Question: I was a rod buster for 16 years but I blew out my back and now I am an inspector. We always put a #4 horizontal bar at the top (and centered between the forms) of every stem wall, step, and curb, within 2 inches of the edge/face of the concrete. I am now in a different area of the state and I routinely run into residential post-tensioned slabs on ground that rarely have a horizontal bar at the top of a stem wall or the step from the main house into the garage. Does the strength the p-t provides make it so that a horizontal bar is not needed at the top of the stem wall?
Answer: First, the building design professional has the final say on an issue of this sort. As an inspector, your responsibility is to assure that the steel is positioned as shown in the contract documents, which includes all plans and shop drawings. However, we can tell you that the IRC, which governs most residential construction in the U.S., in Section R404.1, Concrete and masonry foundation walls, says that foundation walls shall be constructed in accordance with ACI 332, Residential Code Requirements for Structural Concrete. In ACI 332, Section 8.2.8 discusses horizontal reinforcement for both plain and reinforced concrete foundation walls. Remember that “plain” concrete, sometimes called “unreinforced” doesn’t mean that there’s no reinforcing steel, only that the steel strength is not relied upon in the design. The steel is there to hold any cracks together. ACI 332 states that, “For all wall heights, a minimum of one horizontal bar shall be located within the top 24 inches and a minimum of one in the bottom 24 inches.” It further states that for any area of the country where earthquakes are likely, “Two #4 horizontal bars shall be located in the upper 12 inches of the wall.” Post tensioning reinforcement in the slab has no effect on the design of the stem wall.