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WEIGHTED EFFECT OF CONCENTRATED CRACKING ON THE STRUCTURAL INTEGRITY OF CONCRETE BRIDGE DECKS
No full textConcrete bridge decks are vital components of transportation infrastructure, yet their deterioration due to aging, environmental, and operational factors poses significant challenges to maintenance and safety. In the United States, approximately 9.1% of bridges require improvement, with millions of daily trips relying on structurally deficient bridges. Cracking is one of the most frequently observed defects on concrete bridge structures. Traditional bridge inspections evaluate cracks based on severity (crack width) and extent (crack area), combining these values with other performance indicators to assess overall bridge health. However, the effect of concentrated cracking in localized areas on bridge integrity remains largely unexplored. Therefore, it is hypothesized that a higher concentration of cracks in local areas may have a more detrimental effect on the structural integrity compared to evenly distributed cracks. This research aims to investigate the weighted effect of localized cracking on the structural integrity of concrete bridge decks.
The study utilizes ultrasound testing to collect pulse velocity data across various surface crack concentrations on concrete bridge deck samples. The dimension of each sample size is 10 feet by 10 feet. Three frequency sensors—54 kHz, 150 kHz, and 250 kHz—are employed to account for cracks of varying extents and severities. Additionally, each sample is photographed using a high-resolution camera, Nikon D3200, and the images are processed and analyzed using deep-learning algorithms, YOLOv11. Then, the Crack Concentration Index (CCI) is calculated for each sample, defined as the ratio of crack areas (length × width) to the boundary area of the cracks. Statistical analysis is conducted to identify the relationships between ultrasound pulse velocities (UPVs) and CCIs for the data points classified by National Bridge Inventory (NBI) condition ratings ranging from 7 to 5 and determine threshold values indicating shifts in UPV-CCI slope.
The research findings reveal several critical insights into the effects of crack concentrations on the structural integrity of concrete bridge decks. Multiple sensors applied to each bridge deck sample demonstrated sensitivity to varying crack extents and severities, highlighting the importance of advanced monitoring techniques. Samples with the same condition ratings exhibited diverse ranges of CCI, with CR-7 samples showing relatively low values, CR-5 samples displaying significantly higher values, and CR-6 samples falling in between. UPV measurements varied widely across samples, influenced by crack severity. While decks rated as CR-7 generally indicated better overall conditions, UPV data revealed poor localized conditions due to concentrated cracks. A similar pattern was observed in deck samples rated as CR-6 and CR-5, where localized crack concentrations also adversely impacted the UPV measurements. Statistical analysis confirmed significant relationships between UPVs and CCIs for each NBI condition rating, showing that UPVs decrease with increasing CCIs, which indicates that higher crack concentrations have a more adverse impact on structural integrity than evenly distributed cracks. Thresholds derived from UPV and CCI derivatives identified critical damage zones, serving as benchmarks for immediate maintenance actions. Additionally, CCI demonstrated a strong correlation with the compressive strength of concrete (f’c), emphasizing the weighted effects of cracks on structural performance. In essence, this research is pioneering a more nuanced approach to evaluating the structural integrity of bridges by combining the weighted effect of locally concentrated cracks along with conventional crack-related measures such as extent and severity. Additionally, this research contributes to the existing body of knowledge regarding the structural implications of cracks in complex patterns. In practice, this research is expected to enhance the accuracy of bridge condition assessment, which provides a more reliable basis for informed decision-making
Recovery of Natural Gas Equipment Emissions into Gas Compression Engines for the Reduction of Potential Greenhouse Gas Emissions
