Swoo-Heon Lee

External Posttensioning of Reinforced Concrete Beams Using a V-Shaped Steel Rod System

This study presents the development of an analysis method to predict the moments at first yielding and at ultimate strength of reinforced concrete beams strengthened using a V-shaped posttensioning steel rod system. The analysis requires determination of a total elongation of the external posttensioning rods, which is interdependent upon the neutral axis depth, deflection, and strains and stresses in beam components at both internal steel yielding and ultimate strength stages. The iteration algorithm was computationally programmed. The test results from a total of 14 full-scale beams were used to verify the analysis method that predicts the yield moment, moment capacity, and corresponding unbonded steel rod stresses. Finally, a flexural design method is developed for reinforced concrete beams externally posttensioned using a V-shaped steel rod system.

Shear Strength of Externally Post-Tensioned Concrete Beams

This paper shows the test results of continuous reinforced concrete beams with external post-tensioning rods. Six three-span beams were prepared and tested to fail. Three beams were designed to have flexure-dominating behavior and the others to have shear-critical behavior. In each group, one beam without external post-tensioning rods was designated as a control beam and two beams had the external post-tensioning rods of 18 mm or 22 mm diameter. External post-tensioning rods were installed within an interior span of 6000 mm. They show V-shaped configuration because two anchorages were located at the top of interior supports and a saddle pin at mid-span was installed at the bottom of the beam. Test results show that the load and shear capacities of strengthened beams were increased when compared with the control beam. Additionally, the measured shear strength was compared with the strength predicted by ACI 318-11 code equations. The detailed ACI 318-11 equation predicted the measured shear strength and failure location of the continuous beam reasonably well.

Flexural Analysis of Full-Scale RC Beam Strengthened with Steel Rods

This paper presents an analytical method of evaluating the flexural behavior of RC beams externally strengthened with unbonded high-tension steel rod. A simple summation method proposed in this paper basically assumes that the total strength of RC beams strengthened with rod is equal to the sum of the strength of RC beam and the strength of rod. The strengthening steel rods connected to beam with U and V shape profile are considered as a truss system for the analysis. This analytical method also includes the effect of compressive force applied to RC beam due to the tension of rod as well as the effect of effective prestress in steel rod. A comparison of the analytical and experimental results leads to the conclusion that the simple summation method can simulate the flexural behavior of RC beam strengthened with rod with a good level of accuracy.