Strengths of Struts and Nodal Zones for Strut-and-Tie Model Design of Reinforced Concrete Corbels

Youjong Lee,Young Mook Yun

doi:10.28991/cej-2021-03091725

Abstract

The strut-and-tie model (STM) method is useful for the limit state design of reinforced concrete (RC) corbels. However, for the rational design of RC corbels, designers must accurately determine the strengths of concrete struts and nodal zones to check the strength conditions of a selected STM and the anchorage of reinforcing bars in nodal zones. In this study, the authors suggested a numerical process for determining the strengths of concrete struts and nodal zones in RC corbel STMs. The technique incorporates the state of two-dimensional (2-D) stresses at the strut and nodal zone locations, 2-D failure envelope of concrete, deviation angle between the strut orientation and compressive principal stress trajectory, and the effect of concrete confinement by reinforcing bars. The authors also proposed the strength equations of struts and nodal zones that apply to the typical determinate and indeterminate STMs of RC corbels. The authors considered the effects of the shear span-to-effective depth ratio, the horizontal-to-vertical load ratio, and the primary tensile and horizontal shear reinforcement ratios in developing the strength equations. The authors predicted the failure strengths of 391 RC corbels tested to examine the appropriateness of the proposed numerical process and strength equations. The predicted failure strength compares very well with experimental results, proving that the rational analysis and design of RC corbels are possible by using the present study's strut and nodal zone strengths. Doi: 10.28991/cej-2021-03091725 Full Text: PDF

Highlights

reinforced concrete (RC) corbel is a representative structural member with static discontinuities due to the concentrated vertical and horizontal loads
For the safe and economical design of RC corbels using the strut-and-tie model (STM) methods, designers must accurately determine the strength of concrete struts and nodal zones
The authors suggested a numerical process for determining the strengths of concrete struts and nodal zones in RC corbels

Summary

Introduction

RC corbel is a representative structural member with static discontinuities due to the concentrated vertical and horizontal loads. It is inefficient to implement in practice since the method requires very complicated numerical calculations and iterative 3-D finite element linear analyses of unreinforced concrete members and selected STMs. strength values of concrete struts and nodal zones applicable to all general cases must be provided for the rational STM design of structural concrete. The process requires numerical calculations and iterative linear elastic finite element analyses of disturbed regions and selected STMs. for use in practice, the authors developed the strength equations of concrete struts and nodal zones for previous studies' typical corbel STMs. The authors examined the validity of strength equations by predicting 391 RC corbels' failure strengths with the typical STMs. In Section 2 of this paper, the authors introduced three types of statically determinate and indeterminate corbel STMs that designers employ in practice.

Strut-and-Tie Model

Strength Equations of Design Codes

Strength of Present Study

Verifications

Strength Prediction Using Determinate STMs

Strength Prediction Using Indeterminate STM

Conclusion

Findings

Author Contributions