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- ItemDesign of Rigid Overlays for Airfield Pavements(1987) Rollings, Raymond Sydney; Witczak, Matthew W.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Existing rigid overlay pavement design methods are empirical and use a specified level of cracking as the defined failure condition. The existing empirical designs are based on tests run thirty years ago, and current analytical models provide greatly improved abilities to examine the overlay pavement structure. Emphasis by many agencies on life cycle cost analysis and more sophisticated maintenance and rehabilitation strategies require methods of predicting pavement performance rather than simply developing safe designs. A layered elastic analytical model was selected to evaluate stresses from applied loads in the pavement structure. Pavement performance was measured in terms of a Structural Condition Index which related the type, degree, and severity of pavement cracking and spalling on a scale of 0 to 100. Models were developed to represent the effect of cracking in base slabs under the overlay, to account for fatigue damage of previous traffic on the base pavement, and to account for the effects of substandard load transfer at slab joints. The predicted performance of overlays and pavements using this analysis was checked against the results of full-scale accelerated traffic tests conducted by the Corps of Engineers and against current overlay design methods and was found to provide reasonable agreement. This methodology using the layered elastic analytical model and analysis of fatigue and cracking in the base slab provides a method of predicting pavement and overlay deterioration in terms of a Structural Condition Index.
- ItemStress-Controlled Versus Strain-Controlled Triaxial Testing of Sand(1994) Alqutri, Samir Ahmed; Goodings, Deborah J.; Civil Engineering; University of Maryland (College Park, Md); Digital Repository at the University of MarylandThe purpose of this research was to compare the strength characterizations of Mystic White Silica Sands using stress-controlled loading versus strain-controlled loading in a standard compression triaxial tests. To this end one hundred sixty-six tests were conducted involving two types of quartz sand, one fine MWSS45 and one medium coarse MWSS18 , tested at three low to intermediate confining stresses of 14 kN/m2, 28 kN/m2 and 55 kN/m2 with only one specimen diameter size of 71.1 mm. Of the one hundred sixty-six tests, eighty-six were stress-controlled tests and eighty were strain-controlled tests. All specimens were dry, but both loose and dense specimens were tested. The results were evaluated individually and as group. Comparison of the two types of loading tests were evaluated for repeatability, stress-strain characteristics and strength parameters. The plots show that stress-controlled loading in general gives more reproducible results with smoother. steeper stress-strain plot s and a larger average deviator stresses at failure than strain-controlled loading at all three levels of confining stresses for both sands. This results in somewhat larger values of Φ' . Stress-controlled specimens were stiffer and failed with a clear cut failure surface while strain-controlled specimens mostly barreled.
- ItemStress Intensity Factors for Structural Steel I-beams(1996) Feng, Daqing; Albrecht, Pedro; Sanford, Robert J.; Civil and Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The application of fracture mechanics to highway steel bridges has been hampered by a lack of stress intensity factor (SIF) solutions for cracks in I-beams. Previous work cannot provide satisfactory solutions. In this study, the finite element analysis method was used to develop accurate SIFs for two-tip and three-tip cracks in I-beams under tension or bending. Cracked I-beams were modeled with eight-node shell elements, with the web and flanges being fully joined along the junction lines. The region around the crack tips, singularity quarter-point elements were used. To ensure accurate and converging solutions, mesh patterns around the crack tips were studied. Also, different methods of extracting SIFs from FEA results were discussed based on benchmark problem studies. Governing parameters for cracked I-beams were determined. For two-tip web cracks, the SIFs are functions of applied stress, crack length, eccentricity, and flange-to-web cross-sectional area ratio. For three-tip cracks in web and flange, the SIFs are functions of applied stress, web and flange crack lengths, and flange-to-web cross-sectional area ratio. The flange-to-web area ratio describes the constraining effect of the flange on the web crack of a two-tip cracked I-beam; the interaction forces between web and flanges greatly affect SIFs for a three-tip cracked I-beam. The SIFs were calculated based on a total of 2,106 FEAs performed for a wide range of the parameters. The results were fitted with equations for ready use by practicing engineers. An example illustrates the calculation of SIFs for a three-tip crack in a composite steel-concrete beam of a steel bridge.
