Nosing bars in reinforced concrete stair flights

[ajk1]

In my review of typical details, I see that nosing bars are usually specified in the treads of stair flights. Since most stairs are not designed to cantilever from the wall, what is the purpose of these bars? They seem very counterproductive in parking garages because the corrosive deicing chemical tracked into stair areas on people's shoes eventually are absorbed by the concrete, reach the rebar and cause concrete spalling due to rebar corrosion. I have seen this on a number of structures, including on the stairs in transit subway stations. I would like to remove the nosing bars from our typical detail, but want to be sure there is not something that I am missing. Perhaps there is unintended cantilever action, but wouldn't the plain concrete be enough to resist this without cracking (based on the slab depth plus the riser depth ± ), since there is no restraint to shrinkage in this direction? Or am I missing something?

 

[JAE]

I don't typically use them unless the client demands them. I see very little purpose in them.

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[hokie66]

Like you, I think they are susceptible to corrosion, without structural benefit.

 

[TehMightyEngineer]

Avoid like the plague. Just down the road from my house is a set of precast stair that have held up great except for a handful of bars near the nosing of the lowest tread. Rust is starting to bleed through the concrete and I imagine spalling is down the road.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[ajk1]

Thank you JAE, hokie66 and TehMightyEngineer (Structural) for your clear answer. You have given me the reassurance, confidence and courage of my beliefs to proceed to delete the nosing bars from our typical detail. I believe I have deleted them in the past from specific projects and there were no subsequent bad effects. I hope everyone else reading this does it from their typical details too.

 

[KootK]

For what it's worth, the last time that I did outdoor stairs for the city of Calgary, they asked for FRP nosing bars. They still probably don't do anything and are annoying to source but, at the least, they've acknowledged the corrosion vectors that the metallic nosing bars represent.

 

[TehMightyEngineer]

Well, at least the FRP bars is the right idea. Waste of money IMO but I suppose it could be useful to protect the nosing from impact damage when someone hits the bottom tread with a snowblower or whatever they use to clean sidewalks up there on Planet Hoth.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[ajk1]

Thanks. Another possibility is stainless steel bars which are available in some areas of the country. But if bars are not necessary, I would not put them in.