Technical Reports, Civil and Environmental Engineering

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Research on Design for Prevention of Ditch Erosion on Virginia Highways
Diplas, Panayiotis; Duncan, J. Michael; Mitchell, J.K.; Coffey, J.; Smith, C.; Stallings, S. (Virginia Center for Transportation Innovation and Research, 1999-12-01)
Roadside ditch erosion has been problematic on Virginia highways. VDOT, through the Virginia Transportation Research Council, requested that roadside ditch erosion be investigated by means of a research project. Virginia Tech was selected to conduct this study. In support of this research, design guidance documents were surveyed to learn the current established policy and procedures for soil data collection and reporting, and the design practice for hydrologic and hydraulic analyses of roadside ditches. Site visits to each of Virginia's nine construction districts were made to interview district personnel about their personal experience with roadside ditch design, performance, and erosion failures. Current ditch design practices in nine other states were investigated through the collection and survey of state drainage manuals, and phone interviews with DOT personnel. Finally, an extensive review of current literature was performed with the intent of investigating current research on ditch erosion and erosion control. Results of the research indicate that three major factors are contributing to the occurrence of erosion in roadside ditches. They include, 1) insufficient soil information collected on road projects and reported in unusable formats for the hydraulic designers, 2) overuse of default values and criteria in hydraulic design, and 3) geographical and management issues not currently encompassed by current VDOT ditch design policies and procedures. Recommendations directed at these factors are provided, along with tables presenting updated correlations between site-specific conditions and hydraulic parameters for design.
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.
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.
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.
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.
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.
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.
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.
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.
Using high-speed texture measurements to improve the uniformity of hot-mix asphalt
McGhee, Kevin K.; Flintsch, Gerardo W.; de León Izeppi, Edgar (Virginia Center for Transportation Innovation and Research, 2003-05-01)
This study introduces Virginia's efforts to apply high-speed texture measurement as a tool to improve the uniformity of hot-mix asphalt (HMA) pavements. Three approaches for detecting and quantifying HMA segregation through measuring pavement surface macrotexture were evaluated: (1) applying the methods proposed in NCHRP Report 441, which build on the ability to predict the expected "non-segregated" macrotexture; (2) using acceptance bands for texture similar to those used for HMA density; and (3) considering the standard deviation of the macrotexture as a measure of construction uniformity. Based on the findings from a series of field tests, the researchers concluded that macrotexture measurement holds great promise as a tool to detect and quantify segregation for quality assurance purposes. None of the available equations for predicting non-segregated macrotexture (the approach in NCHRP Report 441) was found to work for all the construction projects evaluated. Additional information is necessary to establish target macrotexture levels. The acceptance bands approach produced reasonable results in most of the field-verification experiments, but it was significantly influenced by the actual variability within the section. An approach that used target levels of standard deviations was selected for further testing and implementation on a pilot basis.
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.
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.
Corrosion Protection Service Life of Epoxy-Coated Reinforcing Steel in Virginia Bridge Decks
Brown, Michael C.; Weyers, Richard E.; Megan C. Wheeler (Virginia Center for Transportation Innovation and Research, 2003-09-01)
The corrosion protection service life extension provided by epoxy-coated reinforcement (ECR) was determined by comparing ECR and bare steel bars from 10 Virginia bridge decks built between 1981 and 1995. The objective was to determine the corrosion protection service life time extension provided by ECR field specimens with various degrees of coating adhesion: disbonded, partially disbonded, and wholly bonded coatings. The size and length distributions of cracks in Virginia bridge decks were investigated to assess the frequency and severity of cracks. Correlation of cracks with chloride penetration was used to characterize the influence of cracking on deck deterioration. Cracks influence the rate of chloride penetration, but the frequency and width distributions of cracks indicate that cracks are not likely to shorten the overall service life of most bridge decks in Virginia. Altogether, 141 drilled cores, 102 mm (4 inches) in diameter, were employed in this study. For each of the decks built with ECR, 10 to 12 cores were drilled through a top reinforcing bar adjacent to the previous study core locations. In addition, approximately 3 cores were drilled through a top reinforcing bar at a surface crack location. Laboratory testing involved nondestructive monitoring using advanced electrochemical techniques to periodically assess the corrosion state of the steel bars during cyclic exposure to chloride-rich solution over 36 months of treatment. Time of corrosion initiation and time of cracking (where applicable), as well as chloride content of the concrete before and after treatment, were used in the analysis. Analysis of the epoxy coating after treatment showed the presence of micro cracks in the surface of some coatings, and moisture uptake and glass transition temperatures, as related to curing of the coatings, were investigated. Less than 25 percent of all Virginia bridge decks built under specifications in place since 1981 is projected to corrode sufficiently to require rehabilitation within 100 years, regardless of bar type. The corrosion service life extension attributable to ECR in bridge decks was found to be approximately 5 years beyond that of bare steel and, therefore, ECR is not a cost-effective method of corrosion prevention for bridge decks. Deleting the requirement for ECR in decks would save Virginia approximately $845,000 per year.
