MS, University of Cincinnati, 2024, Engineering and Applied Science: Civil Engineering

The study summarizes a comparative analysis of three partial debonding guidelines: AASHTO 8th edition, AASHTO 9th edition, and recommendations of NCHRP 12-91 project presented in NCHRP 849 report. For this purpose, 570 prestressed bridge girders, encompassing different shapes, were designed. In these designs, only partial debonding was employed to control extreme fiber concrete tensile stresses. Debonding requirements were substantially changed in AASHTO 9th edition. The research presented herein was conducted to assess how the new debonding provisions would impact the maximum possible span length and whether shallower girders and/or wider girder spacing can be used for similar scenarios. In comparison to AASHTO 8th edition, AASHTO 9th edition guidelines were found to allow span length to be increased by as much as 25 ft, girder depth be reduced by up to 24 in., and girder spacing be increased by up to 4 ft. The provisions of AASHTO 9th edition are more stringent than the recommendations made in NCHRP research report 849. In comparison to AASHTO 8th edition, NCHRP guidelines were found to allow span length to be increased by as much as 35 ft. In terms of girder depth reduction and girder spacing increase, no difference was found between AASHTO 9th edition and NCHRP report recommendations compared to AASHTO 8th edition. Most bridges selected in the study were impacted in terms of span length, girder depth, and girder span by using AASHTO 9th edition instead of AASHTO 8th. The difference between AASHTO 9th edition and NCHRP 849 recommendations was limited to fewer cases.

Committee: Bahram Shahrooz Ph.D. (Committee Chair); William Potter M.S. (Committee Member); Richard Miller Ph.D. (Committee Member) Subjects: Engineering

MS, University of Cincinnati, 2021, Engineering and Applied Science: Civil Engineering

The LRFD Bridge Design Specifications (LRFD-8) govern the design and construction of prestressed concrete bridge girders in the United States and currently does not address the use of prestressing strands larger than 0.6-in. dia. Larger, 0.7-in. dia. strands have the potential to permit longer spans, shallower girder depths, and/or less congested cross-sections. Relatively few studies have been performed on full-scale beams utilizing the larger strand. Further research is required to investigate how the provisions of LRFD-8 apply to 0.7-in. dia. strands, and if changes are needed to accommodate the use of the larger strand. In this thesis, the performance of full-scale bridge girders was investigated with respect to key provisions of LRFD-8. Various cross-sections, concrete strengths, reinforcement levels, and debonding levels were tested to investigate effects on (1) transfer length, (2) development length, (3) end-zone confinement performance (4) flexural behavior, and (5) shear behavior. To investigate these issues, 12 full-scale girders were fabricated and tested to failure; these tests are reported here. The results of these tests indicate that the LRFD-8 provisions for transfer and development length are conservative for 0.7-in. dia. strands – as they are for smaller diameters. Measured girder capacities exceeded the LRFD-8 predicted capacities, except where confinement reinforcement was not sufficiently extended beyond the debonding termination point. While some states require confinement to be extend further in the presence of debonded strands, LRFD-8 only requires confinement reinforcement to extended 1.5d from the girder end. Extending confinement reinforcement 1.5d beyond the debonding termination point improved ductility and performance at extreme load levels in girders with debonded strands.

Committee: Bahram Shahrooz Ph.D. (Committee Chair); Kent Harries Ph.D. (Committee Member); Richard Miller Ph.D. (Committee Member) Subjects: Civil Engineering

PhD, University of Cincinnati, 2020, Engineering and Applied Science: Civil Engineering

