This research was performed at the School of Mechanical Engineering , Tel Aviv University by Moshe Fuchs. A major obstacle in the design of structures is the need for multiple reanalysis of the structure. Indeed, when the geometry of the structures or the stiffnesses of its elements are modified one has to reanalyze the structure in its new configuration in order to assess its stresses and displacements. This is the reason for the development of reanalysis techniques or for approximate explicit expressions for the internal forces and displacements in terms of the design variables. When the design variables are the cross-sectional characteristics of truss and frame structures, this author has found the exact explicit expressions for the internal forces in these structures in terms of the design variables. These exact equations are rather interesting, however difficult to implement, due to the large number of terms involved.

- M.B. Fuchs (1997),
**The Exact Dependency of the Internal Forces on the Element Stiffnesses of Framed Structures**,*WCSMO-2, The Second World Congress on Structural and Multidisciplinary Optimization*, Zakopane, 26-30 May.

This poster paper explains in simple steps how to construct the explicit expressions for the internal forces*N*in trusses in terms of the cross-sectional areas*A*of its members, and for the internal forces*M,S,N*in frames in terms of the cross-sectional areas*A*and the moments of inertia*I*of its members. The method hinges on determining all the statically determinate substructures which are embedded in the original structure. Having found the internal forces in every substructure, when one applies to it the external loads, the explicit expressions follow naturally. The problem is that there are many determinate substructures in most engineering structures. (*Postscript*file, 168K)