Evaluating Residual Capacity Of Reinforced Concrete Beams Exposed To Fire-An Approach
Authors: Ankit Agrawal; Venkatesh Kodur
Abstract: Reinforced concrete (RC) structural members exhibit high fire resistance due to relatively low thermal conductivity, high thermal capacity, and slower degradation of mechanical properties of concrete with temperature. Also, owing to advancements in active fire protection systems and fire-fighting strategies, complete collapse due to fire is rare. In most cases, RC structural members retain much of their structural capacity after a fire incident. However, this does not ensure safety of the building for immediate reoccupation after fire is extinguished. Unlike fire induced spalling, which is a visible sign of damage, structural deterioration due to degradation of mechanical properties at elevated temperatures and redistribution of stresses within the member is not too apparent. Thus, it is imperative to ascertain the residual capacity of structural members through rational engineering methods. Such an assessment would be indispensable for subsequent retrofitting strategies as well. This study is aimed at developing an approach for assessing residual capacity of fire exposed reinforced concrete beams. For this purpose, response of normal strength concrete (NSC) beams 3.96 m in span and of rectangular cross section has been simulated using finite element package ABAQUS under standard and design fire scenarios. Data from the numerical studies is being used to develop a simplified approach based on maximum experienced rebar temperatures and post fire residual deformations that can be applied in practice to evaluate residual capacity of fire exposed RC beams.
Intelligent Structural Damage Detection Using Data From Self-Powered Wireless Sensor
Authors: Amir H. Alavi; Hassene Hasni; Nizar Lajnef; Karim Chatti
Abstract: In the last decade, significant attention has been devoted to the utilization of new sensing technologies for structural health monitoring. The complexity of analysis of the valued information offered by such smart sensor technologies implies the necessity of developing robust interpretation approaches. This study presents a new methodology for the structural damage detection based on the simulation of the compressed data stored in memory chips of self-powered wireless sensors. An innovative data interpretation system integrating finite element method and probabilistic neural network based on Bayesian decision theory is developed for damage detection. Several features extracted from the cumulative limited static strain data are used as damage indicator variables. Another important contribution of this study is to define effective indicator variables that simultaneously take into account the effect of array of scattered sensors. This enables the method to detect damage at any location in a structure with a sparse distribution of the sensors. The performance of the proposed approach is evaluated for the case of U10 gusset plate of the I-35W Bridge in Minneapolis, Minnesota at the time of the bridge collapse. The gusset plate is analyzed as a 3D FE model utilizing the Abaqus computer software. A detailed uncertainty analysis is performed through the contamination of the damage indicator features with different Gaussian noise levels. The results indicate that the proposed method is efficiently capable of detecting different damage states in spite of high-level noise contamination.
Effect Of High-Temperature Creep On Response Of Reinforced Concrete Structures
Authors: Saleh Alogla; Venkatesh Kodur
Abstract: Concrete structures when exposed to high temperatures undergo significant deformations due to the development of mechanical and thermal stresses. Thermal stresses play a major role in changing the deformation behavior of concrete since they induce thermal and transient strains, and amplify creep and load induced mechanical strains in concrete and steel reinforcement. It is hypothesized that creep strains primarily govern the failure of concrete structures when exposed to high temperatures above 500 °C commonly encountered in fire. While the characterization of thermal and mechanical strains is well established for different concrete types, there are limited studies on high-temperature creep and transient strains. Available concrete creep and transient strain models have numerous drawbacks and indicate significant variability. Furthermore, most of the creep models are based on tests conducted in 1970’s and 1980’s, and do not represent current concrete mixes used in practice. To overcome these limitations, experimental studies are currently underway to characterize high-temperature creep and transient strains of different concrete types. Data from uniaxial compression tests on concrete cylinders is being utilized to develop constitutive models for high-temperature creep of concrete. This paper presents a comparison of different high-temperature creep and transient models available in literature for concrete. Through this comparison the variability of creep and transient strains in current models will be illustrated and the factors which lead to this variability will be discussed. Also, the need for reliable creep models for evaluating fire response of reinforced concrete structures is highlighted.
A Fracture Mechanics-Based Approach For Quantifying Delamination Of Spray-Applied Fire-Resistive Insulation From Steel Moment-Resisting Frame Subjected To Seismic Loading
Authors: Amir Arablouei; Venkatesh Kodur
Abstract: This article presents a numerical approach based on fracture mechanics theory for evaluating crack initiation, propagation and delamination of fire insulation at the interface of spray-applied fire insulation and steel surface of a moment resisting frame under the action of earthquake loading. Progression of delamination at the fire insulation-steel interface during cyclic loading is simulated through contact interaction analysis in which Cohesive Zone Model is adopted to model the interface damage and softening. The developed 3D finite element model is validated by comparing predictions from the model, namely crack initiation, crack propagation pattern and the extent of delamination of insulation, against test data generated both at material and structural levels. The validated model is applied to quantify the effects of cyclic damage accumulation at SFRM-steel interface through a parametric study in terms of interfacial critical fracture energy. The influence of local buckling occurring in flange on the extent of delamination is considered in the analyses. Results from the parametric studies indicate that critical fracture energy at steel-insulation interface has significant influence on the extent of damage accumulation over the plastic hinge zone. Further, flange local buckling can substantially enhance the development of tensile stresses at the crack tip leading to delamination over a larger surface area.