Partial strand debonding is an option for reducing extreme-fiber concrete tensile stress and splitting forces in the end regions of pretensioned concrete beams. The prestressing force in partially debonded strands is transferred to the concrete at a distance from the end regions. In this manner, the total prestressing force is introduced to the member gradually, thereby reducing stress concentrations and associated cracking at the beam ends. Debonding of strands is easily and economically accomplished and can be used where harping is not practical (due to girder shape or fabrication infrastructure) or in combination with harping. Excessive debonding, however, can reduce the flexural and shear capacity near the beam ends as the local tensile resistance provided by prestressing reinforcement is reduced. The concrete component of shear strength is also reduced because of smaller prestressing force in regions of partial debonding. AASHTO LRFD Bridge Design Specifications, 8th Edition (2017), place a limit of 25% on the total area of strands in a pretensioned girder that may be partially debonded. Despite this limit, many states allow higher percentages of debonding to be used in design based upon successful past practices. This dissertation reports an experimental study conducted to provide guidance in the development of a unified approach to the design of partially debonded strand regions in prestressed highway bridge girders that addresses all aspects of the service and strength performance of the girders. Both ends of six full-scale pretensioned concrete bridge girders (12 tests total), each end having different debonding ratios, were tested to failure. The test variables were: (1) girder shape (single-web, box, or U); (2) proportion of partially debonded strands (ranging from zero to 60% of the total stand area); (3) concrete compressive strength; and (4) strand diameter (0.5, 0.6, and 0.7-in.). The test results show that pretensioned girders with pa (open full item for complete abstract)

Committee: Bahram Shahrooz Ph.D. (Committee Chair); Rachel Chicchi Ph.D. (Committee Member); Kent Harries Ph.D. (Committee Member); Richard Miller Ph.D. (Committee Member) Subjects: Civil Engineering

Master of Science, University of Toledo, 2019, Civil Engineering

Many residential buildings in the United States of America are light wood structures which get damaged considerably due to high-speed winds, hurricanes, and tornadoes all year-round. Specifically, the roof-to-wall connections are very vulnerable when subjected to these extreme loadings. The objective of this study is to evaluate the application of FRPs as a roof-to-wall connection using finite element analysis (FEA) ANSYS Mechanical APDL software program. The FEA models of the wood roof-to-wall GFRP connection were validated with an experimental study in the literature. The experiment involved component level shear and uplift tests under static loading representing the effect of high-speed wind on the connection. The FEA models and experimental results were in good agreement which were further validated through Monte Carlo Simulation. The validated models were then employed to perform comprehensive parametric study. To mitigate the contact failure, anchorages were added to GFRP ties and their performances were compared with the FEA validated models of shear and uplift tests which had no anchorage and was under static load. Besides the validated model of the GFRP connection, uplift model was examined under monotonic cyclic loads with various intensities to better simulate the effect of wind load. Furthermore, carbon and basalt FRP sheets were introduced as wood roof-to-wall connections and their performances were examined under cyclic loads. To validate the efficiency of GFRP ties with and without anchorages, the shear and uplift design loads specified in ASCE 7-16 were calculated for comparison purposes. Similarly, the shear and uplift capacities of typical hurricane clips evaluated in the same experimental study used for validated FEA model were also compared with the GFRP ties with and without anchorages. Furthermore, a formula was proposed to calculate the shear strength of the GFRP connection in comparison with double shear bolted metal plate connections using N (open full item for complete abstract)

Committee: Azadeh Parvin (Advisor); Eddie Chou (Committee Member); Mohamed Hefzy (Committee Member) Subjects: Civil Engineering

