The method of joints is good if we have to find the internal forces in all the truss members. In situations where we need to find the internal forces only in a few specific members of a truss, the method of sections is more appropriate.
The method is created the German scientist August Ritter (1826 - 1908).
The Method of Sections (Ritter Method)
1. This method consists of passing an imaginary section through the truss, thus cutting it into 2 parts (a cut through the members of interest)
2. Try to cut the least number of members (preferably 3).
3. Draw Free body diagram FBD of the 2 different parts of the truss.
4. Enforce Equilibrium to find the forces in the 3 members that are cut.
5. Either of the two parts of the truss can be considered and the three equations of equilibrium can be applied to solve for member forces.
∑ Fx = 0, ∑ Fy = 0, and ∑ M = 0
Example:
Find the value of forces for member BC, EC, and ED of in the truss as shown in figure.
1.The support reactions of Ra and Rd should be determined.
2.A virtual cut is introduced through the only required members which is along member BC, EC, and ED. as shown in fig.
3.Divide the truss in to two parts, and introduce the member forces in cut members as shown in fig.
4. Solve the unknowns by using the equilibrium equation for forces, using ∑ Fx = 0, ∑ Fy = 0, and ∑ M = 0
Comments
Post a Comment