Experimental Behavior Of Steel Bridge Girders Under Fire Conditions
Authors: Esam Aziz; Venkatesh Kodur
Abstract: In the current practice, no special measures are applied for enhancing structural fire safety of steel bridge girders. Further, there is very limited information and research data in the literature on the fire resistance of structural members in bridges. Experimental study was carried out to evaluate the fire response of uninsulated composite steel-concrete bridge girders. In the experimental work, the critical factors that influence fire resistance, namely fire scenario, load level, web slenderness ratio, web/stiffeners aspect ratio, composite action arising from steel-concrete interaction are investigated. Results from experimental work show that fire resistance in steel bridge girder could be as low as 35 minutes. Furthermore, the web slenderness and web/stiffeners aspect ratio can alter the failure limit state from flexural yielding to shear web buckling.
This work was supported in part by National science foundation
Statistical Validation Of 3D Finite Element Models For Reinforced Concrete Bridge Columns And Their Use For Predicting Damage Limit States For Performance-Based Seismic Design
Authors: Ata Babazadeh; Rigoberto Burgueño
Abstract: Performance-based seismic design of reinforced concrete (RC) bridges requires precise knowledge about the onset of intermediate damage states on the columns at different demands. Large-scale experiments have been traditionally the only source to obtain these limit states. Finite element (FE) simulations provide the opportunity to study the performance of columns in detail and predict limit states for new designs in lieu of experimental data. However, model validation and data extraction are critical steps for their appropriate use. It is well accepted that visual validation methods through graphical comparison of experimental data and simulation results by means of overlaid plots provide little information about the reliability of the models. In contrast, quantitative methods of validation are less subjective ways to find the extent of confidence in FE simulations. Being validated through rigorous hypothesis testing and determining the confidence level, the applicability of FE simulations for determining damage limit states in flexure-dominated ductile RC bridge columns is presented. The work is shown within the context of six large-scale RC columns units, which were experimentally tested and simulated using 3D FE models. Results from the FE simulations were further analyzed to extract responses at local and global levels. Damage limit states were determined based on these data and compared to experimental measurements. Damage states of onset of yielding, initiation and significant growth of spalling of the cover concrete were found to be predicted with adequate accuracy using FE simulations.
This work was supported in part by NSF under Grant CMMI-1000549
Energy Harvesting From Localized Dynamic Transitions In Post-Buckled Elastic Columns Under Quasi-Static Loading
Authors: Wassim Borchan; Nizar Lajnef; Rigoberto Burgueño
Abstract: The deployability of structural health monitoring self-powered sensors relies on their capability to harvest energy from signals being monitored. Many of the signals required to assess the structure condition are quasi-static events which limits the levels of power that can be extracted. Several vibration-based techniques have been proposed to increase the transferred level of power and broaden the harvester operating bandwidth. However, these techniques require vibration input excitations at frequencies higher than dominant structural response frequencies which makes them inefficient and not suitable for ambient quasi-static excitations. Therefore development of new devices capable of harvesting energy at very low frequencies is needed.
This research proposes a technique to harvest energy at very low frequencies (less than 1 Hz) using the snap-through behavior between multiple equilibrium positions of postbuckled elastic elements. When the quasi-static load reaches a certain threshold, a sudden snap-through transition occurs generating a high-rate motion. These sudden transitions excite piezoelectric scavengers that are attached to the elastic elements with high-rate input accelerations, generating then electric power. Extractable energy levels depend on the piezoelectric properties and the accelerations generated within the transitions. Therefore number, spacing and accelerations of snap-through transitions of elastic elements have to be controlled for enhanced power management.
The main objectives are to develop energy harvesting devices capable to harvest energy efficiently under quasi-static excitations using snap-through transitions between equilibrium positions of elastic elements, model the postbuckling behavior of the elastic elements and essentially the sudden transitions and finally control the behavior by tailoring geometry and material properties of the buckled elements or stacking them into system assemblies.
Process Of Local Calibration Of Rigid Pavement Performance Models In The Pavement-ME Using PMS Data In Michigan
Authors: Wouter Brink; Syed W. Haider; Neeraj Buch
Abstract: The local calibration of the performance models in the mechanistic-empirical pavement design guide is a challenging task, especially due to the lack of needed data. The data requirements for the selected set of pavement sections from the PMS for local calibration include (a) a wide range of inputs related to traffic, climate, design and material characterization, (b) a reasonable extent and occurrence of observed performance data over time. This paper highlights the process for local calibration of performance models. Statistical sampling concepts were used to determine the adequate number of pavement sections for robust calibrations. The next step was to identify candidate projects in the PMS database based on the pavement type, age, geographical location, and number of performance data collection cycles. Subsequently, the final set of pavement projects were selected based on the distress magnitude over time. It is important to categorize the selected projects based on the measured performance (i.e., poor, normal and good performing pavements) because the locally calibrated models are typically used to predict normal pavement performance at the design stage. For the selected projects, the as-constructed input variables were collected from the construction records. However, when such input information was unavailable, the best estimates were used to represent MDOT pavement design and construction practices. Lastly, the typical steps for local calibration i.e., verification, calibration and validation were executed for the rigid pavement performance models. The above mentioned process is demonstrated with the help of examples and discussed for cracking and IRI models in the paper.
