Building a Bolt Tester Thread
Building a Bolt Tester Thread
Hi Matt, I've utilized all Hydrajaws tensile testers for applying loads to industrial rope access and climbing anchors. They are excellent, although expensive, with specific issues unique to each model, which I'll explain below. A critical point is that Hydrajaws design testers for proof loading construction fixings, not necessarily for anchor extraction. Practically, this results in very short cylinder stroke lengths, typically only 1" (25mm). For certified climbing anchors, resetting the tester multiple times is necessary for extraction, assuming that's intended. A newer model (2050) has a 2" draw, which is a significant improvement, but most are limited below that. Their clevis pins generally fit through most glue-in anchor eyes but not expansion bolt hangers, as the pin is too thick. Even if the clevis pin fits, the clevis block's clearance against the rock surface prevents attachment. Using a connector can solve this issue but may create another (assuming it's strong enough). This time it's the load bridge standoff versus leg length vs. cylinder draw issue. Consequently, there may be insufficient space with the load bridge at maximum standoff from the rock to link to the anchor, contract the cylinder, and apply a load to extraction at full anchor embedment.
Other issues involve the tester load capacity. The junior model of the one pictured in your post connects easily, has a good cylinder stroke but is limited to around 20kN. For proof loading, this is sufficient but useless for extracting climbing anchors. The updated version of this model has a 2" cylinder stroke and a higher rating of 50kN, but that's still too low for glue-ins. If you opt for the high-capacity tester (100+kN), you're hit with a short cylinder stroke. The best model I've used was the 2050 model (pictured), but the clevis block shaft is not thick enough, and applying up to the max load of the tester (50kN) would easily bend the rod unless the tester is perfectly aligned over the fixing—something of a challenge on uneven rock surfaces. This is why these testers are designed for a flat, concrete surface.
I asked Jim to build a custom puller for me in 2012 because of these issues. The testers available at the time couldn't exact any decent loading without needing to be airlifted in. Jim can easily make one to spec. It'll rip out most fixings, apart from any of his tested ones! :) Cheers
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Jim Titt
· Joined Nov 2009 · Points: 490
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Feb 4, 2020 · Germany
As Francis mentioned, the main issues (besides cost) are the limited stroke and capacity of commercial testers. To rip out most bolts, you need 50+kN and a 5-6" stroke. Commercial testers typically only test the bolt, not pull it out, and if they need to extract them, things get large and expensive.
I've made four of these, with two different models. The base is a cheap Chinese hole punch made for steelwork (making holes in steel shuttering) available in 10 and 15-ton variations. As with most Chinese hydraulic equipment, the rated capacity is the limit before failure, not the achievable capacity. Generally, count on about half the capacity unless you're very heavy and can jump on the handle.
The pull cylinder is designed for a threaded adaptor which is useless for us, so you unscrew the top cap (they aren't very tight, so an oil filter wrench works). There's a spring inside! Remove the piston and drill through 20mm (it's already bored most of the way, so it's easy with a pillar drill). Drill through the top cap with a 30mm bit or similar.
You need an extension to the piston to attach a nut to the pull rod (20mm stainless threadall). A piece of heavy-wall pipe does this. Add a clevis or similar to the bottom of the pull bar and a nut and washer for the top. I make the nut easier to handle by welding a rod onto it; it's only finger-tight anyway.
Then, create a suitable base that's strong and high enough for the range you need, maybe 8". Mine is a ring to hold the ram (there's a locking screw visible on the front that locates into a dimple drilled into the ram). The legs are 35mm thick-walled tube with M20 nuts welded on the bottom for 20mm threaded rod feet (60-100mm long) to adjust for uneven rock. A tie rod runs around the bottom to prevent the legs from spreading. The legs are actually slightly angled outwards.
Choosing Measurement Devices
Then you need to decide how to measure the force. There are four primary options. A normal S-beam strain gauge, a pancake strain gauge, a normal hydraulic gauge, or an electronic pressure gauge. The first two are large, heavy, expensive, and usually require a computer to read them out. Normal hydraulic pressure gauges (manometers) are cheap but hard to read accurately. I've used two different ones: a 200bar and a 600bar (operating pressure) to try for more accuracy with weaker bolts.
Digital manometers are the way to go nowadays as they’ve become much cheaper, under $100 or so. They are essentially small strain gauges inside, so they are pretty accurate and have peak load readout. You need to create a conversion chart from pressure to actual pull force, but that's easy once you've measured the piston diameter while taking apart the ram. Mine is fitted into an adapter between the quick coupler and the ram body using the old coupler hole. Some hole punches don't come with the coupler, and the hose can be permanent (you can retrofit them if desired). Adapters are difficult to find and costly. For newer versions, I drill into the ram body and tap them to 3/8"BSP or whatever suits the manometer.
The rod loop protects the gauge when you throw it down the cliff! Directly under the ram on the base, there is a loop welded on that you can't see. This is at the balance point to hang it up on the cliff while setting it up.
I also modify the pump. It's fine on the ground where you can press against the rock or the ground, but on a rope, you're only squeezing the handle and the pump together. I weld up the original pivot holes on the handle and re-drill them to get better mechanical advantage.
To use it, hook it all up and pump away. The stroke is 25mm, so before it ends, release the pressure and take up the slack with the wing nut before pumping again. If you pump until the stroke ends, the manometer records this as the maximum force, so you have to reset each time. A red line on the tube extending the cylinder can help so you know when to stop.
If you use weak connectors like a steel biner and it breaks, the hydraulic shock may jam the valves in the coupler, preventing you from retracting the ram. A tap on the pin in the coupler will free this off.
The whole setup weighs about 12kg, much better than my big one at 35kg! It takes about a day to make, and the whole thing looks like this (a different one). For more details, visit TRM.
What is an Anchor Pull-Out Test?
Caution is necessary if the drilling method deviates from the approval requirements, such as using an impact drill when the ETA specifies a rotary drill for the substrate. When no load-bearing capacity values are specified in the ETA for the existing substrate or drilling method, anchor pull-out tests must be carried out. These tests provide the data to prove the total load-bearing capacity of the ETIC system and determine the required number of anchors.
How is an Anchor Pull-Out Test Performed?
A special, tested, and calibrated extraction device is required, typically operated by a specially trained EJOT field engineer with building stakeholders present. At least 15 tests are performed at various points on the building. Tests should cover the entire facade and be recorded in a corresponding log.
After drilling the hole to the required depth and setting the anchor to the (minimum) anchoring depth, the pull-out test follows. The extraction device, equipped with special adapters for the respective EJOT product, applies a constant and defined load speed to avoid falsifying results. Loads are continuously increased until failure occurs. Failure may occur in the substrate or the anchor area. The failure reason and load at failure are documented in the log.
Contact us to discuss your Bolt Pull Test requirements. Our experienced sales team can help you identify the best options for your needs.