As the North Carolina Department of Transportation (NCDOT) explores the use of fiber reinforced polymers (FRP) in its structures, there is a need to further investigate the use of FRP in substructure components that are considered disturbed regions, such as bent caps and footings. When these substructure components are constructed with conventional steel reinforcement, they can corrode, leading to early and costly repairs or replacement, particularly in coastal environments. The use of internal FRP reinforcement in substructure components eliminates the need for costly interventions resulting from steel corrosion and can greatly increase the service-life of these structures.
This proposal will focus on developing design and assessment procedures for concrete bridge substructure disturbed regions utilizing FRP. In the design and analysis of reinforced concrete deep beams, such as bridge bent caps and footings, the use of sectional design methods results in unnecessarily conservative structures. The application of strut-and-tie methods often results in more efficient structural designs that better represent the load carrying mechanisms of the members. However, these procedures are based on various implicit assumptions that did not originally contemplate the use of longitudinal and/or transverse FRP reinforcement. Additionally, existing AASHTO LRFD methods for the design of deep beams using strut-and-tie methods are general in nature, and not tailored to the structural typologies typically used by NCDOT.
The proposed research will investigate the use of internal FRP for both longitudinal and transverse reinforcement, and will develop recommended design procedures for typical bridge substructure components in North Carolina.
The overall research objective is to develop recommendations and procedures for the design and assessment of deep FRP reinforced concrete substructure components in North Carolina. The following is a detailed list of research objectives:
- Identify candidate bridge substructure components that the NCDOT uses, are classified as deep beams, and are strong candidates for implementing internal FRP reinforcement.
- Conduct several large-scale experiments to investigate the response of deep members designed using FRP (CFRP and GFRP) for both the longitudinal and transverse reinforcement.
- Conduct nonlinear finite element modelling to supplement experimental results.
- Develop procedures for the design of FRP reinforced deep beams based on the AASHTO LRFD strut-and-tie method.
- Provide recommendations that can be implemented into the NCDOT workflow for the design of bridge substructure components with FRP reinforcement.
These anticipated research products will result from completion of the proposed tasks:
- Procedures to conduct strut-and-tie design and analysis of deep FRP reinforced bridge substructure components for candidate and common structures identified.
- Nonlinear finite element analysis results for FRP reinforced substructure component designs including predicted performance at service and ultimate loads.
- Results from large-scale experiments of representative component designs.
- Recommendations for changes to the Structure Management Unit Design Manual and overall Structures Management Unit policies.
- Guidance and documentation for the implementation of the developed procedures into existing NCDOT workflows.
- Design examples and associated workshops to explain the procedures and processes developed.
