steel stair tread embed (it ryhmes)

[bdruehl]

thread507-337096

it seems to me that if you got an 8 inch concrete (outside retaining wall say), carve a slot in the form and wet set embed 6.5" a full 10 inch wide (say 1/2" thick) steel stair tread, 300# pt load say at the end of the 3.5' wide stair cantilever, maybe a bolt for "dynamic load" pullout on the inside, whats the problem, why all the rigaremole? must be missing somethin....

 

[manstrom]

vibration?

 

[bookowski]

You would have to run the numbers but gut feeling says that 1/2" x 10" steel plate with 42" cantilever and 300# point load is going to have a lot of deflection, probably > 2". You're also going to have vibration issues as manstrom said - like walking up a series of diving boards. You might even have a strength problem with those numbers.

If your question is just about embedding then yes you could embed into the wall - assuming the wall can take the moment. Although it seems easier to just embed plates with anchors and then weld the treads to the embed rather than try to prop up all the treads and bury them in the wall prior to the concrete pour.

 

[bdruehl]

yes, indeed, the deflection of L/240 will create issues - im gettin a 1 3/4" vs say .2" allowed..no good.... i swear i have seen countless architectural digest fancy pants buildings with these floating stairs, with no signs of alternate attachment, just the pretty lines of the actual tread themselves protruding from the *usually concrete wall. maybe they use 1 inch thick, nope that doesnt cut it either.. hmm..but getttin close.... perhaps diagonal kcickers or a prewelded gusset(s) with post install bolt to wall to reduce cantilever in half and reduce required thickness... so how exactly you mean bookowski? i prefer to not require field welding for my client! seems silly there isnt a "standard" for dummies way to do it out there tried and true .. maybe its the embed plates with anchors?!! if there is one thing i don't like is re-designing the wheel, i feel that eventually im gonna make a square.

 

[CANPRO]

I have designed similar stairs with cantilevered treads and have always used HSS. If you don't want to field weld you're going to see some bolts in the finished product...unless you get into some funky connection details.

I would never wet set treads into a concrete wall...thats just a disaster waiting to happen. I would embed flush plates into the wall and then weld the treads on after. Sometimes field welding is the most economical solution.

 

[KootK]

At closer to 3 inches deep, you might be able to get away with a pan stair with stiffening lips. The really aggressive staircases are often quite marginal wrt to performance.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[bookowski]

I wouldn't be overly concerned with field welding. If this is is some kind of even moderately slick stair then the the field welding shouldn't be an issue.

You need depth, limitless ways to get it and you probably want input from the architect. I've done lots of these and as canpro said using HSS is typical, you can use T shapes, tapered T shapes, have stiffening lips etc. etc. Flat plate isn't going to work well though.

Figuring out the performance (vibration) is not an incredibly easy task if you really want to get into it properly.

 

[bdruehl]

well, the client is barely paying us, so there will very unlikely be any input from an architect... why is wet setting a "disaster" waiting to happen? what about an embbedded C channel, weld a gusset for transverse skewage . you get plenty of depth for the cantilever and reduced thickness. route out the form in the shape of the channel, slip in the steel secure it and pour - bolt on your railing.. done..... gives you a nice surface for attaching wood treads and would get you out of the problem of having open "rises" which im not sure you can do in CA anyway ( like with the simple plate cantilever). i suppose i must be beaten into submission submission and go in circles before i do the "standard typical tried and true" method.. (been down this road before)

 

[bdruehl]

i meant to say "unequal leg" channel (not c channel)

 

[KootK]

What will be the finish on the face of the wall? Drywall? If it's exposed concrete, just use some nice shiny bolts.

I've run into the open riser issues too. If you're forced to have a riser, it may open up some options. In that situation, I've used flat plate treads and risers perforated with 4" holes to increase openness. If you shear connect the risers to the treads, it's a way to solve your depth problem without increasing tread profile.

While I hate to squelch creative thinking, I also think that the wet set idea is a sketchy one. I suspect that it will be a constructibility nightmare and I'm not at all confident that the treads wont drift around on you. But hey, somebody's got to go first. Prove us wrong and post pictures! You can be the Orville Wright of wet set stair treads.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[jayrod12]

I agree with the wet setting of the tread being a nightmare waiting to happen. At least with a weld plate you've got some possible adjustment to account for the weld plate not being in the exact right spot. The tolerance required on stairs is too tight to trust the concrete subs to correctly locate the treads.

 

[bdruehl]

this particular job is for outside stairs adjacent to a big (11 foot) retaining wall......still beating dead horse... =) but, if you route out the shape of whatever steel member section you are going to use for the "slot" to slide it into, and then use posts at far cantilever end and other such kickers or whatever to hold "steady" during pour? or have a big bubba just move them level and true in the wet concrete/hahahha ah, skaroo it.. be easier just to have a big typical manufactured steel monstrosity like for apartments with the single big center steel "stringer" and supported only at top and bottom.. right against the wall, would look ok (but with considerably less cool factor) esepcially after considering needing solid risers and then throw in ballusters required ... this aint gonna be in Arch Digest now <sigh> {and yes indeed KOOTK, the risers could definetly be the structural element of the stairs and use just post installed bolts and span the tread between em -- for the zig zag look...... anybody ever get away wit having open rises in stairs in CA ( you mean to tell me none of the ones i have seen are in ca??)

 

[bdruehl]

wait a second.. now i think about it... concrete typical apartment stairs have no risers ......

 

[jayrod12]

I believe if the gap between the top of step and underside of the next step is less than 4" then you don't need a riser backing.

Assuming a 7-8" rise on the stair and an approximate 3-4" tread thickness that leaves about 4" between stairs.