Wall Reinforcement

[ack]

How should I design vert. reinforcement for the outer face of a foundation wall spanning vertically betweem two levels? Should I just put in some minimum reinf.? Inner face vert. reinf. will be designed for moment = wl^2/8. Is this resonable?

A similar question for slab having only one span, if bottom reinf. is designed for M=wl^2, should I just put in min. top reinf. at the ends of span?

 

[ack]

sorry, the slab positive moment should read M=wl^2/8.

 

[HochwaltPE]

In both of the situations described I would provide some minimum reinforcing. Even though you have designed the structural element to be simply supported, the reality is that there will be some fixity until the concrete cracks to release the fixity. It would be prudent, then, to provide some minimum reinforcing to control the cracking.

In general, I would provide 1/3 to 1/2 as much reinforcing at the supports of a simple span as I have designed at midspan. If I had to provide a rationale for this, I would point to the ACI coefficients in Section 8.3 which list a moment of wl^2/16 for a column support and wl^2/24 for a beam support. Of course, if minimum wall reinforcing requirements require a greater amount of steel, I would provide that.

 

[JAE]

For the foundation wall, if your lateral force is due to earth, it is permanent and will not ever produce moment on the opposing side. However, there could be small amounts of moment at the top and bottom due to any fixity produced by dowels at the top and bottom which tie in the upper floor and the lower foundation to the wall. Usually, the dowels can deal with the minor moments produced.

However, with earth pressure, you won't get a moment = wL^2/8 as the earth load is a triangular load, increasing with depth.

If the lateral load is wind or seismic, the forces will be in either direction, necessitating reinforcing on both faces.

I concur with HochwaltPE that for the beam, we usually provide the 1/2 to 1/3 reinforcing in the top at each end.