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5.3.10
Trusses
An important example of network structures is a truss system which is formed of pin-
connected members. It is assumed that the bars only extend or compress and transmit only
axial forces; no bending moments or shear forces are generated. For an ideal truss with
ideal, frictionless pins or hinges, this is not an assumption as each bar, in fact, according
to equilibrium requirements, can only transmit axial forces. All forces and motion will be
(assumed to be) in the xz plane, i.e., this is a planar problem with no out-of-plane motion.
Element Coordinate Transformations and Stiffness Matrices
Local and global coordinate systems, forces, and displacements are shown in Fig. 5.16.
Because of the fundamental truss assumption of bars being pin-connected, with the
FIGURE 5.16
Local and global orientation of coordinates, displacements and forces for trusses. For simplicity, only forces are
displayed at one end of the bar, while only displacements are shown at the other end.
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