Tham khảo tài liệu 'crc press - mechanical engineering handbook- mechanics of solids part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1-20 Section 1 2. Section the truss by making an imaginary cut through the members of interest preferably through only three members in which the forces are unknowns assume tensions . The cut need not be a straight line. The sectioning is illustrated by lines l-l m-m and n-n in Figure . 3. Write equations of equilibrium. Choose a convenient point of reference for moments to simplify calculations such as the point of intersection of the lines of action for two or more of the unknown forces. If two unknown forces are parallel sum the forces perpendicular to their lines of action. 4. Solve the equations. If necessary use more than one cut in the vicinity of interest to allow writing more equilibrium equations. Positive answers indicate assumed directions of unknown forces were correct and vice versa. FIGURE Method of sections in analyzing a truss. Space Trusses A space truss can be analyzed with the method of joints or with the method of sections. For each joint there are three scalar equilibrium equations YFX 0 YFy 0 and Fz 0. The analysis must begin at a joint where there are at least one known force and no more than three unknown forces. The solution must progress to other joints in a similar fashion. There are six scalar equilibrium equations available when the method of sections is used YFx 0 IFy 0 YFZ 0 YMX 0 TMy 0 and TMz 0. Frames and Machines Multiforce members with three or more forces acting on each member are common in structures. In these cases the forces are not directed along the members so they are a little more complex to analyze than the two-force members in simple trusses. Multiforce members are used in two kinds of structure. Frames are usually stationary and fully constrained. Machines have moving parts so the forces acting on a member depend on the location and orientation of the member. The analysis of multiforce members is based on the consistent use of related free-body diagrams. The solution is often facilitated by representing .