- ItemFINITE ELEMENT ANALYSES OF PARTIALLY REINFORCED MASONRY SHEAR WALLS(1996) Love, Aaron Ray; Chang, Peter; Civil & Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Partially reinforced shear walls are used in regions of relatively low seismic risk. Nevertheless, these structures should be capable to resist some lateral motion. The purpose of this paper is to examine the behavior of in-plane cyclic load tests of typical partially-grouted masonry shear walls and the capability of FEM/I in simulating their response. FEM/I is a nonlinear finite element program originally developed for reinforced masonry shear walls with a uniform grid of orthogonal reinforcement at close spacing. FEM/I has successfully simulated the response of fully grouted uniformly distributed reinforced masonry walls [Ewing, 1987]. FEM/I uses a smeared property approach in which the reinforcing steel and masonry composite is modeled as a single material. The applicability of FEM/I to partially grouted partially reinforced masonry shear walls is measured by comparing FEM/I force-displacement cycles, peak lateral forces, strains, energy dissipation and crack patterns with those generated from the experimental tests conducted at the National Institute of Standards and Technology. Partially reinforced shear walls can be modeled in FEM/I by smearing the steel over the blocks which are grouted and reinforced. The ungrouted blocks can be modeled as reinforced blocks with a reinforcement ratio of zero. This approach was shown to be adequate when the displacements and cracks were small. As the cracks increase in size, the smeared property assumption can no longer adequately represent the wall• s geometry and it's property. The result is a poor prediction of both local and global behavior at large displacements. The ratio of the lateral loads at the first major event (FME) demonstrate a good relationship in the forces generated by FEM/I for each wall with the exception Wall I. Results from Walls 3, 5, 9 and 11 exhibit FEM/I was able to predict the lateral load adequately up to the FME. The ratio of the lateral load up to the FME ranges from 0.9 - 1.3. After the occurrence of the FME, FEM/I overpredicts the lateral load considerably. In each of the finite element analyses, FEM/I overestimated the peak strength of the masonry specimens. The FEM/I models for Wall 11 and Wall 3 produced the best prediction of the peak strength. The difference for these two walls in the FEM/I predicted maximum lateral load and experimental data were 31 o/o and 41 o/o, respectively. Individual force displacement cycles are plotted at the various stages in the displacement history. FEM/I performs fairly well in predicting the force displacement response of the experiment. Walls 3, 5, 9 and 11 exhibit a good force displacement relationship for the first half of their displacement history until the development of major cracks. Wall 7 corresponded well with the experiment during the initial stages (Cycles 1 -17) of its displacement history. FEM/I did not produce good results in representing the cracking pattern generated by the experimental study. The inability of modeling the crack pattern is also shown in the differences in the plots for the amount of energy dissipated. FEM/I did reasonably well in the prediction of yielding in the vertical reinforcement. Local stress and strain of masonry predicted by FEM/I did not match the experimental data.
