Cyclopedia of architecture, carpentry, and building : a general reference work . thod of Sections. To determine the stress in a mem-ber of a truss by the method explained in the foregoing (the method of joints ), we begin at one end of the truss and drawpolygons for joints from that end until we reach one of the joints 196 STATICS 63 to which that member is connected. If the member is near themiddle of a long truss, such a method of determining the stressin it requires the construction of several polygons. It is some-times desirable to determine the stress in a member as directly aspossible wi
Cyclopedia of architecture, carpentry, and building : a general reference work . thod of Sections. To determine the stress in a mem-ber of a truss by the method explained in the foregoing (the method of joints ), we begin at one end of the truss and drawpolygons for joints from that end until we reach one of the joints 196 STATICS 63 to which that member is connected. If the member is near themiddle of a long truss, such a method of determining the stressin it requires the construction of several polygons. It is some-times desirable to determine the stress in a member as directly aspossible without having first determined stresses in other method for doing this will now be explained ; it is called themethod of sections. Fig. 39 (a) is a partial copy of Fig. 16. The line LL is in-tended to indicate a section of the trus3 cutting members24, 84 and 36. Fig. 39 (/>) and (c) represents the parts of the trussto the left and right of the section. By part of a truss wemean either of the two portions into which a section separates itwhen it cuts it Fig. 39. Since each part of the truss is at rest, all the forces acting oneach part are balanced, or in equilibrium. The forces acting oneach part consist of the loads and reactions applied to that part to-gether with the forces exerted upon it by the other part. Thus theforces which hold the part in Fig. 39 (/>) at rest are the 1,500-and 3,000-pound loads, the reaction 6,000 and the forces whichthe right part of the cut members exert upon the left parts. Theselatter forces are marked F/, Fg and F3; their senses are unknown. 197 64 STATICS but each acts along the axis of the corresponding member. Theforces which hold the part in Fig. 39 (c) at rest are the two 3,000-pound loads, the 1,500-pound load, the right reaction 6,000pounds and the forces which the left parts of the cut membersexert upon the right parts. These are marked F/, F/ and Fg;their senses are also unknown but each acts along the axis of
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