Engineering Commons^™

Numerical Modeling To Evaluate The Performance Of Slow-Release Candles For Groundwater Remediation, Chuyang Liu

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Slow-release candles (SRC) have been developed as a cost-effective technology to treat groundwater contaminants by passively delivering oxidants into the subsurface over a long time. In this thesis, a numerical model has been developed to simulate oxidant release kinetics, transport, and reaction in a field scale. Parameters of the model were obtained from a field site with SRC installed. Modeling results showed that the radius of influence of oxidants was influenced by the relative contribution of reaction and solute transport, and the limited lateral spreading could be an issue to restrict the application of SRC.

Enhanced aeration could increase or …

Viscoelastic Analysis And Fatigue Characterization Of Bituminous Materials In Two Length Scales Under The Influence Of Aging, Santosh Reddy Kommidi

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Fatigue cracking in asphalt concrete (AC) is of immense importance to pavement design and analysis because it is one of the most important forms of distress that can lead to structural failure in pavement. Once started, these types of cracks can be combined with other environmental factors leading to detrimental effects such as faster rates of pavement deterioration and shortened pavement life and functionality.

Currently AASHTO TP101, also known as linear amplitude sweep (LAS) specification, is being widely used to evaluate the ability of an asphalt binder to resist fatigue. The LAS method, although mechanistic in its approach, has certain …

Simulation And Prediction Of The Groundwater Level In The Surrounding Area Of The Nebraska Management System Evaluation Area Site In Central Nebraska., Cesar Augusto Gomez Peña

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

An efficient water budget is necessary to develop sustainable practices in irrigated lands and determine future trends. Despite a lack of detailed knowledge, climate change is found to profoundly influence groundwater resources through changes in groundwater recharge, groundwater elevation, and groundwater flow processes. Prediction of the groundwater level (GWL) under a changing climate is essential to improve agricultural management.

The goal of this research is to predict the GWL from 2056 to 2060 in the surrounding area of the MSEA. In order to achieve the target, the first research task is to develop a groundwater flow model and then simulate …

Molecular Dynamics Modeling And Simulation Of Bitumen Chemical Aging, Farshad Fallah

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Chemical aging of asphalt binder leads to significant changes in its mechanical and rheological properties, resulting in poor pavement behavior and distress. Various laboratory methods have been used to simulate asphalt aging during the service life of the pavement. However, controversy exists regarding the capability of these methods to predict field aging, as various factors interact with the pavement during service and the mechanism behind aging is not fully understood. The two main outcomes of chemical aging are oxidation of asphalt molecules, and change in asphalt SARA (saturate, aromatic, resin, and asphaltene) fractions. Reaction of oxygen with asphalt components forms …

Hyperelastic Structural Fuses For Improved Earthquake Resilience Of Steel Concentrically-Braced Buildings, Francys López-Mosquera

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Improving structural resilience (i.e., reducing service interruptions and improving rapidity of function restoration) following extreme events is one of the primary contemporary challenges in structural engineering. While massive casualties have successfully been avoided through the adoption of modern building codes, the sole codified performance objective has been limited to the life safety/collapse prevention range of response. Christchurch, NZ, highlighted the insufficiency of this approach, with large sections of the city nonfunctional after a major earthquake, and with subsequent collapses induced by significant aftershocks. Engineering advances to improve building and community resilience are necessary to mitigate hazards from becoming disasters. This …

Broadening Understanding Of Roundabout Operation Analysis: Planning-Level Tools And Signal Application, Ahmed Buasali

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

In United States, roundabouts have recently emerged as an effective and efficient alternative to conventional signalized intersections for the control of traffic at junctions. This thesis includes two investigations related to the operations of roundabouts.

