chetzread said:
move on to the lower part of note, i found that the author take the clockwise moment at LHS as positive while at RHS , the author take anticlockwise moment as positive,why is it so?Clever Penguin said:If I had a beam, and applied a force acting upwards on the left, it would rotate clockwise.
If I was to instead apply a force acting downwards, but on the right, the beam would still rotate clockwise.
Sum of the clockwise moments = sum of the anti-clockwise moments. It is not about whether the force is acting up or down but whether the result of that force would cause it to rotate clockwise or anti-clockwise.
So, the moment clockwise considered as positive in this case?Clever Penguin said:If I had a beam, and applied a force acting upwards on the left, it would rotate clockwise.
If I was to instead apply a force acting downwards, but on the right, the beam would still rotate clockwise.
Sum of the clockwise moments = sum of the anti-clockwise moments. It is not about whether the force is acting up or down but whether the result of that force would cause it to rotate clockwise or anti-clockwise.
The sign convention of shear force and bending moment is a set of rules used to determine whether a force or moment is positive or negative in a structural analysis. It is based on the principle of equilibrium, where all external forces and moments acting on a structure must sum to zero.
Shear force is typically represented as positive when it causes a clockwise rotation in a structure, and negative when it causes a counterclockwise rotation. This convention is used to determine the direction of the force acting on a particular point in the structure.
The sign convention is crucial in structural analysis as it helps engineers and scientists to accurately determine the forces and moments acting on a structure. It also ensures that the sum of forces and moments at any point is equal to zero, which is necessary for a stable and safe design.
The sign convention for bending moment is similar to that of shear force, where it is positive when it causes a clockwise rotation and negative when it causes a counterclockwise rotation. However, the sign convention for bending moment also takes into account the curvature of the structure, with positive bending moment associated with convex bending and negative bending moment associated with concave bending.
While the sign convention is generally consistent, there are a few exceptions that may arise in certain structural elements. For example, in a cantilever beam, the sign convention for shear force is reversed due to the nature of the support. Additionally, in some cases, the sign convention may vary depending on the type of analysis being performed.