MortarThePoint Posted January 24 Share Posted January 24 I'm positioning my lower newel posts to have one centre line aligned with the front of the riser and the other centre line aligned with the stringer's centre line. I can't so easily do that at the top since the riser is forward of the steel beam (red) that forms the edge of the landing. The plan is to clad the beam with plasterboard and have a piece of timber above that which then has the balustrade assembly on. That means the centre line of the newel post needs to align with the centre line of the balustrade which needs to be suitably far behind the edge of the timber above the plasterboard. As far as I can tell, that leaves 2 options: Push the newel post back relative to the riser, moving its centreline to above the beam Build out the full length of the beam (could overhang the timber slightly) to provide something for the balustrade to sit on. Option 1 is easier but looks a bit funny (see images below). The size of the move here is 38mm which comes from riser thickness (20mm) minus the plasterboard thickness (15mm) plus half the handrail width (60mm/2) and plus a small margin (5mm). I guess I could lose the 5mm. Option 2 could be made up of double cladding the beam to give and extra 15mm of plasterboard thickness, losing the extra 5mm and then overhanging the timber above the plasterboard by 18mm. @joe90 looks to have had timber extend out from the edge to create something like option 2 (image copied below) @Gus Potter you've had some good ideas on these stairs, what would you suggest? I'm slightly unclear how I would anchor the larger posts of the balustrade if I move it's centre line past the edge of the beam. I have been assuming using something like a zip bolt or threaded bar through the centre of these posts and through the flange of the steel. With the posts moved forward of the beam I would have more meat on them to straddle the front of the beam and perhaps bolt to the web? Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 24 Author Share Posted January 24 6 minutes ago, MortarThePoint said: Option 2 could be made up of double cladding the beam to give and extra 15mm of plasterboard thickness, losing the extra 5mm and then overhanging the timber above the plasterboard by 18mm. This is what that would look like in section Link to comment Share on other sites More sharing options...
Bonner Posted January 25 Share Posted January 25 Option 1 is too far back, normal arrangement is about half newel width in front of the riser and landing facia to enable through fixing. Can’t see any fixing from the bottom of a newel post being stiff enough. 1 Link to comment Share on other sites More sharing options...
joe90 Posted January 25 Share Posted January 25 9 hours ago, MortarThePoint said: Option 1 is easier but looks a bit funny And will annoy you forever. I agree option 2 will look better (but then I am OCD) 9 hours ago, MortarThePoint said: Option 2 could be made up of double cladding the beam to give and extra 15mm of plasterboard thickness, losing the extra 5mm and then overhanging the timber above the plasterboard by 18mm. If I understand that correctly you will be bolting the newel post through plasterboard 🤷♂️ that would worry me as plasterboard can crush and newl posts can have high loads (think Kids swinging on them) and there is a lot of leverage on the fixings. 2 Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 1 hour ago, joe90 said: bolting the newel post through plasterboard I wouldn't do that, but would have plasterboard in between any posts. Newel post is easier than the balustrade posts (same post shape as newel). It still leaves the challenge of how to anchor the posts since the centre is past the edge of the steel. Some options that occur to me include: Bolt a piece of flat bar to the top and bottom flanges of the beam and then drill holes in that through which I could pass a threaded bar which then goes up into the balustrade post(s) Timber infill in the beam which is bolted to the web of the beam. The post(s) then get screwed to that. Bolting the timber infill to the beam would require tapping the hole in the web as I don't have access to the other side of the beam to use a nut. Link to comment Share on other sites More sharing options...
