CESS Seminar : Strut-and-Tie Method : Recent Advances and US Bridge Design Code Provisions
Abstract
The strut-and-tie method (STM) has become a fundamental approach for designing D-regions in reinforced concrete members for its simplicity, rationality, and conservatism. A comprehensive research program, supported by the Texas Department of Transportation (TxDOT), has further refined the accuracy and applicability of STM to bridge elements through large-scale structural experiments and in-depth analyses across four major aspects: (i) Tri-axially tensioned nodes, (ii) curved-bar nodes, (iii) nodal confinement, and (iv) crack control reinforcement detailing.
The study on drilled shaft reinforcement behavior under tri-axial tension proposed novel design expressions for anchorage and available anchorage length checks, utilizing a 3D fan-shaped compression zone approach observed in tests.
Insights from testing curved-bar nodes within closing knee joints underscored the significance of appropriate bend radius for longitudinal reinforcement at the outside of joints, with proposed design expressions for various scenarios to fully develop the reinforcing bars and prevent premature joint failures.
Deep beam tests revealed a 10% enhancement in nodal zone strength when both nodal zones of a strut are adequately provided with confining reinforcement, alongside of well-defined detailing methods, which are the first reported guidelines in literature for nodal confinement.
Deep beam tests regarding crack control reinforcement spacing advocate for potential modifications in design provisions. Test results suggested relaxation from the current specifications without compromising conservatism while maintaining the STM's predictive ability, reducing congestion, and improving constructability.
Advancing our understanding and refining STM-based design approaches ensures confidence in the application of the STM on reinforced concrete members, thereby potentially influencing future Model Code developments within the International Federation for Structural Concrete (fib).
Short bio
Oguzhan Bayrak is a distinguished teaching professor, holder of the Cockrell Family Chair in Engineering No.20, and a faculty member in the Department of Civil, Architectural and Environmental Engineering at the University of Texas at Austin. His research and teaching interests are related to the behavior, analysis and design of reinforced and prestressed concrete structures, bridge engineering, evaluation of structures in distress, structural repair, and evaluation of aging effects.
Bayrak’s research on concrete bridges has been widely referenced by the American Association of State Highway and Transportation Officials’ Bridge Design Specifications. Notably, the Strut-and-Tie Modeling (STM) design provisions of this document is largely based on the findings developed by Bayrak’s research group.
Bayrak serves as the inaugural director of the Concrete Bridge Engineering Institute (CBEI) at the University of Texas. The mission of CBEI, a national center of excellence, is to serve the concrete bridge community as the leading resource on the most pressing issues encountered in concrete bridges across the U.S. In addition, Bayrak serves as the director of the Phil M. Ferguson Structural Engineering Laboratory at the University of Texas.
Sandwiches are offered at the end of the seminar.
The strut-and-tie method (STM) has become a fundamental approach for designing D-regions in reinforced concrete members for its simplicity, rationality, and conservatism. A comprehensive research program, supported by the Texas Department of Transportation (TxDOT), has further refined the accuracy and applicability of STM to bridge elements through large-scale structural experiments and in-depth analyses across four major aspects: (i) Tri-axially tensioned nodes, (ii) curved-bar nodes, (iii) nodal confinement, and (iv) crack control reinforcement detailing.
The study on drilled shaft reinforcement behavior under tri-axial tension proposed novel design expressions for anchorage and available anchorage length checks, utilizing a 3D fan-shaped compression zone approach observed in tests.
Insights from testing curved-bar nodes within closing knee joints underscored the significance of appropriate bend radius for longitudinal reinforcement at the outside of joints, with proposed design expressions for various scenarios to fully develop the reinforcing bars and prevent premature joint failures.
Deep beam tests revealed a 10% enhancement in nodal zone strength when both nodal zones of a strut are adequately provided with confining reinforcement, alongside of well-defined detailing methods, which are the first reported guidelines in literature for nodal confinement.
Deep beam tests regarding crack control reinforcement spacing advocate for potential modifications in design provisions. Test results suggested relaxation from the current specifications without compromising conservatism while maintaining the STM's predictive ability, reducing congestion, and improving constructability.
Advancing our understanding and refining STM-based design approaches ensures confidence in the application of the STM on reinforced concrete members, thereby potentially influencing future Model Code developments within the International Federation for Structural Concrete (fib).
Short bio
Oguzhan Bayrak is a distinguished teaching professor, holder of the Cockrell Family Chair in Engineering No.20, and a faculty member in the Department of Civil, Architectural and Environmental Engineering at the University of Texas at Austin. His research and teaching interests are related to the behavior, analysis and design of reinforced and prestressed concrete structures, bridge engineering, evaluation of structures in distress, structural repair, and evaluation of aging effects.
Bayrak’s research on concrete bridges has been widely referenced by the American Association of State Highway and Transportation Officials’ Bridge Design Specifications. Notably, the Strut-and-Tie Modeling (STM) design provisions of this document is largely based on the findings developed by Bayrak’s research group.
Bayrak serves as the inaugural director of the Concrete Bridge Engineering Institute (CBEI) at the University of Texas. The mission of CBEI, a national center of excellence, is to serve the concrete bridge community as the leading resource on the most pressing issues encountered in concrete bridges across the U.S. In addition, Bayrak serves as the director of the Phil M. Ferguson Structural Engineering Laboratory at the University of Texas.
Sandwiches are offered at the end of the seminar.
Practical information
- Informed public
- Free
Organizer
- Prof. Olga Fink (IMOS), Prof. Alexandre Alahi (VITA), Prof. Dusan Licina (HOBEL), Prof. Alain Nussbaumer (RESSLab)
Contact
- Dr David Fernández-Ordóñez (fib)