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Bond behavior of post-installed Glass fiber reinforced polymer (GFRP) rebars

thesis
posted on 2023-06-16, 19:18 authored by Juhi AgarwalJuhi Agarwal

  

Glass Fiber Reinforced Polymer (GFRP) rebars are frequently used to construct offshore structures, bridges, and airport terminals due to their high tensile strength, lightweight, and non-corrosive nature. GFRP rebars are also non-magnetic, electrically non-conductive, and have a higher strength-to-weight ratio than steel rebars. Consequently, many studies have been conducted to investigate the bond behavior of cast-in GFRP rebars, leading to the formulation of ACI 440. 

Post-installed rebar technology has become increasingly popular due to its flexibility in retrofitting and extending existing structures. Given the growing demand for post-installed technology and the superior qualities of GFRP rebars, there is a keen interest in understanding the behavior of post-installed GFRP rebars. Post-installed connections involve inserting a rebar in a pre-drilled hole in hardened concrete using an injectable epoxy. The post-installed system allows for construction between existing and new concrete for structural extension and rehabilitation purposes.

Currently, only limited work has been performed on post-installed GFRP rebars at relatively small embedment depths. The adhesive mortars used for post-installation generally have a high bond strength. Most of the connections with post-installed rebars are made close to the edges of the members. Due to edge proximity, concrete-related failure modes (concrete splitting) govern, and the high bond strength of the post-installed system is not utilized. 

This study aims to understand the bond-splitting behavior of GFRP rebars post-installed using epoxy-based adhesive (DeWalt Pure200+). Experimental and Numerical investigations were conducted with various parameters that influence the bond-splitting. These parameters include but are not limited to, concrete cover, embedment depth, concrete strength, rebar diameter, and transverse confinement. 

An optimal experimental program was designed to test the minimum concrete cover, relative concrete cover, rebar diameter, rebar surface characteristics, and rebar embedment depth. The experimental investigation was carried out in two phases to determine the local bond strength by conducting confined pullout tests away from the edges at shallow embedment depths and the bond-splitting tests at varying parameters. Due to its low transverse strength, a unique grip using a steel pipe grouted with epoxy grout was used for the pullout tests. A new test specimen and test setup were designed to execute the experimental program at deeper embedment depths successfully.

Numerical simulations were then performed using the macroscopic space analysis (MASA) program to investigate additional parameters and cases. The numerical models were first validated using results obtained from experimental investigation. Solid tetrahedral elements were used for modeling concrete elements with microplane models to simulate the damage in concrete. GFRP rebars were modeled using solid hexahedral elements with linear elastic material properties. The connection between concrete-to-GFRP rebar was modeled using 2-node bar elements embedded in the contact layer. The bond-slip curve gives the characteristic properties of the bar elements.

The influence of individual parameters on the bond strength of the post-installed GFRP rebars was calculated, and comparisons were made with existing bond-splitting models for post-installed steel rebars. This thesis presents the details of the experimental program, the test specimen, the test setup, numerical modeling, and the results obtained on the GFRP bars post-installed with different sets of parameters. The studies prove the feasibility of using GFRP bars as post-installed for structural extensions/retrofitting and highlight certain aspects that must be considered while designing such connections.

History

Degree Type

  • Master of Science in Civil Engineering

Department

  • Civil Engineering

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Akanshu Sharma

Additional Committee Member 2

Amit H. Varma

Additional Committee Member 3

Julio A. Ramirez

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