This work was supported in part by Michigan Department of Transportation
Advanced Test Method For Evaluation Of The Chemical Composition And Deterioration Condition Of Concrete
Authors: Iman Harsini; Parviz Soroushian; Amirpasha Peyvandi
Abstract: The potential of nuclear magnetic resonance (NMR) as a powerful and convenient tool for comprehensive condition assessment of the concrete-based infrastructure was demonstrated. Non-destructive and supporting destructive test methods and data analysis procedures were developed. A first-generation portable unilateral NMR system was designed and fabricated. The capabilities of this system in non-destructive monitoring and quantification of concrete structure and strength development over time, assessment of the depth profile of concrete moisture content, field evaluation of concrete transport properties, and assessment of the concrete microcrack conditions were demonstrated.
This work was supported in part by U.S. DOT
Tailoring The Elastic Postbuckling Response Of Thin-Walled Cylindrical Composite Shells Under Axial Compression
Authors: Rigoberto Burgueño; Nan Hu; Annelise Heeringa; Nizar Lajnef;
Abstract: The buckling of cylindrical shells has long been regarded as an undesirable phenomenon but increasing interests on the development of active and controllable structures open new opportunities to utilize such unstable behavior. In this paper, approaches for modifying and controlling the elastic response of axially compressed laminated composite cylindrical shells in the far postbuckling regime are presented and evaluated. Three methods are explored: (1) varying ply orientation and laminate stacking sequence; (2) introducing patterned material stiffness distributions; and (3) providing internal lateral constraints. Experimental data and numerical results show that the static and kinematic response of unstable mode branch switching during postbuckling response can be modified and potentially tailored.
Micro-Structural Evaluation Of The Interaction Mechanisms Of Crumb Rubber And Asphalt Binders
Authors: Anas Jamrah; M. Emin Kutay
Abstract: Several studies have been conducted evaluating the properties and characteristics of Crumb Rubber (CR) modified asphalt blends. Despite the improved performance of the modified asphalt blends, the mechanisms of interaction between different asphalt binders and CR have not been fully understood. This study is aimed at effectively quantifying the stiffening and rheological effects of modifying asphalt binders with CR at the microscale. The material behavior at this scale is important due to the fact that asphalt coating thickness of aggregates is in the order of a few microns.
An experimental approach was taken to investigate the mechanisms of interaction between different asphalt binders and different CR (engineered and raw) particles. Asphalt binders were mixed with CR particles at elevated temperatures (130, 160, and 190C), and then drained such that no rubber particles were present in the residual asphalt binder. The residual material was then tested for the rotational viscosity, creep compliance (D(t)), and the main rheological property; complex shear modulus (|G*|) of the asphalt binder. The characteristics obtained were used to quantify the changes in the asphalt rheology and stiffness due to the absorption/diffusion of the light fractions (aromatic oils) of asphalt binder into CR particles.
To fully understand the interaction between rubber and asphalt binders, a 3D Finite Element (FE) based micromechanical model of the |G*| test is being developed using the commercially available ABAQUS software. The FE model will provide insight on the relationship between the microscale and macroscale material behavior, in addition to the stiffening and interaction effects of rubber particles on asphalt binders. In addition to the experimental approach and the FE based analyses, the Atomic Force Microscopy (AFM) technique will be used to investigate the interface between the rubber particles and the asphalt binder. The AFM is an ideal tool for characterizing the behavior within a composite material as it is capable of measuring nano- and micro-scale forces. Once the interaction mechanisms of CR and asphalt binder are fully understood, this will lead to optimized CR-asphalt binder blends, which in turn leads to optimized CR-asphalt mixtures.
This work was supported in part by Michigan Department of Environmental Quality (MDEQ)
Performance Evaluation Of Post-Buckled Strip Negative Stiffness Damper
Authors: Pengcheng Jiao; Nizar Lajnef; Rigoberto Burgueño
Abstract: The usefulness of supplementary energy dissipation devices is now well-known in the seismic design and retrofit of civil engineering structures. However, as an effective structural control approach, negative stiffness system has rarely been applied. Therefore, the main objectives of this study are to examine the behavior of negative stiffness damper and evaluate it in seismic structural applications.
For this purpose, a two-phase simulation will be elaborated. Firstly, characterization evaluation will be performed on the negative stiffness damper to provide information on the behavior of load vs. displacement, energy dissipation, damping effect, and stability of performance. Secondly, an earthquake simulation is going to carry out on a moment-resisting steel frame with and without the negative stiffness damper-bracing assembly. Simulation results will be compared with published testing results.
