All ETDs from UAB

Advisory Committee Chair

Christopher J Waldron

Advisory Committee Members

Vinoy Thomas

Virginia P Sisiopiku

Abdullahi M Salman

Nasim Uddin

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) School of Engineering

Abstract

Considerable damage to the highway bridge system in the Gulf Coast area was observed during the Hurricane Katrina disaster, of which the primary failure mode, caused primarily by the storm-induced loading, is believed to be the superstructure-substructure connection failure which caused further unseating and drifting of the decks. A new Carbon-fiber Interfacial Epoxy-Polyurea Matrix (C-IEPM) composite is investigated as a potential retrofit option for vulnerable girder-to-cap connection-details in coastal highway bridges. Six scaled concrete girders were tested using a modified simulated storm surge and slamming wave force function, derived using regional maps for a 100-year return-period Hurricane Katrina. Two girders, designed using current AASHTO field connection-details, failed catastrophically (concrete shear failure) in less than one-half load cycle. The CF/E-strengthened girder, failing in less than one load cycle, experienced severe damage to its girder-to-cap connection, including fiber and epoxy matrix breakage, delamination, unsustainable girder-end rotations, and transient hysteresis. However, after 12 load cycles, the C-IEPM-strengthened girder, providing substantial energy transferability (material damping) through its connection-details, experienced only local cracking. For a more in-depth understanding of the material C-IEPM and improving material properties, a series of material investigations were conducted in a coupon-scale and nano-scale. Using Generalized Maxwell models, the viscoelastic properties of epoxy, polyurea, and C-IEPM are predicted, and results are verified using Dynamic Mechanical Analysis (DMA). The Maxwell models for x-DCEPI, as a function of tc, are used in a finite element analysis (ABAQUS) to control performance of dynamically loaded structures. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) elucidate interfacial nanoscale morphology and chemical structure via reaction kinetics of curing epoxy (as a function of time, tc) and fast-reacting (pre-polymerized) polyurea. Nano-Infrared Spectroscopy (nano-IR) spectra, per non-negative matrix factorization (NMF) analysis, reveal that simultaneous presence of characteristic epoxy and polyurea vibrational modes, within a nanoscale region, along with unique IEPM characteristics and properties following thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA), indicates chemical bonding, enabling IEPM reaction kinetics, as a function of tc, to control natural bond vibrations and type / distribution of interfacial chemical bonds and physical mixtures, likely due to the bond mechanism between –NCO in polyurea, and epoxide and –NH2 in epoxy hardener (corresponding to characteristic absorption peaks in nano-IR results), leading to enhanced IEPM quality (fewer defects/ voids). Test results of ballistics-resistant panels, integrated with thin intermediate layers of x-IEPM-b-tc, confirm that lower tc significantly enhances loss modulus (∝ material damping and per DMA) in impact dynamics environments.

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