1. Concrete is Brittle
It fails (cracks) at the angle of principal tension

2. Principal Tension is Horizontal
Concrete is Brittle
It fails (cracks) at the angle of principal tension
High Moment, No Shear
Principal Tension is Horizontal
Crack is vertical

3. Principal Tension is Horizontal
Concrete is Brittle
It fails (cracks) at the angle of principal tension
Low Moment, High Shear
High Moment, No Shear
Principal Tension is Horizontal
Crack is vertical

4. Principal Tension is Horizontal
Concrete is Brittle
It fails (cracks) at the angle of principal tension
Neutral Axis.
No Bending Stress
Only Shear Stress
Crack at 45 degrees
Low Moment, High Shear
High Moment, No Shear
Principal Tension is Horizontal
Crack is vertical

5. Concrete is Brittle
It fails (cracks) at the angle of principal tension

6. Concrete is Brittle
It fails (cracks) at the angle of principal tension