Gus Potter Posted January 25 Share Posted January 25 (edited) 21 hours ago, MortarThePoint said: you've had some good ideas on these stairs, That's a pig of a detail! Thanks for thinking of me. Questions.. 1/ Is there any risk of you making the effective width of the stair to narrow? probably not but check anyway. 2/ Is that a glass ballustrade or just a sketchup thingy? 3/ What are dimensions of the newal post? Would this concept work? It sounds a bit odd but on occasion we embed steel in timber.. like fish plates. Say the newal is 80 x 80mm Get a bit of 50 x 50 x 6.0mm SHS box section and weld that to the top of the steel. Make it extend 2/3 of the height of the newal post and get it bang on plumb. You may need to check the box section and carry the leg down to the botttom flange.. will take time but it should work. Cut a chase in the newal post say 51 - 55 mm wide x 60mm deep so it fits over the box section. You could resin (maybe use a slightly flexible construction adhesive) it in or secret screw it. I would go for resin / adhesive as the screw penetration will be small. Then fit a ~ 10mm cover piece to hide the steel and give it a bit of a sand, it will test your marketry skills but could be fun! Now you still have plenty meat of timber at the top at the top to fix the handrails etc. You'll know but few folk will spot it as the eye is drawn to the ballustrade / glass / spindals especially as the chase is cut on the top landing ballustrade side and not facing into or down the stair. Now you can check the post as much as you like below the level of the top of the steel to get the visual appearance you want. The 6.0mm thickness is partly so you don't burn through the section when welding and mucking about. To add a bit.. using the SHS up to two thirds height means that you reduce the bending force in the timber where the timber is thin by ~ 2/3 compared with having thin timber at the bottom subject to all the bending forces and the associated onerous forces on the fixings. Edited January 25 by Gus Potter Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 Thanks Gus 29 minutes ago, Gus Potter said: 1/ Is there any risk of you making the effective width of the stair to narrow? probably not but check anyway. Shouldn't be as the changes are associated with moving it parallel to the stringer direction so not narrowing the stair flight and the landing is plenty wide enough. 28 minutes ago, Gus Potter said: 2/ Is that a glass ballustrade or just a sketchup thingy? It will be all timber (posts, spindles and handrail) 30 minutes ago, Gus Potter said: 3/ What are dimensions of the newal post? 90mm x 90mm with height TBD (whatever gives the right handrail height etc) 31 minutes ago, Gus Potter said: Get a bit of 50 x 50 x 6.0mm SHS box section Nice and strong approach, that hadn't occurred to me. The posts are going to be centred 20mm in front of the beam so if it was 40mm SHS it could simply be welded across the front of the beam's flanges (see image below). Do you think 40mm SHS would be substantial enough I can't weld, but can bolt things together. Should I consider getting a length of SHS fabricated with two bits of plate attached to bolt to the beam flanges? The fabricator would probably struggle to get the spacing of those plates perfect, but as long as they were square to the SHS and less than the flange spacing I could pack it out. As an example, I have sketched up one (bottom two images) with 60mm long tabs of 10mm thick plate with a 10mm hole. I could drill the holes in the beam (or this part) slightly oversize to allow perfect plumb alignment. I am expecting a single M10 bolt both top and bottom be strong enough, does that sound right? Alternatively, if there is anything vaguely standard of a similar shape that could work I guess. Link to comment Share on other sites More sharing options...
joe90 Posted January 25 Share Posted January 25 3 minutes ago, MortarThePoint said: The fabricator would probably struggle to get the spacing of those plates perfect, A decent fabricator could do this accurately (a shame you’re not just down the road, I could weld it directly for you). If it were 1mm too big a penny washer would pack it tightly, if 1 mm too tight then an angle grinder would free it up enough 🤷♂️ 2 Link to comment Share on other sites More sharing options...
