Technical Reports, Civil and Environmental Engineering

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Image Processing Approach For Creating An Alert System For Active Induction/Stove
Baishya, Ronit (2023-12-15)
The problem-focused to be solved through this project is that after cooking many times people forget to switch off the burner or induction. This might be a serious issue as it might cause a house fire. For the project, a Pi camera along with Raspberry Pi would be used as the setup, where the camera will collect data that can be used for computer vision and image processing. The techniques used in this project are divided into two parts. First is to separate the light source in the regulator area image and second use edge detection to separate the utensils on the stove/burner and empty the stove/burner. The creation of the actual alert system was not covered in the presentation.
Review Of Bridge Structural Inspection Aided By Augmented Reality
Baishya, Ronit (2023-12-15)
In tackling the pressing concern of deteriorating infrastructure, the integration of element-level condition ratings and the digitization of the national bridge inventory stands out as a crucial response, not only refining the quality of inspection data but also unlocking the potential for machine learning and statistical methods to forecast future infrastructure conditions. AR emerges as a beacon of promise, touted as a tool capable of elevating the quality, precision, and efficiency of bridge inspections. AR is a technology that blends computer-generated information with the user's real-world environment in real time. Unlike virtual reality, which creates a completely artificial environment, augmented reality enhances the existing surroundings by overlaying digital information, such as images, videos, or 3D models, onto the physical world. AR is typically experienced through devices like smartphones, tablets, smart glasses, or AR headsets. It has applications in various fields, including gaming, education, healthcare, manufacturing, and navigation. For example, AR can be used to display additional information about a product when a user points their smartphone camera at it, or it can provide real-time navigation cues overlaid on the street view seen through smart glasses. However, the technology, despite its potential, remains in its infancy within this domain, grappling with various implementation challenges in structural and infrastructure health monitoring. The purpose of this review is to provide an overview of both state of the practice and state of the art applications of AR and related technologies in the bridge inspection context. Based on this overview, key research gaps are identified and discussed. This study ventures into the exploration of Augmented Reality (AR) and immerses itself in the latest developments and the transformative influence it could wield on the digital aspects of bridge inspection. It addresses many aspects of bridge structural inspection aided by augmented reality, such as (i) the process of AR bridge inspection (ii) the present stage and future implementation in the industry (iii) software (iv) challenges, and (v) the future of AR.
Design Of A Miniature Base Isolation Demo
Patil, Saurabh; Baishya, Ronit; Li, Yuhao (2023-05-15)
In this project, we will design a miniature base isolation demo. The objective is to design the total mass, stiffness, and damping (mb, kb, cb) of a base isolation system for a single-story building, subject to the design spectrum described below. An effective isolator will result in a maximum moment that is significantly lower than that of the no-isolation case (fixed base). The target reduction in the base moment is shown in Table 1. The challenge is that as you make the isolator more flexible, it will also deform more and could break as well, so we also will place a limit on the maximum allowed deformation.
Full-Scale Laboratory Evaluation of Hybrid Composite Beams for Implementation in a Virginia Bridge
Moen, Cristopher D.; Roberts-Wollmann, Carin L.; Cousins, Thomas E. (Virginia Transportation Research Council, 2018-08)
This research project studied a steel-reinforced concrete and fiber-reinforced polymer (FRP) structural element called the Hybrid-Composite Beam (HCB). The beam was used in a skewed simple span superstructure replacement project over the Tides Mill Stream in Colonial Beach, Virginia. For typical HCB construction, each beam is transported to site as a lightweight FRP beam shell. Self-consolidating concrete is pumped into the shell interior arch form, and when the concrete hardens, it stiffens and strengthens the beam so that it can act as falsework to carry the weight of a cast-in-place concrete bridge deck. Unstressed prestressing strands are embedded in the FRP shell bottom flange during the resin placement, and these strands equilibrate thrust in the arch and stiffen the beam to meet service deflection criteria. After the deck is placed, the HCB system performs as a longitudinal flexural member, with the bridge deck resisting compression and prestressing strands and the FRP bottom flange resisting tension. The primary research goal was to document the HCB as a structural component and as a bridge system, with the outcome being validation of key assumptions that can be applied to future designs such as, for example, strain compatibility between the FRP shell and steel strands. The research was conducted in five phases. In Phase 1, the HCB flexural rigidity and through-depth strain distributions were quantified considering just the FRP shell with unstressed