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Floating shelves - load capacity of resin fix studding

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siggy_7

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I'm currently building a pair of shelves for the kitchen, each will be around 2400mm long and 280mm wide. They are a torsion box construction and I'll be attaching them to the walls using steel studding resin-fixed into the walls.

My concern is that as kitchen shelves, they will be taking quite a bit of weight (cookery books, large Kilner jars and the like). I'm planning to use M16 studs, but the problem I'm faced with is the wall is single-skin brick. The bricks are quite old (the house was built in the 1850's) and previous experience has been that some of the bricks are quite soft. I've checked the load tables provided by Fischer for what I'm intending to use (FIS VL Vinylester resin) and the minimum insertion depth they supply data for is 120mm for an M16 stud. I'm particularly worried about the bending moments going through the fixing (60Nm quoted for insertion in cracked concrete at 120mm depth, or just 10Nm for M12 studs into solid brick at 50mm or 80mm depth).

If I assume a load is placed on the shelf 200mm from the wall, I'd expect around 2Nm of bending moment per kg of load on the shelf, so I'm quite concerned about getting enough strength from the fixings. I'm thinking around one stud every 300mm should be sufficient, but even then my shelf loading could be limited by bending moments to around 15kg/m which feels very marginal to me. Any guidance or words of reassurance from those who have done this before gratefully received.
 

profchris

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I'm as much of an engineer as I am a brain surgeon, but isn't most of the load taken by friction of box against the wall, so your studs are mainly taking the tensile load of clamping, and only some of the bending load?

Of course I have no idea how much, with luck a real engineer can tell you.
 

siggy_7

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Thanks both for the replies. The YouTube video has made me feel more relaxed about my situation - the guy is using studs the same size as I am intending to and each one seems to be able to take about 50kg of weight applied at a distance of what looks to be a little over 300mm, so somewhere above a 150Nm bending moment (looks like the load capacity would be limited by the bending strength of the rods themselves rather than the fixing into the wall). His fixings are a comparable depth to mine (~70mm, but screwed into a stud rather than resin-fixed into masonry) - I would bet that the resin -fix is of comparable strength. So I reckon my planned layout will have sufficient strength.

profchris - I think the load path you are referring to arises where the shelf is positively bolted into the wall, i.e. there is significant tension on the studs pulling the shelf towards the wall (i.e. the first method of attaching towards the end of the video). When you place a load on the shelf in such a configuration, the shelf attempts to rotate downwards due to the moment but can't do so because it's pinned against the wall, so the distance beneath the fixing axis acts as a moment arm (i.e. the deeper the shelf, the more moment arm there is and the more load capacity there is). For mainly constructional reasons, I'm looking to use the second method shown in the video where the shelf is just pushed onto the studs with no positive hold, save a couple of locating screws to prevent it walking off the wall. As the shelf will only be 40mm thick, the moment arm to resist the bending motion is only small anyway, so I think it would be of limited benefit.
 
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