Failure of concrete anchors explained (video)

[Wayland Smith]

Found this on Youtube
I know it's concrete, and I have no idea how accurate it is,
but it looked worth watching.
https://www.youtube.com/watch?v=bOjYQZtA3xY

 

[Bob Mehew]

One point understandably not covered is the assumption that the concrete is uniformly strong.  Limestone beds are not necessarily well stuck together, so a shear can occur along a bedding plane (just like splitting slate).  Or blasting can create stress cracks which allow layers to shear off.  And some types of limestone are not that strong.  Oolitic limestone can be so soft that the anchor just pulls out.  These failure modes have been witnessed in testing.  And one other point also understandably not covered is corrosion of the anchor.

Otherwise a good video which would have saved me days of research using the Hilti design program. 

 

[Pitlamp]

Thanks OP - I took away a couple of very useful points from that ("prying" and overlapping stress cones).

 

[royfellows]

Regardless of debate, I stay with the basic rule of all belays, "Never rely on a single anchor point".
Maybe preaching to the converted on here?

 

[Cantclimbtom]

It's very useful resource but I think better placed for say people designing how to bolt down a gantry or large roadsign or whatnot. Climbing and caving type anchors have their own very specific considerations like a glue in anchor being twisted just as one example (not a failure mode discussed in video). There is a well documented body of knowledge built up from climbing, caving, high-lining etc that covers useful rules of thumb on installing them (pretty important to get that right) and removing them as well as placements and anchor choice. The "bolting Bible" (https://www.mountainproject.com/forum/topic/118673283/the-bolting-bible-2020-version-is-done) is a free pdf or a series of videos. I'd bet CNCC have built up a pretty good body of knowledge of their own too!

I think Roy's comment about redundancy is pretty obvious, but so important it bears repeating anyway. Backup!

 

[Leclused]

It's very useful resource but I think better placed for say people designing how to bolt down a gantry or large roadsign or whatnot. Climbing and caving type anchors have their own very specific considerations like a glue in anchor being twisted just as one example (not a failure mode discussed in video).

Those concrete anchors are 'often' used during cave exploration to leave almost no trace afterwards.

 

[pwhole]

I had some issues putting anchors into reef limestone in Castleton, both throughbolts and screws, most of which were down to the nature of the rock, which is probably worth considering as badly-mixed concrete, as the variability of density and homogeneity in any given area is enormous, and there's no real bedding sequences as such - plus the surfaces are very bumpy, even at small scales. Often there are small voids within the rock, and some bits just fall off with the slightest touch. Also lots of fossils and small mineral inclusions, even off the vein, as there's calcite pipes traversing through it too. We had to screw in direct to that sometimes (below).

Due to the need for endless moving and replacement as we sunk further down the shaft we had to use screws, and a hand-spanner was the only way really as you need to feel what it's going through, and abandoning if necessary. And lots of hammering first to test the sound, usually the best indicator.