Temporary Stairs - Cut and Join two Halfs

[MortarThePoint]

  On 07/04/2023 at 12:40, Conor said:

Later one of the treads failed

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I was wondering, did the screw shear or the wood split?

[Conor]

  On 07/04/2023 at 19:16, MortarThePoint said:

 

I was wondering, did the screw shear or the wood split?

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Wood split. Guys carrying plasterboard up at the time. 

[Onoff]

If you look at commercial stairs, the stringers are routed and the treads fit into them. 

[TerryE]

We built our own.  There's probably some pics on my blog.

• We use some spare roof joists for the stringers
• I just cut a load of rhombus shaped bits of ?15 mm? OSB that acted at tread spacers: put in the next tread, then left and right spacers directly sitting on top with a couple of screws to fix them and repeat until we reach the top. 
• I used 22mm chipboard flooring for the treads but each had a 40 × 60 (IIRC) bracer glued and screwed to the underside.  This bracer was 2×15 shorter than the tread so it would butt against the spacer.
• The treads were directly fixed, but instead I put 2 × 100mm self tapping fixing screwed in from the outside through the stringer and into the center of the bracer.  

Two staircases because we have 3 stories, with the ground floor one using a platform to do a 90° turn halfway up.  They were solid as rock, and did the job well.

 

I precut all of the bits on my table saw so these were pre-toleranced to better than ½ mm.  When I say "I" above, I really mean "we" as we swapped roles for the top set and Jan did the erection / assembly whilst I did the fetching and carrying.

Edited April 7, 2023 by TerryE

[Conor]

Trying to think back what happened to the stairs. I'm pretty sure we ended up using 90% of the 8x2 timber in some way. Think most of it was used to line the opening around the stairwell - was mix of steel beam and slab.

[MortarThePoint]

  On 07/04/2023 at 09:24, MortarThePoint said:

My intuition is telling me that the moment and stress ends up along the lines of considering a joist with length equivalent to the horizontal projection (L_joist=L_stringer/COS[angle]=h_stair/TAN[angle]) of the stair and joist height equivalent to the vertical depth of the stringer (so h_joist=h_stringer/COS[angle]). Is that correct?

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Thinking about it again, that wouldn't be right. The Joist dimensions would be the same as the stringer dimensions, but the load would be reduced by COS[angle]. So if 47x250 the span can happily be 4.47m span @600mm spacing and live load of 1.5kN/m2 / COS[30] = 1.73kN/m2. Point loading mid span two joists -> 1.73kN/m2 * (2*0.6*4.47) / 2 = 4.6kN load capacity. Very similar.

 

38x145 the span can happily be 2.85m span @400mm spacing and live load of 1.5kN/m2 / COS[57] = 2.75kN/m2. Scale for width 2.75kN/m2 * (27/38) = 1.96kN/m2. Point loading mid span two joists -> 1.96kN/m2 * (2*0.4*2.85) / 2 = 2.2kN load capacity. Very similar.