This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...such as the one above, it is advisable to adopt some convention regarding the treatment of the various joints, and the method adopted is to go round each joint in a clockwise direction, each joint at a time, starting from the left-hand side, and so form the polygon of forces for each joint. Starting then at the left-hand abutment, we are at once beset with a difficulty, inasmuch as the reactions are unknown in either magnitude or direction. Passing on, then, to the apex point, we find there are three forces, of which one is known in magnitude and direction, while the directions of the other two are known. Going round this point clockwise, and starting with our known force BC, we find in our force Fig. 57. polygon the line bc representing it; the next force in order is CE, and from c we now draw a line ce parallel to the member CE, while the third force is EB, and therefore we draw, from 6, a line be parallel to EB (we draw from b in this instance, because, as yet, the point c is not fixed). Join eo, and ed. Then eb and ec represent the stresses in EB and EG respectively, while ea and ed represent the magnitude and direction of the reactions. Simple Roof Truss with Single Tie rod.--Fig. 58 shows the previous type of roof modified so that the outward thrust of the rafters is taken by a tie-rod CD instead of by the abutments, thereby making the frame self-contained. In this case, since the reactions have no lateral components, they will be perpendicular, and the effect of this on the loads px and p2 is worth noticing. Considering any oue of these points, we have a state of matters as shown in Fig. 58 (a). We have a point E acted on by a force R, which is the total reaction at that point caused by the load on the truss; and also by a force pv in the same straig...