- ItemSCALING OF SURFACE ENERGY FLUXES USING REMOTELY SENSED DATA(2001) French, Andrew Nichols; Brubaker, Kaye L.; Civil and Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Accurate estimates of evapotranspiration (ET) across multiple terrains would greatly ease challenges faced by hydrologists, climate modelers , and agronomists as they attempt to apply theoretical models to real-world situations. One ET estimation approach uses an energy balance model to interpret a combination of meteorological observations taken at the surface and data captured by remote sensors. However, results of this approach have not been accurate because of poor understanding of the relationship between surface energy flux and land cover heterogeneity, combined with limits in available resolution of remote sensors. The purpose of this study was to determine how land cover and image resolution affect ET estimates. Using remotely sensed data collected over El Reno, Oklahoma, during four days in June and July 1997, scale effects on the estimation of spatially distributed ET were investigated. Instantaneous estimates of latent and sensible heat flux were calculated using a two-source surface energy balance model driven by thermal infrared, visible- near infrared, and meteorological data. The heat flux estimates were verified by comparison to independent eddy-covariance observations. Outcomes of observations taken at coarser resolutions were simulated by aggregating remote sensor data and estimated surface energy balance components from the finest sensor resolution (12 meter) to hypothetical resolutions as coarse as one kilometer. Estimated surface energy flux components were found to be significantly dependent on observation scale. For example, average evaporative fraction varied from 0.79, using 12-m resolution data, to 0.93 , using 1-km resolution data. Resolution effects upon flux estimates were related to a measure of landscape heterogeneity known as operational scale, reflecting the size of dominant landscape features. Energy flux estimates based on data at resolutions less than 100 m and much greater than 400 m showed a scale dependent bias. But estimates derived from data taken at about 400-m resolution (the operational scale at E l Reno) were susceptible to large error due to mixing of surface types. The El Reno experiments show that accurate instantaneous estimates of ET require precise image alignment and image resolutions finer than landscape operational scale. These findings are valuable for the design of sensors and experiments to quantify spatially-varying hydrologic processes.
- ItemEstimating the Spatial and Temporal Distribution of Snow Water Equivalent Within a Watershed(2003-10-30) Menoes, Michael Charles; Brubaker, Kaye L.; Civil EngineeringThe goal of this research was to develop a spatial-temporal model to forecast the snow water equivalent (SWE) within a watershed. This model defined the relationship between the physical parameters of a watershed and the spatial distribution of SWE within that watershed. Many models of snowmelt runoff rely on snow depletion curves, which describe the seasonal decline of snow covered fraction and SWE, assuming some interannual uniformity of basin response. The null hypothesis associated with this research was that the spatial and temporal variability of SWE within a watershed is a random process that is independent of the physical characteristics of the watershed. A conceptual model of spatially distributed SWE accumulation and depletion that can be calibrated and validated with spatially distributed observations was created. The effects of the physical variables and parameters on the SWE distribution within a watershed were demonstrated, and both significant and insignificant physical variables and parameters were identified. How data were used in the calibration/validation of the model was demonstrated, including showing the benefit of additional data on model accuracy. Finally, the proper calibration and validation of the model using an actual watershed was demonstrated on three different watersheds. Results of the research were mixed in terms of accepting or rejecting the null hypothesis. Created SWE maps and satellite images of the Upper Rio Grande Watershed visually suggested that similar SWE patterns exist for this watershed. An analysis of the data from the SNOTEL sites within the Upper Rio Grande Watershed also suggested the existence of similar interannual SWE patterns within the watershed. This analysis supports the Depletion Curve Theory. However, an analysis of the SWE distributions for the three watersheds, performed utilizing the Kolmogorov-Smirnov Two-Sample Nonparametric Test, suggested that consistent interannual SWE patterns do not exist for the watersheds studied. This analysis contradicts the Depletion Curve Theory.
- ItemBehavior and Performance of High Performance Concrete for Pavements(2003-11-24) Kim, Haejin; Goulias, Dimitrios G; Schwartz, Charles W; Aggour, M. S; Civil EngineeringUnder TE 30, High Performance Concrete Pavement program, several states are undertaking a variety of innovative research in high performance concrete pavement materials and innovative design/construction features. This project addressed the needs of Maryland State Highway Authority in exploring the use of fiber reinforced and low shrinkage concrete in pavements. Past experience with these materials have indicated i) potential benefits in flexural fatigue resistance and reduction in crack development, and ii) potential reduction in slab warping effects with implications on pavement slab longevity. The objective of this study was to examine the design and lab performance of these materials for Maryland conditions, monitor their lab and field performance, and quantify potential benefits. Extensive fatique modeling was undertaken for developing the fatigue relationships and SN curves for these mixtures. In addition, finite element analysis (FEM) was used to model the behavior of these materials in field conditions and developing the base analytical model to be used in comparing future behavior and performance of the pavement test sections with these mixtures.
