You are not summing moments correctly. All perpendicular distances must be measured between the force and the point (Ra) about which you are summing moments.Jamesnikko said:ok so my first force which is before point Ra on an overhang should be negative whereas the other two forces are positive? assuming i use a negative reaction at b of course. therefore formula would be, -(5x1.5) + (5x3) + (5x6) - (Rbx4.5)?
To determine the reactions at the supports of a simply supported beam, you need to first calculate the sum of all the external forces acting on the beam, including any applied loads and moments. Then, using the equations of equilibrium, you can solve for the reactions at the supports.
The two types of reactions that can occur in a simply supported beam are vertical reactions and moment reactions. Vertical reactions are forces acting perpendicular to the beam's surface, while moment reactions are rotational forces acting on the beam.
The direction of the reactions at the supports can be determined by analyzing the direction of the external forces and moments acting on the beam. The reactions will be in the opposite direction of the applied loads and moments in order to maintain equilibrium.
Yes, the reactions at the supports can be negative. This occurs when the support is pulling on the beam instead of pushing, or when the moment reaction is in the opposite direction of the applied moment.
Some common mistakes to avoid when finding reactions in simply supported beams include forgetting to consider all external forces and moments, using the wrong equations of equilibrium, and not properly considering the direction of the reactions. It is also important to check your calculations and make sure they are consistent with the beam's geometry and boundary conditions.