Nonlinear Real-Time Hybrid Test of a Two Story, Two Bay Structure

Overview of Hybrid Test Structure

On March 2, 2005 a Fast Hybrid Test was carried out on the structure illustrated above in the NEES Laboratory at the University of Colorado. This structure was subjected to approximately 78 percent of the El Centro base motion in the x or shearing direction, as recorded on May 18th, 1940 in the Imperial Valley of California.

The analytical substructure, shown in blue, was modeled in 2 dimensions utilizing nonlinear beam-column structural elements for all vertical members and linear-elastic structural elements for all horizontally oriented elements. These are standard elements contained within the library of structural components in OpenSees. All Degrees of Freedom (DOF) for the base of the structure were fixed, that is DOFs numbers 1, 2, 3, 10, 11, 12, 19, 20 and 21.

The test was carried out in real-time with no temporal distortion of the recorded El Centro base motion. The substructure physically tested is shown in red above and is captured in the video clip that may be replayed below. Displacement continuity and force equilibrium were maintained at DOFs 13, 14 and 15 between the analytical (blue) substructure and the experimental (red) substructure. These conditions were maintained and the test was carried using a special adaptation of the alpha method (Hilbert, Hughes and Taylor) which is central to the FHT system at CU.

Experiment Video

The video clip on left features the W8x35 physical specimen being subject to an 78% scaled real-time test using the El Centro earthquake ground motion. During the test, the bolts attaching the I-beam to the lower reaction fixture yielded under the 90,000 lbs shearing force. The yielded bolts allowed the I-beam to displace on the reacture fixture resulting in the loud "popping" sound that can be heard in the video clip.