- ItemIntegrated Management of Highway Maintenance and Traffic(2003-12-05) Chen, Chun-Hung; Schonfeld, Paul M; Civil EngineeringHighway maintenance, especially pavement rehabilitation or resurfacing, requires lane closures. This work develops an integrated model to help highway agencies in developing traffic control plans for maintenance activities and in efficiently managing traffic around highway work zones. Thus, the objective of this study is to develop methods for optimizing work zone characteristics in order to minimize the combined total costs for highway agencies and users. Work zone models are developed for three cases. For Case 1, with steady traffic inflows, four alternatives for two-lane highways and four alternatives for four-lane highways are proposed. Analytical solutions are found for optimized work zone lengths and diversion fractions based on minimizing the total cost. Guidelines for selecting the best alternative for different characteristics of traffic flows, road and maintenance processes are developed by deriving thresholds among alternatives. In Case 2, the models for two-lane highway and four-lane highway work zones for time-dependent inflows are developed. Two optimization methods, Powell's and Simulated Annealing, are adapted for this problem and compared. In numerical tests, a Simulated Annealing algorithm yields better solutions using less computer time than Powell's Method. The SAUASD (Simulated Annealing for Uniform Alternatives with a Single Detour) algorithm is developed to find the best single alternative within a maintenance project. The SAMASD (Simulated Annealing for Mixed Alternatives with a Single Detour) algorithm is developed to search through possible mixed alternatives and diverted fractions in order to further minimize total cost. Thus, traffic management plans with uniform alternatives or mixed alternatives within a maintenance project are developed. For Case 3, work zone optimization models for a road network with multiple detour paths and the SAMAMD (Simulated Annealing for Mixed Alternatives with Multiple Detour paths) algorithm are developed. Analyses based on the CORSIM simulation are used not only to estimate delay cost, but also to evaluate the effectiveness of optimization models. A comparison of the results from optimization and simulation models indicates that they are consistent. The optimization models do significantly reduce total cost, including user cost and maintenance cost, compared to the total cost of the current resurfacing policy in Maryland.
- ItemDEVELOPMENT OF AN INTEGRATED NETWORK SIMULATOR FOR REAL TIME TRAFFIC MANAGEMENT: I-95/US-1 TRAFFIC SIMULATOR(2003-12-12) Zou, Nan; Chang, Gang-Len; Schonfeld, Paul M; Haghani, Ali; Civil EngineeringThis study presents a network simulator that integrates the knowledge base with a microscopic traffic simulation model for real-time traffic management. The proposed system offers three main functions: incident management, work-zone operations and recurrent congestion monitoring. The knowledge base is used to inventory the operational experience and traffic impacts associated with all previously recorded incidents. Such information will be used along with an embedded prediction module to estimate the duration of a detected incident. The proposed system will enable traffic control operators to perform two critical tasks during the incident management period: (1) establishing a reliable estimate of traffic impacts; and (2) performing a subsequent real-time analysis of network traffic conditions. The simulation results will also offer information for estimating travel time at varying departure times for different origins and destinations during the period of incident operations.
- ItemINTEGRATED ANALYSIS OF VERTICAL ALIGNMENTS AND SPEED PROFILES FOR RAIL TRANSIT ROUTES(2003-12-16) Yeh, Shu-Ta; Schonfeld, Paul M; Civil EngineeringFrequent accelerations and decelerations for rail transit trains adversely affect in the major performance measures of travel time, tractive energy consumption and braking wear between stations. A dipped vertical alignment between rail transit stations provides trains some added advantages from gravity in accelerating as well as in decelerating. A deterministic simulation model based on basic kinematics and resistance relations has been developed to compute train motions and energy consumption on specified vertical alignments. A baseline case study and the sensitivity of results to parameter changes are analyzed. Vertical alignments and operating characteristics such as speeds and coasting distances are jointly optimized. Powell’s Method is used for numerically optimizing total costs and other objective functions. Without speed constraints, the optimized total cost savings exceed 6.5%. The optimized alignment depths and total cost savings decrease as speeds are constrained to lower values. The methods developed here may significantly improve rail transit systems.
