Technical Reports, Civil and Environmental Engineering

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Acceptance Procedures for New and Quality Control Procedures for Existing Types of Corrosion-Resistant Reinforcing Steel
Stephen R. Sharp; Larry J. Lundy; Harikrishnan Nair; Moen, Cristopher D.; Josiah B. Johnson; Sarver, Brian E. (Virginia Center for Transportation Innovation and Research, 2011-06-01)
As the Virginia Department of Transportation (VDOT) continues to move forward with implementing the use of corrosion-resistant reinforcing (CRR) bars, it is important for VDOT to have a means of characterizing the candidate bars as well as ensuring that the quality of approved CRR bars is preserved. This is vital to ensure the bars respond physically in a manner that is consistent with VDOT's expectations. The purpose of this study was to provide VDOT's Materials Division with a method/specification for evaluating CRR bars. The study determined that visual assessment cannot be relied on to determine bar type. Further, steel fabricator markings cannot be relied on to identify the type of steel. However, when questions arise regarding the identification of bars, magnetic sorting provides a quick and easy method for differentiating between magnetic and nonmagnetic alloys. If more quantitative results are required, X-ray fluorescence provides a practical and much-needed method for positively identifying bars. Physically, the bars differ among producers. Relative rib area should be monitored as it also varies among producers. Further, alloying changes not only the corrosion resistance but also other important properties. The results of uniaxial tensile tests showed that the stress-strain behavior, elongation, and reduction in cross-section upon fracture could vary significantly for different CRR alloys. Therefore, mechanical testing, in addition to corrosion testing, of CRR is necessary to identify the most cost-effective bars with acceptable properties. Finally, the study determined that quality control measures need to be established to ensure VDOT receives the corrosion protection it needs. Further, care should be taken when relying upon international standards for acceptance criteria. The report recommends that VDOT's Materials Division implement the set of test methods provided in the appendices of this report as Virginia Test Methods for CRR acceptance criteria. To simplify the implementation of CRR in Virginia and elsewhere, VDOT's Materials Division should work with the American Association of State Highway and Transportation Officials to develop a single specification for the testing and acceptance of CRR. VDOT's Materials Division should also investigate retrofitting the uniaxial tensile test equipment with a non-contact extensometer to guarantee that stress vs. strain measurements of CRR can be made and ensure the yield strength is determined
Access Control Design on Highway Interchanges
Rakha, Hesham A.; Flintsch, Alejandra Medina; Arafeh, Mazen; Abdel-Salam, Abdel-Salam Gomaa; Dua, Dhruv; Abbas, Montasir M. (Virginia Center for Transportation Innovation and Research, 2008-01-01)
The adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical to the safety and traffic operations of both the freeway and the crossroad. The research presented in this report develops a methodology to evaluate the safety impact of different access road spacing standards. The results clearly demonstrate the shortcomings of the AASHTO standards and the benefits of enhancing them. The models developed as part of this research were used to compute the crash rate associated with alternative section spacing. The study demonstrates that the models satisfied the statistical requirements and provide reasonable crash estimates. The results demonstrate an eight-fold decrease in the crash rate when the access road spacing increases from 0 to 300 m. An increase in the minimum spacing from 90 m (300 ft) to 180 m (600 ft) results in a 50 percent reduction in the crash rate. The models were used to develop lookup tables that quantify the impact of access road spacing on the expected number of crashes per unit distance. The tables demonstrate a decrease in the crash rate as the access road spacing increases. An attempt was made to quantify the safety cost of alternative access road spacing using a weighted average crash cost. The weighted average crash cost was computed considering that 0.6, 34.8, and 64.6 percent of the crashes were fatal, injury, and property damage crashes, respectively. These proportions were generated from the field observed data. The cost of each of these crashes was provided by VDOT as $3,760,000, $48,200, and $6,500 for fatal, injury, and property damage crashes, respectively. This provided an average weighted crash cost of $43,533. This average cost was multiplied by the number of crashes per mile to compute the cost associated with different access spacing scenarios. These costs can assist policy makers in quantifying the trade-offs of different access management regulations.
