Analyze the grade beam for all anticipated loading conditions, and develop an enveloped shear and moment diagram. Make sure your reinforcement is adequate to carry that enveloped shear and moment. Don't forget to check deflections!
As for designing it as a doubly reinforced beam, I wouldn’t...
Be careful with the 5% provision. I've recently done some work in the telecom industry (adding antennas and equipment shelters to rooftops), and on a few occasions have come across sites where engineers have used the 5% rule of thumb on one retrofit after another. Sure, it may be within the 5%...
In terms of determining a Response Modification Coefficient, System Overstrength Factor, and Deflection Amplification Factor for a lateral system where's the cutoff between a shear wall with openings and a moment frame? Is there specific IBC or ASCE language that directs which values to use...
