, has a much lower strength rating, despite being heavier.

The only "oval" wiregates I found were the BD Ovalwire and the OP Doval (which are both actually D-shaped), which will put most of the load on the spine.

steverett wrote:There indeed are additional mechanics going on. Loading w/the gate open causes bending on the spine in addition to tensile loading; this amplifies the stresses on the spine. The bending increases as the carabiner deforms and the load moves away from the spine.

Sounds right. The bending creates a higher stress point on the inside edge, and once it starts cracking at that point, continues to total failure.

when the gate is open you basically go from a simply supported beam to a cantilever beam. so, in the case of an oval biner, not only are you doubling the axial stress you are also adding a significant bending stress. the effects aren't as pronounced in a d shaped biner, but still matters.

yes, the wire is surprisingly strong for it's size, and is in double shear at the nose and the hinge.

youtube.com/watch?v=lTcvl4n…

slim wrote:yes, the wire is surprisingly strong for it's size, and is in double shear at the nose and the hinge.

Even a single steel wire is strong enough e.g. the Petzl Ange biners.

John Wilder wrote:Don't forget that the wire is steel, not aluminum, which also adds to the equation.

Also true; they are not as "puny" as they look, as evidenced by the fact that wiregates are just as strong as solid gates. But I wanted to emphasize that the gate alone is not taking the additional 16kN.

DrRockso wrote:My guess is that once the wire engages the force is shared 50/50ish between the spine and the gate.

Unless it's an oval, that's not the case (and technically not even so with ovals). The spine holds the majority of the load. Basically the pin stops the aluminum carabiner from deforming to the point of failure and it carries part of the load. However, the spine is ultimately responsible for the majority of the strength of the carabiner which is why triaxial loading or loading the biner over the nose will cause it to fail at a much lower load than printed on the side of the biner. So I guess my answer to the OP would be the gate prevents the carabiner from deforming to failure by retaining the designed shape therefore keeps the load close to the spine as intended, and as a secondary responsibility it carries part of the load.

IIRC, the carabiner behaves like a hook when the gate is open and it's loaded. It behaves like a metal ring when the gate is closed and it is loaded. A solid metal ring is strong than a hook, all else equal.

I was thinking about that the other day. I came to the conclusion that once the gate was open, the top part of the biner was not equally loaded and torque took over with the corner, if you will, of the biner acting as the axis of rotation and the top part acting as the lever arm.

Thoughts?

Biggie Fresh wrote:I was thinking about that the other day. I came to the conclusion that once the gate was open, the top part of the biner was not equally loaded and torque took over with the corner, if you will, of the biner acting as the axis of rotation and the top part acting as the lever arm. Thoughts?

In a sense, yes. The concepts of torque and bending moment in a beam are similar. The further out the force is applied, the higher the bending moment (or torque) at the corner. This is why a D-shape will have higher open-gate strength than an oval.