Browsing by Subject "Bridges"

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An analysis of practices for concrete bridge deck durability
(Texas Tech University, 2000-12) Yasmin, Ashfia
With increasing roadway congestion, there is increasing pressure to open newly constructed concrete bridge decks to full traffic early. Generally, highway agencies open bridge decks as soon as possible to traffic without sacrificing long-term durability of the structure. Thus, there is a ''critical loading age" at which time applied design loads have no applicable detrimental effect on the long-term durability of concrete bridge deck. Currently, there are no specific methods to determine this critical loading age for different concrete mixes or for site cast concrete. So, difficulties arise when one attempts to (a) define this critical loading age for a number of concrete mixes and (b) determine when site cast concrete actually reaches this critical loading age. This thesis analyzes the current practice for loading age of concrete. Typically, after a minimum number of days of wet mat curing and a given compressive strength (f'c) are reached, traffic is allowed on a concrete bridge deck. In Texas, the requirement for wet mat curing is 8 days for decks with Type I cement and 10 days for decks with Type II or I/II cement or mixtures containing fly ash. The most recent Special Provision to Item 420, "Concrete Structures," effective 9-98, allows opening to traffic after design strength is achieved and concrete surface treatment has been applied. This allows opening to all traffic after specification requirement of 8-10 days wet mat curing plus a day for the surface to dry and a day to apply concrete surface treatment, for a total of 10 to 12 days. In the past, the minimum number of days before full traffic load has been 30 days is 1982 specification and 21 days, as stated in the 1995 specification. The longer time of loading was preferred because of concerns that the concrete would reach it critical loading age at some point before opening the deck to traffic. The main problem the concrete shows at the early age if it is open to traffic earlier than the critical loading age is the appearance of micro-cracks. Significant efforts have been made to develop concrete mix designs to improve early strength and durability of concrete in recent years. However, the minimum number of wet mat curing days to achieve sufficient concrete durability is not known yet.
Analysis and response mechanisms of blast-loaded reinforced concrete columns
(2009-05) Williams, George Daniel; Williamson, Eric B., 1968-; Williamson, Eric B., 1968-
Terrorism has been an international threat to high occupancy civilian structures, government buildings, and military installations for many years. Statistical data from past terrorist attacks show that transportation infrastructure has been widely targeted, and a bombing of an ordinary highway bridge is a realistic scenario. Recent threats to bridges in the U.S. confirm this concern and have caught the attention of the bridge engineering community. Given that many ordinary highway bridges in the United States support critical emergency evacuation routes, military transportation plans, and vital economic corridors, the loss of a key bridge could result in severe national security, economic, and socioeconomic consequences. Therefore, in this research, a simplified procedure is developed to predict blast loads on bridge columns, and an understanding of the mechanisms that cause damage and ultimately failure of blast-loaded reinforced concrete bridge columns is advanced. To that end, computational fluid dynamics models are constructed and validated using experimental data. These numerical models are used to characterize the structural loads experienced by square and circular bridge columns subjected to blast loads, which is followed by the formulation of a simplified load prediction procedure. Additionally, nonlinear, three-dimensional, dynamic finite element models of blast-loaded reinforced concrete bridge columns are developed and validated using qualitative and quantitative data from recent experimental tests. The results of these analyses illustrate the fact that circular columns cannot be assumed to experience less base shear demand than a square column simply because they experience less net resultant impulse. Furthermore, the column response models developed in this research are used to identify and explain the mechanisms that lead to the spalling of side cover concrete off blast-loaded reinforced concrete members observed in recent experimental tests. Therefore, the results of this research advance the understanding of the structural loads on and the resulting response of reinforced concrete bridge columns subjected to blast loads, and as such these contributions to the structural engineering community enhance the security of the U.S. transportation infrastructure.