Performance Evaluation Of Ground Tire Rubber Modified Hot Mix Asphalt At Macro Scale
Authors: Salih Kocak; M. Emin Kutay
Abstract: The use of sustainable materials has been becoming more and more important, as the consumption of virgin earth materials has increased significantly during last couple of decades. In pavement construction industry, many departments of transportation and local road agencies have been looking for ways to cut down costs and the use of virgin materials. Increased use of reclaimed asphalt pavements (RAP) is one approach that is being taken. Furthermore, scrap tires have been becoming a growing environmental problem all over the world. Currently in the U.S., more than 300 million of scrap tire are buried in the landfills and only 12 million of them are being converted into ground tire rubber (GTR) for use in the asphalt pavement applications each year. The researchers and some industry have been working on engineered GTR particles and GTR modified asphalt binders to design long-lasting asphalt pavements and to minimize the initial construction cost. The GTR is typically introduced into asphalt mixture via two processes: i) wet process (i.e., pre-mixing GTR with asphalt binder) and ii) dry process (dry GTR particles added to asphalt mixture as aggregates). Although wet process has been successful in enhancing the reflective, fatigue and thermal cracking resistance, dry process has historically provided limited success. However, in terms of ease of production and economic reasons, dry process is more advantageous.
The objective of this study was to investigate the performance of asphalt mixtures made with different GTR modification methods combined with high percentages of reclaimed asphalt pavement (RAP). High percentages of RAP (40% by weight) were introduced into HMA along with rubberized asphalt using both wet and dry processes. The performances of the mixtures were evaluated via an extensive laboratory testing program that includes the following major tests: i) flow number (FN) for rutting, ii) dynamic modulus (DM) for linear viscoelastic properties, iii) tensile strength ratio (TSR) for moisture damage, iv) indirect tensile strength (IDT) for low temperature (thermal) cracking and v) push pull (PP) for fatigue cracking. Data analysis revealed that the macro scale performance of HMA mixtures including high amount of RAP and GTR along with some polymer modifiers yielded to similar performance results on FN, TSR and PP tests and better performance on low IDT and DM results. This means that the performance improvements typically gained by use of polymer-modified binders can also be achieved with GTR modified binders/mixtures. It is noted that the initial costs of GTR and polymer modified asphalt binders are generally equivalent. Considering the sustainable aspects of GTR (e.g., use of recycled tire), its use may be a better alternative as compared to some polymer modified asphalt mixtures.
This work was supported in part by Michigan Department of Environmental Quality (MDEQ)
Evaluation Of Pavement Treatments Effectiveness
Authors: Gopikrishna Musunuru; Gilbert Baladi
Abstract: After the initial construction, pavements deteriorate due to environmental and traffic factors. At certain pavement conditions, treatments are applied to either restore or extend the service life of the l pavement and/or to decrease its rate of deterioration. There are various treatment types that can be applied to a given pavement section. The appropriate treatment type is a function of the pavement surface type and conditions, causes of distress, traffic volume and load, and the environmental conditions.
The effectiveness of a given pavement treatment for a given pavement section is typically measured by short- and long-term benefits. Short term benefits are typically measured by the improvement in the ride quality and the other pavement conditions. Long term benefits include the improvement in the remaining service life of the pavement.
In this study, which is sponsored by the Federal Highway Administration, the long term pavement performance (LTPP) program, short- and long-term benefits of various treatment types of numerous pavement sections were analyzed. Results of the analyses are presented and discussed in this paper.
Data Analysis - Long Term Pavement Performance
Authors: Gopikrishna Musunuru; Gilbert Baladi
Abstract: In this study, which is sponsored by the Federal Highway Administration (FHWA), time-dependent pavement performance data that were collected through the Long Term Pavement Performance (LTPP) program were analyzed. The objectives of the analyses were to assess the longevity of the various pavement section, and to develop pavement performance prediction models. The models can be used where to study the effectiveness of various pavement treatment types that were used by the LTPP program.
Results of the analyses are presented and discussed in this paper along with the definitions of pavement performance and pavement conditions.
This work was supported in part by Federal Highway Administration
Numerical Investigation Of Composite Action On Shear Response Of Fire Exposed Steel Girders
Authors: Mohannad Naser; Venkatesh Kodur
Abstract: In current practice, failure in beams under fire conditions is evaluated based on flexural limit state without any consideration to shear capacity. This is in contrast to ambient temperature design, where a beam is generally designed to satisfy flexural limits state and then checked for shear resistance. Deriving failure in fire exposed beams based on flexural limit state, although valid for most common scenarios, may not be representative in certain situations, such as transfer girders and coped beams where shear forces are dominant or shear capacity degrades at a rapid pace with fire exposure time.
