Semester

Spring

Date of Graduation

2019

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

P.V. Vijay

Committee Co-Chair

Ever J. Barbero

Committee Member

Ever J. Barbero

Committee Member

Udaya B. Halabe

Committee Member

Hema J. Siriwardane

Committee Member

Radhey Sharma

Abstract

The civil infrastructure industry has been dominated by traditional materials such as steel, timber, and concrete. Although these materials offer great advantages, they have major durability issues in terms of corrosion, decaying, and cracking. Traditional material-based structures deteriorate frequently and require regular-interval repairs with huge expenditures. To resolve these maintenance and durability issues associated with traditional materials, fiber reinforced polymer (FRP) composites have gained some popularity in the past few decades because of their superior mechanical properties and durability. Carbon-FRPs (CFRPs) and glass-FRP (GFRPs) are the most commonly used FRPs in the market. However, in civil engineering applications, CFRPs are less preferred due to their very higher initial costs compared to that of GFRPs, and thus, GFRPs which are relatively cheaper are preferred in civil engineering applications. GFRPs are used extensively in the repair and rehabilitation of older structures; however, in new construction of civil structures, they have not gained momentum since decades due to their major drawbacks in terms of lower stiffness, lower shear capacity, brittle failure, lack of ductility, and connection issues, apart from their higher initial cost compared to traditional construction materials. This research focuses on hybridizing GFRP beams and bridge-deck panels through embedment of steel plates to improve their overall structural properties for their use in new constructions.

As a preliminary study, a 46”x8.5” multi-cellular GFRP section was manufactured with two embedded 3”x0.375” steel plates using a vacuum assisted resin infusion process. The GFRP-steel hybrid panel was tested in a 4-point and 3-point bending setup; the results showed an increase in bending rigidity (EI) of the hybrid section by 66%, resulting in an improvement in serviceability limit with 38% reduction in deflection. Further, the hybrid section did not show any signs of stiffness or strain energy degradation under fatigue load for 50k cycles. The overall structural performance of the hybrid section was improved with an embedment of two steel plates inside the GFRP composite section.

After successful initial results, the research further focused on steel plates embedded GFRP 6”x6”x0.5” box-beams. The control GFRP and hybrid GFRP-steel box-beam sections were investigated in terms of their bending, shear, and fatigue performance, flexural and shear stiffnesses, bolted connection strengths, failure modes, GFRP-steel interfacial bond behavior, and cost comparison. The 8 ft. long box-beams were tested in a 3-point bending setup at different L/D ratios to characterize the beam’s bending and shear stiffness. The experimental results showed a gain of 270% in flexural stiffness of hybrid GFRP-steel sections. Under fatigue, the hybrid beams did not show any signs of stiffness or strain energy degradation even after three million load cycles. The hybridized sections showed bilinear stress-strain behavior with adequate reserve strength within code specified serviceability limits. The bolt-connected GFRP-steel hybrid members showed increased joint strength and stiffness and ductile failure modes due to yielding of steel plates. The research also discusses the modeling of hybrid box-beams in the finite element modeling (FEM) software to characterize the structural behavior and response of hybrid GFRP-steel sections. The finite element analysis results were found to be clearly matching with the experimental and theoretical results. The GFRP-steel specimens cut from the fatigue-tested hybrid beams were observed through scanning electron microscopy (SEM) to study the GFRP-steel interface and its bond integrity. The GFRP-steel interface regions were examined in terms of degree of resin cure through digital scanning calorimetry (DSC) tests. The cost comparison between GFRP and hybrid sections showed that the initial cost/stiffness of the hybrid section was only about 23% of the initial cost of the equivalent non-hybrid GFRP section.

This research has contributed towards the development of cost-effective hybrid GFRP-steel members that can satisfy higher serviceability limits. The outcome of this work will be beneficial to engineers and designers in using hybrid GFRP-steel composite sections as primary structural members in new construction of buildings, highway bridges, pipelines, navigational gates and other pertinent structures.

Embargo Reason

Publication Pending

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