Get PDFSince the turn of the millennium, the United States (U.S.) oil and natural gas (ONG) industry has nearly doubled its natural gas production rate. As a result, the ONG industry has recently come under increasing scrutiny for its contributions to greenhouse gas (GHG) emissions. Consequently, various solutions to this problem have been proposed and formulated to reduce the impacts of GHG emissions on the environment. West Virginia University (WVU) have found it important to research the impacts of recovering vented gas streams into prime-mover engines. The U.S. Department of Energy (DOE) and National Energy Technology Laboratory (NETL) have granted WVU funding to research and develop a “Methane Mitigator” (M2 ) - a “Scalable Vent Mitigation Strategy to Simultaneously Reduce Methane Emissions and Fuel Consumption from the Compression Industry.” One of the main areas of interest for this research was the collection of emissions from natural gas equipment into a Caterpillar G3508J natural gas compression engine. The parameters being analyzed from the engine were brake-specific emissions and power output. The emissions sources considered for this research were pneumatic controllers (PCs), reciprocating compressor vents, and the engine’s open crankcase breather. The compressor vent and PC emissions were simulated using a mass flow controller (MFC) and flowed into the engine using two separate methods: (1) directly into the air intake, and (2) through a retrofitted closed crankcase ventilation system (CCV), serving as a buffer volume. The crankcase emissions were quantified without the CCV, and the impact on exhaust emissions from circulating the crankcase gases into the intake was measured. The simulated compressor vent and PC flows from the MFC had limited effect on the steady state operation of the engine and resulting performance. When the simulated flows were fed directly into the engine’s air intake, the changes within the engine’s continuous performance and emission parameters were larger but lasted for shorter durations. Conversely, when the simulated flows were fed into the CCV before entering the air intake, the changes in the engine’s performance and emission parameters were less pronounced for continuous analysis but lasted for longer durations. In either case, the continuous emission changes in both emissions and performance varied in size depending on the test scenario being run, but the cycle average changes in emissions and performance showed little impact overall compared to the engine’s baseline operation. As a result, the inclusion of a CCV shows a decrease in baseline carbon dioxide equivalent (CO2-eq.) engine emissions (from combined exhaust and open crankcase) of almost 4%. Likewise, the CCV inclusion reduced baseline total methane (CH4) from combined exhaust and open crankcase by upwards of 16%. These atmospheric emissions only decreased further with the inclusions of collected PC and compressor vent flows. The resulting changes in time-averaged rated exhaust behavior (or lack thereof) prove that the proposed M2 system could likely be deployed at sites with modern lean-burn natural gas engines as a viable option for reducing and eliminating potential GHG sources that would have otherwise been unutilized as energy sources
Modeling of Thermal and Mechanical Behavior of Concrete Containing Supplementary Cementitious Materials
No full textIn high-volume concrete structures, the temperature increment due to hydration can be extremely high. At the same time, the exterior surfaces release heat rapidly, this phenomenon causes large temperature gradients and increases the cracking risk. When the thermal stresses exceed the concrete’s tensile strength, cracking is highly possible. These cracks can reduce the durability of the concrete structures and lead to the corrosion of rebars. Concrete structures with the risk of experiencing thermal cracks are known as “mass concrete”. In RP-312 research projects from WVDOT, finite element models (FEM) were developed to estimate the thermal cracking probability of three different concrete mix designs. Based on the experimentally measured thermal and mechanical properties of three Class M concrete during RP-312, mass concrete definition tables were constructed for three types of pier-stem geometries using the FEM. However, Pier caps and footers can be massive and may have a high probability of early-age cracking. In this study, mass concrete definition tables for four common types of pier-caps with three different mix designs, the 6-bag straight Ordinary Portland Cement (OPC) mix design (Class M Option 1), as well as two thermally friendly mixes with 50% slag replacement (Class M Option 2) or 30% fly ash replacement (Class M Option 3) were developed. The material properties of these mix designs were experimentally measured and used in the thermal stress analysis of the pier caps and footers. Additionally, the mass definition tables were constructed with an insulation value of R = 5 to maximize the size of the non-mass elements. The detailed dimensions of each pier cap type were obtained from the default cross-sections shown in Open Bridge Modeler by Bentley. In West Virginia, three types of pier caps are commonly used in the construction of bridges: hammerhead and pier caps supported on two or three pier stems depending on the number of lanes. The hammerhead pier cap was analyzed for two different lengths, 14-ft (simulating one-lane) and 36-ft (two-lanes). A rectangular pier stem was located at the center of the hammerheads and had a