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Chockstone Forum - General Discussion

General Climbing Discussion

 Page 1 of 2. Messages 1 to 20 | 21 to 21
Author
upside down P's
rowan
31/10/2011
9:06:58 PM
Apparently the info is on here already, but I'm not allowed to read the bolting section. Chris Coghill told me he read that putting p bolts in upside down to reduce the sideways torque on the bolt is not a good idea and greatly reduces the strength of the bolt. He said he couldn't remember the reason but it was a real good one. I've been putting them in up this way, is there a good reason not to?
Dr Nick
31/10/2011
9:39:47 PM
It's in the soft rock bolting guide, which I can't see on safercliffs.org, but is in the tech tips on the left. Essentially the bolt can bend backwards so that the "P" of the ring comes out of the glue, and then there's no resistance to spinning so the bolt works loose pretty quickly.
rowan
31/10/2011
10:04:20 PM
rad. thanks man. I'll have a nosey through it.

nmonteith
31/10/2011
10:32:52 PM
On 31/10/2011 rowan wrote:
>Apparently the info is on here already, but I'm not allowed to read the
>bolting section.

You can read it now.
mikllaw
31/10/2011
11:11:34 PM
stainless steel rod is cold drawn which increases its yield strength from ~ 100 MPa to ~ 500 MPa
Bending it inot a ring or Ubolt increases the strength further.
Welding it heats the metal and anneals it, dropping the strength so low that the ring bends
rowan
1/11/2011
7:44:36 AM
>You can read it now.

Thanks Neil.
rowan
1/11/2011
8:05:28 AM
On 31/10/2011 mikllaw wrote:
>stainless steel rod is cold drawn which increases its yield strength from
>~ 100 MPa to ~ 500 MPa
>Bending it inot a ring or Ubolt increases the strength further.
>Welding it heats the metal and anneals it, dropping the strength so low
>that the ring bends
>

Ok. I'll probably start putting them in the other way.
MPA not associated with concrete is a little lost on me. But even 10 MPa is quite strong no? Out of curiosity if the ring was counter sunk past the weld by the distance of the weld again would this change anything?

Thanks for replying so quickly.
mikllaw
1/11/2011
9:13:26 AM
On 1/11/2011 rowan wrote:
>Ok. I'll probably start putting them in the other way.
Please

>MPA not associated with concrete is a little lost on me. But even 10 MPa
>is quite strong no?
no. Especially not for metal. Most concrete is 50 MPa compressive strength, most metals are > 400 MPa yield

>Out of curiosity if the ring was counter sunk past
>the weld by the distance of the weld again would this change anything?
it would improve things slightly, but the major improvement is that they would be taking much of the load.

basically it depends on how many falls you want them to take until they need replacing
uwhp510
1/11/2011
9:53:31 AM
On 1/11/2011 rowan wrote:
>But even 10 MPa is quite strong no?

It depends on the cross section.

for example;

Concrete column in compression, 10 MPa yield * 1m^2 cross section = 10,000,000 N = 1190 volkswagons

10mm bolt, 100 MPa yield * 0.0001 m^2 cross section = 10,000 N = 1.19 volkswagons
rightarmbad
1/11/2011
11:27:48 AM
I don't get that you were out there placing them without full prior knowledge of how to do it properly.
What were your reasons for placing upside down?
What was the perceived benefit?

I suggest that you note all current placements somewhere for future reference.
I also suggest that you do a thorough review of your complete placement methods.
Is there something else you have missed?

Maybe a few missions under the guidance of a more experienced bolter are called for.