The first investigation examines the ability of a planning-level tool (the critical sum method) to serve as an indicator variable for the results of the Highway Capacity Manual’s average delay per vehicle measure for a roundabout facility; to what extent do the results of one predict the results of the other? The critical sum method was found to accurately predict the HCM average delay per …

Injury Severity Of Truck Drivers In Crashes At Highway-Rail Grade Crossings, Waleed Ali Khan

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

There is a noticeable difference between different road users, specifically between passenger vehicles and heavy vehicles such as its length and weight. The majority of previous research were focused on general highway traffic that included passenger cars, trucks, buses, motorcycles, etc. Moreover, HRGC safety studies of specific types of vehicles are relatively few and heavy vehicle safety at grade crossing is even more under-explored.

This research thus focuses on the following objectives: Identify factors related to different injury severity levels of heavy-vehicle drivers (truck/truck-trailer) drivers in crashes reported at HRGCs; to identify a more suitable statistical model for injury severity …

Bias And Other Error In Gridded Weather Data Sets And Their Impacts On Estimating Reference Evapotranspiration, Philip A. Blankenau

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Gridded weather data sets are increasingly used in a variety of hydrologic and agricultural applications due to their complete spatial and temporal coverage. One application of gridded data sets is the estimation of evapotranspiration (ET). Several operational remote sensing (RS) approaches for estimating ET, such as the SEBAL, METRIC and EEFlux models, require estimates of reference ET (ETref), where ETref is expected ET from a hypothetical reference crop of clipped grass or alfalfa. Gridded weather data provide for the computation of ETref in all areas of a remote sensing image, and therefore potentially remove the need for dense weather station …

Impact Of Using Spatially Distributed Soils Information On Flood Hydrograph Simulation With Hec-Hms, Matthew J. Nelson

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Hydrologic rainfall-runoff models employ numerical equations to simulate the soil absorption of rainfall and resulting runoff. A number of methods have been developed to model these processes, but the parameters used to define these methods can be difficult to directly measure due to the variable nature of soil properties. They often rely on estimation of hydraulic and hydrologic parameters and calibration to produce accurate results.

A challenge with runoff method parameterization is the need for oversimplification using a lumped modeling approach. While distributed hydrologic modeling techniques are now available, distributed runoff methods are limited in use due to the tradition …

Hyperelastic Structural Fuses For Steel Buildings, Francys López

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Why to upgrade traditional systems?

The FEMA P-58-1 listed some of the limitations in present-generation procedures:

Questions regarding the accuracy and reliability of available analytical procedures in predicting actual building response.

“High” level of conservatism underlying the acceptance criteria.

Inability to reliably and economically apply performance-based procedures to the design of new buildings; and Lack of alternative ways of communicating performance to stakeholders that is more meaningful and useful for decision making purposes.

Performance based design (PBD) emerges as the methodology aiming to bridge this gap, raising the design level performance from life safety (traditional systems) to keep structures fully …

Impact-Resistant Behavior Of Reinforced Concrete Bridge Columns, Chen Fang

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

The damage caused by a vehicle collision on a pier column can be catastrophic for the functionality of a bridge, even a total collapse of the bridge. ❖ A vehicle collision and a subsequent vehicle blast cause more damages on the bridge. ❖ Limited researches have been conducted to investigate the behavior of the bridge subjected to the combined effect of vehicle collision and blast. ❖ It is necessary to analyze the responses of the bridge under the vehicle collision and blast and provide some design suggestions to strengthen the bridge.

Conclusions ❖ The finite element models including column, pile …

In-Vehicle Evaluation Of Rumble Strips In Pre-And Post-Chip Sealed Maintenance Periods, Ernest Tufuor, Laurence Rilett

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Chip sealing will reduce the depth of rumble strips (RS) by approximately 1/8".  Will this depth reduction affect RS functional characteristics (audible and tactile warnings)?

There is no detailed study on the effectiveness of RS that have been chip sealed. USEFULNESS The results will be useful to the Nebraska Department of Roads to determine:

Operations: Whether RS will need to be re-milled after chip sealing. Cost & safety implications.

Design: New RS guidelines for highways expected to be chip sealed in the future.

