As pontes de madeira com tabuleiro multicelular protendido são uma das mais recentes tecnologias usadas na construção das modernas pontes de madeira. Nesta tese é realizado o estudo teórico e experimental do comportamento estrutural destas pontes. Os principais métodos de cálculo são apresentados e discutidos. A investigação experimental foi realizada em dois modelos reduzidos em escala 1:3 com as mesmas dimensões externas mas diferente quantidade de nervuras. Os modelos foram ensaiados com diferentes posições de carregamento enquanto os deslocamentos, deformações e forças nas barras, eram monitorados. Os resultados obtidos demonstraram que os modelos de Placa Ortotrópica Equivalente e Elementos Finitos podem ser empregados para o dimensionamento das pontes de madeira com tabuleiro multicelular protendido. O método de Viga Equivalente pode ser empregado desde que utilizado o correto Fator de Distribuição de Carga. Os estudos realizados neste trabalho, indicam a viabilidade da utilização deste sistema estrutural para pontes com vãos de 12 a 25 m / Timber bridges with multicellular prestressed decks is one of the most recent technology for modern timber bridges construction. In this thesis the theoretical and experimental study of the structural behavior of these bridges is accomplished. The main calculation methods are introduced and discussed. Two reduced models on scale 1:3, with the same external dimensions but different number of webs, were used for the experimental investigation. The models were tested with different load positions meanwhile displacements, strains and bar forces were measured. The obtained results have show that either model of Equivalent Orthotropic Plate or Finite Elements can be used for the design of this type of bridge. The Equivalent Beam model can also be employed as long as the correct Load Distribution Factor is chosen. The accomplished studies demostrate that this structural system is viable for bridges with span from 12 to 25 m

The primary objective of this research project was to perform live load tests on a bridge deck with GFRP reinforcement in the field under service conditions. The strains and deflections in the span reinforced with GFRP in the top mat were recorded under a series of truck crossings, and these were compared to the span reinforced with all steel bars under identical loading conditions, as well as design values and other test results. Transverse strains in the GFRP bars, girder distribution factors, girder bottom flange strains, dynamic load allowances, and weigh-in-motion gauge results were examined. From the live load tests, it was concluded that the bridge was designed conservatively for service loads, with measured strains, stresses, distribution factors, and impact factors below allowables and design values. The second objective was to monitor the construction of the bridge deck. To carry out this objective, researchers from Virginia Tech were on site during the bridge deck phase of the construction. The construction crews were observed while installing both the all-steel end span and the steel bottom/GFRP top end span. The installation of the GFRP bars went smoothly when compared to that of the steel bars. The workers were unfamiliar with the material at first, but by the end of the day were handling, installing, and tying the GFRP bars with skill. It was concluded that GFRP bars are an acceptable material in bridge deck applications with respect to constructibility issues. The third objective was to set up the long term monitoring and data collection of the bridge deck. Electrical resistance strain gauges, vibrating wire strain gauges, and thermocouples were installed in the deck prior to concrete casting to provide strain and temperature readings throughout the service life of the bridge. It was concluded that the span reinforced with GFRP was instrumented sufficiently for long-term health monitoring. / Master of Science

Accelerated Bridge Construction (ABC) techniques have resulted in innovative options that save time and money during the construction of bridges. One such group of techniques that has generated considerable interest is the usage of individual precast concrete members. Utilizing precast concrete decks allows for offsite curing, thus eliminating long delays due to formwork and concrete curing time. These precast concrete decks have inherent joints between the individual panels. These joints are locations for potential leakage, which can lead to corrosion or inadequate long-term performance. Post-tensioning the precast deck panels helps to eliminate leakage; however, conventional longitudinal post-tensioning systems require complete deck replacement in the event of a single faulty deck panel. A proposed post-tensioned, curved-strand connection allows for a single panel to be replaced. The capacity of the proposed curved-strand connection was investigated in order to compare its behavior to other systems that are currently in use. Tests were performed in composite negative bending, beam shear, and positive bending. The curved strand connection was found to behave similarly to the standard post-tensioning system in positive bending and shear. The curved-strand connection was found to be comparable to a standard post-tensioning system. The ultimate capacity of the curved-strand connection in negative bending was found to be 97% of the standard post-tensioning. Pre-stress losses were measured and predicted for the service life of the connection and were found to be 6% at the 75- year service life of a bridge.