Macciza
1/11/2011
1:02:07 PM
I believe I was the one who came up with upwards-facing P idea
The benefits of upwards-facing P's are the lack of rotational force exerted on the shaft due to off-axis loading - fairly obvious if you suss out the mechanics of it all.
It would seem the only objections to this is the possible loss of strength due to heat from welding, which is obviously also shared by downwards-facing P's. If you are using cast P's then this is no longer an issue.
When placed upwards there is less support along the shaft compared to downwards which has the P supporting it - of course this depends on angle of P closure as well.
This is most relevant for a straight down force but changes for off-axis loads. With off-axis loads the upwards P's are extremely stable - but downwards P's get twisted by this force and potentially leveraged by the often ineffective counter-sinking of the P. This countersinking also exerts more outwards force on the shaft then upwards-facing P's due to leverage.
Add to this the often ineffective 'grooving' of the shaft and it becomes more of a problem. Compare the standard home-made job with production Petzl and Kong and you will see what I mean - long groove down shaft, chamfered shaft, large surface area/volume of intruding glue - they put your average home made P to shame.
There are many ways to place bolts and many different types of bolts. The home-made P (even those 'industrially-made' bought cheap from China) are not necessarily the best. And their method of placement may not be the best either, it is simply accepted by people - most of whom never bother to think about the physics involved.
Bottom line though is that most P's used in Australia are unrated, untested, non-QC'ed etc. so you are taking a chance regardless of how they are placed . . .

benjenga
1/11/2011
1:07:04 PM
I made the same mistake when i started bolting, but I was mistaken because although I read as much info as I could find the only pradical info with diagrams I could find at the time was the fixe bolting guide.

http://www.fixeusa.com/guide_14a-gluein.htm

They recommend placing their bolts weld up 15 deg off vertical.

You learn from your mistakes.

rodw
1/11/2011
1:21:16 PM
Macca is right in terms that rotational force is the greater evil in practical terms of a P bolt placement failing. Most p's and U's are actually over engineered and the main danger of real world failure is crappy rock failing or failing bolt glue bond with rotational forces being the main cause for failing glue bond.

Yeah upside down P, properly recessed and glued might not be the "optimal" placement method but more than likely good enough for the job.

Macciza
1/11/2011
1:31:32 PM
On 1/11/2011 benjenga wrote:
>
>They recommend placing their bolts weld up 15 deg off vertical.
>
>You learn from your mistakes.

And yet most people in Aus would probably place those the same as home-made P's, and end-up with them being weld-side down and horizontal.
Not everyone learns from mistakes or 'thinks' about what they are doing . . .
stsopon
1/11/2011
2:52:53 PM
On 1/11/2011 Macciza wrote:
>Not everyone learns from mistakes or 'thinks' about what they are doing

Yeah they just cling to there own ideas of "superior physics" ... eh macca? Read page 21 of the soft rock bolt guide ffs

Macciza
1/11/2011
6:49:29 PM
Great second post - far better than your first . . .
Great 'thinking' there - to quote something you accept as true . . .
I've read page 21 - so what? No quantification there, just theory . . .
I don't think the failure hypothesis is quite correct either . . .
Personally I would prefer glue-in bolts to rings any day . .
rowan
1/11/2011
7:38:50 PM
On 1/11/2011 rightarmbad wrote:
>I don't get that you were out there placing them without full prior knowledge
>of how to do it properly.
>What were your reasons for placing upside down?
>What was the perceived benefit?
>
>I suggest that you note all current placements somewhere for future reference.
>I also suggest that you do a thorough review of your complete placement
>methods.
>Is there something else you have missed?
>
>Maybe a few missions under the guidance of a more experienced bolter are
>called for.

It wasn't without prior knowledge man. The technique is from someone with over a decade of bolting experience.

The reason was as Macca had said and I had heard that they were slightly weaker but this is only in the hypothetical upmost of extreme force to destruction. Not tested as they are actually treated in real life. With hundreds of small impacts over years.

The bolts I have been told of that have failed have all been to rotational force cracking the glue like Macca said.

I am not 100% convinced yet but am starting to err towards downwards facing.
mikllaw
1/11/2011
9:42:03 PM
downward facing with deep notching is great.
Tommo
2/11/2011
3:01:13 AM
Or just use u-bolts.
mikllaw
2/11/2011
6:55:01 AM
hush your crazy talk

 Page 1 of 2. Messages 1 to 20 | 21 to 21
There are 21 messages in this topic.

 

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