Analytical study of orthotropic steel bridge decks
(Texas Tech University, 1972-10) Daiguji, Hisashi
Not available
Assessment of critical parameters that affect the seismic performance of bridge steel pedestals
(2009-05-15) Srivastava, Siddharth
The Georgia Department of Transportation has been installing steel pedestals on bridges, ranging in height up to 33?? (0.85m) to increase the vertical clearance of many multi-span simply-supported and multi-span continuous bridges in Georgia. But there is a concern about the performance of these steel pedestals as they are designed without seismic consideration and may perform poorly compared to high-type steel ?rocker? bearings, which were found to be unstable supports in previous earthquakes. This research models a candidate bridge using experimental data that captures the force-displacement hysteretic behavior of the steel pedestals. The results show how these steel pedestals behave when subjected to a range of ground motions. Nonlinear time history analysis is conducted using SAP 2000 software on a three-dimensional model of the candidate bridge. In addition, parametric studies of various critical parameters that can affect the seismic performance of the bridge are investigated, such as 1) varying the mass of the structure, 2) varying the stiffness of the deck joint, 3) varying column heights, and 4) seismic retrofitting using cable restrainers. The results show that these pedestals should not be used in regions of high seismicity, and in regions of low seismicity, it is likely that they need to be retrofitted. They can, although, be used safely in regions of low seismicity. In addition, it was shown that the mass of a superstructure and height of the columns significantly affect the behavior of these steel pedestals, and should be given a careful consideration before usage. It was also shown that the stiffness of the expansion joints does not significantly affect the displacement of the steel pedestals and the forces transmitted to them. However, if the expansion joints are too stiff compared to the adjacent bridge components, then the forces transferred during pounding of superstructure is increased significantly.
Characterization of cracks in bridge beams with welded wire fabric reinforcement using image processing
(Texas Tech University, 2001-12) Turkyilmaz, Selim
The Texas Department of Transportation (TxDOT) widely uses prestressed concrete I-beams as bridge girders. The current TxDOT policies allow the substitution of an equal area of Welded Wire Fabric (WWF) for the traditional vertical steel reinforcement. However, TxDOT does not provide details for the WWF substitution. A research project was conducted to study the behavior of WWF as shear reinforcement m the high shear regions of prestressed concrete beams. The main purpose of the project was to test the anchorage capacity of the WWF bars. As alternatives, a simplified WWF design and an equivalent strength WWF design were also proposed. Another main objective of this research was the study of the cracks to have a better understanding for the performance of these alternative designs. The crack controlling behaviors of different WWF vertical shear reinforcement details were studied by using "digital image processing" techniques. Image processing techniques provide a faster and easier analysis of concrete cracks than manual crack measurement methods. A fast and accurate technique has been tried to provide for this analysis. The digital images of the crack regions were taken of the beams with different shear reinforcement details under common loads near failure. These digital images were converted into binary images by using a series of digital image processing techniques. Then the crack properties such as areas, lengths, and average widths were computed automatically. The results showed that the crack properties of the different WWF reinforcement designs were consistent with those of the standard reinforcement design. The equivalent strength designs exhibited the widest cracks and largest total crack areas.
Comparison between epoxy-coated steel and glass fiber reinforced polymer bars in a concrete highway bridge deck
(Texas Tech University, 2002-12) Bice, Jacob
The use of fiber reinforced polymer (FRP) bars as reinforcement in concrete highway bridges potentially provides a means that can extend the useful life of the bridges in selected cases. Resistance of glass fiber reinforced polymer (GFRP) rebars to corrosion associated with the use of de-icing salts on bridges makes these bars particularly attractive to the transportation industry. However, questions concerning the bars' relatively low modulus of elasticity, bond slip properties, and in situ corrosion resistance must be answered prior to widespread implementation in highway bridges. The Sierrita de la Cruz Creek Bridge near Amarillo, Texas provides a means of making a direct comparison between the performance of an epoxy coated steel (ECS) reinforced bridge deck and a fiber reinforced polymer (FRP) reinforced bridge deck. Short-term comparisons are presented in this thesis, and the long-term monitoring potential of the two bridge sections is also discussed. With the exception of a longitudinal crack that formed in the cast-in-place bay in the GFRP-reinforced span, this thesis found that the GFRP-reinforced sections perform almost identically to the steel-reinforced sections. The research performed for this thesis also determined that the FRP may be exposed to internal temperatures which may cause long-term deterioration of the FRP bars. The data collected in the live load tests set a benchmark for any future live load testing performed on the bridge. Long-term monitoring of the bridge will be required to assess the durability of the GFRP bars in the concrete bridge deck.
