In BBS for ductile beams, there should be no lap splice within the joint and within 2D from the face of the column. (ACI 318M – 14 cl. 18.6.3.3)
(Currently, lap splices are still drawn within the restricted locations.)
Reply:
RCDC design the reinforcement as per the forces available at all sections in the beam. It takes 13 stations (i.e. 12 zones) for design of beams. Based on the forces available in each zone, reinforcement is calculated. Lapping locations are available as per user inputs. Default location for lapping of top reinforcement is L/4. As RCDC design the beam for 12 zones, the options of L/3,L/4 and L/6 are available for lapping at top and bottom reinforcement
At top location, the lapping is provided at curtailment locations. i.e. L/3,L/4 or L/6 distance from column face. Here the distance 2xD is not checked for curtailment. If we start providing curtailments for beams as per the beam depth, it would be complicated. The curtailment location will vary as per the beam depth. The location of curtailments might fall between two stations. Checking reinforcement curtailments at any location as per 2D would not be simple and might not give the desire result. Interpolation of forces is not possible for in between values. Even if we consider on higher side, it would not be consistent to all beams and curtailments will not match the distance 2D for all beams. Also, it is very difficult to handle Ast calculations and shear check location for individual beams.
For Bottom location, RCDC provides the lapping at face of the beam. The higher diameter rebars extends to lower diameter to make sure that the it satisfies the bending and shear check criteria. Also, the confining of the reinforcement exists up to twice the distance from the column face.
If we provide lapping away from the twice the beam depth, it might reach in the middle zone of the beam which is also needs to avoid as it is governed by permanent loads. In this case we might need to handle ductile and Non-ductile beams separately. For ductile beam lapping will place away from the 2D and for Non-ductile it is possible to provide within 2D.
For such cases, we would recommend user to use detailing options available in RCDC.
For Top rebars use max dia. Option: here the same diameter rebar is continued at outer most layer to avoid lapping.
For Bottom rebars use max dia. Option and try to provide same rebar numbers and diameter to adjacent beams to avoid lapping.