strands. These tests confirmed flexural rigidity estimated by hand calculations and strain compatibility under uniform loads. Phase 2 evaluated flexural behavior of the HCB FRP shell and poured concrete arch. Phase 3 testing was performed after three HCBs were made integral with cast-in-place concrete end diaphragms and a reinforced concrete bridge deck. Point loads, to simulate an HL-93 design truck as specified in American Association of State Highway and Transportation Officials (AASHTO) LFRD Bridge Design Specifications, were applied to the bridge deck to maximize shear, flexure, and torsion in the skewed bridge. Live load distribution between the three girders was approximately equal and the assumption of strain compatibility between the bridge deck, FRP shell, and steel strand was confirmed. Stresses in bottom flange FRP strands and the top of deck concrete were less than 30% of material limits under service level live loads. The concrete arch fell below the composite neutral axis, placing it in tension along the span. After the live load system tests, a more detailed investigation was performed in Phase 4 to explore transverse deck behavior. Transverse flexural demands were approximately 20% of the design capacity and standard truss bars, as specified by the Virginia Department of Transportation, are not necessary because of the small clear span of the slab between beams. In Phase 5, the bridge system was saw-cut longitudinally to separate it into three individual HCB composite beams. Two beams were load tested to failure at the Structures Laboratory at Virginia Tech. For one of the two beams tested at Virginia Tech, 14 out of a total 22 strands were cut at mid-span to simulate strand deterioration and for comparison the other beam remained undamaged prior to testing. The observed beam failure modes were mid-span concrete crushing for the undamaged beam and mid-span strand-FRP bond failure for the damaged beam. In support of Phase 5, a three-dimensional (3D) finite element model was developed to explore flexural and shear force distributions along the span, which led to a shear design procedure in which shear force is distributed based on the relative moments of inertia of the FRP shell and arch. Shear resistance is provided by the FRP shell webs and the concrete arch and fin.
Implementation of a Precast Inverted T-Beam System in Virginia: Part II: Analytic and Field Investigations
Menkulasi, Fatmir; Cousins, Thomas E.; Roberts-Wollmann, Carin L. (Virginia Transportation Research Council, 2018-08)
The inverted T-beam superstructure is a bridge system that provides an accelerated construction alternative for short-to-medium-span bridges. The system consists of adjacent precast inverted T-beams with a cast-in-place concrete topping. This bridge system is expected to not experience the reflective cracking problems manifested in short-to-medium-span bridges constructed with traditional adjacent voided slab or adjacent box beams. This report presents the results of three phases of a comprehensive research project to develop and implement an inverted T-beam system for Virginia. The three phases are: investigation of time-dependent and temperature effects, investigation of end zone stresses, and live load testing. The first investigation is of time-dependent effects in composite bridges with precast inverted T-beams. The analysis was performed for a two-span continuous bridge. An analytical study was performed to quantify the stresses generated as a result of differential shrinkage, creep and temperature gradient at various sections in both directions. At the cross-sectional level, an elastic sectional analysis approach using the age-adjusted effective modulus method was used to perform the investigation. At the structure level, the effects of uniform temperature changes, thermal gradients and differential shrinkage and creep were investigated and quantified in terms of axial restraint forces and restraint moments. It is shown that, by paying attention to detailing and by selecting a mix design for the cast-in-place topping that has relatively low shrinkage and high creep, the potential for excessive cracking can be reduced. The second investigation is of the stresses in the end zones of such a uniquely shaped precast element. The transfer of prestressing force creates vertical and horizontal tensile stresses in the end zones of the beam. A series of three-dimensional (3D) finite element analyses were performed to investigate the magnitude of these tensile stresses. Various methods of modeling the prestressing force, including the modeling of the transfer length, were examined and the effect of notches at the ends of the precast beams was explored. Existing design methods were evaluated; strut-and-tie models, calibrated to match the results of 3D finite element analyses, are proposed as alternatives to existing methods to aid designers in sizing reinforcing in the end zones. The final section reports the results of live load testing performed on the first inverted T-beam bridge in Virginia on U.S. 360 over the Chickahominy River. A finite element model of Phase I of the U.S. 360 Bridge was created and the live load distribution factors were analytically determined. Live load tests using a stationary truck were performed on Phase I of the U.S. 360 Bridge with the purpose of quantifying live load distribution factors and validating the results from the finite element analyses. It is concluded that it is appropriate to estimate live load distribution factors using AASHTO provisions for cast-in-place slab span bridges.
