Compression vs Tension Lap Splice Development Length
Compression vs Tension Lap Splice Development Length
(OP)
I'm sure this question has been asked, but I did not find an answer that was satisfactory in the threads.
In a doubly reinforced concrete beam that is a part of a moment frame, does ACI 12.2 govern the length of splice of the top reinforcement or 12.3. The building is already built and uses 12" splices for all top bars at midspan. 12" does not meet 12.3 for the bar size used, but it is way off if 12.2 governs. I doubt that the intent of the top bars was to carry compression loads (most likely for ductility and to satisfy 12.11/12.12), but technically they could fall in the compression zone under most gravity loadings.
Thanks!
In a doubly reinforced concrete beam that is a part of a moment frame, does ACI 12.2 govern the length of splice of the top reinforcement or 12.3. The building is already built and uses 12" splices for all top bars at midspan. 12" does not meet 12.3 for the bar size used, but it is way off if 12.2 governs. I doubt that the intent of the top bars was to carry compression loads (most likely for ductility and to satisfy 12.11/12.12), but technically they could fall in the compression zone under most gravity loadings.
Thanks!





RE: Compression vs Tension Lap Splice Development Length
RE: Compression vs Tension Lap Splice Development Length
RE: Compression vs Tension Lap Splice Development Length
RE: Compression vs Tension Lap Splice Development Length
The bars may have simply been provided to support the stirrups.
RE: Compression vs Tension Lap Splice Development Length
You are required to have full development of reinforcement at all sections where the reinforcement is required, with the exception noted in 12.2.5. If the beam is truly "doubly reinforced" as you state, the top bars at midspan do need to be fully developed because they do act as compression reinforcement at that section. If the beam was designed as only tension reinforced, with top bars carried for convenience, then they would not need to exist at all for design purposes, so a short splice would be inconsequential.
RE: Compression vs Tension Lap Splice Development Length
What about in the case of perimeter beams? 7.13.2.2 At least 1/6 of negative moment reinforcement continuous over the span length (2 bar min). If a splice was present in top bars at midspan, it must be class b splice, no?
Also, 21.2 is the minimum for every SDC, but A. It requires two longitudinal bars continuous top and bottom (min) developed at the face of support. If a splice was present in top bars at midspan, it must be class b splice, no?
RE: Compression vs Tension Lap Splice Development Length
ACI 318-11 7.13.2.4 requires class B for the top bars required in 7.13.2.2.
In the context of 21.2, the requirement for continuous bars would appear to require full splice, based on 12.10.4. 12.15.2 requires all tension laps to be class B unless you have twice the required reinforcement. I'm not sure this could be construed to allow shorter slices even when there are plenty of bars. That said, if the distance between bars complies with the intent for non-contact lap splices, you could use adjacent bars which lap with the short splice to assure that the splice is adequate. (That isn't terribly clear: imagine a three-bar splice, where two bars are in a 12 inch contact lap, and the third bar overlaps each of these bars by class B length and is within the non-contact lap distance requirement.)