Gus Potter Posted January 25 Share Posted January 25 9 minutes ago, MortarThePoint said: I can't weld, but can bolt things together. You could do it with the lugs and bolt. I would need to check if 40 x 40 would still work, probably would but not going to say yes without checking. But there is an argument to be made that it is braced both ways by the handrail? .. but then the lower post needs to do more work... technically. The lug welds on the inside will foul the underside of the top flange of the beam. It looks like the beam you have could cope with having a "scuff" taken off the under edge of the top flange locally to let the SHS sit in tight. M10 grade 8.8 bolts should be fine. Mind you I would add a lock nut with a touch of Araldite glue to make sure they don't come lose later. Cut a piece of wood the exact lug spacing you need and take that to the welder. They will use it as the template. I think they will clamp the lugs to the timber and then weld them to the SHS... or something like that. A tip.. the bolts are 10mm nominal diameter. The holes usually 12mm nominal to allow for fabrication tolerances. Squeeze the glue in and around the bolt to fill in the gaps. From memory Hilti do a system like this where you flood the thing with resin so there is no slip. 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted January 25 Share Posted January 25 27 minutes ago, joe90 said: I could weld it directly for you That's the easiest way! Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 An alternative that comes to mind, but is less substantial is to make the setup below. It's two 10mm plates each 50mm x 90mm with a 16mm hole and a 10mm hole along the centre line, 16mm hole 20mm from one end and 10mm hole 25mm from the other end. The 10mm holes could bolt the plates to the beam flanges and then a length of 16mm threaded rod could be passed through the 16mm holes and bolted to the plates. That would create the third image when attached to the beam (nuts not shown). The plates could be stacked during drilling so the alignment of the two plates would be perfect. Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 I could even beef it up to M20 threaded rod, or larger: https://www.orbitalfasteners.co.uk/products/m16-x-1m-high-tensile-grade-8-8-studding-threaded-rod-steel-bright-zinc-plated-din-975 https://www.orbitalfasteners.co.uk/products/m20-x-1m-high-tensile-grade-8-8-studding-threaded-rod-steel-bright-zinc-plated-din-975 Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 40 x 40 x 4 is the biggest SHS section I can get at 40mm. That is still probably stiffer than a 16mm solid cylinder (core of M20 rod) Using https://amesweb.info/section/second-moment-of-area-calculator.aspx 50 x 50 x 6 SHS: 347072 mm^4 40 x 40 x 4 SHS: 125952 mm^4 16mm round bar: 3217 mm^4 [M20 rod?] 25mm round bar: 19175 mm^4 [M33 rod?] perhaps grade 8.8 has a higher Young's Modulus and Tensile Strength than Mild Steel though? Link to comment Share on other sites More sharing options...
Gus Potter Posted January 25 Share Posted January 25 A 16 dia rod is too bendy. The amount it will flex is related to it's second moment of area Ixx = pi *radius^4 / 4 = 3.142 x 16*16*16*16/4 = 51478mm^4 A 40 x 40 x 5.0mm thick SHS section of has a value of Ixx = 134000mm^4 134000 / 51478 = 2.6 = about 260% stiffer than the rod. A 50 x 50 x 6.3mm thk section 328000 mm^4 328000 / 51478 = 6.3 = about 630% stiffer than the rod. You can see from the above why I mentioned a 50 x 50 section as being something that looks promising. For handrails and the like we need them to not just be strong enough but "feel strong and stiff" to the touch. Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 Using this calculator: https://calcresource.com/statics-cantilever-beam.html suggests a 106mm deflection on a 600mm long cantilevered 16mm steel rod (210 GPa) if exposed to a 1kN load at it's tip. Wow! The 40x40x4 SHS would deflect just 2.7mm by comparison. I am amazed by the deflection of the threaded rod given that a product like the ZipBolt exists 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 Cross post, but same conclusion. Link to comment Share on other sites More sharing options...
