Reddy, Dronnadula V.

This dissertation is a study of a 1:3.5 scale model of an externally post-tensioned single cell segmental bridge model of the Long Key bridge. The behavior of the bridge system was evaluated in terms of deflections, strains, joint openings, etc. under static and ultimate load conditions. The precast segmental bridge was cast, assembled, and tested at the Department of Ocean Engineering, Florida Atlantic University for AASHTO HS20-44 truck loadings at typical locations. The study addressed the joint opening behavior and the response of external tendons during service and ultimate load levels. The analytical nonlinear behavior of the bridge upto the ultimate load level has been predicted using a finite element software PCFRAME developed at University of California, Berkeley. Creep and shrinkage strains were predicted using computer program CRACK developed at University of Calgary, Canada. Creep and shrinkage coefficients evaluated from short term tests, were used in predicting the long term behavior. A method for reliability analysis of post-tensioned segmental bridges has also been presented for serviceability and ultimate limit state conditions.

The acoustic emission investigations reported herein are divided into two experimental sets. In the first, the concrete specimens were stressed internally, and the resulting acoustic emissions were monitored. In the second, specimens were subjected to fracture mechanics tests and simultaneously studied for AE signals. For both sets, two kinds of concrete were studied--regular concrete and concrete containing fly ash. The specimens were stressed internally by subjecting them to an accelerated state of corrosion in a marine environment. The corroded specimens were then tested for impact and flexural strengths to study the effect of fly ash replacement on rebar corrosion in a marine environment, and to ascertain any correlation between the monitored AE signals and residual strength. Furthermore, an attempt was made to predict the remaining life of the specimens. For the externally stressed specimens, AE was used to determine the load at initiation of unstable crack propagation terms of ultimate load. These tests have immediate and relevant applications to field problems.

This thesis presents a finite element analysis of the viscoelastic (creep) behavior of a spray ice island under its own self-weight and three levels of lateral loads. Spray ice and its use as a construction material are described in the context of other natural ice forms and the ice environment of the Beaufort Sea. The analytical results indicated that creep settlement in the absence of volumetric contraction was nominal over the course of a simulated 21-day construction period and a 79-day service life. The effects of the applied lateral loads were very localized and did not result in any appreciable deformations in the central working area of the structure. Some evidence of shear plane development and upward passive failure of the island perimeter was observed.

This thesis presents the experimental investigation of durability and fracture toughness (K IC) of fly ash concrete in the marine environment. The findings indicate that the deterioration rate of durability parameters, such as compressive strength, weight loss, and dynamic modulus of elasticity, due to 450 wet and dry cycles exposure (the Accelerated Durability Testing), was inversely proportional to the amount of fly ash replacement. On the other hand, tensile strength properties, such as modulus of rupture and fracture toughness, were independent of fly ash replacement, but increased with the period of accelerated testing. The mean K IC values of fly ash concrete mixes showed that they are closely related to their compressive strengths and size effects. According to AE, unstable crack propagation initiated at 93-97% maximum load. With SEM observations, it was found that crystallized particles were precipitated in the void spaces due to chemical reaction between the cement paste and seawater.

This dissertation is a study of 1:3.5 scale model of a two-span transversely and longitudinally post-tensioned continuous double-tee bridge system, representing a target bridge of 70 ft. span. Theoretical analysis was carried out for comparison using different modelling techniques, such as isotropic and orthotropic material behavior, and the load distribution theory. Behavior of the bridge system was evaluated in terms of deflections, wheel load distributions, crack patterns and growth with increasing number of cycles of fatigue loading. The precast model beams were assembled and tested at the Department of Ocean Engineering, Florida Atlantic University. AASHTO HS20-44 truck loading was simulated by applying constant amplitude fatigue loading at typical locations. The study established the feasibility and structural adequacy of the precast prestressed concrete double-tee concept for short and medium span interstate highway bridges for use in Florida and elsewhere.

This thesis presents an experimental investigation of a 1: 20 scale acrylic model to study the behavior of a multicellular box beam bridge system. The design of a 1: 2 scale concrete model is presented in the early part of the thesis. The acrylic model was tested under simulated AASHTO HS 20-44 loading. The load distribution characteristics of the bridge system was evaluated based on the strains and deflections at various points on the bridge model. The experimental results are presented by transverse distribution curves of strains and deflections for various load locations. Grillage analysis of the bridge system was performed and the results compared well with the experimental values.

This thesis presents an analytical and experimental investigation
of the remaining impact strength of concrete beams with corroding
reinforcement. Concrete beams were subjected to impact using a
centrally loaded instrumented dropweight system. Three different
amounts of steel corrosion were used to simulate ten, twenty, and thirty
years of seawater exposure.
The first part in the analytical investigation involved the use of
the finite element code ADINA. The second included development of three
physical models; the first based on a beam impact equation of forced
vibration for a pin-ended beam with center span impact, the second a
two-degree-of-freedom model, and the third a three-degree-of-freedom
model taking into account the stiffness of the supports for the impacted
beam specimens.
The different analytical results showed good correlation with the
test values of the impact energies. Also, the energy values for the
different corrosion periods obtained from the ADINA analysis compared
well with experimental ones.

Steel reinforced concrete beams were placed in contact with
seawater in a state of accelerated corrosion, for varying
periods of time. Some of them were simultaneously monitored
for acoustic emission and the results were analyzed to
evaluate the effectiveness of acoustic emission as a
non-destructive monitor of corrosion induced damage. It was
shown that, in a laboratory environment, counts are good
indicators of the extent of corrosion damage. A review of
acoustic emission monitoring techniques and theoretical
background is included. The concrete beams were tested for
flexural strength after being corroded. Reduction in rebar
section was found to have a very good correlation with
da mage. An attempt was made to predict remaining life of
the beams based on data obtained from the tests.

This thesis presents the experimental and analytical
investigation of the fiber (steel, glass and Kevlar), and
latex-modified concrete structural members exposed to
varying periods of marine environment.
The findings indicate superior behavior of fibers in
flexure (toughness) and impact. Fibers affect the compressive
strength only marginally. Kevlar fibers are more
stable in the marine environment compared to steel and
glass. The addition of latex significantly improves the
durability characteristics. Endochronic constitutive
modeling enables realistic prediction of beam flexural
behavior.
The smallness of the size and number of specimens
tested indicates the need for further experimentation with
an increased number of members of larger dimensions.

This thesis presents an experimental investigation for evaluating effects of fire exposure on properties of structural elements retrofitted by carbon fiber reinforced polymers. Mechanical properties of CFRP-strengthened reinforced concrete members, protected with secondary insulation, were investigated, before and after (residual) direct fire exposure. Direct fire contact resulted in a reduction in capacity of 9-20% for CFRP-strengthened RC beams, and 15-34% for CFRP-strengthened RC columns. Furthermore, a dimensional analysis was developed for a heat transfer relationship between full and small-scale specimens, allowing a ¼ exposure time reduction for the latter. Results from experimental investigations demonstrate benefits of employing secondary fire protection to CFRP-strengthened structures, in spite of the glass transition temperature being exceeded in the early stages of the elevated-temperature exposure. Therefore, it is suggested, that fire protection is necessary for a CFRP-strengthened structural member to retain integrity throughout the duration of the fire exposure, and upon return to ambient temperature.