Bridge design approaches are increasingly based on a displacement performance philosophy using static pushover analysis. This type of bridge design requires an estimate of the passive force-displacement relationship for abutments and pile caps. Proper modeling of the abutment load-displacement relationship is critical and the assumptions regarding the stiffness and the hysteretic and geometrical damping of the abutment have been shown to have profound effects on the global seismic response and performance of the bridge. Various design recommendations are given for the passive force-deflection relationships for abutments and pile caps. Limited research suggests that resistance is substantially greater and that some design recommendations are leading to costly increases in the number of piles to handle lateral load. In addition, various pile cap connections are presently used but very little guidance is available to define how these connections affect ultimate resistance and stiffness relationships. Connections are often designed as 'fixed' or 'pinned,' but actual performance of these connections is uncertain. In some cases, specifications call for limited compacted backfill around bent pile caps, but it is unknown how this will reduce the passive resistance relative to complete backfill. Finally, design recommendations often ignore increased resistance due to damping which could also lead to greater economy and existing damping values are based on small strain tests. Full-scale dynamic tests can provide answers to these design issues and lead to significant cost savings and improved design.

1. Develop passive force-deflection relationships for static and dynamic loads 2. Measure damping coefficients for pile caps and backfills as a function of displacement. 3. Determine the effect of pile cap connection details on abutment stiffness. 4. Evaluate existing design recommendations and develop modifications to improve prediction of measured response

Task 1-Literature Review and Collection of Existing Test Data Collect available test results involving pile-cap connection details. Assemble existing large-scale test results involving passive force-deflection relationships for static and dynamic tests on pile caps or abutments. Summarize current AASHTO and relevant state DOT design procedures. Task 2-Pile Cap Testing to Evaluate Connection Details Four common pile-cap connection details will be evaluated with full-scale field tests. Connection details will range from 'pinned' conditions to 'fixed' conditions. Each pile cap will be connected to two 12 inch steel pipe piles which were previously driven for pile group testing and are available for use in this study. Load, deflection, rotation and strain measurements will be made during each test. Measurements will allow development of stiffness-rotation relationships. Task 3-Pile Cap Testing to Determine Static and Dynamic Passive Force-Deflection Relationships Construct pile caps for testing which have different width/height ratios from previous test and typical connection details. Again, full-scale pile groups are available from previous testing at no cost. Perform static and dynamic lateral load tests on the pile caps with and without backfill in place to evaluate the force-deflection curve for backfill materials. Static loads will be applied in increments using two 650 kip actuators. At each deflection increment, dynamic loading will be carried out with 100 kip capacity eccentric mass shakers to evaluate damping at a variety of strain levels. Tests will be performed over a range of frequencies. Tests will be repeated with granular backfill extending to progressively greater distances from the pile cap until the full failure zone is contained within the backfill. If funding permits, tests will also be conducted will MSE walls containing each side of the backfill. Task 4-Analysis of Test Results Reduce the test data. Develop stiffness vs. rotation curves for the various pile-cap connection details. Determine ultimate passive force. Develop static and dynamic passive force-displacement relationships for the various tests. Evaluate variation of passive force-displacement relationships as a function of soil type, cycling and frequency, etc. Determine change in passive force as a function of partial compacted backfill relative to the complete backfill condition. Determine damping factors as a function of displacement level soil type, etc. Evaluate factors to account for 3-D or end shear effects for pile caps with various dimensions. Task 5- Evaluate Existing Methods and Recommend Improvements Compare the measured test results from this and other studies with available design methods for predicting response. For example, compare measured ultimate passive force with various earth pressure theories (Rankine, Coulomb, log-spiral, etc.) to determine best approach. Compare passive-force displacement relationships with those recommended by Caltrans, Mokwa and Duncan, Shamsabadi, etc. and determine best approach. Evaluate measured damping ratios with ratios predicted using small-strain vibration theory. Develop modifications or new simple approaches, where necessary, to improve the agreement. Task 6-Prepare Final Report A final report will be prepared detailing the testing procedures, test results, analysis methods, as well as comparisons between measured and computed response. The report will contain an implementation summary describing recommended design approaches and appropriate example calculation procedures.

Specialized dynamic testing equipment and personnel will be mobilized to Utah from California during summers 2005 and 2006 for a related study funded by NSF which reduces the cost of testing. Tests in this study will be performed to compliment the results from the NSF study with different pile cap dimensions, soil conditions, connection details. Sponsor Contact: Daniel Hsiao, 801-965-4638, dhsiao@utah.gov Technical Contact: Kyle Rollins, 801-422-6334, rollinsk@byu.edu