Alternative Design Methods for Parallel-Chord Space Trusses

A proposed plastic design method, depending on tension chord yield, for two-layer parallel-chord space trusses is discussed. The method is compared with the conventional
elastic method and the strip method originally used in reinforced concrete slab design. The disadvantages of these last methods are shown in a comparison of complete
analyses of three designs. The essential point made is that when tension chords begin to yield a set of membrane forces is developed: these forces are compressive in the region of the yielding tension members and increase in magnitude as the yielded tension zone increases. The proposed design method allows for this change of force distribution so that no compression member instability occurs, thereby furnishing a favourable load-deflexion characteristic for the structure. Reference is made to experimental results of tension member yield in planar trusses in order to justify the use of yielding tension members; it is noted that further work is necessary.

L.C. Schmidt