Composite action in a steel girder span with precast deck panels :the I-81 bridge over the New River in Radford, Virginia
Cousins, Thomas E. (Virginia Center for Transportation Innovation and Research, 2003-10-01)
Two parallel bridges carry I-81 north and south over the New River in southwest Virginia, near the city of Radford. The bridges are identical in design and have been in place since 1985. In recent years, a number of maintenance issues have been reported, primarily related to cracking of the cast-in-place topping over partial-depth precast deck panels. A study was undertaken to determine the influence of the observed deterioration on the structural capacity of the affected bridge spans. The analysis indicated that the full potential of the composite slab-girder system is no longer being realized. Continued deterioration of the deck is likely, especially given the frequency of heavy truck traffic on this structure and the inherent vibration. It appears that the presence of precast cast-in-place deck sections has reduced the overall stiffness of the deck as compared to the original design. The movement, in conjunction with a poor deck panel support detail, is likely to cause a continual maintenance problem, as additional precast panels begin to move and fracture of the cast-in-place topping occurs. As a potential mitigation option, replacement of the fiber bolster material between the top flange of the girders and the precast panels with more rigid steel shims and/or concrete is recommended to increase the bearing surface of the panels, reduce vertical displacement of panel edges, and minimize dynamic impact at the joints.
Assessment of the Performance of Several Roadway Mixes under Rain, Snow, and Winter Maintenance Activities
Flintsch, Gerardo W. (Virginia Center for Transportation Innovation and Research, 2004-02-01)
The purpose of this study was to assess the relative functional performance, including skid resistance and splash and spray, of five hot-mix-asphalt (HMA) surfaces and a tinned portland cement concrete highway surface during controlled wet and wintry weather events. The study compared the way that these surfaces respond to various deicing and anti-icing snow removal and ice control techniques under artificial wintry conditions. In addition, the splash and spray characteristics of the surfaces during and immediately after rain were also evaluated. The study focused on the surfaces placed within the all-weather testing area at the Virginia Smart Road. The winter maintenance techniques tested include the application of sodium chloride (salt) in granular, pre-wetted, and liquid forms. The snow removal and ice control measures that were used followed the recommendation of the FHWA Project T & E 28 and variations thereof. The experiments to compare the splash and spray characteristics of the mixes were conducted using artificial rain. The study defined and tested a methodology for testing winter maintenance operations under controlled, artificial wintry events. The winter maintenance test results were inconclusive, as the various maintenance treatments were unable to significantly improve the functional condition of the road. Under the temperature and precipitation conditions encountered, there were no significant differences in the performance of the different surface mixes tested. However, conditions encountered did not correspond to conditions normally encountered with natural snow. The researcher concluded that at temperatures at and just below freezing, artificial snow might not be appropriate for evaluating the effectiveness of winter maintenance chemicals. Studies that depend upon imitating the on-road attributes of natural snow, such as testing effectiveness of winter maintenance chemicals, should adhere to the ideal temperature-humidity guidelines for the snowmaking equipment. The open-graded friction course appears to have enhanced spray and splash performance when compared with the dense HMA surface mixes; however, a more objective measure of splash and spray characteristics of the surfaces is needed to quantify the beneficial effect of this type of mixes. No visual difference in performance was observed among the other mixes.
Plate & tube bridge deck evaluation in the deck test bed of the Troutville, Virginia, weigh station
Cousins, Thomas E.; Lesko, John J. (Virginia Center for Transportation Innovation and Research, 2004-03-01)
This report addresses the laboratory and field performance of multi-cellular fiber-reinforced polymer (FRP) composite bridge deck systems. We focus specifically on FRP decks produced from adhesively bonded pultrusions where the core of the deck possesses a square geometry running transversely to traffic. In laboratory tests, two schemes of loading patches were designed: a steel patch dimensioned according to the American Association of State Highway and Transportation Officials (AASHTO) Bridge Design Specifications, and a simulated tire patch constructed from an actual truck tire reinforced with silicon rubber. The stiffness, strength, and failure characteristics of the cellular FRP decks were examined using both loading patches. Our research shows that the effects of the stiffness and contact conditions of loading patches are significant. The simulated tire loading develops greater deflections given the same static load. The failure mode is localized and dominated by transverse bending failure of the composites under the simulated tire loading as compared to punching shear for the AASHTO recommended patch load. A field testing facility was designed and constructed in which FRP decks were installed, tested, and monitored to study the decks' in-service field performance. No significant loss of deck capacity was observed after field service. However, the long-term field monitoring and testing results showed that the unsupported edges (or free edges) are undesirable.
