With increased use of pallets constructed utilizing structural panel decks, there is a need for a standardized, reliability-based design system, PDS-PANEL, to assist in the design and manufacture of panel-deck pallets. The primary objective of this research was to develop finite element models which predict the static bending behavior of pallets with at least one panel deck. stringer and block pallets were modeled using plate elements to simulate deck behavior and were validated by comparing predicted deflections to experimentally measured deflections. Differences were considerably less than the allowable 15 percent for both stringer and block models. Sensitivity studies conducted with these models provided a rational basis to simplify models for use in the existing PDS-PANEL program developed at Virginia Polytechnic Institute & State University. Simplified models were required to have solution times of less than 2 minutes on a 286 type or more powerful personal computer (PC). / Ph. D.

After 17 years in service, a 3 ft by 3 ft closure pour section of an Interstate 81 (I-81) bridge deck failed by punching through near Marion, Virginia. Visual inspection noted that there was considerable corrosion on some of the reinforcing bars in the vicinity of the construction joint, while other failure bars had little or no corrosion. Sections of the bridge deck were cut and delivered to Virginia Tech for further investigation. It was clear from an initial investigation that shrinkage of the deck concrete had caused the construction joints to open and thereby allow water and chlorides to enter the joint. In addition, it was observed that several bars across the closure pour construction joints had suffered significant section loss due to corrosion, but it was not clear if fatigue and strength failure of the reinforcing bars were also contributing factor in the closure pour failure. To study the problem four fatigue tests and five strength tests performed. The specimens included six slab strips cut from the I-81 bridge deck, with the 3-ft closure pour included, and three additional specimens that were cast in the laboratory to represent a base line for performance. A three-point loading setup was used for both fatigue and strength tests. However, for the final strength and fatigue tests, a jacking system was designed and implemented in an effort to open the closure pour construction joints to simulate the open joints of the I-81 bridge. The objectives of this research program are to provide a better understanding of the closure pour failure mechanism, develop inspection procedures for Virginia Department of Transportation (VDOT) to assess its bridge inventory containing similar construction joints, and to develop recommendations for future construction of similar construction joints. / Master of Science

The purpose of this research is to evaluate the performance of new corrugated-type embossments developed by Vulcraft Research and Development for their 2VLI and 3VLI composite deck. Performance of deck with the proposed embossment types is compared with that of deck with the existing embossment type, resulting in the recommendation of which type to further investigate for production. The evaluation consists of uniformly loaded full-scale slab tests whose flexural strengths are compared with those given by different strength prediction methods that are alternatives to full-scale testing. The methods used in this study are the First Yield Method (Heagler 1992), the ASCE Appendix D Alternate Method (Standard 1992), and Widjaja's (1997) Iterative Method. Shear bond tests are also performed for deck with each embossment type to evaluate shear resistance specifically, and to provide shear bond data needed to perform the Iterative Method. / Master of Science

Shallow geothermal energy (SGE) systems are becoming increasingly popular due to both their environmental and economic value. By using the ground as a source and sink for thermal energy, SGE systems are able to more efficiently heat and cool structures. However, their utility beyond structural heating and cooling is being realized as their applications now extend to slab and pavement heating, grain and agricultural drying, and swimming pool temperature control. Relatively recently, SGE systems have been combined with deep foundations to create a dual purpose element that can provide both structural support as well as thermal energy exchange with the subsurface. These thermo-active foundations provide the benefits of SGE systems without the additional installation costs. One of the novel applications of thermo-active foundations is in bridge deck deicing. Bridge decks experience two main winter weather related problems. The first of which is preferential icing, where the bridge freezes before the adjacent roadway because the bridge undergoes hastened energy loss due to its exposed nature. The second problem is the accelerated deterioration of concrete bridge decks resulting from the application of salts and other chemicals that are used to prevent accumulation and/or melt the frozen precipitation on roads and bridges. By utilizing the foundation of a bridge as a mechanism by which to access the shallow geothermal energy of the subsurface, energy can be supplied to the deck during the winter to melt and/or prevent frozen precipitation. An experimental ground-source bridge deck deicing system was constructed and the performance is discussed. Numerical models simulating the bridge deck and subsurface system components were also created and validated using the results from the numerical tests. Furthermore, the observed loads that result in a foundation from bridge deck deicing tests are shown. In order to better design for these loads, tools were developed that can predict the temperature change in the subsurface and foundation components during operation. Mechanisms by which to improve the efficiency of these systems without increasing the size of the borehole field were explored. Ultimately this research shows that SGE can effectively be used for bridge deck deicing. / Ph. D.