Anchorage Zone Design for Pretensioned Precast Bulb-T Bridge Girders in Virginia
E.D. Crispino; Cousins, Thomas E.; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2009-06-01)
Precast/prestressed concrete girders are commonly used in bridge construction in the United States. The application and diffusion of the prestress force in a pretensioned girder cause a vertical tension force to develop near the end of the beam. Field surveys of the beam ends of pretensioned bridge girders indicate that many of the precast bulb-T (PCBT) beams used in Virginia develop cracks within the anchorage zone region. The lengths and widths of these cracks range from acceptable to poor and in need of repair. Field observations also indicate deeper cross sections, very heavily prestressed sections, and girders with lightweight concrete tend to be most susceptible to crack formation. This research examined a new strut-and-tie based design approach to the anchorage zone design of the PCBT bridge girders used in Virginia. Case study girders surveyed during site visits were used to illustrate the nature of the problem and support the calibration of the strut-and-tie-based model. A parametric study was conducted using this proposed design model, and the results of this study were consolidated into anchorage zone design tables. The results of the parametric study were compared to the results obtained using existing anchorage zone design models, international bridge codes, and standard anchorage zone details used by other states. A set of new standard details was developed for the PCBT girders that incorporates elements of the new design approach and is compatible with the anchorage zone design aids. A 65-ft PCBT-53 girder was fabricated offsite and tested at the Virginia Tech Structures Lab to verify the new strut-and-tie-based design model. This girder contained anchorage zone details designed with the new model. The new anchorage zone details were successful at controlling the development of anchorage zone cracks. The new design approach is recommended for implementation by the Virginia Department of Transportation.
Asphalt Materials Characterization in Support of Implementation of the Proposed Mechanistic-Empirical Pavement Design Guide
Flintsch, Gerardo W.; Loulizi, Amara; Diefenderfer, Stacey D.; Galal, Khaled A.; Diefenderfer, Brian K. (Virginia Center for Transportation Innovation and Research, 2007-01-01)
The proposed Mechanistic-Empirical Pavement Design Guide (MEPDG) procedure is an improved methodology for pavement design and evaluation of paving materials. Since this new procedure depends heavily on the characterization of the fundamental engineering properties of paving materials, a thorough material characterization of mixes used in Virginia is needed to use the MEPDG to design new and rehabilitated flexible pavements. The primary objective of this project was to perform a full hot-mix asphalt (HMA) characterization in accordance with the procedure established by the proposed MEPDG to support its implementation in Virginia. This objective was achieved by testing a sample of surface, intermediate, and base mixes. The project examined the dynamic modulus, the main HMA material property required by the MEPDG, as well as creep compliance and tensile strength, which are needed to predict thermal cracking. In addition, resilient modulus tests, which are not required by the MEPDG, were also performed on the different mixes to investigate possible correlations between this test and the dynamic modulus. Loose samples for 11 mixes (4 base, 4 intermediate, and 3 surface mixes) were collected from different plants across Virginia. Representative samples underwent testing for maximum theoretical specific gravity, asphalt content using the ignition oven method, and gradation of the reclaimed aggregate. Specimens for the various tests were then prepared using the Superpave gyratory compactor with a target voids in total mix (VTM) of 7% - 1% (after coring and/or cutting). The investigation confirmed that the dynamic modulus test is an effective test for determining the mechanical behavior of HMA at different temperatures and loading frequencies. The test results showed that the dynamic modulus is sensitive to the mix constituents (aggregate type, asphalt content, percentage of recycled asphalt pavement, etc.) and that even mixes of the same type (SM-9.5A, IM-19.0A, and BM 25.0) had different measured dynamic modulus values because they had different constituents. The level 2 dynamic modulus prediction equation reasonably estimated the measured dynamic modulus; however, it did not capture some of the differences between the mixes captured by the measured data. Unfortunately, the indirect tension strength and creep tests needed for the low-temperature cracking model did not produce very repeatable results; this could be due to the type of extensometers used for the test. Based on the results of the investigation, it is recommended that the Virginia Department of Transportation use level 1 input data to characterize the dynamic modulus of the HMA for projects of significant impact. The dynamic modulus test is easy to perform and gives a full characterization of the asphalt mixture. Level 2 data (based on the default prediction equation) could be used for smaller projects pending further investigation of the revised prediction equation incorporated in the new MEPDG software/guide. In addition, a sensitivity analysis is recommended to quantify the effect of changing the dynamic modulus on the asphalt pavement design. Since low-temperature cracking is not a widespread problem in Virginia, use of level 2 or 3 indirect tensile creep and strength data is recommended at this stage.
