L2: Structural loads and internal responses

Types of loads

Section cut and internal forces

Internal forces are distributed throughout beam actions in the form of stresses and known as…

Stress resultants

Notation: N, Q, M

N - normal axial forces within

Q - shear force

M - bending moment

Section cut and internal forces N, Q, M

• coordinate x is always with direction of beam and points to right

• If normal vector n is in opposite direction of x, then face is negative

• M is positive when it causes the upper surface of the beam to become concave and the lower surface convex (sagging bending moments)

Positive moment

Negative moment

In stress resultant diagrams we always draw M where?

On the tensile side of a beam

The section cuts must be taken how?

One before and one after the position of the concentrated load. If we have only distribution load then one cut is enough as there will be only one value for all stress resultants. So the number of cuts depend on the jumps of discontinuity