In order to further investigate this phenomenon, a three-dimensional nonlinear finite element model is developed using ANSYS. This model takes into account temperature-dependent properties of constitutive materials, sectional instabilities, and composite action arising from steel beam-concrete slab interaction. The developed model is used to evaluate flexural and shear response of composite girders subjected to high shear forces and simultaneous thermal (fire) loading. Results from this analysis show that shear capacity of a steel girder can degrade at a higher rate than flexural capacity in certain scenarios, thus shear limiting state can be a dominant failure mode. Loading pattern, slenderness ratio and composite action are critical factors that influence shear response in steel girders under fire conditions.
This work was supported in part by National Science Foundation under Grant number CMMI-1068621
Winter Circulation, Ice Cover And Exchange In The Saginaw Bay – Lake Huron System: Field And Satellite Observations And Numerical Modeling
Authors: Tuan D. Nguyen; Guoting Kang; Phanikumar Mantha
Abstract: We use an unstructured-grid, three-dimensional hydrodynamic model of Lake Huron coupled with ice processes to understand the nature of circulation and the extent of ice cover over the lake during winter seasons and to quantify exchange rates between the Saginaw Bay and Lake Huron in winter. The model used hourly atmospheric forcing data for the years 2009-2010, and 2012-2013. We deployed thermistor chains and bottom-mounted, up-looking acoustic Doppler current profilers (ADCPs) during the winter season and collected hydrodynamic and temperature data to test the numerical models. We also extracted Moderate Resolution Imaging Spectroradiometer (MODIS) data from both Terra and Aqua satellites for ice cover extent with a relatively high spatial resolution of 463 m with daily temporal resolution. Here we present the comparisons between the field data, satellite remote sensing data and model simulations of currents, temperature, and ice cover extent. New estimates are provided for the mean flushing times and residence times for the Saginaw Bay for winter seasons. These novel results are expected to aid in our understanding of how contaminants are flushed out of the bay during winter seasons and how lake processes are changing in this important ecosystem.
A Coupled Recharge And Groundwater Model To Predict Stream Index Flow
Authors: Xiaojing Ni; Shuguang Li; Huasheng Liao
Abstract: The State of Michigan limits groundwater withdrawals by comparing index flow (i.e., the median flow during the summer months) with the expected stream flow removed due to pumping. The current approach for implementing this policy is to predict total streamflow using a regression model based on many hydrologic parameters. While this approach succeeds for predicting large-scale trends of baseflow, it fails in a number of small area studies. The aim of this research is to use process-based numerical modeling as an alternative to predicting baseflow in small watersheds and site studies.
The representative small area watershed is in Hillsdale County, MI. In the process-based model, groundwater from/to adjacent cells, from/to sources and sinks and stored in cells will be considered. A water balance is solved to estimate baseflow, which can be considered as streamflow in summer used to calculate index flow. Recharge is a critical source of groundwater and estimated as output from a watershed model. Forty years of climate data including precipitation, maximum and minimum temperature and soil/vegetation data are used as inputs in the watershed model. The groundwater model calibration compares hydraulic head from monitoring wells with simulated water levels and streamflow records from USGS gaging stations with baseflow from the model for one known precipitation event.
The current model is in the process of calibration and the final results of baseflow will be used to calculate index flow. This index flow can be compared with proposed water withdrawals to assess whether pumping will significantly affect the steam.
Relationship Of Pavement Condition To Subgrade Soil Type
Authors: Michael Prohaska; Gilbert Baladi; Dennis Chase
Abstract: Understanding the effects of material properties, construction quality, and environmental factors on pavement are all essential to cost-effective pavement management. While the effects of construction quality, environmental factors, and pavement, base, and subbase materials are extensively understood there continues to be an insufficient understanding of the role of subgrade in pavement life. Previous research studies addressed the effects of subgrade soils on pavement design and construction but neglected their effects on the long term pavement performance. To bridge this knowledge gap, a study sponsored by the Federal Highway Administration is being conducted at Michigan State University to relate the time dependent pavement condition data to the type of subgrade soils. The soil types will be based on the AASHTO soil classifications and their effects on four pavement distresses; lateral cracking, longitudinal cracking, alligator cracking, and rut and on the ride quality expressed by the international roughness index (IRI). For each pavement section, the results will be standardized based on the annual average daily traffic (ADT), percentage trucks, drainage conditions, and climatic zone. Results of this study will be presented and discussed in this presentation.
This work was supported in part by Federal Highway Administration
Prediction Of Frost Heave
Authors: Pegah Rajaei; Gilbert Y. Baladi
Abstract: In cold regions, the ground freezes when the temperature drops below the freezing point causing heave in the soil layers. The thickness of the frozen region and the thickness of the ice lenses increase over time and are function of temperature, soil type and capillarity, the availability of water sources, the proximity of the ground water table and the applied load or overburden pressure. Since the 1930s, several models were developed by researchers to estimate the amount of soil heave due to freezing. Unfortunately, none of the model has received universal acceptance. In general, the majority of the existing frost heave models are based on two different theories; capillary theory and frozen fringe theory. The capillary theory has some limitations which result in inaccurate prediction of frost heave. Whereas the frozen fringe theory assumes the existence of a frozen fringe region below the frozen soil where unfrozen water exists at temperatures below the freezing point. This assumption is controversial and is being debated by researches. In a research study sponsored by the Michigan Department of Transportation (MDOT), the Gilpin Model (Gilpin, 1980) was applied to Road Weather Information System (RWIS) data in the State of Michigan. Frost heaves were calculated based on no frozen fringe and the existence of frozen fringe model. Results of the analyses were compared and a revised model was developed. This paper introduces the modified models along with its advantages and shortcomings.