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.
Bridge Deck Service Life Prediction and Costs
Williamson, Gregory; Weyers, Richard E.; Brown, Michael C.; Sprinkel, Michael M. (Virginia Center for Transportation Innovation and Research, 2007-12-01)
The service life of Virginia's concrete bridge decks is generally controlled by chloride-induced corrosion of the reinforcing steel as a result of the application of winter maintenance deicing salts. A chloride corrosion model accounting for the variable input parameters using Monte Carlo resampling was developed. The model was validated using condition surveys from 10 Virginia bridge decks built with bare steel. The influence of changes in the construction specifications of w/c = 0.47 and 0.45 and w/cm = 0.45 and a cover depth increase from 2 to 2.75 inches was determined. Decks built under the specification of w/cm = 0.45 (using slag or fly ash) and a 2.75 inch cover depth have a maintenance free service life of greater than 100 years, regardless of the type of reinforcing steel. Galvanized, MMFX-2, and stainless steel, in order of increasing reliability of a service life of greater than 100 years, will provide a redundant corrosion protection system. Life cycle cost analyses were conducted for polymer concrete and portland cement based overlays as maintenance activities. The most economical alternative is dependent on individual structure conditions. The study developed a model and computer software that can be used to determine the time to first repair and rehabilitation of individual bridge decks taking into account the time for corrosion initiation, time from initiation to cracking, and time for corrosion damage to propagate to a state requiring repair.
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.
A Cellular Automata Approach to Estimate Incident-Related Travel Time on Interstate 66 in Near Real Time
Wang, Zhuojin; Murray-Tuite, Pamela M. (Virginia Center for Transportation Innovation and Research, 2010-03-01)
Incidents account for a large portion of all congestion and a need clearly exists for tools to predict and estimate incident effects. This study examined (1) congestion back propagation to estimate the length of the queue and travel time from upstream locations to the incident location and (2) queue dissipation. Shockwave analysis, queuing theory, and cellular automata were initially considered. Literature indicated that shockwave analysis and queuing theory underestimate freeway travel time under some conditions. A cellular automata simulation model for I-66 eastbound between US 29 and I-495 was developed. This model requires inputs of incident location, day, time, and estimates of duration, lane closures and timing, and driver re-routing by ramp. The model provides estimates of travel times every 0.2 mile upstream of the incident at every minute after the start of the incident and allows for the determination of queue length over time. It was designed to be used from the beginning of the incident and performed well for normal conditions and incidents, but additional calibration was required for rerouting behavior. We recommend that the Virginia Department of Transportation (1) further pursue cellular automata approaches for near-real time applications along freeways; and (2) consider adopting an approach to address detector failures and errors. Adopting these recommendations should improve VDOT's freeway real-time travel time estimation and other applications based on detector data.
Characterization of the Punching Shear Capacity of Thin Ultra-High Performance Concrete Slabs
D.K. Harris; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2005-06-01)
Ultra-high performance concrete (UHPC) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel. The main characteristics that distinguish UHPC from conventional reinforced concrete are its very high compressive strength (20 to 33 ksi), the addition of steel fibers which enables tension to be carried across open cracks without conventional reinforcing steel, and a very high resistance to corrosion and degradation. The mechanical properties of UHPC allow for smaller, thinner sections as compared to conventional reinforced concrete sections. However, as it is a new material, the use of UHPC has been limited to a few structural applications due primarily to the high cost of the material and the lack of established design guidelines. In previous research, a material model based on physical tests was used in conjunction with finite element models to develop an optimized cross-section for a prestressed UHPC girder for bridge applications. The cross-section is a double-tee with bulbs at the bottoms of the webs to accommodate the prestressing strands. As it is envisioned in bridge applications, the double-tees will be placed directly adjacent to one another, and the top flange will act as the riding surface after a thin asphalt overlay is placed. Based on the longitudinal compressive stresses, the top flange of the girder can be quite thin. However, there exists the possibility that a punching shear failure could occur from the application of a point load such as a wheel patch load if the flange is made too thin. The research reported herein was initiated to characterize the punching shear capacity of thin UHPC plates and to develop recommendations on the minimum top flange thickness for the optimized double-tee. Twelve small slabs (45 in x 45 in) were tested to failure to characterize the punching shear strength of UHPC. The variables considered were the slab thickness (2, 2.5, and 3 in) and loading plate dimensions (from 1 in x 1 in to 3 in x 3 in). The results of the testing were compared to several existing models for punching shear. The two equations that predicted strengths most reliably were the current ACI punching shear equation and a modified bolt pull-out equation. After evaluation of the test results, the minimum slab thickness required to prevent a punching shear failure in the top flange due to an 8 in x 20 in wheel patch was determined to be 1 in. Three larger slabs were also tested. These slabs had the same clear span length as the top flange of the optimized double-tee and were loaded with a wheel patch load. The slabs were all approximately 3 in thick and all failed in flexure rather than punching shear. It was concluded that the casting method has a strong influence on the orientation of the steel fibers, which in turn influences the flexural strength in orthogonal directions in the slab. The top flange thickness will be governed by transverse bending rather than punching shear, and the 3 in slabs were not able to support the full wheel load plus impact and load factor. The results of this research help in the continued optimization of a UHPC shape for use in highway bridges. If material use in the girder is minimized, UHPC bridges can become economically competitive with HPC bridges, but offer the benefits of more rapid construction and better durability.
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.
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.
Composite Pavement Systems: Synthesis of Design and Construction Practices
Flintsch, Gerardo W.; Diefenderfer, Brian K.; Orlando Nunez (Virginia Center for Transportation Innovation and Research, 2008-11-01)
Composite pavement systems have shown the potential for becoming a cost-effective pavement alternative for highways with high and heavy traffic volumes, especially in Europe. This study investigated the design and performance of composite pavement structures composed of a flexible layer (top-most layer) over a rigid base. The report compiles (1) a literature review of composite pavement systems in the U.S. and worldwide; (2) an evaluation of the state-of-the-practice in the U.S. obtained using a survey; (3) an investigation of technical aspects of various alternative composite pavement systems designed using available methodologies and mechanistic-empirical pavement distress models (fatigue, rutting, and reflective cracking); and (4) a preliminary life cycle cost analysis (LCCA) to study the feasibility of the most promising composite pavement systems. Composite pavements, when compared to traditional flexible or rigid pavements, have the potential to become a cost-effective alternative because they may provide better levels of performance, both structurally and functionally, than the traditional flexible and rigid pavement designs. Therefore, they can be viable options for high volume traffic corridors. Countries, such as the U.K. and Spain, which have used composite pavement systems in their main road networks, have reported positive experiences in terms of functional and structural performance. Composite pavement structures can provide long-life pavements that offer good serviceability levels and rapid, cost-effective maintenance operations, which are highly desired, especially for high-volume, high-priority corridors. Composite pavements mitigate various structural and functional problems that typical flexible or rigid pavements tend to present, such as hot-mix asphalt (HMA) fatigue cracking, subgrade rutting, portland cement concrete (PCC) erosion, and PCC loss of friction, among others. At the same time, though, composite systems are potentially more prone to other distresses, such as reflective cracking and rutting within the HMA layer. Premium HMA surfaces and/or reflective cracking mitigation techniques may be required to mitigate these potential problems. At the economic level, the results of the deterministic agency-cost LCCA suggest that the use of a composite pavement with a cement-treated base (CTB) results in a cost-effective alternative for a typical interstate traffic scenario. Alternatively, a composite pavement with a continuously reinforced concrete pavement (CRCP) base may become more cost-effective for very high volumes of traffic. Further, in addition to savings in agency cost, road user cost savings could also be important, especially for the HMA over CRCP composite pavement option because it would not require any lengthy rehabilitation actions, as is the case for the typical flexible and rigid pavements.
Construction of a Virginia Short-Span Bridge with the Strongwell 36-Inch Double-Web I-Beam
Cousins, Thomas E.; Lesko, John J. (Virginia Center for Transportation Innovation and Research, 2005-10-01)
The Route 601 Bridge in Sugar Grove, VA, spans 39 ft over Dickey Creek. The bridge is the first to use the Strongwell 36-in-deep fiber-reinforced polymer (FRP) double-web beam (DWB) in a vehicular bridge superstructure. Construction of the new bridge was completed in October 2001, and field testing was undertaken shortly thereafter as well as in June of 2002 to assess any potential changes in structural performance. This paper details the field evaluation of the Route 601 Bridge. Using midspan deflection and strain data from the October 2001 and June 2002 field tests, AASHTO bridge design parameters were determined, namely wheel load distribution factor g, dynamic load allowance IM, and maximum deflection. The wheel load distribution factor was determined to be S/4, a dynamic load allowance was determined to be 0.50, and the maximum deflection of the bridge was L/1110. Deflection results were lower than the AASHTO L/800 limit. This discrepancy is attributed to partial composite action of the deck-to-girder connections, bearing restraint at the supports, and contribution of guardrail stiffness. It was found that diaphragm removal had a small effect on the wheel load distribution factor. An examination of the 36-in DWB capacity and failure mode indicates that the strength of the girder is controlled by compression failure in the flange and not shear failure, as originally thought. An attempt to predict the girder fatigue performance shows that small losses in bending stiffness would be expected at fatigue loads 26% of the ultimate capacity, which was confirmed through experiments. Moreover, there is no concern that fatigue alone will cause a failure during the reasonable life of the structure as presently operated.
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.
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.
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.
Design of Bridging Layers in Geosynthetic-Reinforced, Column-Supported Embankments
Filz, George M.; Miriam E. Smith (Virginia Center for Transportation Innovation and Research, 2006-04-01)
The cost of column-supported embankments depends, in part, on the spacing between the columns and the size of the columns and pile caps. Geosynthetic reinforcement is often employed in bridging layers to enhance load transfer to the columns and to increase the column spacing. The number, stiffness, and strength of geosynthetic layers are selected based on considerations of load transfer and deformation. In this research, a new method was developed for calculating the load on the geosynthetic reinforcement. The new method employs one of the existing mechanistically based approaches and combines it with consideration of the stiffnesses of the embankment, geosynthetic reinforcement, columns, and existing site soil. The new method was verified against the results of a large numerical parameter study, for which the numerical procedures themselves were verified against closed-form solutions for membranes, pilot-scale experiments, and field case histories. The new method for calculating load on the geosynthetic was integrated into a 10-step design procedure for geosynthetic-reinforced bridging layers in column-supported embankments. The design procedure addresses such details as the thickness and type of the bridging layer soil, selection of the geosynthetic reinforcement, if needed, and the embankment settlement. The necessary calculations have been programmed into a Microsoft Excel workbook. The workbook may be accessed at www.virginiadot.org/vtrc/main/online%5Freports/pdf/geogridbridge.pdf
Design Recommendations for the Optimized Continuity Diaphragm for Prestressed Concrete Bulb-T Beams
Koch, Stephanie; Roberts-Wollmann, Carin L. (Virginia Center for Transportation Innovation and Research, 2008-11-01)
