Eigen analysis of a two-story shear frame

Example Provided by: Vesna Terzic, UC Berkeley

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This example demonstrates how to perform eigenvalue analysis and plot mode shapes. Two-storey shear frame (Example 9.1a from "Dynamic of Structures" book by Professor Anil K. Chopra) is used for this purpose. Geometry and material characteristics of the frame structure are shown in Figure 1. Node and element numbering is given in Figure 2.

Instructions on how to run this example

To execute this ananlysis in OpenSees download this file: EigenAnal_twoStoreyShearFrame.tcl

To run this example, place the OpenSees.exe to the same directory with the downloaded file. By double cliking on OpenSees.exe the OpenSees interpreter will pop out. To run the analysis the user sholud type "source EigenAnal_twoStoreyShearFrame2-1.tcl" in OpenSees interpreter and hit enter. To create output files of eigenvectors (stored in directory "modes") the user has to exit OpenSees interpreter by typing "exit".

equalDOF

Create the model

Spatial dimension of the model and number of degrees-of-freedom at nodes are defined using model command.

In this example, the beams and columns of the frame are defined elastic.