Do 1/2” expansion bolts have more pull out strength than 3/8”?

Good discussion in my local route development committee meeting last night. One question arising from it - what is the tangible advantage of 1/2” vs 3/8” wedge anchors?  The increase in shear strength (roughly double) seems unimportant as the 3/8” bolt has more than enough to begin with.  But what about increased force applied from the wedge to the clip and then to the rock?  The higher torque of the 1/2” bolt (40 ft-lb vs 25 ft-lb) would translate into higher radial force between the cone, the clip and the rock.  Also the larger diameter would result in a larger radial distance of the clip being driven into the surrounding rock.  Do these two factors translate to a measurable improvement in pull out strength?  And maybe most importantly, a 1/2” bolt may be less likely to become a spinner 25 years down the road?  

Look up the technical sheet for the specific model of bolt. There should be a table showing tension strengths.

Are these wedge bolts being placed in significantly overhanging terrain? Beyond 10 or so degrees overhanging I switch to 5-piece bolts. It just gives me more piece of mind.  

Dylan Pike wrote:

Look up the technical sheet for the specific model of bolt. There should be a table showing tension strengths.

Not looking for tensile strength comparison of the bolt itself, as you say that’s easy enough to obtain. It would never fail in that axis in a climbing application so it’s not really relevant.  I’m thinking of the strength of the “bond” between the clip and the rock, aka pull-out strength. 

Kent Krauza wrote:

Not looking for tensile strength comparison of the bolt itself, as you say that’s easy enough to obtain. It would never fail in that axis in a climbing application so it’s not really relevant.  I’m thinking of the strength of the “bond” between the clip and the rock, aka pull-out strength. 

I think the data sheet lists both tensile and sheer, I believe the tensile is referring to pull out strength. Someone correct me if I’m wrong but it appears at the time of initial placement (once corrosion occurs im sure it’s a different ball game) both tension and sheer numbers are more than adequate. I linked the Hilti quikbolt fact sheet here. hilti.com/medias/sys_master…

a beach wrote:

I think the data sheet lists both tensile and sheer, I believe the tensile is referring to pull out strength. Someone correct me if I’m wrong but it appears at the time of initial placement (once corrosion occurs im sure it’s a different ball game) both tension and sheer numbers are more than adequate. I linked the Hilti quikbolt fact sheet here. hilti.com/medias/sys_master…

You’re right, that data sheet shows the tensile strength for varying compressive strengths of the concrete (rock), so it must be accounting for the “bond” as well as the intrinsic tensile strength of the stud itself.

Edit - this table is perfect.  It clearly shows the weak link in the chain is the bond with the rock (tensile of the bolt itself is almost an order of magnitude higher), and that 1/2” bolts have 25-50% higher net tensile strength than 3/8”, with 25% for softer rock and 50% for harder rock.  So to the heart of my question, the 1/2” bolt will be considerably less likely to spin after many years of service. 

Kent Krauza wrote:

Not looking for tensile strength comparison of the bolt itself, as you say that’s easy enough to obtain. It would never fail in that axis in a climbing application so it’s not really relevant.  I’m thinking of the strength of the “bond” between the clip and the rock, aka pull-out strength. 

Gotcha. I'm not an expert, but don't they also tabulate test data for pull out strength in tension?

ETA: Looks like I was beat to the punch. The above post explains what I'm talking about.

I pull tested a SS 3/8x2.25 5-piece a couple weeks ago.  My pull system only goes to 6,000# and although the hanger was way deformed, the bolt would not pull at 6,000#

Building a 8,000# puller right now.  I video everything with a I-phone on a tri-pod.  Oh yea, no asca bolts or hangers are used in my testing.  I have no plans for testing 1/2" stuff because I think 1/2" is overkill in good granite.  When a 3/8" bolt will not fail at 6,000# and the human body fails at 2,000# I think 3/8 is enough. 

When I am told about a 5-piece with a issue I have always found that the issue was caused by the placement.  I seldom find an issue, spinner or otherwise with a properly placed, hand drilled, unmodified,  5-piece bolt/hanger.  

EDIT

Roger Brown wrote:

I pull tested a SS 3/8x2.25 5-piece a couple weeks ago.  My pull system only goes to 6,000# and although the hanger was way deformed, the bolt would not pull at 6,000#

Building a 8,000# puller right now.  I video everything with a I-phone on a tri-pod.  Oh yea, no asca bolts or hangers are used in my testing.  I have no plans for testing 1/2" stuff because I think 1/2" is overkill in good granite.  When a 3/8" bolt will not fail at 6,000# and the human body fails at 2,000# I think 3/8 is enough. 

When I am told about a 5-piece with a issue I have always found that the issue was caused by the placement.  I have yet to find an issue, spinner or otherwise with a properly placed, hand drilled, unmodified,  5-piece bolt/hanger.  

Most good rock has higher compression strenght than the 6000 psi numbers the bolt manufactures use for good concrete. 

For me the choice for bigger bolt than 3/8 in hard rock is situation dependant. Like a stick clip bolt that will get whipped on a lot. Or a replacement where I have to drill a larger hole.

Mandatory 1/2 for all bolts is just dumb to me.

Yes, 1/2" bolts have more pull-out strength but that doesn't mean they are less likely to become spinners.  I would argue that 1/2" bolts might be more likely to spin because their proper torque spec is higher than most people are used to cranking.  IMO, In good granite a 3/8" x 3" bolt is sufficient in all but the most extreme cases.  I have come to this conclusion through my bolt replacement efforts over the years.  A 1/4" x 1 1/4" button head can take repeated large whips if placed properly.  A 5/16" Buttonhead in good granite is really hard to replace without the proper tuning fork.  I have removed one 3/8" x 2" split shaft bolt with just a funkness and hammer and it took close to 2 hours of effort.  Probably would have been easier with a Hurley Jr, but those had not been invented yet.

How is all of this relevant you may ask?  If I can generate enough force with a funkness in a straight out pull on a bolt to break carabiners, i feel confident in that bolt.  I have broken many carabiners pulling bolts over the years before I switched to double quick-links on my funkness device.  If 30 year old rusty 1/4" and 5/16" bolts can break carabiners to remove, why would we think we need a bolt with 4-10 times the compression and pull-out strength to replace it?

My bigger concern with the trend towards oversizing hardware is that it makes eventual replacement all that much more difficult.  What makes people think that a 1/2" SS bolt with hanger is going to last longer than a 3/8" one?  What are we going to replace the 1/2" bolt with in 50 years, and how are we even going to be able to remove it without a core drill?  

In super steep and softer rock I think 1/2" wedges/5-piece bolts are amazing.  Other than that I think it's overkill.

Removing 1/2" wedge bolts without power tools is a challenge but doable.  1/2" 5-Piece spinners are just about as hard.  

Would heating a glue-in, then twisting it, allow it to snap off down in the hole?  I don't know much about glue-ins but I do know that if you can belay-lower off directly thru the eye some people will.  I have replaced Fixi double ring hangers with big grooves in them from people doing just that in Yosemite.  I am waiting for someone to tell me about a glue-in with an issue.  After I remove it and patch the hole I will post how it was done.