Carbon Fiber Reinforced Polymer Grids for Shear and End Zone Reinforcement in Bridge Beams
Ward, John; Magee, Mitch; Roberts-Wollmann, Carin L.; Cousins, Thomas E. (Virginia Transportation Research Council, 2018-01)
Corrosion of reinforcing steel reduces life spans of bridges throughout the United States; therefore, using non-corroding carbon fiber reinforced polymer (CFRP) reinforcement is seen as a way to increase service life. The use of CFRP as the flexural reinforcement in bridge girders has been extensively studied. However, CFRP transverse reinforcement has not been investigated as rigorously, and many of those studies have focused on carbon fiber composite cable (CFCC) stirrups. The use of C-Grid or NEFMAC grid as options for transverse reinforcing has not been previously investigated. This testing program first determined the mechanical properties of C-Grid and NEFMAC grid and their respective development lengths. Five 18-ft long, 19-in deep beams were fabricated to test the C-Grid and NEFMAC, as well as conventional steel and CFCC stirrups. The beams were loaded with a single point load closer to one end of the beam to create a larger shear load for a given moment. Overall beam displacement was measured, and beams were fitted with rosettes and instrumentation to capture initiation of shear cracking. Test results were compared to theoretical shear capacities calculated using four different methods. The design method which provided the best prediction of shear strength was the AASHTO modified compression field theory, using equations for β and θ. The manufacturer’s guaranteed tensile strength should be used for design, as long as that strength is the average strength, as determined by at least five tests, reduced by three standard deviations. Shear cracks were controlled to a similar width as in beams with steel stirrups when at least two layers of grid were in place. An additional study was undertaken to determine if CFRP grids, either alone or in combination with traditional steel stirrups, could be used to control cracking in the end zones of pretensioned I-beams. Unfortunately, it was determined that, due to its low modulus, the amount of CFRP grid required to control cracking in the end zones was not economically feasible. Nevertheless, this study concluded that C-Grid and NEFMAC grid are both viable shear reinforcement options outside of the end regions. This report presents the initial recommendations for design.
Roanoke Urban Stormwater Research: Lick Run / Trout Run Phase V Final Report
Dymond, Randel L.; Brendel, Conrad E.; Woodson, David (2018-12-19)
Effective management and restoration of urban watersheds requires considerable information describing the watershed’s land surface, drainage system, and receiving streams, in order to understand the important hydrologic and ecologic processes, and to make informed decisions about how to allocate resources for watershed improvements. Previous research has focused on the creation of Watershed Master Plans to provide recommendations for maintaining and improving the function of City of Roanoke watersheds. This year, research has focused on the creation of tools to assist the City in making informed decisions pertaining to land development and stormwater best management practice (BMP) design. This report outlines 1) the development of web apps to assist the City with data synthesis and analysis, 2) the creation of a hydrology and hydraulics model to simulate watershed hydrology under existing conditions and a variety of development and/or stormwater BMP implementation scenarios, and 3) the review of stormwater management design manuals for various states and municipalities. This report is submitted in tandem with a literature review of stormwater management design manuals that is generally organized according to the tasks outlined in the 2018 Phase V Scope of Research. Section 1 is an Introduction that describes the ongoing relationship between the City and the Virginia Tech Via Department of Civil and Environmental Engineering that made this work possible, and also describes the layout of subsequent sections. Section 2 describes the Stream Hydrology and Rainfall Knowledge System (SHARKS) web app that was developed to provide the City with a platform to rapidly synthesize, visualize, and analyze data from various meteorological and hydrologic data sources. Section 3 describes the library of storm event precipitation and runoff data contained in Appendix II. This section also presents the MINNOWS web app that was developed to complement the SHARKS app and to provide an interactive platform to identify spatial and temporal trends in the storm event library. Section 4 describes the development of the hydrologic and hydraulic model for the combined Lick Run/Trout Run watersheds and Section 5 provides an overview of the stormwater management design manual review. Section 6 provides the references used in this report. Finally, Appendix I contains the relative flow/depth rating curves created for the nine Roanoke storm sewer depth sensors and Appendix II contains a library of storm event precipitation and runoff data for each 2018 event. Although the submittal of this report marks the end of the 2018 Scope of Research, the work performed during this period has continued the development of a long-term collaboration between the City and VT for expansion of the science of urban stormwater management, and its application to the City’s watersheds.
