This can be due to several reasons:

• There is a maximum value in the negative moment envelope (positive moment for foundation beams) at that point and it cuts the reinforcement anchoring the top assembly bars and bottom reinforcement. It is the equivalent of a support. It may occur in a long alignment which passes through other beams or in a waffle or flat slab when the beam is close to a support. If the envelope of that alignment is consulted, a sinusoidal diagram can be seen which is cut off at the previously mentioned maximum values.
• If the beam is longer than 12 m, the program is obliged to divide the reinforcement.
• There is a change in the dimensions of the beam.