Stair Nosing Bar - Conflict w/ Recessed Step Light

[cwyoung411]

Hello everyone,

I work at a civil firm and we are currently working on a project where we need to install recessed step lights in the risers of a CIP concrete stair.
The light back box is in conflict with the location of the nosing bar. Our detail currently shows the nosing bar stopping at either side of the light. See attached for our current detail.

Our structural engineer (subconsultant) says they are okay with this proposed solution, but that it will likely result in cracking where the nosing bar stops.
We see these types of lights installed in many sets of concrete stairs with no issues (cracking at the lights, etc.).

Any thoughts on how to resolve this potential issue? Remove the nosing bars all together?
Any additional thoughts/tips on our detailing of this stair riser?


-Chris

 

[Agent666]

Is the light box rigid? I'd be concerned that you only have 1" concrete over the thing if it's plastic and offers no rigid support to the concrete over it. That definitely seems like a recipe for cracking due to foot traffic.

But in terms of the nosing bar, I'd tend to put another bar behind and/or below the light and keep the current bars. An alternative would possibly be some form of lighter gauge galvanised mesh basically sitting on the light fixture. So the concrete over the fixture has some limited flexural capacity.

 

[EdStainless]

So I went an looked a local place that has these. Of course I don't where the bar is, but the light are set lower than you show. And they are even angled down slightly. When I look up the flight I cannot look directly in to any of them. My hunch is that they are set just below the bar.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dflva]

Eliminate the 3/4" x 1" dirt collector at the bottom of the riser and lower the light box. You need more concrete over the light.

 

[dik]

Check to see if the nosing bar is required. I've done a lot of reports where nosing bars have been responsible for the concrete spalling off the nosing due to corrosion. I haven't use nosing bars for over 40 years... generally a bad idea.

Dik

 

[Ron]

Agree with dflva....that recess is a potential tripping hazard as well.

dik is correct as well, particularly if you are in any type of corrosive environment.

 

[hokie66]

The others have said it all. The light should be lowered so that some worthwhile concrete thickness is maintained above the box. That architectural recess is silly and a maintenance headache.

As to the nosing bar, those things serve no purpose. They just provide a corrosion and spalling hot spot.

 

[r13]

Used to see in movie theaters. You at least have to come up a thickness adequate to support the full design load, with the span equal to the width of the lighting fixture, and accommodate the stair nosing and its embedment.

 

[dik]

You said it all... in addition to corrosion issues, they are a hard 'spot' and generate tensile stresses in the concrete...


Dik

 

[cwyoung411]

Thanks everyone who responded to this previously. Attached is our revised detail.
Nosing bar is staying per the project structural engineer, but we removed the recess and lowered the recessed step light all the way to the bottom of the riser.

Any concerns with this solution if it were your project (other than the nosing bar...which is not up to us)?

Project is located in Charlotte NC if that matters at all from an environmental conditions perspective.

https://files.engineering.com/getfi...-4d2a-b6c7-f3a019ac99cd&file=Riser_Detail.jpg

Thanks,
Chris

 

[r13]

It looks much sturdy than before. How about a few bars in transverse direction, if concrete cover permits.

 

[dik]

You could make the box out of 1/4" plate and use headed studs to secure it... Nosing bars are a thing of the past and should be avoided, IMHO (not so humble, sometimes). HDG or stainless rebar?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik