The nasty shiny silver screwbolts we often get given at work with the purple tips are rubbish. Tried one recently in Castleton and it just jammed and snapped off - just as they did at work!

Bit of thread resurrection here:I've been looking at the stats for concrete screws again, and your report Simon. Looking at the data from the Heco documents, the maximum allowed tension load for axial leaving for a 7.5/55mm Heco MMS is only 2kN for cracked concrete, but I can't work out what the safety factor is. That's not too disturbing given you got about 24kN for a slightly longer version. What worries me a bit more is that that length of 7.5 have the same rating for both cracked and non-cracked concrete at 3.6kN due to 'steel failure', a pattern which also appears for their longer of two lengths for each diameter. It looks like they pick the shortest length, for each diameter, where the bolts fail in shear due to steel failure making extra length irrelevant for shear loading.Given that you didn't test a radial pull, is there a danger that they might give high strength values axially but all fail in shear at say 5kN?I can see them being really useful for some things and much better from a conservation point of view on expedition; I'm just worried by the very low ratings. Maybe the safety factor are really high and everything is actually fine...

Thanks, I hadn't found the English translations and I didn't know I was looking for the 'characteristic resistance'.So looking at that, a 7.5-diameter anchor will fail at a shear load of ~6.1kN due to steel failure (and 13.6kN for the 10-diameter anchor)?I think I've worked out that pryout failure is 1-2x the pullout strength depending on the length of the anchor (i.e. higher than the shear failure of the steel), using the pull-out strength (or 1-2x the concrete cone failure, which I haven't worked out).I presume concrete edge failure isn't relevant (since we shouldn't be near edges/other bolts anyway)?Edit: using the supplied k-factor 11.0 for cracked concrete, and the formula N = k * sqrt(concrete cubic compressional strength in MPa) * (anchor depth in mm)^1.5 (Newtons), and plugging in 25MPa concrete (to match the other things on the datasheet), I get 25kN for a 60mm anchor, so it seems concrete cone failure will still be irrelevant compared to the steel shearing?So if you use the size 10 anchors (8mm drill bit?) in 65mm length, you get 13.6 kN shear from the steel and (in 50MPa limestone pretending to be cracked concrete) a 14.2 kN pullout (which pretty much matches), and you get to use a standard 13mm spanner and (with a bit of fiddling) 8mm hangers. Looks like that might be the way to go (possibly with longer bolts just for security in case of poor rock)...

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