Computer study. The objective is to compare the behavior of a determinate and an indeterminate structure. The forces in members of determinate trusses are not affected by member stiffness. Therefore, there was no need to specify the cross-sectional properties of the bars of the determinate trusses we analyzed by hand computations earlier in this chapter. In a determinate structure, for a given set of loads, only one load path is available to transmit the loads into the supports, whereas in an indeterminate structure, multiple load paths exist. In the case of trusses, the axial stiffness of members (a function of a member’s cross-sectional area) that make up each load path will influence the magnitude of the force in each member of the load path. We examine this aspect of behavior by varying the properties of certain members of the indeterminate truss shown in Figure P4.54. Use E = 29,000 kips/in.².

Case 1: Determine the reactions and the forces in members 4 and 5 if the area of all bars is 10 in.².

Case 2: Repeat the analysis in Case 1, this time increasing the area of member 4 to 20 in.². The area of all other bars remains 10 in.₂.

Case 3: Repeat the analysis in Case 1, increasing the area of member 5 to 20 in.². The area of all other bars remains 10 in.². What conclusions do you reach from the above study?

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100 kips - 2 20' 5 15'