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Module 5 : Force Method - Introduction and applications

Lecture 2 : The Force Method

	(b) Choice of Basic determinate Structure for minimum Computation work The computational effort required in calculating the response of a given structure using the force method can vary significantly depending on the choice of basic determinate structure. In this regard, there are two issues to consider:
	1. Select the basic determinate structure such as the displacements can be easily computed (i.e. converting it into simple structure). 2. Select the basic determinate structure to maximize the number of flexibility coefficients equal to zero.
	These issues are illustrated in the following examples. Consider a fixed beam as shown in Figure 5.8(a). The beam is non-prismatic with degree of indeterminacy 2. Three basic determinate structures are shown in Figures 5.8(b), (c) and (d). Among the three structures the computation effort will be minimum for the beam as in Figure 5.8(b) as the resulting basic determinate structure consists of two uniform cantilever beams.