The correct answer is: D. Bending moment, shear and torsion
A beam curved in plan is designed for bending moment, shear and torsion.
Bending moment is the internal resisting moment developed in a beam to counteract the external loads applied to it. Shear force is the internal resisting force developed in a beam to counteract the external loads applied to it. Torsion is the internal resisting moment developed in a beam to counteract the twisting loads applied to it.
A beam curved in plan is subjected to all three of these forces. The bending moment is caused by the vertical loads applied to the beam. The shear force is caused by the horizontal loads applied to the beam. The torsion is caused by the twisting loads applied to the beam.
The design of a beam curved in plan must take all three of these forces into account. The beam must be strong enough to resist the bending moment, the shear force, and the torsion. The beam must also be stiff enough to prevent excessive deflection.
The design of a beam curved in plan is a complex process. It is important to consult with a structural engineer to ensure that the beam is designed properly.