Experimental Investigation of P-Delta Effects to Collapse During Earthquakes
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This report addresses structural safety and the risk of damage, by determining the collapse performance limit in engineering terms. It documents an experimental study of the P-delta effect on a Single Degree of Freedom (SDOF) test structure subjected to earthquake ground motion. Fifteen four-column frame specimens were subjected to progressive unidirectional ground shaking and structural response was measured up to collapse. An example of how to use the experimental data for analytical model verification is provided. A full series of tests with a single specimen were analyzed using a simple SDOF dynamic analysis program. The example illustrated the shortcomings/inaccuracies of a particular simplified model of structural damping. Test structure performance was compared with proposed limits for minimizing P-delta effects in highway bridge piers. The stability factor was found to have a strong relationship to the relative structural performance in this regard. Performance was also compared with currently used strength, and stability limits for axial-moment interaction. Specimens generally reached accelerations and, maximum base shear (as a fraction of the system's weight) in excess of the maximum spectral accelerations calculated considering second order effects, but less than that considering only member strength.