Roanoke Urban Stormwater Research: Phase 1 - Discovery Final Report
Dymond, Randel L.; Aguilar, Marcus F.; Bender, Paul; Hodges, Clayton Christopher (2014-12-01)
This report is the final product of an 8 month long collaboration between the City of Roanoke’s Environmental, Engineering, Public Works, GIS, and Planning staff, and researchers in the Via Department of Civil and Environmental Engineering at Virginia Tech. This relationship was borne out of a mutual desire for improved urban stormwater science, with an anticipation that a long-term municipal-academic partnership would bring innovation to municipal stormwater management while providing opportunities to further the body of knowledge in this field. This report illustrates the City of Roanoke’s present political and environmental climate with respect to stormwater management by historical account and geographic context. It is descriptive and observational, providing both a foundation to proceed with future work, and a benchmark to measure success. The objective of this report is to characterize the regulations, people, and information that constitute stormwater management in the City of Roanoke. The Introduction is a summary of the City of Roanoke/Virginia Tech Urban Stormwater Research collaboration, and introduces the City as a densely urbanized political entity in the Upper Roanoke River watershed. The Introduction leads into Section I, a review of the Federal and State regulations that compel the City to prevent and treat stormwater runoff pollution, and a description of the City’s compliance strategies. Conversations with City staff and other stakeholders characterized these programs and helped contextualize stormwater management in the City and regionally; these conversations are recorded in Section II. City staff also supported the synopsis of City Geographic Information System data found in Section III by providing the necessary access. Section IV relates the quality and relevance of geographic datasets from external sources, and Section V does the same for water quality and quantity data. Section VI describes the pathways for general public engagement in stormwater in the City and regionally. The report body is bookended by Tables of Contents, Figures, and Tables at the front, and Index of Terms, References, and alphabetized Bibliography in the back. Supplemental information, including additional tables, figures, and text is found in the Appendices, organized using the same structure as the report. The submission of this report marks the end of the initial Discovery Phase of this research relationship; the resources have been discovered, collected, and organized. This also marks the commencement of the second phase, which focuses on a single City watershed as a precedent for future watershed planning. The completion of this first Phase, and even the anticipated completion of the next, do not bring finality to this work, but represent benchmarks along the way to the now unified objective of improving water quality in the City’s waterways – the terminal measure of success in this research project.
Investigation of the Resistance of Pile Caps and Integral Abutments to Lateral Loading
Mokwa, Robert L.; Duncan, J. Michael (Virginia Center for Transportation Innovation and Research, 2002-02-01)
This research provides a means of assessing and quantifying many important aspects of pile group and pile cap behavior under lateral loads. The program of work performed in this study includes developing a full-scale field test facility, conducting approximately 30 lateral load tests on pile groups and pile caps, performing laboratory geotechnical tests on natural soils obtained from the site and on imported backfill materials, and performing analytical studies. A detailed literature review was also conducted to assess the current state of practice in the area of laterally loaded pile groups. A method called the "group-equivalent pile" approach (abbreviated GEP) was developed for creating analytical models of pile groups and pile caps that are compatible with established approaches for analyzing single laterally loaded piles. A method for calculating pile cap resistance-deflection curves (p-y curves) was developed during this study, and has been programmed in the spreadsheet called PYCAP. A practical, rational, and systematic procedure was developed for assessing and quantifying the lateral resistance that pile caps provide to pile groups. Comparisons between measured and calculated load-deflection responses indicate that the analytical approach developed in this study is conservative, reasonably accurate, and suitable for the use in design of pile caps and integral abutments. The results of this research are expected to improve the current state of knowledge and practice regarding pile group and pile cap behavior.