Reinforced concrete (RC) bridge decks are exposed to chlorides from deicing salts. Chloride ingress in RC initiates corrosion of the reinforcing steel. The high costs of corrosion have sparked interest in service life design of bridge decks. This thesis characterized the exposure conditions of Virginia, including temperature and surface chloride concentration, as well as Virginia concrete mix properties, including initial chloride concentration and chloride migration coefficient. The service life estimations for a case study bridge in Virginia from three service life models were compared. The first model is based on the fib Bulletin 34 Model Code for Service Life Design, the second is a finite element solution of the fib Bulletin, and the third accounts for a time-, temperature-, moisture-, and concentration-dependent apparent diffusion coefficient. A sensitivity analysis was completed on the three models showing that the most important variables in these models are the aging coefficient and surface chloride concentration. Corresponding life cycle cost analyses were completed for plain and corrosion resistant reinforcing steel. This thesis showed that the error function solution underestimates chloride ingress. The life cycle cost analysis of plain and corrosion resistant reinforcing steels show that overestimation of service life leads to underestimation of life cycle costs. / Master of Science

Deterioration of bridge decks is an ongoing problem faced by transportation agencies across the country. In past decades, Non-Destructive Evaluation (NDE) techniques, capable of detecting various deteriorations types, e.g., cracking, delamination and reinforcing steel corrosion, have emerged. These techniques generate large amounts of data representing different underlying physics, (decibels for ground penetrating radar and volts for half-cell potential), making data interpretation and comparison difficult for bridge owners and practitioners. The deterioration threshold, or the transition between healthy and deteriorated areas, is essential in understanding NDE data. However, this threshold is determined empirically in former research and engineering practice. In the present research, a probability-based method is proposed to identify deterioration thresholds for specified confidence levels. NDE data measuring different underlying physics are transformed into a binary format by threshold values to compare and combine multiple NDE techniques for bridge deck assessment. The finite element method is also implemented to correlate bridge deck surface stresses with deteriorations measured by NDE techniques, and to study the causes on concrete bridge deck degradation. The general methodology developed in this study will be demonstrated on three bridges, i.e., Virginia, New Jersey and New York Pilot Bridges, which were studied under Federal Highway Administration (FHWA)'s Long-Term Bridge Performance (LTBP) Program. / Ph. D.

Experimental and analytical research was conducted to address the vibration properties of Long Span Deck Floor Systems (LSDFS). The research comprised three stages. In the first part, experimental in-situ tests were conducted on thirteen bays of buildings under construction. The natural frequencies and acceleration responses were captured to observe the vibration behavior of the tested floors. In the second part, a laboratory footbridge was constructed to determine the fixity level attained at the supports when a LSDFS is supported by CMU walls. For this purpose, the footbridge was tested with three support conditions, and a number of experiments were carried out to determine the dynamic properties of the structure. Static tests using both point and distributed loadings were conducted to measure the deflections at the footbridge midspan. The static test results were compared to the theoretical deflections for a pinned-end beam and a fixed-end beam. Dynamic tests using experimental modal analysis techniques were conducted to determine the natural frequencies and mode shapes of the structure. The measured fundamental natural frequency of the footbridge was compared to the frequencies calculated for a simply supported beam and a beam with fixed ends, to determine the degree of fixity attained in the connection between the LSDFS and the supporting walls. In the last part of the research, three analytical procedures to predict modal characteristics of long span deck floor systems are studied. Floor frequencies are calculated using finite element analyses. Two design guides for floor vibration analysis were used to calculate natural frequencies and response accelerations. The predicted results obtained from the analytical methods are compared to the experimental results to determine their accuracy. Recommendations for the use of the analytical methods are provided. / Master of Science