Design of a bridge bumper to protect bridge girders against collisions of overheight vehicles
(2009-05-15) Sharma, Hrishikesh
Bridges with low clearance are vulnerable to collision with overheight vehicles. Collisions of overheight vehicles can cause fatalities and injuries to the drivers and passengers of the overheight vehicles, and damage to bridge girders. The repair of the damaged bridges can be costly and time consuming. This research investigates the feasibility of developing a bridge bumper that minimizes the physical injuries and the likelihood of fatalities and protects the structural elements of bridges by absorbing the impact energy. The thesis describes a small-scale impact experiment using the proposed bridge bumper with several options of energy absorbing materials to protect a reinforced concrete beam. A finite element analysis is done to simulate the small-scale impact experiments. Optimization of the finite element model is carried out for the response quantities of interest with respect to the geometrical parameters and the material properties of the proposed bridge bumper. Such analysis can guide the design of an optimal bridge bumper that maximizes the energy dissipation and minimizes the damage to the bridge girder and the likelihood of fatalities and injuries.
Effect of curing on permeability and freeze-thaw durability of bridge deck concrete
(Texas Tech University, 2002-05) Afroze, Montasheema
Durability of bridge deck concrete may be defined as the ability of concrete to remain fully functional over an extended period under prevailing service conditions for the purpose for which it was designed. The durability of concrete structure is closely related to its permeability. The permeability dictates the rate at which aggressive agents can penetrate to attack the concrete and the steel reinforcement. Also, the most destructive weathering agent is the freezing and thawing of water in the concrete. During cold weather, pavements and bridge decks are subjected to freezing and thawing. For the purpose of removing the snow and ice, de-icing agents are applied, which causes the surface disintegration in the form of scaling and consequently, the chemicals accelerate the corrosion of reinforcement. This thesis is a part of a research project titled "Effects of Wet Mat Curing and Earlier Loading on Long-Term Durability of Bridge Decks" sponsored by Texas Department of Transportation (TxDOT). The project investigates the long-term effects of wet-mat curing duration and "early" loading on the durability of bridge decks. This thesis outlines the effect of curing on the chloride-ion Permeability and freeze-thaw resistance of different mix designs.
Effects of curing on shrinkage cracking in bridge deck concrete
(Texas Tech University, 2003-12) Aamidala, Hari Shankar G
Shrinkage cracking is a critical factor affecting the durability of concrete bridge decks. Since cracks in reinforced concrete decks provide a path for corrosive agents to enter the concrete, thereby accelerating the deterioration of the reinforcing steel. Concrete undergoes volumetric changes due to variation in temperature and moisture. When concrete is prevented by a surrounding structure from undergoing these volumetric changes freely, tensile stresses are developed. Depending on the amount of restraint applied, these tensile stresses potentially lead to cracks in the structures. This type of cracking can be reduced by providing rebars in the form of mesh to take the tensile stresses and/or the use of shrinkage-reducing admixtures (SRAs). Recent studies performed on SRAs show that the use of such admixtures is an effective method to reduce shrinkage cracking. Simulating restraint experienced in highway pavements and bridge decks is a challenge to researchers. This challenge has led to the development of different methods to assess the potential of restrained shrinkage cracking. Currently, there exists no standard test to assess cracking due to restrained shrinkage, though several researchers have simulated the effects of restraint in various ways to better understand the behavior of concrete shrinkage. The objective of this research is the evaluation of the different concrete mix designs used in bridge decks in Texas. Specifically, the influence of curing duration on the cracking potential of concrete bridge decks has been investigated based on the unrestrained (free) linear shrinkage measurements of prismatic specimens. In addition to free shrinkage tests, tests have been performed to study the weight loss, modulus of elasticity and split tensile strength of the concrete mix designs. Using the data obtained from these tests, shrinkage stresses developed due to full-restraint (100%-restraint) have been estimated and compared with the split tensile strength to estimate the age at which a first crack can be observed in the concrete. The approach presented assists in better understanding the effect of shrinkage on the cracking of bridge decks under full-restraint. Using the weight loss measurements and weight of oven-dried specimens, internal moisture content was tracked. This data is used to compare the behavior of the material to the development of shrinkage strains. Comparing the different curing durations did not indicate a significant difference in the development of either modulus of elasticity or split tensile strength. However, a favorable correlation was observed between the tensile strength of concrete and shrinkage stresses developed due to full restraint based on different curing durations. The results did not show a significant delay in the age of first crack with increase in curing duration from 4 days to 7 days. Thus, based on the research to date, one can conclude that 4 day curing suffices for durability of bridge decks from a shrinkage cracking perspective.