- ItemCharacterization of Unbound Pavement Material for Mechanistic-Empirical Performance Prediction(2003-12-16) Wambura, Gervas Kehengu; Schwartz, Charles W; Civil EngineeringUnbound materials provide a significant portion of the structural capacity of layered flexible pavement systems. Recent advances in mechanistic-empirical modeling for pavements make it now possible to predict pavement performance in terms of fundamental engineering properties such as the resilient modulus and permanent deformation characteristics. The resilient modulus and permanent deformation characteristics of four coarse-grained unbound base materials and four fine-grained natural subgrade materials are evaluated via laboratory testing in this study. Specific details of the testing protocols including differences between large vs. small specimen response, sample conditioning effects, and the influence of stress level are investigated. The material property data measured in this study provide a valuable contribution to the small but growing database of typical values as required in the forthcoming new national pavement design guide (2002 Design Guide, 2003).
- ItemTracking Vehicles using the geolocation capabilities of the Celluar Phone: Is is feasible?(2003-12-16) Anderson, Leon Ffloyd; Lovell, David J; Civil EngineeringIn 1996, the U.S. Federal Communications Commission (FCC) made it mandatory for all wireless communications services, such as mobile phones, to be equipped with Automatic Location Identification (ALI) capability. This required that all public safety answering point (PSAP) attendants who answer a 911 call from a cellular phone be able to locate the caller to a specified degree of accuracy. This requirement was the impetus that led to momentous technological activity to provide means to geo-locate wireless phone calls. The interest amongst transportation professionals in using this technology for fleet management applications was supervenient. This thesis investigates the feasibility of tracking vehicles, for example school buses, using the cellular phone geo-location technology. Specifically, the accuracy (or errors) of the RadioCamera technology of TrafficMaster (formerly US Wireless Corporation) will be evaluated and a conclusion on its suitability for vehicular tracking made.
- ItemMapping Snow Cover in Siberia Using GIS and Remote Sensing(2003-12-16) Saini, Aditya; Brubaker, Kaye L; Civil EngineeringThe seasonal snowpack dynamics of the Siberian mountains and plains play a critical role in the freshwater fluxes of northern rivers into the Arctic Ocean. This study is part of a larger project seeking to quantify the freshwater discharge of the Ob River (Russia) to the Arctic, using satellite remote sensing and hydrologic modeling. Subareas of the Tom River watershed (a tributary to the Ob) are delineated using digital elevation and land cover data within a Geographical Information System (GIS). Daily satellite snow images for 1981 to 1985 are analyzed with the GIS to give time series of percent snow cover for each subarea. These time series are compared with model-generated snow cover visually and statistically, allowing spatially distributed evaluation of the model's snow sub-routines. This study will contribute to improved models and better understanding of important and climate-sensitive snow processes and freshwater supply in Arctic river basins.
- ItemForecasting Odor Levels for Biosolids Production Based on Ambient Conditions(2004-01-06) Vilalai, Sirapong; Gabriel, Steven A.; Seagren, Eric A.; Baecher, Gregory B.; Civil EngineeringBiosolids are the solid residuals of wastewater treatment that have been treated to reduce pathogens and can be used as fertilizer for agricultural purposes. The major disposal option of biosolids from wastewater treatment plants is land application. Since biosolids odor quality is inconsistent, there is a possibility that odorous biosolids can be distributed to field sites nearby residential areas. The objective of this thesis was to create statistical models using the processing data and ambient conditions at Blue Plains wastewater treatment plant to predict biosolids odor levels. The model shows that FeCl3 addition in the primary process, lime addition, the number of centrifuges out of service and the temperature at the plant are parameters that can be used to predict biosolids odor.
