Here we will deal with the concept of bending moment. It is simply strength multiply by frame or a pair of forces. To determine a positive (+) or negative (-) value, you must take into account the direction in which it “spins” the force. If the force turns in a clockwise direction, then we get a positive value (+), if the force turns counter-clockwise, then we get a negative value (-). The following picture shows exactly what is going on.
Okay, now I’ll show it by example. We have such a free beam with a concentrated force of 10kN.
We will consider creating a bending moment for two points A and B visible in the drawing.
Let’s start alphabetically from point A.
Calculating the moment for point A, we get the equation.
The value of the clustered force with the positive sign (+) multiply by the frame (distance) on which the moment works (force distance to point A), so we have.
We see that the force turns to point A while moving in a clockwise direction.
Well, now point B we get the equation.
Value of concentrated force with negative sign (-) multiply by frame (distance) on which the moment works (force distance to point B).
We see that the force turns to point B and moves counter-clockwise.
This is how we got through the next stage of the course. Let’s move on.