Gus Potter Posted January 25 Share Posted January 25 10 minutes ago, MortarThePoint said: Cross post, but same conclusion. Good to see we have both identified how flexible the rod appraoch can be. The zip bolts work in a different way I suspect where they work in tension and the edge of the newal post is compressing against something solid... but few things are that "solid" and often your bog standard stair is far from solid. I made a post a while ago about the forces that you encounter when designing glass ballustrades.. they are significant. Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 Instead of welding plate onto the 50 x 50 SHS could I use any form of angle bracket bolted to the SHS and to the beam flange. I would want it to be substantial and may not find anything beefy looking enough enough. I guess an alternative is to make a 'bracket' out of a short length of SHS laid on its side along the surface of the beam flange. Two vertical holes to bolt that to the beam flange and one horizontal hole to bolt it to the vertical SHS which is what I'm trying to mount. I could have one such short length of SHS on each flange. I wondered about some arrangement with U bolts, but that wouldn't work being sleeved by the timber. Link to comment Share on other sites More sharing options...
joe90 Posted January 25 Share Posted January 25 1 minute ago, MortarThePoint said: Instead of welding plate onto the 50 x 50 SHS could I use any form of angle bracket bolted to the SHS and to the beam flange. Ha great minds think alike!!!! I was just going to post the same idea. A short piece of chunky angle iron say 50mm x 50mm as the brackets. Will the heads of the bolts be in the way? 1 Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 (edited) 5 minutes ago, MortarThePoint said: may not find anything beefy looking enough enough Actually, these look beefy: 90 DEGREE RIGHT ANGLE 1X1 HOLE - TYPE (P1026) - HOT DIP GALV. 53X41X5MM https://directchannel.uk.com/90-degree-right-angle-1x1-hole 14mm hole is a bit bigger than ideal but that could allow adjustment with M12 bolts Edited January 25 by MortarThePoint Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 25 Author Share Posted January 25 (edited) Cutting a round hole in the timber post is easier than a square one. A 32mm piece of circular hollow section (CHS) with 4mm wall would have a second moment of area of 38892 mm^4 which is a quarter of the 40x40x4 SHS but would allow the use of a 32mm auger bit which is cheap. 1kN would bend it by about 10mm at 600mm cantilever. A 50mm CHS would be getting on for the 50x50 SHS but trying to drill a 50mm hole in a 90x90 post could be tricky to say the least. I may be able to outsource that though. I could mount a round tube against the flat surface of an angle bracket, but it would be nice to have something that mated to the curve. Edited January 25 by MortarThePoint Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 26 Author Share Posted January 26 (edited) Unistrut steel channel looks like a possible half way house. It's 41 x 41 x 2.5 which isn't as stocky. It feels fair to model it as equivalent to a T section in terms of bending in a direction parallel to the red arrow (conservative since the parts circled in blue would add stiffness). The calculator gives a value for the second moment of area of 51,940 mm^4 which is 41% of the 40x40x5 SHS or 15% of the 50x50x6 SHS. That sounds like a massive downgrade, but the 1kN force at 600mm would give a deflection of about 6mm or L/91 which doesn't feel too bad for what is a pretty large force (100kg lateral force). If the mountings are 150mm apart, the force on the top mounting would be 5 times the load at the tip, so 5kN. I don't know how much force would pull out a T-piece from the channel. Edited January 26 by MortarThePoint Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 26 Author Share Posted January 26 29 minutes ago, MortarThePoint said: If the mountings are 150mm apart, the force on the top mounting would be 5 times the load at the tip, so 5kN. I don't know how much force would pull out a T-piece from the channel. Looks like it's 6kN for a single M10 so if I used a bracket that allowed two M10 it would give over a ton of pull out strength What do you think @Gus Potter, could Unistrut be an option as it is super easy to work with and to source (e.g. TLC)? A lot less strong than 50x50x6 SHS (only 15% of the stiffness) but do you think it is 'enough'? Link to comment Share on other sites More sharing options...