It can be shown that a 1/8" reduction in the current milled RS design depth, as …

Optimizing Steel Railway Truss Bridge Health Monitoring, Ahmed Rageh, Daniel Linzell

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Problems - Steel Railway Trusses • Aging • Large system – bridge AND railway • Labor intensive condition eval • Reported conditions: Stringer-to-floor beam connections [Haghani 2012] Stringer flange clip angle cracks [Haghani 2012] Unequal eyebars stress distribution [DelGrego 2008] Displaced eyebar pins [DelGrego 2008

Problems – Condition Evaluation • Visual inspection: Prescribed frequency Costly Subjected to human interpretation • Sensors: Focused on a single bridge Extensive array Costly

Influence Of Skew And Nonlinear Deck On Elastic Versus Inelastic Distribution Behavior And Ultimate Capacity Of Steel Girder Bridges, Fayaz Sofi, Joshua Steelman

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Research Objectives

• Assessment of alternative load distribution methodologies for potential discrepancies that arise when evaluating distribution behavior of skewed steel girder bridges.

• Investigate the influence of skew and material nonlinearities (concrete cracking and steel yielding) on

• Load distribution behavior (elastic versus inelastic).

• System capacities (yielding and ultimate).

Summary and Conclusions • Influence of skew was examined on load distribution behavior, and nonlinear system-based capacities (yielding and ultimate) of composite steel girder bridges in presence of full material nonlinearities. In addition, assessment of two general definitions (beam-line and response fraction approaches) for quantifying load distribution behavior was …

Indicators Of Assessing Vehicle Safety Status Under Platoon Conditions At Freeway, Jianan Zhou

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Issue on level freeway segment (Interstate 80) in Nebraska: • High truck percentage (higher than 25%) • Different speed profile - The speed of trucks are set to 67 mph, on average. - The speed of passenger cars are 75 mph, on average. • Result platoons - Approximately 85% of vehicles are observed in platoon. - the degree of freedom to maneuver for drivers are constrained by other in-platoon vehicles. - Vehicles in platoons may face unsafe situation. Goal: Develop indicators to assess the safety status of vehicles under platoon conditions at level freeway segment.

The data were collected at …

Chemical-Rheological Evaluation Of The Short-Term And Long-Term Effectiveness Of Binder Rejuvenators, H.F. Haghshenas, S. Kommidi, D. Nguyen, Y-R Kim

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Many previous studies have investigated how rejuvenators affect/alter mechanical/chemical characteristics of aged binders. However, it has not been actively examined how the rejuvenated binders will perform for the next round of service after the rejuvenation was made. A better understanding of the short-term and long-term effect of rejuvenating agents in RAP blended asphalt mixtures is necessary to achieve more appropriate selection and use of rejuvenating agents.

Evaluation Of Thin Asphalt Overlay Pavement Preservation In Nebraska: Laboratory Tests, Mepdg, And Lcca (17-2624), Soohyok Im, Taesun You, Yong-Rak Kim, Gabriel Nsengiyumva, Robert Rea, Hamzeh Haghshenas

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Thin asphalt overlays offer an economical resurfacing, preservation, and renewal paving solution for roads that require safety and smoothness improvements. Recently, thin asphalt overlays have been used in Nebraska as a promising pavement preservation technique that needs evaluations.

Effects Of Rejuvenators On High-Rap Mixtures Based On Laboratory Tests Of Asphalt Concrete Mixtures And Fine Aggregate Matrix Mixtures, Hesamaddin Nabizadeh, Hamzeh Haghshenas, Y-R Kim, F. T. S. Aragão

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Although the linear viscoelastic stiffness, fracture characteristics, and permanent deformation behavior of AC mixtures can be determined through experiments, it is generally time-consuming and expensive to reach statistically repeatable results. Thus, it is attractive to pursue alternative methods that are cheaper, faster, and repeatable in order to efficiently evaluate and predict asphalt mixtures’ core mechanical characteristics (such as stiffness, fatigue, and plastic deformation).