Experimental study of bridge stay cable vibration
(Texas Tech University, 1999-08) Gardner, Thomas Blane
Rain and wind induced vibration in the stay-cables of stay-cable bridges is a problem that is generating greater attention as more of these bridges are constructed around the world. At issue is the possibility of fatigue of the stay-cable attachments at the bridge deck and tower as well as the material that makes up the stay-cable itself. The vibrations are most prevalent during moderate to heavy rain and light wind conditions below 30 mph, but also occur at high wind speeds with no rain. The proposed cause of the vibration problem is the change in cross-sectional shape of the stay-cable that occurs when rain forms one or more beads, or rivulets, along the cable surface. This modified cross section affects the aerodynamics of the stay-cable and, as a result, large vibrations occur at wind speeds well above the known vortex shedding wind speeds for cylindrical bodies. Often, these large magnitude vibrations were not accounted for by the bridge designers and engineers and modification of existing cables becomes necessary. This work presents the existing schools of thought on the mechanism that causes the extreme vibrations of stay-cables. In addition, a section model suspension and force measuring system is developed to study the behavior of stay-cables in the wind tunnel. Data are presented from a stay-cable section model study using the above mentioned force measuring system. Further, suggestions are made for future study of the stay-cable vibration problem based on the results of this work and the work of other researchers.
Petrographic evaluation of bridge deck concrete durability
(Texas Tech University, 2001-08) Lee, Sang-Yun
This thesis is a part of a research project (project numer: 0-2116) titled "Effects of Wet Mat Curing and Earher Loading on Long-Term Durabihty of Bridge Decks" sponsored by Texas Department of Transportation (TxDOT). The project investigates the long-term effects of wet-mat curing duration and "early" loading on the durability of bridge decks (Phelan et al., 2001). Research tasks for the project include: (a) casting and monitoring of model deck slabs located across the state, (b) laboratory testing and (c) dynamic testing of the test bridge deck slabs. This research project is focused on the effect of reduced wet mat curing time and earher loading on long-term durability of concrete bridge decks. Research findings potentially will be used to update current wet mat curing and time-to-loading requirements in appropriate TxDOT specifications.
Predicting the behavior of horizontally curved I-girders during construction
(2010-08) Stith, Jason Clarence; Williamson, Eric B., 1968-; Helwig, Todd Aaron, 1965-; Frank, Karl H.; Engelhardt, Michael D.; Liechti, Kenneth M.
The majority of a bridge designer’s time is spent ensuring strength and serviceability limit states are satisfied for the completed structure under various dead and live loads. Anecdotally, the profession has done an admirable job designing safe bridges, but engineering the construction process by which bridges get built plays a lesser role in the design offices. The result of this oversight is the complete collapse of a few large bridges as well as numerous other serviceability failures during construction. According to the available literature there have been only a few attempts to monitor a full-scale bridge in the field during the entire construction process. Another challenge for engineers is the lack of analysis tools available which predict the behavior of the bridge during the intermediate construction phases. During construction, partial bracing is present and the boundary conditions can vary significantly from the final bridge configuration. The challenge is magnified for complex bridge geometries such as curved bridges or bridges with skewed supports. To address some of the concerns facing engineers a three span curved steel I-girder bridge was monitored throughout the entire construction process. Field studies collected data on the girder lifting behavior, partially constructed behavior, and concrete deck placement behavior. Additional analytical studies followed using the field measurements to verify the finite element models. Finally, conclusions drawn from the physical and analytical testing were utilized to derive equations that predicted behavior, and analysis tools were developed to provide engineers with solutions to a wide range of construction related problems. This dissertation describes the development of two design tools, UT Lift and UT Bridge. UT Lift is a macro-enabled Excel spreadsheet that predicts the behavior of curved I-girders during lifting. The derivation of the equations necessary to accomplish these calculations and the implementation are described in this dissertation. UT Bridge is a PC-based, user-friendly, 3-D finite element program for I-girder bridges. The basic design philosophy of UT Bridge aims to allow an engineer to take the information readily available in a set of bridge drawings and easily input the necessary information into the program. A straight or curved I-girder bridge with any number of girders or spans can then be analyzed with a robust finite element analysis for either the erection sequence or the concrete deck placement. The development of UT Bridge as well as the necessary element formulations is provided in this dissertation.
