Tham khảo tài liệu 'bruhn - analysis and design of flight vehicles structures episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | A7. 33 . Truss Deflection by Method of Elastic Weights If the deflection of several or all the Joints of a trussed structure are required the method of elastic . . eights may save considerable time over the method of virtual work used In previous articles of this chapter. The method In general consists of finding the magnitude and location of the elastic weight for each member of a truss due to a strain from a given truss loading or condition and applying these elastic weights as concentrated loads on an Imaginary beam. The bending moment on this Imaginary beam due to this elastic loading equals numerically the deflection of the given truss structure. Consider the truss of diagram 1 of Fig. At 49. Diagram 2 shows the deflection curve for the truss for a AL shortening of member be all other members considered rigid. This deflection diagram can be determined by the virtual work ex pression Ô UAL. Thus for deflection of Joint 0 apply a uhlt vertical load acting down at Joint 0. The stress m In bar be due to this unit load 2 . 2P 4P . Therefore 3 r 3r 5a ALftc . 4P . The deflection at other 3r lower chord Joints could be found in a similar manner by placing a unit load at these Joints. Diagram 2 shows the resulting deflection curve. This diagram is plainly the Influence line for stress In bar be multiplied by ALfcC. Diagram 3 shows an Imaginary beam loaded with an elastic load ALbc acting along a vertl-r cal line thru Joint 0 the moment center for obtaining the stress In bar be. The beam reactions for this elastic loading are also given. Diagram 4 shows the beam bending moment diagram due to the elastic load at point 0. It Is noticed that this moment diagram Is Identical to the deflection diagram for the truss as shown In diagram 2 . The elastic weight of a member Is therefore equal to the member deformation divided by the arm r to Its moment center. If this elastic load Is applied to an Imaginary beam corresponding to the truss lower chord the bending moment on .
