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0-7039, The strut-and-tie method (STM) is a reliable and widely used approach for designing reinforced concrete members, but there are still gaps in knowledge that need to be addressed to optimize its use in common design scenarios. Addressing these gaps would lead to more efficient and cost-effective design solutions. This requires additional experimental data to inform design codes and practices related to key areas, such as tri-axial tension anchorage, curved-bar nodes, confining reinforcement in nodal zones, and crack control reinforcement spacing. Chapters 3-6 of the research report describe the experimental investigations conducted to address some of these knowledge gaps. Chapter 3 presents insights into the behavior of drilled shaft reinforcement under tri-axial tension and the validity of the design recommendation. Chapter 4 investigates the effect of the bend radius on the behavior of closing knee joints and recommends an equation for designing curved-bar nodes. Chapter 5 examines the effect of nodal zone confinement on nodal strength, concluding that effective confining reinforcement can increase nodal strength. Lastly, Chapter 6 investigates the possibility of relaxing crack control reinforcement spacing and recommends a new maximum spacing. Overall, the research findings provide valuable insights into the behavior of reinforced concrete members and suggest improvements for STM design practices.

0-7039, The strut-and-tie method (STM) is a simple and widely used method for designing D-regions in reinforced concrete members. Despite its incorporation into major design codes and continuous refinement over the past century, there are still areas that require further research. These include the use of 3D strut- and-tie models for designing drill shaft footings under eccentric axial loads, the use of curved- bar nodes in closing knee joints, the provision of appropriate confinement to enhance nodal strength, and the relaxation of the “d/4 limit” on crack control reinforcement spacing based on experimental data. Addressing these knowledge gaps would improve the applicability and cost- effectiveness of STM in reinforced concrete deep member design.