Classification of longitudinal welds in an aluminum bridge deck
Cousins, Thomas E.; Richard F. Hezel II; Jose P. Gomez (Virginia Center for Transportation Innovation and Research, 2002-02-01)
An aluminum bridge deck (called ALUMADECK) has been developed by Reynolds Metal Company and is made of extruded aluminum sections welded together at the sides to form a bridge deck. The longitudinal welds used to connect the extrusions do not match any of the fatigue category details in the AASHTO LRFD Bridge Specifications. In order to classify these welds, two fatigue tests were performed on a two-span ALUMADECK section fabricated over "simulated" bridge girders. Certain locations on the longitudinal welds were tested at a constant amplitude fatigue stress of at least 13.8 MPa (equivalent to the 1994 AASHTO LRFD Bridge Specification Category C Detail) to determine if the welds could be conservatively classified as a detail category C. The ALUMADECK was subjected to 10,000,000 cycles of fatigue loading. There was no sign of fatigue crack initiation during this loading. Once the fatigue loading was complete a residual strength test was performed. The residual strength of the ALUMADECK after fatigue loading was 33% greater than the ultimate strength of an earlier generation of the ALUMADECK. From the data collected and observations made during the fatigue loading the longitudinal welds in the ALUMADECK can be conservatively classified as an AASHTO detail category C.
Erosion Protection for Soil Slopes Along Virginia's Highways
Scarborough, Jessee A.; Filz, George M.; Mitchell, James K.; Brandon, Thomas L. (Virginia Center for Transportation Innovation and Research, 2000-10-01)
A survey of the state of practice for designing slope erosion control measures within VDOT's nine districts has been conducted. On the basis of the survey, it is clear that there are no specific design procedures currently in use within VDOT for dealing with slope erosion. VDOT designers generally try to limit erosion by diverting runoff from adjacent areas, controlling concentrated flows on slopes, and establishing vegetation on slopes as quickly as possible. In addition, the Federal Highway Administration (FHWA) and the Departments of Transportation in states surrounding Virginia (Maryland, West Virginia, Kentucky, Tennessee, and North Carolina) were contacted. The state of practice for the FHWA and for these states appears to be similar to that used by VDOT. A review of the literature for soil erosion was performed. The universal soil loss equation (USLE), an empirical equation developed by the U.S. Department of Agriculture, was found to provide the best available quantitative tool for evaluating factors controlling the erosion process and determining what level of protection is appropriate. The authors recommend that the USLE be used to supplement VDOT's current principle-based design practices.
Experimental and Analytical Investigations of Piles and Abutments of Integral Bridges
Arsoy, Sami; Richard M. Barker; Duncan, J. Michael (Virginia Center for Transportation Innovation and Research, 2002-03-01)
This research investigated, through experimental and analytical studies, the complex interactions that take place between the structural components of an integral bridge and the adjoining soil. The ability of piles and abutments to withstand thermally induced cyclic loads was investigated by conducting large-scale cyclic load tests. Three pile types and three integral abutments with hinges were tested in the laboratory. Experiments simulated 75 years of bridge life. Numerical analyses were conducted to analyze the interactions among the abutment, the approach fill, the foundation soil, and the foundation piles. The results indicated that H-piles are most suitable for supporting integral abutments. Concrete piles and pipe piles were too stiff in response to repeated lateral loads, resulting in tension cracks at the connection with the abutment. Further, a hinge in the integral abutment effectively reduces pile stresses by absorbing some of the rotational movement.
Field performance of epoxy-coated reinforcing steel in Virginia bridge decks
Pyc, Wioleta A.; Weyers, Richard E.; Weyers, Ryan M.; Mokarem, David W.; Jerzy Zemajtis; Sprinkel, Michael M.; Dillard, John G. (Virginia Center for Transportation Innovation and Research, 2000-02-01)
In this study, the corrosion protection performance of epoxy-coated reinforcing steel (ECR) was evaluated using approximately 250 concrete cores from 18 bridge decks in Virginia. The decks were 2 to 20 years old at the time of the investigation. The deck field inspections included a crack survey and cover depth determination in the right traffic lane. A maximum of 12 cores with the top reinforcement randomly located in the lowest 12th percentile cover depth were taken from each bridge deck. Because of the safety concerns associated with taking cores from the lower steel mat, and to minimize damage to the bridge, a maximum of only 3 cores were taken through the truss bars. The laboratory evaluation of the concrete cores included a visual examination and a determination of the carbonation depth, moisture content, absorption, percent saturation, and chloride content at a 13-mm depth. The rapid chloride permeability test was also performed for the surface and base concrete on samples obtained from the cores taken through the truss bars to determine chloride permeability. The ECR inspection consisted of a visual examination, a damage evaluation, and a determination of coating thickness and adhesion. The condition of the steel underneath the epoxy coating was also evaluated. Adhesion loss of the epoxy coating to the steel surface was detected in all but one deck that was 4 years old and older. The epoxy coatings were debonding from the reinforcing bars. Whereas a bonded coating can be expected to protect the steel, a debonded coating allows chlorides, moisture, and oxygen to reach the steel and initiate a rapid corrosion mechanism. Reinforcing bars in various stages of adhesion loss showed visible signs of a corrosion process underneath the coating, suggesting that ECR will provide little or no additional service life for concrete bridge decks in comparison to bare steel. Other systems that will provide longer protection against chloride-induced corrosion of the reinforcing steel with a higher degree of reliability should be considered.
