Sugyu Lee

Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Civil Engineering


Civil Engineering

First Advisor

Seyedali Abolmaali


This dissertation focused on development of new carbon fiber joint systems for all types of underground gravity and sewer pipe systems. Specifically, the external CFRP wrap and, particularly, the carbon fiber reinforced polymer (CFRP) internal coupler can be used for concrete pipes with regular or reduced wall thicknesses. The concrete pipes with reduced wall thickness are classified as semi-rigid pipe and are referred to as thin-wall (TW) concrete pipe. The performance of the CFRP coupler is presented in this report based on full-scale experimental tests and three dimensional non-linear finite element studies for regular and thin wall pipes. Finally, design equations and contour guidelines are presented for the CFRP internal couplers. This study was conducted with three Phases: (1) Phase I focused on joint performances of Carbon Fiber Reinforced Polymer (CFRP) sheet externally wrapped with different widths (3, 6, 9, and 12 in.) and curing time of epoxy chemicals in ambient temperature of 72 and 99 Fahrenheit degrees; (2) Phase II focused on experimental tests on the CFRP internal coupler with joint shear and hydrostatic tests in accordance with ASTM C497-16a. This phase also included the development of three dimensional non-linear finite element method (FEM) analyses of CFRP internal coupler for parametric studies. Additionally, a series of material tests with different thicknesses were conducted for obtaining accurate non-linear material properties for the use in the analysis algorithm. After several experimentations with types of sealants, it was shown that the CFRP internal coupler is water tight based on ASTM C497-16a; and (3) Phase III focused on experimental testing of various inside diameters of TW concrete pipes (48, 54, 72, and 84 in.) with the CFRP internal couplers. Furthermore, the modification of the developed FEM models for the large diameter joint shear tests and derivation of design equations and guidelines of the CFRP internal couplers was one of the main themes in Phase III. To evaluate structural performance of the joint systems using the CFRP sheet, eight (8) full-scale externally wrapping joint shear tests and eleven (11) full-scale CFRP internal coupler (CFRP Coupler) joint shear tests were performed in accordance with the ASTM C497-16a. The external CFRP wrapping joint of 3 in. width met the aforementioned ASTM standard of shear strengths. The evaluation of epoxy chemical and its curing time indicated that at least 3 hours was required for curing in order to provide bond between the CFRP fabric material and concrete pipe. The effects of various CFRP internal coupler thicknesses (0.0625, 0.125, 0.1875, 0.25, and 0.375 in.) were investigated based on performance evaluations during testing for different internal diameters of TW concrete pipes (36, 48, 54, 72, and 84 in.). It should be noted that since the CFRP internal coupler targets internal diameter for a given pipe, a distinction between regular (conventional) wall thickness concrete pipe and the novel thin wall concrete pipe should not be made. In another word, the CFRP internal coupler can be used for both types of pipes. The joint shear test results showed that an average of 20.5% higher coupler shear strength was obtained by using CFRP internal coupler when compared with the requirements of ASTM C497. A total of 243 parametric cases was performed by using the experimentally verified FEM analyses in order to develop design equations which could predict the behavior of the joint shear tests for the CFRP internal coupler based on internal diameter, coupler width, and coupler thickness. Finally, Four-dimensional design contour plots for CFRP internal coupler were developed.


Design of joint system, Infrastructure, Concrete pipes, Finite element method


Civil and Environmental Engineering | Civil Engineering | Engineering


Degree granted by The University of Texas at Arlington