Prof.Kodali Srinivas

Assignment - S.M.2,Unit-6 1.Find the internal forces in member AB,AC,BC by using Method of Joints. 2.Find the internal forces in all members of a pin jointed truss by using Method of Joints. P= 12kN 3.Find the internal forces in all members of a pin jointed truss by using Method of Joints. 4.Find the internal forces in BD, CD and CE members of a pin jointed truss by using Method of sections. 5. Find the internal forces in GF,GC,FC members of a pin jointed truss by using Method of sections. Objective questions and answers  1. How many equilibrium equations do we need to solve generally on each joint of a truss?      a) 1    b) 2      c) 3       d) 4 2. If a member of a truss is in compression, then what will be the direction of force that it will apply to the joints?    a) Outward     b) Inward     c) Depends on case     d) No force will be there 3.What should be ideally the first step to approach to a problem using method of joints?    a) Dra

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.

A  truss  is a structure composed of rod members arranged to form one or more triangles. The joints are pinned (do not transmit moments) so that the members must be triangulated.  Perfect truss A  truss  or a frame that doesn't collapse when loaded is called as a  perfect truss  or a  perfect  frame. Example for a  perfect truss  or a frame is a simple triangle. The totall number of members in the frame is m , and total joints in the frame is j , then the  condition for  perfect truss  or a frame is m=2(j)-3 for simply supported truss m=2(j) for cantilever truss If the truss is not satisfied  the truss is called imperfect truss.  Determinacy  Trusses are statically determinate when the entire bar forces can be determined from the equations of statics alone. Otherwise the truss is statically indeterminate.  A truss may be statically (externally) determinate or indeterminate with respect to the reactions (less than three or more than 3 reactions ) Ther