Stabilizing techniques for curved steel I-girders during construction
(2010-05) Petruzzi, Brian James; Helwig, Todd Aaron, 1965-; Engelhardt, Michael D.
There are many issues and challenges to deal with when designing a curved I-girder bridge. These challenges primarily deal with the many performance stages that curved I-girder bridges have such as the erection, construction, and in-service stages. When design engineers assess the stability of a bridge system, they typically evaluate the system in its final configuration with all cross frames attached and the hardened concrete deck placed. The evaluation of girder stability during erection and early stages of construction stages is difficult because of the limited presence of bracing in the system. Due to a lack of readily available analytical tools, many contractors do not conduct detailed analytical evaluations of the bridge behavior during early stages of the construction when stability is often critical. Instead, many contractors use rules of thumb and experience to ensure stability during erection. Erection and construction practices typically vary among contractors and consistent erection methods are a rarity. Although some rules of thumb may be quite conservative, others are much less so. Therefore, coming up with design guidelines based on parametric studies rather than rules of thumb are desirable to help allow the contractor and the designer to work together to prevent issues that may occur due to the lack of communication between the two professions. Lastly, many challenges arise due to the complex geometry of curved I-girders. To prevent excessive rotation in erected girders, three points of vertical support are often provided. Two of these points usually consist of permanent supports in the form of bridge piers or abutments. The third point of support may consist of a temporary support in the form of a shore tower or holding crane. Cases where a holding crane may be satisfactory over a shore tower are also not well understood. To improve the understanding of lifting practices and temporary support requirements, parametric studies were conducted using the finite element program ANSYS. Field data consisting of displacement, stress, and girder rotations gathered from two tests were used to validate both the linear and geometric non-linear three-dimensional FEA models. Upon validation, the finite element model was used to conduct linear and geometric non-linear analyses to determine critical factors in curved I-girder bridges during construction. Specifically, serviceability limit states were studied for the lifting of curved girders. For partially constructed states, parametric studies were conducted to determine optimal locations to place temporary supports as well as to investigate stability differences between using a shore tower and a holding crane. Recommendations are presented to provide guidance for the lifting of curved I-girders as well as to maximize stability of partially constructed bridges.
Structural Reliability of Bridges Elevated with Steel Pedestals
(2012-09-19) Bisadi, Vahid 1980-
Overheight vehicle impact to bridge decks is a major problem in the transportation networks in the United States. An important factor that causes this problem is inadequate vertical clearance of bridges. Using steel pedestals to elevate bridge decks is an efficient and cost-effective solution for this problem. So far, steel pedestals have been used in the low seismic regions of the United States and therefore, their design has been based on providing enough strength to carry vertical loads and the lateral behavior of bridges elevated with pedestals have not been a major concern. But even in low seismic zones the seismic hazard should not be completely ignored. Also there might be some bridges in medium or high seismic regions that need to be elevated because of the lack of enough vertical clearance and using steel pedestals can be considered as an option for elevating those bridges. To address the mentioned needs, this dissertation proposes a framework to determine the structural reliability of bridges elevated with steel pedestals by developing probabilistic capacity and demand models for the slab-on-girder bridges subjected to lateral loads. This study first compares the behavior of previously tested pedestals with the behavior of elastomeric bearings in low seismic regions using statistical tests. Then, to provide a general framework, which can be applied to all bridges that are elevated with steel pedestals, this dissertation develops probabilistic capacity and demand models for steel pedestals considering all the aleatory and epistemic uncertainties of the problem. Using the developed probabilistic models along with the available models for other components of bridges, seismic fragility curves for elevated bridges are obtained and used to determine the structural reliability. Finally, this study uses the developed framework in a decision analysis that helps the engineering community and decision makers to check if the installation of steel pedestals on a specific bridge has financial justification or not. Results show that for a typical two-span slab-on-girder bridge, the use of steel pedestals has financial justification only in low seismic regions and if the societal benefits of elevating the bridge can at least cover the installation cost of pedestals.

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