The objective of the research presented in this thesis was to develop a concrete bridge deck topping mixture that resists the effects of differential shrinkage by decreasing shrinkage and increasing creep. . In addition, the amount of tensile creep that concrete experiences under long-term tensile stresses were quantified and compared to compressive creep values in order to gain a better understanding of how concrete behaves under tension. Test results show that the amount of tensile creep exceeded compressive creep by a factor of 2-5. Various shrinkage and creep models were compared against test data in order to quantify results and determine the best model to use for the mixes examined during this research project. Data analysis revealed that the AASHTO time dependent effects (shrinkage and creep) models outperformed the other models used in this research project. Other material property data including compressive strength, splitting tensile strength, Young's modulus of elasticity, and unrestrained shrinkage was also collected to compare against a common bridge deck topping mix to ensure that the mixes used in this research project are suitable for use in the field. A parametric study utilizing the Age Adjusted Effective Modulus (AAEM) method was performed which showed that the most important factor in reducing tensile stresses was to decrease the amount of shrinkage experienced by the concrete bridge deck topping mixture. Three concrete mixtures, one included saturated lightweight aggregates (SLWA), one including ground granulated blast furnace slag (GGBFS), and one incorporating both were tested. Preliminary results show that the inclusions of SLWA into a concrete mixture reduced shrinkage by 25% and overall tensile stress by 38%. / Master of Science

Bridge engineers and managers in coastal areas and cold regions frequently specify the application of surface treatments on concrete bridge decks as barriers against chloride ingress. In consideration of concrete cover thickness and the presence of stay-in-place metal forms (SIPMFs), the objective of this research was to determine the latest timing of initial surface treatment applications on concrete bridge decks subjected to external chloride loading before chlorides accumulate in sufficient quantities to initiate corrosion during the service life of the deck. Chloride concentration data for this research were collected from 12 concrete bridge decks located within the I-215 corridor in Salt Lake City, Utah. Numerical modeling was utilized to generate a chloride loading function and to determine the diffusion coefficient of each deck. Based on average diffusion coefficients for decks with and without SIPMFs, chloride concentration profiles were computed through time for cover thicknesses of 2.0 in., 2.5 in., and 3.0 in. The results of the work show that the average diffusion coefficient for bridge decks with SIPMFs is approximately twice that of decks without SIPMFs and that, on average, each additional 0.5 in. of cover beyond 2.0 in. allows an extra 2 years for decks with SIPMFs and 5 years for decks without SIPMFs before a surface treatment must be placed to prevent excessive accumulation of chlorides. Although the data generated in this research are based on conditions typical of bridge decks in Utah, they clearly illustrate the effect of cover depth and the presence of SIPMFs. Given these research findings, engineers should carefully determine the appropriate timing for initial applications of surface treatments to concrete bridge decks in consideration of cover depth and the presence of SIPMFs. For maintenance of concrete bridge decks with properties similar to those tested in this study, engineers should follow the guidelines developed in this research to minimize the ingress of chlorides into the decks over time and therefore retard the onset of reinforcement corrosion; altogether separate guidelines may be needed for decks having substantially different properties. Surface treatments should be replaced as needed to ensure continuing protection of the concrete bridge deck against chloride ingress.

No description available.

Modeling of chloride-induced deterioration of bridge decks by using Fick's Second Law of diffusion was performed. The objective of this study is to select suitable input parameters for the model to estimate the service life of bridge decks. Five bridge decks, one in each of the following states, Virginia, Florida, New Jersey, New York, and Minnesota were evaluated. Data collection process involved visual inspections, damage surveys, corrosion testing including continuity, one-point resistivity, four-point resistivity, half-cell potentials, and three-electrode linear polarization, reinforcement cover depths, chloride samples. The Virginia bridge deck was built with epoxy-coated reinforcement as top reinforcement mat and black bar as the bottom mat. The Florida bridge is a segmental prestressed box girder structure built with black bar. The New Jersey bridge deck was overlaid with latex modified concrete. The New York bridge deck, which was built in 1990, is six inch concrete topping over prestressed adjacent box beams structure with epoxy-coated bar in the negative moment area. The Minnesota bridge was rebuilt in 1984. The deck was rebuilt with epoxy coated reinforcing steel in the top and bottom mats. The probabilistic Fickian model requires reinforcement cover depths, surface chloride concentration, chloride initiation concentration, and diffusion coefficients as input parameters. The chloride initiation concentration was input via parametric bootstrapping, while the other parameters were input as simple bootstrapping. Chloride initiation concentration was determined from the chloride concentration at the reinforcement bar depths. The modeling results showed that the deterioration of the Virginia bridge deck was corrosion controlled and the bridge will undergo increasingly severe damage in the future. Florida bridge deck is not undergoing corrosion and will not experience corrosion damage within 100 years. New Jersey bridge deck's service life has been most likely extended by the overlay. Deterioration of the New York bridge was not corrosion controlled, but was related to longitudinal cracking of the topping at match lines of adjacent box beams. Minnesota bridge deck is delaminated and contained a large number of cracks that should be included in service life modeling; otherwise the service life estimate is underestimated. In addition to service life corrosion performance modeling, analyses were conducted on the relationships and interrelations of resistivity, corrosion potential, corrosion current and chloride at the reinforcing bar depth. / Ph. D.

