Project Details

Executive Summary
In the design and analysis of reinforced concrete deep beams, such as bridge bent caps, the use of sectional design methods may result in unnecessarily conservative structures. The application of strut-and-tie procedures can result in more efficient structural designs that also better represent the load carrying mechanisms of the members. The research needing investigation, is to identify typical bridge bent caps for North Carolinian bridges and develop specific strut-and-tie design procedures for these members. Given the complexities associated with strut-and-tie procedures, the investigation will also develop practical tools that the Department can use when conducting such design and analyses. The investigation will examine how the Department's current design practices compare with the proposed procedures. For typical member typologies, several large-scale experiments will be conducted to verify and validate the recommended procedures and tools at various limit states. The procedures will be developed so that they can ultimately be implemented into the existing NCDOT design software and design workflows.

The overall research objective is to develop strut-and-tie procedures for the design and assessment of bridge bent caps in North Carolina. The research objective is to tailor these guidelines for use by the NCDOT in the context of typical members. The overall research objective is to develop procedures that result in more efficient structural designs for deep beams that are also more representative of the stress distributions in the members. Achieving these overarching research objectives will ultimately lead to more ubiquitous use of strut-and-tie procedures for members other than bent caps.

                  Recent deep beam test conducted at the CFL, NCSU​

To accomplish these holistic objectives the following five specific objectives and their corresponding tasks will be conducted:

1. Identify typical deep beam bent caps that are appropriate for design by strut-and-tie methods.
2. Develop procedures and guidelines for the design of deep beam bent caps with rigorous validation and verification using nonlinear finite element software.
3. Conduct a critical analysis of the differences between the proposed design approach and corresponding designs with the existing methodology and corresponding designs.
4. Conduct large-scale experiments to assess the performance of typical members designed using the proposed strut-and-tie procedures.
5. Formulate the proposed design guidelines and procedures in a manner conducive to implementation in the NCDOT workflow and existing design software.

 The research products that will result from these tasks includes:

1. Procedures to conduct strut-and-tie design and analysis of bridge bent caps for typical typologies identified.
2. Nonlinear finite element analysis results for typical bent cap typologies and designs, including predicted performance at service and ultimate loads.
3. Results from large-scale experiments of representative bent cap designs using the proposed procedures.
4. Recommendations for changes to the Structure Management's Design Manual Guidelines and overall Structures Management Unit policies.
5. Guidance and documentation for the implementation of the developed procedures into existing NCDOT design software and workflows.
6. Design examples and associated workshops to explain the procedures and processes developed.