cross-section equal to the bottom of the pier cap to maximize the boundary constraint. For the two-column pier cap, the length was set to be 30-ft (two-lanes) with rectangular columns located 3.3-ft from the end of the pier cap. Similarly, for the three-column pier cap, the length was set to be 40-ft with additional support at the center. Besides, mass concrete definition tables were constructed for four common rectangular footers. Mass concrete definition tables were constructed for rectangular footers with the following dimensions: H (thickness) x 4H (width) x 4H (length), H x 3H x 4H, and H x 4H x 5H. The footer’s templates are for single-column pier stems. An additional case for merged (spread) footers was also analyzed. These footers are commonly H (thickness) x 4H (width) and 6-ft longer than the pier-cap length (i.e., 36-ft length for two-column pier cap). The tables were constructed based on a “worst-case” soil scenario. First, the cracking probability was evaluated for different soil conditions such as dry or wet, and for four types of soils in West Virginia. These cases included steel formwork with and without R = 5 insulation layers. A layer of compacted aggregate was considered as the subbase and analyzed on top of the soil. Furthermore, the tensile stresses developed due to the restrictions from the piles and reinforcements were checked. The mass definition tables were based on the assumptions of the daily ambient temperature variation from 60 °F to 90 °F for summer weather and 30 °F to 60 °F for winter weather conditions. The initial concrete temperature for the summer weather was set to be 75 °F and a placement temperature of 62 °F was considered during the winter conditions. FORTRAN subroutines were developed to perform non-linear thermal stress analysis using ABAQUS during the RP-312 project. The methodology used for creating the pier stem’s mass concrete definition tables was improved to analyze the pier caps and footers with different boundaries. A comparable methodology was implemented for another popular commercially available software, ANSYS Mechanical. A set of subroutines was developed to perform the non-linear transient thermal and viscoelastic stress analysis using ANSYS mechanical considering the degree of hydration-based material properties of early-age concrete. Two separate user material subroutines, USERMATTH for thermal and USERMAT for stress were developed for ANSYS and used in this study. The methodologies were then verified by comparing the temperature and strain measurements of 4-ft cubes against analytical models. The best time to remove the insulated formwork (R=5) was studied using a 14-ft Hammerhead pier cap geometry. Besides, safe construction practices for early insulated formwork removal of different geometries were established. Linear relationships were found between the crack index versus the time of formwork removal for different thicknesses. Besides using R=5 insulation layers, analyses were performed for different geometries with R=2.5 insulation layers as an alternative to increase the maximum allowable sizes. In addition, mass definition tables for non-insulated pier caps and footers were developed for mixes with a water cementitious ratio of 0.42. Furthermore, the thermal shock of hot concrete surface exposed to cold water was extensively analyzed and discussed. The temperature drop of concrete surface after contact with water was measured experimentally and compared to FEM. Using the FEM stress results, an equation was developed to estimate the peak of max principal (tensile) stress. Besides finite element modeling, a multi-component material model was partially developed and validated with experimental measurements. Different cement replacements using GGBFS or Class F fly ash were considered in this model. Different types of GGBFS were hydrated in limewater solution to measure their heat generation separately. The hydration behavior of different GGBFS types was mathematically modeled and incorporated in the multi-component material model to consider the change of degree of hydration based on different GGBFS. Using the material model, the hydration behavior of concrete such as heat of hydration, adiabatic temperature rise, strength, and modulus of elasticity can be evaluated considering the chemical properties of Portland cement, different types of GGBFS, water cementitious ratio, and percentage replacement of GGBFS and Class F fly ash. The material model can potentially improve to provide the thermal and mechanical properties of different concrete mixes for the engineers without the need for time-consuming and expensive experimental measurements. All the analytical models and guidelines developed in this study will enable engineers to take preventative actions to reduce early-age tensile cracking of mass concrete structures
What Standard of Proof Must Employers Satisfy to Demonstrate the Applicability of a Fair Labor Standards Act Exemption?