This work was supported in part by Michigan Department of Transportation (MDOT)
Prediction Of Frost Depth
Authors: Gilbert Y. Baladi; Pegah Rajaei
Abstract: Knowledge or accurate prediction of frost depth is an essential step for pavement, foundations, utility lines, and other engineering designs. The actual frost depth is a function of the material types, their thermal properties, water content, and climatic condition, such as temperature, wind speed, precipitation and solar radiation. Although frost depth could be estimated using numerical or analytical modeling techniques, the required input data are not available and/or expensive to collect. Few elements of the required data are available in most State Highway Agencies (SHA). Hence, the use of the numerical or analytical models requires the estimations of the missing data which make the results unreliable. In a research project sponsored by the Michigan Department of Transportation (MDOT), soil temperature data from Road Weather Information System (RWIS) were used to check the accuracy of the frost depth outputs obtained from the various analytical and semi-empirical frost depth prediction models including Stefan model (Stefan, 1889), Modified Berggren model (Aldrich et al 1953) and Chisholm and Phang empirical model (Chisholm and Phang ,1980). Unfortunately, none of the models yielded accurate results. Therefore, a revised empirical model was developed that requires one input parameter, air temperature. The model predicted the frost depth data in the State of Michigan more accurately than the available models. This paper presents the developed empirical model and compares the prediction of frost depths with the measured frost depth data.
This work was supported in part by Michigan Department of Transportation (MDOT)
Macropore Flow Through Earthen Covers
Authors: Duraisamy Saravanathiiban; Milind Khire; M. Emin Kutay
Abstract: In the U.S., landfilling is the most common means to dispose off municipal solid waste. Earthen cover, composed of compacted clay soil, is constructed once a landfill reaches its capacity and is scheduled for closure in order to impede the flow of water into the waste and to prevent the landfill to be filled with liquid which can be a long term environmental hazard. The formation of large openings (macropores) due to shrinkage, desiccation, freeze-thaw cycles, vegetation root growth and death, rodent holes, and worm holes in earthen covers is one of the major challenges in landfill cover design as it impacts long term percolation during service. The liquid flow in macropores is predominantly downward due to gravity. Presently available water balance models used for designing earthen covers are based on Richards equation that simulates only the flow through microscopic pores (micropores), not the macropores. Hence, there is a need to develop a model capable of simulating flow through micropore as well as macropore to design earthen covers. In this study, evaluation of macropore flow was carried out using a field scale test section constructed at a landfill near Detroit. Also, laboratory test were carried out on intact compacted clay samples and compacted clay samples with macropores. These samples were used to develop digital data of macropores using X-ray CT. A model based on Lattice Boltzmann Method (LBM) that can simulate fluid flow through micropores and macropores is developed. The model was validated using laboratory measured data.
This work was supported in part by National Science Foundation (Grant No. CMMI-1100020); Waste Management, Inc; Environmental Research and Education Foundation
Mix Design Procedures Based On Packing Density Models For Ultra-High-Performance Concrete (UHPC) Nanocomposites
Authors: Libya Ahmed Sbia; Parviz Soroushian
Abstract: Ultra-high-Performance concrete (UHPC) mixtures require high-quality aggregates and fillers with particular size distributions, which may not be readily available in many locations. In order to broaden the selections of UHPC raw materials, mix proportioning methods were developed based on packing density models. The blend of all particulate matter (aggregates, cement, supplementary cementitious materials, mineral powder, nanomaterials, etc.) used in UHPC should provide a combined particle size distribution which favors achievement of high packing densities. The purpose of the this research is to develop guidelines for proportioning readily available particulate (granular) matter for realizing dense particle packing and desired fresh mix characteristics. The reduced porosity and finer pore size distribution of this matrix would favor improved interactions with nanomaterials and fiber. Models and criteria were developed for selection of particulate materials at different scales (and their blends) with the objective of enabling effective use of nanomaterials. Nanomaterials were found to benefit the packing density of the particulate matter in UHPC, even at very low volume fractions, by extending the particle size distribution into the nano-scale region.
Behaviour Of Prestressed Concrete Hollowcore Slabs Under Standard And Design Fire Exposure
Authors: Anuj Shakya; Venkatesh Kodur
Abstract: Prestressed concrete (PC) hollowcore slabs are widely used in building floor systems due to numerous advantages, they offer over other types of floor systems. Currently, fire resistance of these slabs is assessed based on standard fire tests, or prescriptive approaches. These fire tests are expensive, time consuming and do not yield realistic fire resistance, as they cover only limited numbers of parameters. To overcome some of these limitations, a numerical model was developed for evaluating fire resistance of PC hollowcore slabs under realistic fire, loading and restraint scenarios. For validating this numerical model, a set of fire resistance tests was carried out on PC hollowcore slabs.
