Question

for a simply supported beam carrying a uniformly distributed gravity load, at any internal section of the beam, what is the nature of the top fibres experience stresses?

Answer 1

For a simply supported beam with uniform gravity load, the bending moment at any section in the beam is sagging. Therefore, the top fibres of the beam always has compressive normal bending stress since the top fibres lie above the neutral axis.

The shear stress at the top most fibre is always zero since that's adjacent to the free surface of the beam.

Therefore, the topmost fibre of the beam at any internal section is always in compression and Shear stress is zero.