Glass fiber reinforced polymer bars as top mat reinforcement for bridge decks
DeFreese, James Michael; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2002-09-01)
The objectives of this research were to characterize the material and bond properties of three commercially available GFRP (glass fiber reinforced polymer) reinforcing bars, and evaluate the effects of the material properties and the current ACI design recommendations (ACI 2001) on the design of a bridge deck with GFRP as top mat reinforcement. The tensile properties evaluated were ultimate tensile strength, tensile modulus of elasticity and ultimate rupture strain. Ultimate bond stress and load-slip behavior of the three types of bars were evaluated using beam-end bond stress tests. For the tensile tests, for each type of GFRP bar, three bar sizes were tested: No. 4, No. 5, and No. 6. For each bar size and manufacturer, five samples were tested. The average ultimate tensile strengths varied from 80.4 ksi to 119 ksi, with coefficients of variation for the five-bar samples ranging from 2.6% to 8.0%. The average moduli of elasticity for the three manufacturers were very similar, with a high of 6340 ksi and a low of 5800 ksi. All bars showed linear elastic behavior to rupture. The bar rupture strains varied from 1.4% to 1.9%. The bars also had similar average maximum bond stresses, with a high of 2600 psi and a low of 2360 psi. The load-slip behaviors exhibited by the three bar types were each unique. Pre-peak behavior was similar, but post-peak behavior varied depending on the surface treatment of the bar. The design material properties for each bar type were determined using the recommendations of ACI Committee 440 (ACI 2001). These properties are presented in Table 14. of the report. The property with the greatest influence on the selection of bar size and spacing for a bridge deck reinforced with GFRP reinforcement is the modulus of elasticity. The reinforcing bar with the highest modulus of elasticity will result in the most economical design in terms of materials required. Realistically, however, a bridge deck design that is based on the lowest value of each measured material property will not greatly increase the quantity of GFRP reinforcing, and will enable any of the manufactures' products to be used successfully in a given project.
High-speed texture measurement of pavements
McGhee, Kevin K.; Flintsch, Gerardo W. (Virginia Center for Transportation Innovation and Research, 2003-02-01)
This study was conducted to validate high-speed texture measuring equipment for use in highway applications. The evaluation included two high-speed systems and a new static referencing device. Tests were conducted on 22 runway and taxiway test sections from the National Aeronautics and Space Administration's Wallops Flight Facility and 7 surfaces from Virginia's Smart Road. Texture estimates recorded with the high-speed (dynamic) equipment correlated extremely well with estimates made with static referencing methods. The system developed by International Cybernetics Corporation was very functional for most conventional highway surfaces. However, a better correlation may be achieved with the referencing methods by using a system (such as the MGPS surface system developed by the Federal Highway Administration) that produces the American Society for Testing and Materials' standard mean profile depth. Finally, an analysis conducted using the CTMeter (circular track meter, a laser-based but static system) demonstrated an important advantage of combining indices produced from high-definition surface profiles. By comparing the mean profile depth with the root mean square data for a particular surface, it is possible to characterize more fully the shapes that contribute to a pavement's macrotexture.
