Section Method

To observe the internal forces one has to cut the structure, however, this is obviously not possible. Therefore, we assume an imaginary cut such that the structure is divided into two parts. At the location of cut, we can then see the internal forces (or internal forces become external).

This technique is called Section Method. In general, there are six internal forces in a structure: An axial force (Nx) which acts along the longitudinal axis of the structural member and makes it stretch or squeeze, two shear forces (Vy and Vz) which act perpendicular to the longitudinal axis of the member, and three bending moments, or simply “moments” (M_x, M_y, and M_z) about the three axes of the structural member. Mx results in the twisting of the member, while My and Mz make it bend about the y and z axes, respectively. If the structure acts as a two-dimensional system, there are only three internal forces (Nx, Vy and Mz).

Section Method

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