This study presents results of fire resistance tests on PC hollowcore slabs subjected to different loading and fire scenarios. Six PC hollowcore slabs, of 4 m in length, 1.2 m in width and 200 mm in depth, were designed according to PCI design specifications. The cores in these slabs were of 150 mm radius and low relaxation prestressing strands, with yield stress of 1860 MPa and diameter of 12.7 mm, were used in these slabs. The test variables included aggregate type, restraint condition, fire scenario and load level. All six slabs developed fire induced cracks, but sustained fire exposure, without failure, for more than 2 hours before undergoing failure reaching limiting temperature on unexposed surface of slab. Hollowcore slabs performed better under design fires than standard fires. Also, slabs with carbonate aggregate exhibited slightly better fire resistance than slabs with siliceous aggregate. In addition, end restraints significantly enhanced the fire resistance of PC hollowcore slabs.
This work was supported in part by Daniel P. Jenny research fellowship, Precast/Prestressed Concrete Institute (PCI)
Development Of Methods For Microbial Gene Quantification
Authors: Jackson Sorensen; Robert Stedtfeld; Marius Vital; James Tiedje; Syed Hashsham
Abstract: The suite of microorganisms present in the human gastrointestinal tract, often called the microbiome, are increasingly believed to play a role in the health of their hosts. Animals free of microorganisms, or “germ free” animals, commonly have developmental abnormalities, suggesting a role for the microbiome in the well being of their host. However, the mode of action that the microbiome utilizes to have this impact on its host is unclear. Many studies on the microbiome center on the presence or absence of certain populations or functions through the sequencing of microbial DNA. While this information is useful, it only indicates the potential of the microbiome to perform certain actions, and does not give a depiction of the functions the microbiome is actively executing. Currently, we are working on methods for the quantification and sequencing of both DNA and RNA of the microbiome present in gnotobiotic mice. Through the utilization of loop mediated isothermal amplification (LAMP), we have been able to absolutely quantify the number of butyryl-CoA transferase(but) genes in the microbial DNA extracted from fecal samples. This methodology allowed for the specific identification and quantification of the microbial species Roseburia intestinalis, Rosburia inulinivorans, and Faecalibacterium prausnitzii. LAMP allows the quantification of this gene in under thirty minutes. To date quantification of RNA using LAMP has proven difficult to reliably and reproducibly achieve. For these issues, RNAseq and directed transcriptomics are being explored to provide a solution.
This work was supported in part by NIEHS
Development And Mechanical Characterization Of Novel Functionally Graded Open-Cell Al/Cu Hybrid Metal Foam Structures
Authors: Yi Sun; Rigoberto Burgueño
Abstract: Cellular/foam materials found in nature such as bone, wood, and bamboo usually have a non-uniform density that is distributed in space to optimize the global mechanical performance of the structure. Inspired by such naturally engineered products, many studies have been conducted in the development of functionally graded cellular/foam materials (FGF). However, most of these studies are limited to FGF with one-dimensional property gradient. An approach has been recently demonstrated for fabricating Aluminum/Copper hybrid foams with enhanced and controllable stiffness, strength and energy absorption capacity by reinforcing open-cell aluminum (Al) with nanocrystaline copper (Cu) coatings. The manufacturing process of Al/Cu hybrid foams can be controlled to fabricate engineered foam structures with three-dimensional property gradients. Nano-copper reinforcement patterns were designed to optimize the performance of beam-type foam structures under quasi-static and dynamic flexural demands. The results show that the reinforcement pattern can be designed to modify the deformation and failure mechanisms of foam structures. It is also shown that functionally graded hybrid foam elements can have reduced deformation and damage, and enhanced stiffness, strength and ductility compared to hybrid foams with a uniform coating in both quasi-static and dynamic loading conditions. By providing a strategic distribution of reinforcement in a three-dimensional domain, the approach presented greatly extends the possible design of functionally graded foam structures with superior mechanical performance. The methods and findings from this study provide valuable information for the development of novel high-performance functionally graded cellular materials and structures.
This work was supported in part by National Science Foundation
Numerical Modeling Of A Coupled Groundwater And Lake System
Authors: Yuting Sun; Huasheng Liao; Shu-Guang Li
Abstract: Many lakes in the U.S. are suffering from decreasing water levels likely caused by climate change. Lake augmentation through the input of extracted groundwater or pumped water from the other surface water source is often used to boost water levels in such lakes, but in many cases it is insufficient due lack of knowledge about complex lake and groundwater interactions. The purpose of this research is use numerical modeling to better understand groundwater and lake interaction and to apply this knowledge to improve management schemes for stressed surface water bodies.