The inverted T-beam system provides an accelerated bridge construction alternative. The system consists of adjacent precast inverted T-beams finished with a cast-in-place concrete topping. The system offers enhanced performance against reflective cracking and reduces the likelihood of cracking due to time dependent effects. Differential shrinkage is believed to be one of the causes of deck cracking in inverted T-beam systems. The objective of this study was to develop mix designs that exhibit lower shrinkage and higher creep compared to typical deck mixtures, recommend a prescriptive mix design and a performance criterion to VDOT that can be further investigated and used in the inverted T-beam system to combat effects of differential shrinkage. Ten different mix designs using different strategies to reduce shrinkage were tested for their compressive strength, splitting tensile strength, modulus of elasticity and unrestrained shrinkage. The four best performing mixes were selected for further study of their time dependent properties. The test data was compared against the data from various prediction models to determine the model that closely predicts the measured data. It was observed that ACI 209.2R-08 model best predicted the time dependent properties for the four mixes tested in this project. Tensile stresses in the composite cross-section of deck and girder, created due to difference in shrinkage and creep are quantified using an age adjusted effective modulus method. In this analysis, it was observed that mixes with normal weight coarse aggregate (NWCA) developed smaller stresses compared to those of mixes with lightweight coarse aggregate (LWCA). Mixes with fly ash as supplementary cementitious material (SCM) developed smaller stresses at the bottom of deck when compared to mixes with slag as the SCM. / Master of Science

Motion sensitive operations at sea are conducted in an unpredictable environment. While occasionally these operations can be planned around suitable weather forecast or delayed until smoother motions are apparent, naval ships conducting flight operations may have little liberty in their mission planning and execution. Tools exist to translate the ocean's harsh conditions into discretely defined low motion operational periods. Particularly of interest, the identification of discrete lull periods or quiescence for shipboard helicopter operations can be better defined using a landing period indicator than with the current method of utilizing static deck angle measurements. While few of these systems exist, assessing their operational benefits is difficult due to a lack of well-defined performance metrics. This thesis defines and examines the use of two methodical approaches to evaluating Landing Period Indicators (LPIs) and their subject ship-helicopter dynamic interface system. First a methodology utilizing the comparison of a basic transparent algorithm is detailed and a case study employing this methodology is examined. Second, a system dynamics approach is taken to pilot workload analysis, utilizing a dynamic systems model characterizing a subset of the Dynamic Interface. This approach illustrates the realistic gains in understanding and development that can be accomplished by utilizing system dynamics in the analysis of the Dynamic Interface and LPI insertion. / Master of Science

Highway bridge decks are often overlaid to extend service life by reducing the rate of chloride ion ingress and the rate of corrosion of reinforcing steel in the sound chloride-contaminated concrete that is left in-place. Bridge deck overlays in Virginia are usually either latex-modified concrete or microsilica concrete, and both types of overlay are considered equivalent in terms of performance. However, the latex-modified concrete overlays are more expensive to construct than the microsilica concrete overlays. Thus, it is important to determine if these overlays do perform equivalently to ensure that short-term savings do not lead to higher long-term costs. Shrinkage is one of the overlay performance parameters. Shrinkage is a three-dimensional deformation of concrete that results in an overall reduction in volume. Total shrinkage may be measured under either restrained or unrestrained conditions. This research examines the shrinkage performances of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures and was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. Based on crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that construction conditions and quality and traffic type and frequency may have a greater effect on cracking than the overlay material. / Master of Science