Evaluation of models for predicting (total) creep of prestressed concrete mixtures
Meyerson, Richard M.; Weyers, Richard E.; Mokarem, David W.; Lane, D. Stephen (Virginia Center for Transportation Innovation and Research, 2002-09-01)
Concrete experiences volume changes throughout its service life. When loaded, concrete experiences an instantaneous recoverable elastic deformation and a slow inelastic deformation called creep. Creep of concrete is composed of two components, basic creep, or deformation under load without moisture loss and drying creep, or deformation under drying conditions only. Deformation of concrete in the absence of applied load is often called shrinkage. The deformation due to creep is attributed to the movement of water between the different phases of the concrete. When an external load is applied, it changes the attraction forces between the cement gel particles. This change in the forces causes an imbalance in the attractive and disjoining forces. However, the imbalance is gradually eliminated by the transfer of moisture into the pores in cases of compression, and away from the pores in cases of tension. Designs typically use one of the two code models to estimate creep and shrinkage strain in concrete, ACI 209 model recommended by the American Concrete Institute or the CEB 90 Eurocode 2 model recommended by the Euro-International Committee. The AASHTO LRFD is based on the ACI 209 model. Three other models are the B3 model, developed by Bazant; the GZ model, developed by Gardner; and the SAK model developed by Sakata. The objectives of this research was the development of performance limits for compressive creep of concrete mixtures used by the Virginia Department of Transportation, specifically concrete mixtures used for prestressed members (A-5 Concrete) and the determination the accuracy and precision of the creep models presented in the literature. The CEB 90 Eurocode 2 model for creep and shrinkage is the most precise and accurate predictor. The total creep strain for the VDOT portland cement concrete mixtures discussed in this study were found to be between 1200 +/- 110 microstrain at 28 days, and 1600 +/- 110 microstrain at 97 days, at a five percent significant level. It is recommended that the CEB 90 model be used in the AASHTO LRFD rather than the ACI 209 model to improve the prediction of prestress loss.
Factors Affecting Strength Gain in Lime-Cement Columns and Development of a Laboratory Testing Procedure
Jesse R. Jacobson; Filz, George M.; Mitchell, James K. (Virginia Center for Transportation Innovation and Research, 2003-06-01)
Lime-cement columns were constructed to improve soft ground as part of a test embankment program at the I-95/Route interchange in Alexandria, Virginia. Two different commercial laboratories performed tests on treated soil, and they produced very different measurements of unconfined compressive strength. Further, both sets of results were different from test results available in the published literature for similar soils. This situation created uncertainties and a conservative design philosophy. The goals of this research project were to assess factors that influence strength gain of lime-cement-soil mixtures, to develop a detailed laboratory test procedure that produces consistent results, and to determine the reasons that the strengths measured by the private firms were so different. A suitable laboratory procedure was developed and applied to three soils: one from the I-95/Route interchange site and two from the site of a potential future application of lime-cement columns in West Point, Virginia, at State Route 33. Key findings from the research were that (1) drying and subsequent restoration of soil moisture prior to treatment can decrease the strength of the mixture, (2) the mixture strength decreases as the ratio of soil water content to cement content increases for 100 percent cement-soil mixtures, (3) the addition of lime can increase the mixture strength for some soils and decrease the strength for others, and (4) presenting the test results in the form of contour plots of unconfined compressive strength can be very useful. The reasons for the different results from the two private firms are explained by differences in the test procedures that were used.
Proof Testing a Bridge Deck Design with Glass Fiber Reinforced Polymer Bars as Top Mat of Reinforcement
Jason K. Cawrse; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2003-06-01)
The primary objective of this project was to test a full-scale prototype of a bridge deck design containing glass fiber reinforced polymer (GFRP) bars as the top mat of reinforcement. The test deck mimics the design of the deck of one span of the new bridge over Gills Creek on Rt. 668 in Franklin County, Virginia. The purpose of the tests was to verify the deck design and provide assurance that the deck will behave as expected. Aspects of the behavior of the bridge deck, such as failure load, failure mode, cracking load, crack widths, deflections, and internal stresses, were examined. Four tests were performed on the deck, all of which tested the deck in negative moment regions. The tests comprised two overhang tests, one test of the deck over an interior girder, and one test of a cantilever section of the composite deck and girder. The cantilever test modeled the deck in a continuous bridge over an interior support. From the tests, it was concluded that the design of the deck was quite conservative. The secondary objectives of this project were to comment on the construction of a bridge deck reinforced with GFRP bars, note the advantages and disadvantages, and critique the current state of the art of designing bridge decks with GFRP reinforcement. It was found that the advantages of construction with GFRP bars easily outweighed the disadvantages and that the placing of the top mat of GFRP bars was much easier than the placing of the bottom mat of steel bars. The state of the art for the design of bridge decks reinforced with GFRP bars was found to be generally conservative. Three primary criteria dictate the deck design: strength, allowable stresses in the GFRP bars, and crack widths. For this deck, the size and spacing of the transverse GFRP bars were governed by crack control criteria. In testing the deck, however, it was found that the measured crack widths were far smaller than the calculated widths. The measured bar stresses, after cracking, were below those calculated, and below the allowable for all but the cantilever test. The ultimate failure loads were between 3.7 and 7.6 times the design wheel load plus impact. All failures were due to punching shear and were between 91% and 149% of the predicted failure load. Current methods for calculating one-way shear grossly under-predicted capacity. The current design is safe and should prove to be low maintenance. Improvements in design approach, particularly for crack widths and one-way shear, could result in more economical designs in the future. Although current methods for calculating strength and serviceability requirement do not result in accurate predictions of behavior, they do result in conservative designs.
