Tham khảo tài liệu 'fundamentals of structural analysis episode 1 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Truss Analysis Force Method Part I by S. T. Mau Solution. We shall give a detailed step-by-step solution. 1 Identify all force unknowns. The very first step in any force method of analysis is to identify all force unknowns. This is achieved by examining the reaction forces and member forces. The reaction forces are exposed in a FBD of the whole structure as shown. Free-Body diagram of the three-bar-truss to expose the reaction forces. Note that in the above figure the subscripts of the reaction forces indicate the direction first subscript and the location of the reactions second subscript . The three reaction forces are Rx1 Ry1 and Ry3. The member forces are F1 F2 and F3. 2 Examine the static determinacy of the structure. Before we proceed to find the force unknowns by the method of joint we must be sure that all the force unknowns can be determined by the static equilibrium conditions alone because that is the essence of the method of joint namely using joint equilibrium equations to find force unknowns. Denote the number of all member force unknowns as M and the number of reaction forces as R the total number of force unknowns is M R. In the present example M 3 R 3 and M R 6. This number is to be compared to the number of equilibrium equations available. There are three nodes in the truss. We can write two equilibrium equations at each node of a plane truss 2 Fx 0 2 Fy 0 1 Thus the total number of equilibrium equations available is 2N where N is the number of nodes in a truss. In the present example N 3 and 2N 6. Thus the number of available static equilibrium equations matches the total number of force unknowns exactly M R 2N. The problem posed in the present example is statically determinate. We can reach the same conclusion if we note that the truss is a simple truss. 35 Truss Analysis Force Method Part I by S. T. Mau 3 Solve for force unknowns. The most obvious next step is to write up the six nodal equilibrium equations and solve for the six unknown forces