MortarThePoint Posted January 27 Author Share Posted January 27 Here are some photos of the Unistrut in situ. It feels stiff. It extends 965mm above the top of the beam and to flush with the bottom of the beam. If a moment is applied to it equivalent to someone leaning on the handrail, the strut is pushed against the beam at the bottom and the top mounting is under tension. I used a top mounting that allows two M10 bolts (could upgrade to M12) to resist the shear and one M12 bolt in tension. All bolts are to be torqued, Loctited and doubled up. An exception to that may be the bottom mount's M10 shear bolt which doesn't really have room for a second bolt. The bolts are grade 8.8 so the M10 bolts have a shear strength of 22.3kN each and the M12 has a tensile strength of 48.6kN [https://eurocodeapplied.com/design/en1993/bolt-design-properties]. That means in terms of the bolts, the top mounting has a strength of 44.6kN. The strut acts as a lever to gears a force applied to its very top by a factor of (965 + 206) / 206 = 5.7. That means the bolt related strength would be 7.8kN before any safety factors are applied. @Gus Potter I know this isn't as beefy as your suggestion, but it feels solid. I could slip a solid rectangle section (e.g. 30x35) into the groove of the channel if I decide I want more strength. That could add up to another 79,000 mm^4 and achieve a total of 130,000 mm^4. However, I think the torsional strength of the 6.1m UC203x203x52kg may be similar to the bending strength of the 41x41x2.5 Unistrut. I could add a brace to the middle of the beam that couples it to the concrete HCF plank that is next to it which also spans 6.1m, but doesn't touch the steel beam. I think I'd rather not couple them though. I'm having two such posts which divide the balustrade up into three 1718mm sections. Discussions on another thread suggest 0.36kN/m UDL on the handrail which would make for a tip load of 0.62kN. That's well under the bolt strengths (~8%) and would create a Unistrut bending deflection of 17mm (L/57). It feels stiffer than that when I have applied a pretty large force. Any recommendation as to the required torques for the nuts? Link to comment Share on other sites More sharing options...
Adrian Walker Posted January 27 Share Posted January 27 5 minutes ago, MortarThePoint said: Here are some photos of the Unistrut in situ. It feels stiff. It extends 965mm above the top of the beam and to flush with the bottom of the beam. If a moment is applied to it equivalent to someone leaning on the handrail, the strut is pushed against the beam at the bottom and the top mounting is under tension. I used a top mounting that allows two M10 bolts (could upgrade to M12) to resist the shear and one M12 bolt in tension. All bolts are to be torqued, Loctited and doubled up. An exception to that may be the bottom mount's M10 shear bolt which doesn't really have room for a second bolt. The bolts are grade 8.8 so the M10 bolts have a shear strength of 22.3kN each and the M12 has a tensile strength of 48.6kN [https://eurocodeapplied.com/design/en1993/bolt-design-properties]. That means in terms of the bolts, the top mounting has a strength of 44.6kN. The strut acts as a lever to gears a force applied to its very top by a factor of (965 + 206) / 206 = 5.7. That means the bolt related strength would be 7.8kN before any safety factors are applied. @Gus Potter I know this isn't as beefy as your suggestion, but it feels solid. I could slip a solid rectangle section (e.g. 30x35) into the groove of the channel if I decide I want more strength. That could add up to another 79,000 mm^4 and achieve a total of 130,000 mm^4. However, I think the torsional strength of the 6.1m UC203x203x52kg may be similar to the bending strength of the 41x41x2.5 Unistrut. I could add a brace to the middle of the beam that couples it to the concrete HCF plank that is next to it which also spans 6.1m, but doesn't touch the steel beam. I think I'd rather not couple them though. I'm having two such posts which divide the balustrade up into three 1718mm sections. Discussions on another thread suggest 0.36kN/m UDL on the handrail which would make for a tip load of 0.62kN. That's well under the bolt strengths (~8%) and would create a Unistrut bending deflection of 17mm (L/57). It feels stiffer than that when I have applied a pretty large force. Any recommendation as to the required torques for the nuts? That looks a lot stronger than most of the balustrades I have seen. Most are cheap wooden posts held on with a couple of screws and maybe some glue. 1 Link to comment Share on other sites More sharing options...
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