Investigation of Transfer Length, Development Length, Flexural Strength, and Prestress Losses in Lightweight Prestressed Concrete Girder
Cousins, Thomas E.; Nassar, Adil (Virginia Center for Transportation Innovation and Research, 2003-04-01)
Encouraged by the performance of high performance normal weight composite girders, the Virginia Department of Transportation has sought to exploit the use of high performance lightweight composite concrete (HPLWC) girders to achieve economies brought about by the reduction of dead loads in bridges. Transfer length measurements (conducted on two AASHTO Type IV HPLWC prestressed girders) indicated an average transfer length of 17 inches, well below the AASHTO and ACI requirements. Two HPLWC AASHTO Type II girders and a 48 x 8 inch normal weight 4000-psi concrete deck were fabricated. The girders were cast of concretes with a compressive strength of 6380 psi and a unit weight of 114 pcf. Full scale testing of the girders was conducted to evaluate development length and flexural strength in HPLWC composite girders. Embedment lengths of five, six, and eight feet were evaluated. Tests indicated a development length of about 72 inches, marginally below the ACI and AASHTO requirements. All tested girders exceeded their theoretical flexural capacity by 24% to 30%. A third composite Type II girder was cast of high performance normal weight concrete and topped with a 48 x 8 inch normal weight 4000-psi concrete deck. This girder was intended as a control specimen. Prestress losses in the HPLWC AASHTO Type IV girders monitored over a nine-month period were found to be less than those calculated using the ACI and PCI models.
Development of concrete shrinkage performance specifications
Mokarem, David W.; Meyerson, Richard M.; Weyers, Richard E. (Virginia Center for Transportation Innovation and Research, 2003-08-01)
During its service life, concrete undergoes volume changes. One of the types of deformation is shrinkage. The four main types of shrinkage associated with concrete are plastic, autogenous, carbonation, and drying shrinkage. The volume changes in concrete due to shrinkage can lead to the cracking of the concrete. In the case of reinforced concrete, the cracking may produce a direct path for chloride ions to reach the reinforcing steel. Once chloride ions reach the steel surface, the steel will corrode, which itself can cause cracking, spalling, and delamination of the concrete. The unrestrained drying shrinkage and restrained cracking tendency of concrete mixtures typically used by the Virginia Department of Transportation (VDOT) were assessed to establish an appropriate limit on drying shrinkage for use in a performance specification. Five existing shrinkage prediction models were assessed to determine the accuracy and precision of each model as it pertains to the VDOT mixtures used in this study. The five models assessed were the ACI 209 Code Model, Bazant B3 Model, CEB 90 Code Model, Gardner/Lockman Model, and Sakata Model. The CEB 90 model performed best for the portland cement concrete mixtures, while the Gardner/Lockman Model performed best for the supplemental cementitious material mixtures. Based on a comparison of the unrestrained drying shrinkage and restrained cracking tendency, it was determined that the potential for cracking could be minimized by limiting the unrestrained shrinkage of the concrete mixtures. Based on the results of this study, the recommended percentage length change specification limits are 0.0300 at 28 days and 0.0400 at 90 days for the portland cement concrete mixtures. For the supplemental cementitious material mixtures, the percentage length change specification limits were 0.0400 at 28 days and 0.0500 at 90 days.

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