Influence of the new LRFD seismic guidelines on the design of bridges in Virginia
Widjaja, Matius Andy; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2004-03-01)
The Virginia Department of Transportation is currently using the AASHTO Standard Specifications for Highway Bridges, with some modifications, for its seismic highway bridge design. In April 2001, the Recommended LRFD Guidelines for the Seismic Design of Highway Bridges were published. The influence of the LRFD Guidelines on Virginia bridges was investigated by analyzing two existing bridges. The first bridge has prestressed concrete girders and is located in the Richmond area. The second bridge has steel girders and is located in the Bristol area. Both bridges were two-span overpass structures with integral abutments. The bridges were analyzed using the methods prescribed in the guidelines. Then, the combined effects of the dead, live, and earthquake loads were compared to the strengths of the columns and the pier caps. The details of the bridge designs were also checked against the corresponding seismic design requirement. Results indicate that typical column spiral reinforcement is not adequate to satisfy the requirements of the new seismic guidelines. For the bridge in the Richmond area, spiral reinforcement was increased from a No. 5 at a 5-in pitch to a No. 5 at a 4-in pitch. For the bridge in Bristol, the increase was greater, from a No. 3 at 10.5 in to a No. 5 at 4 in. In addition to the increase in spiral reinforcement, other details, such as beam-column joint reinforcing and splice locations, require modifications. The calculated cost increases for the two bridges were 0.1 and 0.3 percent. An associated parametric study explored the effects on substructure design of different column heights, superstructure lengths, and soil classifications in different parts of Virginia. The study indicated that for bridges located on good soil (Class B), typical column longitudinal reinforcing ratios (about 1.5%) provide adequate strength to resist seismic forces. For bridges on poor soils (Class D) in regions of low to moderate seismic activity, column longitudinal reinforcing may need to be increased, particularly in bridges with short columns, long spans, and sliding bearings at the abutments. For bridges on poor soils in regions of higher seismic risk (Southwestern Virginia), column sizes may need to be increased. For columns designed as spiral columns, the increases in transverse column reinforcement will not be great, but for columns designed as tied columns, the increases will be significant.
Creep of high-strength normal and lightweight concrete
Edward C. Vincent; Bradley D. Townsend; Weyers, Richard E. (Virginia Center for Transportation Innovation and Research, 2004-05-01)
In addition to immediate elastic deformations, concrete undergoes time-dependent deformations that must be considered in design. Creep is defined as the time-dependent deformation resulting from a sustained stress. Shrinkage deformation is the time-dependent strain that occurs in the absence of an applied load. The total strain of a concrete member is the sum of elastic, creep, and shrinkage strains. Test beams for the Pinner's Point Bridge were produced by Bayshore Concrete Products Corp. using a high-strength normal weight concrete (HSC) mixture and the Chickahominy River Bridge beams using a high-strength lightweight concrete (LTHSC) mixture. The test beams and the Chickahominy River Bridge beams were fabricated with thermocouples to track interior concrete temperatures, and vibrating wire gages (VWGs) were placed at the center of prestressing to record changes in strain. Laboratory creep and shrinkage testing was conducted on specimens prepared with identical materials and similar mixture proportions in the casting of the bridge beams. The temperature profile from the beams during steam curing was used to produce match-cured specimens for laboratory testing. Two match-cured batches were produced, along with two standard cured batches. The creep room had a temperature of 23.0 1.7C (73.4 3F) and a relative humidity of 50 4%. Companion shrinkage specimens were also placed in the creep room. Measurements were taken on the creep and shrinkage specimens using a Whittemore gage. Four HSC cylinders were also equipped with embedded VWGs so that the interior and exterior strains could be compared. The Whittemore and VWG elastic and creep strains were similar, while the VWGs recorded significantly less shrinkage. The measured creep and shrinkage strains were compared to different prediction models to determine which model was the most accurate. The models considered were ACI 209, ACI 209 modified by Huo, CEB Model Code 90, AASHTO-LRFD, Gardner GL2000, Tadros, and Bazant B3. The ACI 209 modified by Huo was the most accurate in predicting time-dependent strains for the HSC mixture. The best overall predictor for the LTHSC time-dependent deformations was the Gardner GL 2000 model for the standard cure LTHSC specimens, whereas the ACI 209 model was the best predictor of the total stains and individual time-dependent deformations for the match-cured LTHSC mixture.

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