Get PDFCase at a Glance: Employees of E.M.D. Sales, Inc., an international food distributor, sued E.M.D., alleging that it violated the Fair Labor Standards Act (FLSA) when it withheld overtime wages from these employees. As an affirmative defense, E.M.D. asserted that the employees were FLSA‑exempted outside salesmen. This case asks the Court to determine whether employers must use the preponderance-of-the-evidence standard or the clear-and-convincing evidence standard to prove the applicability of an exemption under the FLSA
Making Something Out of Nothing: Immobility as an Operant
Get PDFThe tradition of research in the experimental analysis of behavior generally emphasizes the analysis of overt, discrete responses such as lever presses or key pecks. Reflecting this emphasis, definitions of behavior involve the observable action or movement of an organism through space. Although continuous responses involving little to no movement, such as “holding still” or “immobility”, fall outside these definitions, immobility is a form of continuous, operant responding that can be learned and experimentally controlled. Three experiments were conducted to investigate parameters surrounding immobility as an operant. In Experiment 1, immobility in the form of platform-standing bouts was shaped and maintained at steady state on a fixed-duration schedule analogous to a fixed-ratio 1 schedule. The effects of two reinforcement contingencies (one that reinforced remaining on the platform and one that reinforced remaining on the platform and then exiting) on reinforced standing-bout durations were assessed. Reinforced standing-bout durations were differentially controlled, where bouts were systematically longer when platform exit was reinforced. In Experiment 2, each pigeon was exposed to a series (5-55 s) of duration requirements across sessions, in which standing on a platform for a minimum duration was reinforced under both aforementioned reinforcement contingencies. Standing bouts were differentially controlled by bout-duration requirements in both conditions and increased in duration as the duration requirements were increased. Postreinforcement pause durations also increased with duration requirements under both conditions. Finally, Experiment 3 examined extinction of the standing bouts and demonstrated spontaneous recovery of immobility. These results collectively suggest that immobility can be shaped, maintained, differentially controlled, and extinguished like other operant responses
α-Hydroxy C–H Functionalization of Alcohols via Boronic Acid, HAT, Photoredox Triad Catalytic System
No full textThis dissertation explores the research that I have conducted in my time at West Virginia University. Most of my work has focused on the development of methods and studies to further understand the α-OH C–H functionalization of alcohols. This work involves a system of catalysts including photocatalysts, HAT catalysts, and boronic acid catalysts. Chapter 1 highlights a background for each of these areas. Photoredox catalysis has been an increasing area of chemistry over the past two decades as this technique can be used to design conditions to form new bonds in a selective manner through the utilization of light energy. HAT catalysis is another rising area of chemistry that forms reactions through radical pathways rather than traditional chemical pathways where reactions are completed through electrons moving as pairs. HAT works by abstracting a hydrogen from a generally inert C–H bond to selectively functionalize the substrate. Boron reagents have been used in a variety of ways to induce the reactivity of alcohol substrates. This is mainly due to the high exchange rate between B–O bonds, which allows for boron oxide catalysts to react with alcohols to form boron esters. While in the boron ester state, additional reagents can be applied to alter the substrate. These techniques have been combined to explore the α-OH C–H functionalization of alcohols through the application of photocatalysis, HAT catalysis, and boronic acid catalysis.
Chapter 2 explores the α-OH C–H functionalization of diols. In this chapter, a method was developed to selectively alkylate the α-OH position of diols with arylboronic acids, quinuclidine, and phtotcatalysis. The mechanism of this reaction proceeds through the abstraction of the α-OH C–H bond of the activated boronate complex formed between the diol, boronic acid, and quinuclidine. Through kinetic analysis, this reaction is observed to be faster with reduction of electron density of arylboronic acids. 1H and 11B NMR experiments indicate that the difference in reaction rates is caused by a more labile equilibrium with the use of electron-poor boronic acids.
Chapter 3 explores the α-OH C–H alkylation of mono-alcohols and how they compare to diols by applying the method developed in Chapter 2. Direct competition shows that the reaction is selective for diols over both primary and secondary mono-alcohols. 1H NMR experiments showed that this is due to a higher binding affinity of the boronic acid to the diol compared to the mono-alcohol. Kinetic analysis shows that the α-OH C–H alkylation of mono-alcohols is increased with the use of electron-poor arylboronic acids, which is again proposed to be due to the difference in equilibrium as indicated by 11B and 1H NMR analysis. A small substrate scope was explored for this reaction, which presents functional group tolerance for a variety of more complex primary mono-alcohols.
Chapter 4 combines the work of the Hilton and Popp groups by exploring the α-OH C–H alkylation of alcohols with ß-carboxyboronic acids. It was hypothesized that these bifunctional boronic acids would form an active substrate-boronate ester in a more favorable manner due to the inclusion of the Lewis basic site on the boronic acid. ß-carboxyboronic acids are applicable to the alkylation of both diols and primary mono-alcohols. Kinetic studies show that the application of ß-carboxyboronic acids significantly increases the reaction rate for primary mono-alcohols compared to the application of arylboronic acids. Additionally, the yield of alkylation for primary mono-alcohols is increased with the use of ß-carboxyboronic acids. NMR studies with both diols and mono-alcohols indicate the formation in the active boronate species as the major species due to the presence of distinct signals in both 11B and 1H spectra. This is different from what is observed with arylboronic acids where multiple species are observed via NMR analysis. Because of the increased rate of alkylation, increased overall yield, and presence of one species observable by NMR, it is proposed that the formation of the active boronate species is more favorable with the utilization of ß-carboxyboronic acids compared to arylboronic acids