Geotechnical engineers estimate foundation movements to design bridge foundations and report their findings to the bridge designer. The bridge designer will then evaluate total movements, including differential movements that can be tolerated to satisfy post-construction bridge performance and to mitigate future maintenance issues. However, the current AASHTO LRFD Bridge Design Specifications do not provide clear criteria for movement limitations. The Specifications indicate that “the tolerable movement criteria shall be established by either empirical procedures or structural analyses or by consideration of both”. Clear criteria and guidance are needed to ensure more efficient bridge designs while protecting the short and long-term integrity of structures.
The objectives of this research are to (1) develop a framework to determine the acceptable levels of bridge foundation movements based upon structure tolerance to total and differential movements considering service and strength limit states, and (2) propose revisions to the AASHTO LRFD Bridge Design Specifications. Foundation movement shall include vertical, horizontal, and rotational movements.
Accomplishment of the project objectives will require at least the following phases.
PHASE I—Literature Review, Proposed Framework, and Updated Work Plan
Deliverables in this phase shall include:
1. A critical review of existing specifications, technical literature, owner experiences, and ongoing research. The review should cover research findings from both foreign and domestic sources.
2. A proposed framework, to be developed in Phase II, to analyze and determine the acceptable levels of bridge foundation movements based upon structure tolerance to total and differential movements considering service and strength limit states. Foundation movement shall include vertical, horizontal, and rotational movements. The framework should include a detailed modeling matrix. The matrix should represent movement criteria; bridge system model parameters (e.g., common deck superstructure, skew and curvature effects, material properties, and short- and long-term settlement, loading scenarios, simple and continuous spans, span lengths, and the flexibility of the foundations); and method of analysis (e.g., 2D, 3D, linear, and nonlinear).
3. A detailed outline identifying the proposed areas of the specifications that will require modification or addition.
4. Interim Report No. 1 that documents deliverables 1 through 3 of Phase I and provides an updated work plan for the remainder of the project no later than 4 months after contract award. The updated plan must describe the process and rationale for the work proposed for Phases II through IV.
PHASE II—Framework Development and Evaluation
Based on the approved work plan, develop the proposed framework. Prepare Interim Report No. 2 that documents the framework development with the supporting parametric studies and also includes an updated work plan on Phases III and IV no later than 18 months after Phase I approval.
PHASE III—Specification Revision Recommendations
Develop recommendations for revising existing AASHTO LRFD Bridge Design Specifications and explain the effects of the proposed revised specifications on bridge performance.
PHASE IV—Final Deliverables
Prepare and submit project deliverables including a final report that documents the entire research effort, and other items identified in the research plan. The proposed revisions to specifications and commentary shall be provided in AASHTO format.
STATUS: A decision was made to discontinue work on the project beyond Phase I. The remaining work will be conducted under NCHRP Project 12-103.