RCDC is considering 'Zero" bending moment at left and right support despite there being some Bending moment at the support.
Reply:
Below is the step by step process which explains why and how RCDC shows Zero BM at supports to satisfy max Ast requirement :
Step 1: RCDC bifurcates the beam in Left, Mid and Right zone and identifies the length of each zone.
Step 2: Based on the length of each zone, RCDC further identifies the number of stations that will fall in each zone.
Step 3: For each station, identifies +ve moment as Top moment and -ve moment as Bottom moment
Step 4: RCDC Calculates As,reqd for each station as follows:
As,reqd = Max{B,B', A+D/2, A+C x (fsc / fyd)+D/2} (for Mu > 0)
As,reqd = Bn (for Mu = 0)
Where,
A = As = Tension reinforcement required for bending moment
B = As,min (flex) = Min area of flexural reinforcement
Bn = As,nominal = Nominal area of reinforcement
Step 5: After identifying Max As,reqd (as per above step) for each station individually, RCDC provides the Max Ast for all the stations of a particular zone under consideration.
Step 6: "If As reqd is governed by As nominal, the RCDC shows Zero BM value in the design calculation report."
Refer attached excel which explains a solved example.
RCDC Logic of designing Beams.xlsx