The strength and ductility of concrete under uniaxial compressive load are dominantly influenced by transverse confinement of core concrete. Confined concrete with transverse reinforcement is influenced by numerous variables such as compressive strength of concrete, yield strength and volumetric ratio of transverse reinforcement. In oder to ensure effective designs of transverse reinforcement in concrete columns, it is necessary to produce accurate predictions for stress-strain relationships of confined concrete.
In this study, two analytical models are proposed in this paper to predict the stress-strain relationship of confined concrete with spiral reinforcements. The first analytical model predicts the stress-axial strain relationship of confined concrete based on the Poisson’s ratio at peak stress of confined concrete with spiral reinforcements. The second analytical model, which incorporates the strain characteristics of confined concrete, predicts both the stress-axial strain relationship and stress-lateral strain relationship of confined concrete by evaluating the influence of spiral reinforcements on core concrete using the Poisson’s ratio-axial strain relationship of confined concrete under uniaxial compressive load.
The analysis results produced from the proposed analytical models were compared with previous experimental test result to verify the validity and accuracy of the proposed models. The research methods and procedures are as follows.

This dissertation consists of five chapters. Chapter 1 provides the research background, objective, and necessity of the study.

Chapter 2 introduces existing theories on the behavior of confined concrete with transverse reinforcement, and describes how the proposed analytical models can be differentiated from past research.

In Chapter 3, a Poisson’s ratio model at peak stress of confined concrete proposed, and verifies the validity and accuracy of the proposed model through the comparison of experimental and analytical results for stress-axial strain behavior of confined concrete.

Chapter 4 proposes a strain characteristic model capable of predicting the stress-axial strain behavior and stress-lateral strain behavior of confined concrete, and verifies the accuracy of the proposed model through the comparison of experimental results with those of the proposed model.

Chapter 5 concludes the dissertation with a quantitative evaluation of experimental and analytical results for the stress-strain behavior of confined concrete.

The conclusions obtained from this dissertation are as follows.

1. Compared to experimental results for axial strain at peak stress of confined concrete with spiral reinforcement, the analytical model based on the Poisson’s model at peak stress showed high accuracy with an average of 1.01 and a coefficient of variation of 21.3%. It is because that the stress of spiral reinforcement based on the Poisson’s model was accurately predicted with an average of 0.95 and a coefficient of variation of 18.3%.

2. The analytical model, which incorporates stress of spiral reinforcement at peak stress of confined concrete using the proposed Poisson’s ratio model, produced accurate predictions with an average of 1.01 and a coefficient of variation of 10.6%.

3. The stress-axial strain relationship of confined concrete was very accurately predicted by applying the stress of spiral reinforcement at peak stress, derived from the analytical method based on the proposed Poisson’s ratio method, to the equation for peak stress of confined concrete and axial strain at peak stress. The Poisson’s ratio model at peak stress can be considered a highly accurate model in predicting the behavior of confined concrete.

4. The proposed strain characteristic model was found to produce very accurate predictions for the Poisson’s ratio-axial strain behavior of confined concrete, which is under the influence of numerous variables such as compressive strength of concrete, yield strength and volumetric ratio of spiral reinforcement.

5. The strain characteristic model, capable of predicting strain relationships between spiral reinforcement and core concrete, gave very accurate predictions for axial strain at peak stress of confined concrete with an average of 1.01 and a coefficient of variation of 27.1%. The strain characteristic model produced accurate predictions for the yield point of spiral reinforcement with an average of 0.94 and a coefficient of variation of 16.4%.

6. In this study, two analytical methods to predict the behavior of confined concrete with spiral reinforcement were proposed, and the accuracy and reliability of the proposed methods were verified through experiments.

The proposed behavior prediction models for confined concrete with spiral reinforcement are able to predict stress and strain of spiral reinforcement that confines concrete until the collapse under compressive strength. By conducting further studies with consideration of main reinforcement and cover concrete, the proposed models can lead to the establishment of more diverse and accurate design conditions for yield strength and minimum reinforcement ratio of spiral reinforcement, which are currently subject to concrete structure design code.