Strains in Ironwork

This historic book may have numerous typos, missing text, images, or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1884. Not illustrated. Excerpt: ... LECTURE VIII. Application of reciprocal diagram to lattice girders--Diagram for Warren girder, with central load supported on top flange--For same with load on bottom flange--For same with additional bays-- For same with distributed load on top flange--For same with load on bottom flange--For lattice girder, with bars intersecting at 45 under concentrated and distributed loads--For lattice girder with vertical bars--Examples. This evening we shall apply the reciprocal diagram of forces to lattice girders of different kinds, and you will see how favourably the system compares with the ordinary parallelogram of forces for such investigations. Very little explanation will be required; the chief difficulty is to know what form the diagram will take for each variety of girder or arrangement of bars. I will sketch them down, and point out any particular part requiring notice, and I hope you will stop me at once, if any part is not quite clear to you, in order that I may explain it. We will take first a Warren girder of 3 bays, with a concentrated load in the centre on top flange, Pig. 150. In this diagram, Fig. 151, we have IJ = full load, and I H, H J each = J full load. There is no strain in I A or J G, which agrees with the result found by other methods. But suppose we have the same load supported by the bottom flange instead of the top, as in Fig. 152. We now get considerable alteration in the strains, and find some difficulty in adjusting the lines showing the application of the external force or load. The weight is acting in the centre of middle bay, but so far as the trussing is concerned, the load is divided between the points a and b, and we must therefore put lines here, each representing half the load, and then letter the spaces as shown. The...