Essentials in the theory of framed structures . ce Vi acting upward must be supplied at G by the upper partof the column, in order that the lower part may be in equilib-rium. The forces required at / (Fig. 80c) are likewiseindicated. M2 = 15 X 1,300 = 19,500 forces at G and / (Fig. 80c) are shown reversed at G and J(Fig. 8od) and the solution may proceed as in Article 66. Structures of this character are seldom, if ever, designed withpinned connections at the column bases, as illustrated in It is equally true that the column connections to thefoundation
Essentials in the theory of framed structures . ce Vi acting upward must be supplied at G by the upper partof the column, in order that the lower part may be in equilib-rium. The forces required at / (Fig. 80c) are likewiseindicated. M2 = 15 X 1,300 = 19,500 forces at G and / (Fig. 80c) are shown reversed at G and J(Fig. 8od) and the solution may proceed as in Article 66. Structures of this character are seldom, if ever, designed withpinned connections at the column bases, as illustrated in It is equally true that the column connections to thefoundation are seldom, if ever, made with sufficient rigidity tojustify the assumption of zero bending moment at one-half thedistance from the foot of the column to the frame, as shown inFig. 806. The point of zero bending moment in nearly aU caseslies somewhere between these two extremes, and is generallyassumed to be one-third the distance from the foot of thecolumn to the first connection with the frame. This assump-tion makes h = 20 ft. in Fig. Fig. 81. 68. Problems. 1. Complete the solution for Fig. 796 and the two solutions in Fig. Sod, where^ = IS ft. in one instance and h = 20 ft. in the other. Compare the results ofthe three solutions. 2. Draw a stress diagram for the Fink truss in Fig. 81, assuming that thepoint of contraflexure in each column is one-third the distance from the baseof the column to the foot of the knee brace. CHAPTER IIIROOF TRUSSES Sec. I. Types anb Loads 69. Standard Types.—Roof trusses have been built in agreat variety of forms in conformance with architecturalrequirements, but under ordinary conditions the form of thetruss is determined by the length of span, slope of roof andthe clear head room underneath. The most common typesused in current practice are shown in Fig. 82. The Howe truss is especially adapted to wood top chord and diagonals are wood, the vertical tensionmembers are steel rods and the bottom chord is either woodor s
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