This study was part of a Washington State Department of Transportation (WSDOT) program to assess the vulnerability of multiple-span highway bridges built before 1984. During the first series of static tests (Phase I), discussed in a previous report, a three-span, reinforced concrete bridge was subjected to large lateral loads. In Phase II, described in this report, the researchers greatly reduced the resistance that the abutments provided so that they could evaluate the lateral-load resistance of the piers. The researchers then subjected the piers to large, transverse cyclic displacements with drift ratios of 0.5, 1.0, 2.0, and 3.0 percent.
The piers resisted repeated loadings to a force equal to one third of the bridge's weight. The envelope to the pier's hysteretic response indicated that the system yielded at a drift ratio of 0.7 percent. Whereas the top of the columns spalled at large drift ratios, the damage to the bottom of the columns was limited to flexural cracks. The pier's measured response was compared to that calculated by the researchers, the California Department of Transportation, and the WSDOT. The calculated responses were found to be strongly sensitive to the assumed steel and soil properties.
On the basis of the experience gained in performing the tests, the researchers made recommendations for those planning to perform future tests of large structures. In addition, while acknowledging the limitations of a single series of static tests, the researchers concluded that (1) the tests should serve as a benchmark against which to evaluate proposed analytical models, (2) at an effective acceleration of 0.2g, the seismic damage to the isolated bridge would probably be minor, (3) at an effective acceleration of 0.4g, the piers would likely sustain heavy damage, and (4) the WSDOT should investigate the influence of soil properties on column damage to determine when geotechnical tests are warranted.