The primary objective of this research was to investigate the shear strength of concrete bridge decks with GFRP top-mat reinforcement. Several models currently exist to predict the shear strength during the design process; however, previous research at Virginia Tech indicates that the existing equations are overly conservative. For this research, a series of concrete decks with varying lengths were tested in a laboratory environment in a two-span continuous configuration, during which data was collected on deflections, rebar strain, crack widths, and ultimate load. It was concluded that the existing equations, particularly the guidelines of ACI 440, are grossly over-conservative for GFRP-reinforced concrete bridge decks continuous over multiple supports. It was suggested that this is due to multiple factors, including additional support provided by the typically-neglected steel reinforcement in the bottom mat and a higher shear strength of the uncracked portion of concrete due to higher compressive stresses in the section as a result of the continuous deck configuration. The second objective of this research was to investigate the effects of environmental exposure on the composite deck and the individual GFRP rebar. Three deck specimens were subjected to differing environmental conditions, including one that was placed into service at an interstate weigh station. All three decks were tested in the same manner as those in the shear investigation. Additionally, live load tests were conducted on the weigh station deck during the time it was in place and tensile tests were conducted on rebar that were extracted from the concrete decks. In the live load testing, the GFRP strains increased by more than 200% over the period of service, which was likely due to a combination of a reduction in GFRP stiffness and a greater amount of cracking. During the laboratory tests on the decks, no clear correlation between conditioning and deflections or cracking was found. The ultimate strength actually increased with conditioning, with the weigh station specimen exhibiting the highest shear strength. Finally, the results of the rebar tensile tests suggested a decrease in both modulus of elasticity and ultimate tensile strength of the GFRP with environmental exposure when compared to unconditioned bars. / Master of Science

The purpose of this research was to investigate the effectiveness and durability of GFRP bars as reinforcement for concrete decks. Today's rapid bridge deck deterioration is calling for a replacement for steel reinforcement. The advantages of GFRP such as its high tensile strength, light weight, and resistance to corrosion make it an attractive alternative to steel. The first objective of this research was to perform live load testing on a bridge deck reinforced with GFRP in one span and steel in the other. The results were compared to the findings from the initial testing performed one year earlier. The strains and deflections of the bridge deck were recorded and the two spans compared. Transverse stresses in the GFRP bars, girder distribution factors, and dynamic load allowances were calculated for both spans. From the live load tests, it was concluded that the GFRP-reinforced span results were within design parameters. The only concern was the increased impact factor values. The second objective was to perform live load tests on a slab reinforced with GFRP installed at a weigh station. Two live load tests were performed approximately five months apart. Peak strains in the GFRP and steel bars were recorded and compared. The peak stresses had increased over time but were within design allowable stress limits. The third objective of this research was to investigate the long term behavior and durability of the GFRP reinforcing bars cast in a concrete deck. The strain gauges, vibrating wire gauges, and thermocouples in the bridge deck were monitored for approximately one year using a permanent data acquisition system. Daily, monthly, and long term fluctuations in temperature and stresses were examined. It was concluded that the vibrating wire gauges were more reliable than the electrical resistance strain gauges. It was further observed that the main influence over strain changes was temperature fluctuations. / Master of Science

This research investigation explores the feasibility of implementing a laser welded sandwich steel panel bridge deck system as a viable alternative to standardized reinforced concrete bridge decks. Generally used in naval ship building applications, steel sandwich panels possess attractive characteristics towards the integration with bridge infrastructure such as service life in excess of 100 plus years, dead load reduction, rapid construction, decreased closure time, and automated mass production. The lack of fatigue data for the laser "stake" welds used to create the enclosed sandwich panel geometry raised concerns with respect to fatigue life. The primary focus of this study was to determine whether or not infinite fatigue life was possible. Two different laser welding technologies were investigated, Laser Beam Welding (LBW) and Hybrid-Laser Arc Welding (HLAW). Test specimens were fabricated and tested in order to examine fatigue resistance based on a localized load effect between adjacent core stiffeners. Finite element models were used to obtain the stress range for each individual test due to complex geometry and partially restrained boundary conditions. In order to assess the fatigue performance of the overall deck system, additional finite element models were created to study the local and global behavior of different sandwich panel configurations. As a whole the investigation yielded promising results. Infinite fatigue life is achievable due to outstanding fatigue performance. The HLAW stake welds demonstrated superior fatigue resistance in comparison to the LBW process. Localized load effects can be minimized through the modification of different panel parameters. Pushing forward, full scale testing is essential to the future employment of this innovative bridge deck system. / Master of Science