Three-dimensional multi-scale modeling of the coupled groundwater-lake system is used because it simplifies the interaction system based on analysis of the sub-model and improved computational scaling. This research will utilize ‘transition probability’ approach to simulate lithology distribution at regional scale and local scale, and then assign similar material types appropriate hydraulic conductivity values to be used in the hydrologic model. Recharge is calibrated with monitor well data and leakage from several years of dry season lake levels, respectively.
Current work focuses on Barron Lake, a Cass County lake without any surface inflow or outflow and a declining lake level. A large-scale model of approximately 147 km2 models regional groundwater flows. A small-scale model with boundaries of approximately 1 km2 is used to simulate the groundwater and lake interaction process. Results from simulations indicate Barron Lake has significant leakage to groundwater and that its water level can be maintained by injecting water from other watershed.
A Viscoelastic Non-Linear Multilayered Model For Asphalt Pavements And Backcalculation
Authors: Sudhir Varma; Emin Kutay
Abstract: Flexible pavements are multilayered structures, with typically top layer as viscoelastic asphalt layer followed by nonlinear (stress-dependent) unbound/bound layers. Conventionally, multilayered elastic analysis is performed to obtain response of flexible pavements for design and inverse analyses, however, assuming asphalt pavement as a linear elastic material is an oversimplification of its actual behavior. It is well known that the asphalt pavements responses are both rate and temperature dependent. In the present work, a computationally efficient model LAVAN has been developed to analyze flexible pavements considering linear viscoelastic asphalt concrete (AC) top layer; followed by stress dependent (nonlinear) base layer; and elastic subgrade. It is shown that the developed model can be used to develop a backcalculation model BACKLAVAN. The BACKLAVAN algorithm utilizes FWD load-response history at different test temperatures to backcalculate |E*| master curve of AC layers as well as linear and non-linear elastic moduli of unbound layers of in-service pavements. The BACKLAVAN algorithm was validated using two FWD test runs on a long term pavement performance (LTPP) section. Comparison between the backcalculated and measured results indicate that, it should be possible to infer linear viscoelastic properties of AC layer as well as nonlinear elastic properties of unbound layers using FWD tests.
This work was supported in part by Federal Highway Administration
A Stochastic Multi-Scale Model Of Stream-Groundwater Interaction In Strongly Heterogeneous Porous Medium And Its Application In South Branch County, Mi
Authors: Xinyu Ye; Shu-Guang Li; Huasheng Liao
Abstract: In this paper, stream depletion is assessed by the approach of multi-scale geostatistics in stressed watershed, South Branch County, Michigan. The watershed is currently under large water demand and representative of the general failure to pass the online Water Withdrawal Assessment Tool. Due to the heterogeneity of porous medium and the high variability of hydrogeological parameters and scale, there is a deviation between field observations and simulated groundwater flow in those areas. The approach of multi-scale geostatistics model based on detailed lithological data and its application in numerical groundwater simulation can be used in stream depletion assessment.
Specifically, the multi-scale transition probability geostatistics approach, supplemented with a 10m Digital Elevation Model, allows for a more realistic integration of heterogeneous medium into the development of correlated spatial variability of hydrogeological parameters at each spatial scale. This approach enables accurate simulation of complex hydrogeology, including vertical shift structural variation and aquifer thickness variations. Systematic hydrology models at the regional, local and site scale allows for simulations of reverse particle tracking and integrated water budget analysis. These simulations are necessary to evaluate the water depletions of targeted streams. The hydrology system is calibrated with the steady state water levels from 200 monitoring wells.
The stability of transition probability geostatistics model depends on the distributions, the heterogeneity of simulated area and other factors. The results show that transition probability geostatistics model provides a reasonable distribution of materials in aquifer medium, improving numerical groundwater modeling in assessing water depletion in streams.
Steel Fiber Reinforced Concrete At Elevated Temperature
Authors: Pratik Bhatt; Vasant Matsagar; Venkatesh Kodur
Abstract: Fire is an extreme event, the occurrence of which affects the behavior of the structures significantly in terms of both serviceability and strength criteria. Concrete is one of the most important building materials and is widely used in many types of engineering structures owing to its low cost/strength ratio. Concrete structural members exhibit good performance under fire situations; however, concrete has inherent brittleness and low tensile strength. Further, significant spalling occurs in case of high strength concrete when it is subjected to elevated temperatures. To overcome these shortcomings researchers have suggested addition of various types of fibers in concrete; one option has been steel fiber reinforced concrete (SFRC). Evaluating the fire resistance of a structure requires the knowledge of high temperature thermal and mechanical properties of constituent materials. The type of aggregate used significantly affects the behavior of concrete at elevated temperature. Here, results of uniaxial compression tests conducted on cylindrical specimen for different combination of volume fractions of steel fibers (0%, 0.5%. 1%, and 1.5%), types of aggregate (siliceous and carbonaceous), strength of concrete (30 MPa, 40 MPa and 60 MPa) in temperature ranging from ambient to 800°C are presented. The test results show that addition of steel fibers significantly improves the fire resistance capacity of concrete at elevated temperature.
This work was supported in part by Indian Institute of Technology (IIT) Delhi, New Delhi, India