- ItemWater Quality Characterization of Highway Stormwater Runoff from an Ultra-urban Area(2004-01-30) Flint, Kelly; Davis, Allen P; Seagren, Eric A; Torrents, Alba; Civil EngineeringWater quality of highway stormwater runoff from an ultra-urban area was characterized by qualitatively and quantitatively defining flushing and determining the event mean concentration (EMC) and annual pollutant loadings for TSS, total phosphorus (TP), NO3-, NO2-, TKN, Cd, Cu, Pb and Zn. Characterization aids in evaluation of the performance of a retrofit bioretention facility. Furthermore, this research contributes to the limited data available on recent characterization of runoff from urban areas. Mean EMC's in mg/L were 0.04, 0.11, 0.22, 1.18, 420, 3.4, 0.96, and 0.56 for Cd, Cu, Pb, Zn, TSS, TKN, NO3+2-, and TP. Median values for the mass flushed in the first 25% of runoff were greater than the mass flushed in a 25% portion beyond the first, except for TSS and Cd. The mass in later 25% portions were greater than in the first 25% in 17% of the events for all pollutants.
- ItemEngineering bioretention for treatment of urban storm water runoff(2004-04-19) Hsieh, Chi-hsu; Davis, Allen P; Civil EngineeringBioretention, a "Low Impact Development" urban storm water best management practice, was developed in the early 1990's. Although bioretention has been used at many areas in the United States, the impact of this technology on ground and surface water quality as well as the optimal design of bioretention media for pollutant removal, have not been systematically investigated. The objectives of this study were to investigate the effectiveness of this technology for storm water runoff treatment and finally to give recommendations for future design. The methods used included developing pollutant removal performance curves for a variety of bioretention media mixes and evaluating the effectiveness of existing bioretention facilities. Synthetic runoff, which contained oil and grease (O/G), suspended solids (SS), lead (Pb), phosphorus (P), nitrate, and ammonium, was employed in laboratory experiments and 6 on-site bioretention evaluations. Two more on-site experiments were conducted during a rainfall event to compare with laboratory investigations. Overall, all bioretention columns and on-site facilities demonstrated excellent removal for O/G and Pb. TSS removal was good in columns, but washing out of media particles was noted in field facilities, mostly from new installations. For nutrients treatment during a 6-hr experiment, the removal efficiency of Total P ranged widely and appears to be related not only to chemical properties of the media, but also to the flow behavior of runoff through the media. Results from batch P sorption tests on six media, three continuous column studies, and two repetitive 6-hr bioretention columns with total 28 repetitions showed that the medium with a higher P sorption capacity can retain more P from the infiltrating runoff after a high P loading. However, the sorption data alone is not adequate to predict the P retention through a bioretention column for a short-term experiment due to the complicated processes occurring between the runoff and media. Unless special provision were made, all media employed in this study were ineffective in removing nitrate and ammonium. The removal efficiency of both pollutants was improved by increasing the water holding capacity of the media and enhancing the development of nitrification and denitrification processes in the bioretention column.
- ItemAN EXPLICATION OF AIRFOIL SECTION BENDING-TORSION FLUTTER(2004-04-30) Wheeler, Philip Curtis; Medina, Ricardo; Civil EngineeringThis thesis examines the dynamic instability known as flutter using a two-degree-of-freedom airfoil section model in both quasi-steady and unsteady flow. It explains the fundamental forces and moments involved in the bending-torsion flutter of an airfoil section, and demonstrates a solution method for determining the critical flutter frequency and speed for both flow cases. Additionally, through the use of a programmed Mathcad 11 worksheet, it evaluates the flutter characteristics of six example sections, illustrating the effects of the elastic, inertial and aerodynamic properties of an airfoil section. For each section, a parametric study of the effect of the section Center of Gravity position along the section chord is performed. The flutter frequency and speed are calculated using both quasi-steady and unsteady aerodynamic forces and moments, and the results compared. Software used was MathSoft Mathcad 11, Microsoft Word and Intergraph Smart Sketch LE.