Master of Science, University of Toledo, 2016, Civil Engineering

The present research in this study is directed towards improving the flexural performance, namely the load and displacement ductility capacities, and exploring the various failure modes, of continuous reinforced concrete (RC) slab strips. This improvement is accomplished by applying fiber reinforced polymers (FRP) of two types: FRP sheets and FRP rods, in both positive and negative regions of moment of the continuous RC slab strip. Currently, experimental research has shown that applying FRP rods using the near surface mounted (NSM) method to strengthen continuous RC structures can greatly improve flexural capacity and moment redistribution. Despite the benefits of FRP rods through the NSM method, applying FRP sheets using the externally bonded reinforcement (EBR) method is more common due to its ease of application and cost. Thus, this study takes into account the benefits of both NSM & EBR strengthening techniques, and presents an alternative strengthening combination using EBR-FRP sheets to strengthen the positive moment or sagging region, and NSM-FRP rods to strengthen the negative moment or hogging region of continuous RC slabs strips. Currently, the challenges faced when using FRP strengthening depends on the type of FRP material used. The EBR-FRP sheets suffer from debonding (loss of stress transfer between concrete-FRP) failures when facing high moments. To prevent these, anchorages can be provided. These anchorages are however, expensive and their applicability is limited. NSM-FRP rods suffer from sudden FRP rupture but are generally safer to use than FRP sheets. However, they require cutting of grooves on the concrete surface limiting their applicability in certain regions as well. The presented alternative strengthening combination aims at overcoming these drawbacks by applying EBR-FRP sheets in most locations while reducing the need for anchorages, and using NSM-FRP strengthening only in locations that benefit from concrete cover. Thro (open full item for complete abstract)

Committee: Azadeh Parvin (Committee Chair); Mark Pickett (Committee Member); Eddie Chou (Committee Member) Subjects: Civil Engineering; Engineering; Polymers

Master of Science, The Ohio State University, 2012, Dentistry

Background: Lasers have become an increasingly popular tool in the field of dentistry due their ability to perform a wide variety of both hard and soft tissue procedures. Recently it has been proposed that lasers may prove to be useful in the removal of some all-ceramic restorations, particularly veneers. The amount of temperature being generated intrapulpally during such a procedure has yet to be studied. Methods: Thirty IPS e.max® Press lithium disilicate veneers were cemented to thirty extracted human premolars with Variolink® Veneer resin cement. Veneers were randomly divided into one of five groups, and scanned with an Er,Cr:YSGG laser at either 0W/0Hz, 25W/25Hz, 35W/25Hz, 25W/35Hz, or 35W/35Hz. During laser scanning, intrapulpal temperatures and debonding times were monitored. Results: Increasing the laser wattage and/or pulse repetition rate resulted in an increase in the temperature generated intrapulpally. Increasing the wattage and/or decreasing the pulse repetition rate resulted in a reduced debonding time. At both 0W/0Hz and 23W/35Hz veneers we unable to be debonded. Conclusions: The laser group at 2.5W/25Hz was the overall safest laser group studied. Based upon the results of this study, laser removal of ceramic veneers should be a safe procedure for the dental pulp if the correct laser settings are used.

Committee: Alejandro Peregrina D.D.S., M.S. (Advisor); John Nusstein D.D.S., M.S. (Committee Member); Dale Sharples D.D.S. (Committee Member); Ronald Kerby D.D.S. (Committee Member) Subjects: Dental Care; Dentistry

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

In this dissertation, finite element models are used to investigate catastrophic failure of thermal barrier coatings (TBCs) due to delaminations along susceptible interfaces of thermally grown oxide (TGO) with the ceramic top coat and the inter-metallic bond coat. The materials and geometries in the studies are chosen to be representative of TBC materials in real applications. The characteristics of the failure modes along the TGO and bond coat interface (e.g. buckling instability and strain energy driven delamination propagation) are investigated using thermo-elastic finite element models. The solution of a linear elastic eigen-value problem determines the onset of the buckling instability with a pre-existing delamination between bond coat and the TGO. The virtual crack extension method is employed to study strain energy release rate driven interfacial delamination at wavy interfaces. The materials and geometries in the study are chosen to be representative of TBC materials in real applications. Extensive sensitivity analyses are conducted to identify the critical design parameters affecting the onset of buckling and extension of interfacial delamination, as well as to develop parametric relations that enhance the understanding of these mechanisms. Finally, a numerical exercise demonstrates that the buckling instability is the leading failure mechanism at flat interfaces or at the locations of minimum cross-section in a wavy interface. However, in the vicinity of waviness, crack extension becomes a dominant mode of failure. The top coat crack initiation and propagation is investigated using a thermo-elastic finite element model with bond coat creep. Cracks are assumed to initiate when the maximum principal stress exceeds rupture stress of the top coat. A sensitivity analysis estimates the contribution of geometric and material parameters and forms a basis to develop parametric relation to estimate maximum principal stress. Subsequently, crack propagation simulati (open full item for complete abstract)

