| Popis: |
Bent substructure systems are being used increasingly in bridge construction. Among the various bent systems, pile bents are considered a popular choice due to their effectiveness in reducing time and cost. They are constructed by first driving piles to a specified elevation above the ground surface. Then, a cast-in-place reinforced concrete bent cap ties the piles together at their top end. The current Louisiana Department of Transportation and Development Bridge Design Manual provides guidelines for the structural analysis and construction details for general use in the preparation of plans for pile bents. The manual allows the use of a simplified method in which ranges of allowable axial compressive loads for different pile sizes can be used in selecting a recommended pile size once the pile axial load is known. The procedure requires axial load demands to be determined due to dead and live load effects only. However, at high wind velocity or as bridge spans become larger, lateral loads and moments acting on the pile increase and cannot be neglected. Therefore, identifying limitations on the use of the simplified procedure is the main motivation behind this research. This study makes an endeavor to analyze many bridges that cover a wide design space including different span lengths, unsupported pile lengths, skew angles, and pile-cap continuity. The bridges are supported on pile bents to investigate the applicability of the simplified design procedure under different limit states. The pile sizes and layouts for the bridges of different configurations were selected considering the existing guidelines. The scope of this study is to determine the load and moment demand on the piles using refined analyses. The capacity of the piles was then determined taking into account the interaction between axial loads and flexure. Based on the results, the capacity utilization for each pile was determined and used to investigate the limitations on the use of simplified method. The results show that the simplified procedure should not be universally used for pile design. At high wind velocity (Strength III limit state) the procedure results in unsafe designs. A summary of the limitations was mapped for the 128 bridge cases considered in this study for pile caps with two pile-to-cap continuity assumptions. Recommendations for future research have been identified to further refine the simplified design procedure. |