- ItemEMBEDDED STRAIN SENSOR WITH POWER SCAVENGING FROM BRIDGE VIBRATION(2004-05-03) Wang, Ming; Chang, Peter C; Civil EngineeringThe Objective of this thesis is to investigate an embedded strain sensor system with power scavenged from highway bridge vibration for structure health monitoring. A power scavenging scheme is developed to power the sensor system so as to eliminate the dependence of batteries. Three mechanisms (PZT patch, cantilever beam and PZT stacks/slugs) are described that are suitable for the remote sensor system to scavenge mechanical energy at different locations in a bridge. Calculations and experiments are taken to examine the feasibility of the idea, and predicted power generation is compared to solar/light power. A scheme of an embedded strain sensor using resonant MEMS beam structure is introduced along with the theoretical analysis and simulation. The last consideration is the signal propagation attenuation in concrete. Measurements are taken to determine the RF signal attenuation at 900 MHz range transmitted through a concrete slab. Theoretical calculations are validated by experimental results.
- ItemMODELING WATER QUANTITY AND WATER QUALITY WITH THE SWMM CONTINUOUS STREAMFLOW MODEL UNDER NON-STATIONARY LAND-USE CONDITION USING GIS(2004-05-04) Medina, William; Moglen, Glenn E.; Civil EngineeringGIS data widely available today can be used to better estimate watershed parameters for the SWMM model. An interface was developed to create SWMM input files from spatial data. The interface delineates watersheds and allows update of land-use parameters. SWMM performs continuous simulation but it assumes a time-invariant land use. A "hot-start" technique was developed that uses end values from one year's simulation to initialize state variables for the next year. This technique allows for dynamically changing the land use model parameters to reflect changes in time. Based on the simulation results, three regression models were developed to adjust constant land-use model results to account for land use changes in peak discharges, baseflow, and total phosphorus loads. These adjustments use imperviousness as an index of land use changes. The regression equations adjust streamflow and water quality results from a constant land use SWMM simulation to conditions with time-varying land use.
- ItemTHE INFLUENCE OF EXPOSURE CONDITIONS ON DELAYED ETTRINGITE FORMATION IN MORTAR SPECIMENS(2004-05-05) Ceesay, Jorgomai; Amde, Amde M; Civil EngineeringThe objectives of this research were to experimentally study the influence of exposure conditions on delayed ettringite formation (DEF) in mortar specimens, and to explore the complex processes of expansive cracking associated with DEF. Different exposure conditions were investigated while other parameters such as water-to-cement ratio, fine and coarse aggregates, cement and curing conditions were kept constant in order to study the influence of storage conditions on mortar damages associated with DEF. Mortar bars and cubes were prepared using Portland cement ASTM Type III, Frederick sand and ordinary tap water. The specimens were steam-cured and then subjected to the Duggan heat cycle to introduce microcracks. Control batches of mortar mixes with no additional potassium (K2O) content and sets with additional potassium increasing the overall potassium level to 1.5% K2O by weight of cement were prepared. Increasing the potassium level has a deleterious effect on the specimen expansion and causes deterioration in compressive strength. Length change measurements according to ASTM C490 and weight changes of the mortar bars were constantly monitored during the study. The pH value, Potassium ion [K+], Sodium ion [Na+] and Calcium ion [Ca2+] concentrations of the storage solutions were also monitored to analyze the amount of alkali being leached into the water. Scanning electron microscope (SEM) equipped with high-energy dispersive analysis X-ray was used to identify materials present in the cavities, transition zones and cracks to determine failure mechanism of the specimens. X-ray computed tomography (X-ray CT), a non-destructive method was employed to reveal the internal crack patterns. Ettringite crystals are mainly found in the cavities, in the interface between the aggregate and cement paste. Mortar bars subsequently stored in exposure conditions 1 (water pH maintained at 12.5) and 2 (plain water) after the Duggan heat cycle, clearly showed expansion against weight change results to be positive linearly correlated over the storage period. This was again observed in the mortar specimens with the higher potassium (K2O) content. Results from the petrography analyses of the expanded mortar specimens revealed delayed ettringite formation (DEF) without detecting alkali-silica reaction (ASR). The results also show that deleterious expansions caused by DEF prevails in exposure conditions with high potential leaching of alkali hydroxide to the storage solution.