C

2.11.9 Gable Frames

The mechanism method is used to determine the plastic limit load of the gable frame shown in Figure 2.102. The frame is composed of members with plastic moment capacity of 270 kip ft. The column bases are fixed. The frame is loaded by a horizontal load H and a vertical concentrated load V. A graph from which V and H cause the collapse of the frame is to be produced.

Solution

Consider the three modes of collapse as follows. 2.11.9.1 Plastic Hinges Form at A, C, D, and E

The mechanism is shown in Figure 2.102b. The instantaneous center O for member CD is located at the intersection of AC and ED extended. From similar triangles ACC1 and OCC2, we have

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