Committee: Somnath Ghosh PhD (Advisor); Mark Walter PhD (Committee Member); James Williams PhD (Committee Member); June Lee PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

This dissertation develops a three dimensional homogenization based continuum damage mechanics (HCDM) model for fiber reinforced composites undergoing micromechanical damage under monotonic and cyclic loading. Micromechanical damage in a representative volume element (RVE) of the material occurs by fiber-matrix interfacial debonding, which is simulated using a hysteretic bilinear cohesive zone model. The proposed HCDM model expresses a damage evolution surface in the strain space in the principal damage coordinate system (PDCS). PDCS enables the model to account for the effect of non-proportional load history. The material constitutive law involves a fourth order orthotropic tensor with stiffness characterized as a macroscopic internal variable. Three dimensional damage in composites is accounted for through functional forms of the fourth order damage tensor in terms of components of macroscopic strain and elastic stiffness tensor. The HCDM model parameters are calibrated from homogenized micromechanical solutions of the RVE for a few representative strain histories. The proposed model is validated by comparing the CDM results with homogenized micromechanical response of single and multiple fiber RVEs subjected to arbitrary loading history. Finally the HCDM model is incorporated in a macroscopic finite element code to conduct damage analysis in structures. The effect of different microstructures on the macroscopic damage progression is examined through this study.To efficiently simulate the dynamic response of heterogeneous microstructures, an assumed stress hybrid Voronoi Cell Finite Element Method (VCFEM) for stress wave propagation is developed. In the proposed formulation, stresses in the domain and compatible displacements at the element boundary are approximated independently. The inertia field is approximated in terms of stresses so as to satisfy the equilibrium a-priori. The weak forms of kinematics and traction reciprocity are obtained by minimization of th (open full item for complete abstract)

Committee: Somnath Ghosh Prof. (Advisor); Gregory Washington Prof. (Committee Member); Stephen Bechtel Prof. (Committee Member); Mark Walter Prof. (Committee Member) Subjects: Aerospace Materials; Design; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy, University of Akron, 2010, Civil Engineering

Carbon fiber composite materials are being used in aerospace applications due to their excellent mechanical properties, such as high strength and stiffness as well as low density. Two dimensional triaxial braided polymer matrix composites have been shown to have improved performance under impact loads. Recently, many of the aircraft engine manufacturers have used such braided carbon fiber/epoxy composite for engine fan cases. A potential problem in application of triaxial braided composite is to understand the cracking, debonding and delamination. Simulation would reduce time and cost in the development of composite fan cases. Development of accurate computer model for simulation is crucial in predicting deformation and failure and to help understand experimental results. Multi-scale modeling is a well established approach to simulating textile composite behavior. This research focused on meso level modeling of triaxial braided composites. The unit cell scheme is used to take into account internal braiding architectures as well as mechanical properties of three phases: fibers tows, matrix and tow interfaces. Model requires local properties of the material so micromechanics approach is used to produce those material parameters for the model. Failure initiation and progressive damage concept has been implemented in the fiber tows by using the Hashin failure criterion and a damage evolution law. The weak/imperfect fiber tow interface is modeled by using a cohesive zone approach, where a zero thickness cohesive element technique is used and a mixed mode cohesive law is adopted based on fracture mechanics principles to evaluate crack initiation and predict crack propagation. This meso scale modeling technique has been used to examine and predict the failure observed in coupon tests. The tensile deformation and damage response of braided specimens is simulated and the results compared to experimentally obtained data. The effects of the fiber tow interface were inve (open full item for complete abstract)

Committee: Wieslaw Binienda PhD (Advisor); Ernian Pan PhD (Committee Member); Yun Gunjin PhD (Committee Member); Gao Xiaosheng PhD (Committee Member); Kevin Kreider PhD (Committee Member); Robert Goldberg PhD (Committee Member) Subjects: Civil Engineering