This research focused on prestressed concrete bulb-T (PCBT) beams made composite with a cast-in-place concrete deck and continuous over several spans through the use of continuity diaphragms. The current design procedure in AASHTO states that a continuity diaphragm is considered to be fully effective if a compressive stress is present in the bottom of the diaphragm when the superimposed permanent load, settlement, creep, shrinkage, 50% live load, and temperature gradient are summed, or if the beams are stored at least 90 days when continuity is established. It is more economical to store beams for fewer days, so it is important to know the minimum number of days that beams must be stored to satisfy AASHTO requirements. In addition, if the beams are stored for 90 days before erection, the positive moment detail must have a factored nominal strength (fMn) greater than 1.2 times the cracking moment (Mcr). In 2005, Newhouse tested the positive moment diaphragm reinforcement detail that is currently being adopted by VDOT. The first objective of this research was to determine if the detail was adequate if beams are stored for 90 days. The second objective was to determine if, based on AASHTO requirements, beams could be stored for fewer than 90 days. After the analysis of all PCBT beam sizes and a wide variety of span lengths and beam spacings, it can be concluded that Newhouse's detail, four No. 6 bars bent 180 and extended into the diaphragm, is adequate for all beams except for the PCBT-77, PCBT-85, and the PCBT-93 when the beams are stored for a minimum of 90 days. For these three beam sizes, three possible solutions are presented: one with two additional bent strands extended into the continuity diaphragm, one with an additional hairpin bar extended into the diaphragm, and one with L-shaped mild reinforcing bars extended into the diaphragm. To determine the minimum number of storage days required to satisfy AASHTO's requirement for compression at the bottom of the diaphragm, a parametric study was performed. The PCA Method was used in this analysis with the updated AASHTO LRFD creep, shrinkage, and prestress loss models. The parametric study included all sizes of PCBT beams, with two beam spacings, three span lengths and two beam concrete strengths for each size. Both two-span and three-span cases were analyzed. It was concluded that about half of the cases result in a significant reduction in the minimum number of storage days if the designer is willing to perform a detailed analysis. The other half of the cases must be stored for 90 days because the total moment in the diaphragm will never become negative and satisfy the AASHTO requirement. In general, narrower beam spacing and higher concrete compressive strength results in shorter required storage duration. A recommended quick check is to sum the thermal, composite dead load, and half of the live load restraint moments. The beam must be stored 90 days if that sum is positive, and a more detailed time-dependent analysis will indicate a shorter than 90 day storage period if that sum is negative.
Determination of remaining fatigue life of welded stud details on overhead aluminum sign panels in Virginia
Cousins, Thomas E.; Lucas, Jeremy L. (Virginia Center for Transportation Innovation and Research, 2005-03-01)
Some overhead highways signs in Virginia using a specific welded threaded stud and clip connection have failed while in service. From inspection of the signs it was determined that the failure was caused by fatigue of the weld connecting the threaded stud to the back of the sign panel. It was also observed that lower edge connections failed first and the failures progressed upwards in an unzipping pattern. A combination of natural and truck-induced wind gusts is the cause for the fatigue failure. Although signs with these connections are no longer produced by VDOT and all production was halted in early 2004, there are still approximately 4,000 signs in Virginia with this connection detail. The objective of the research project described here in was to determine priorities for an inspection and retrofitting plan for the remainder of the signs in Virginia. Specifically an S-N curve, which is a plot of stress range versus the number of cycles to failure, was to be developed to aid in predicting the remaining service life of sign panels using this connection detail. The authors opted to test single connections instead of multiple connection systems (i.e., an entire sign or portion thereof) because of material availability, the timeliness of testing, and the readily available equipment for testing. Connections simulating interior and exterior connections were tested under a pseudo-static load as well as for fatigue. Fatigue tests of interior and exterior sign connections developed failures of the aluminum panel instead of the expected weld fracture. Because the failure and fatigue threshold were not representative of failures found in the field, a proper S-N curve to help develop retrofitting priorities could not be developed. Recommendations from this program include increasing retrofit and inspection efforts, gauging and monitoring full-scale signs in service to understand loading conditions, and testing full-scale signs.
Determination of the In-Place Hot-Mix Asphalt Layer Modulus for Rehabilitation Projects Using a Mechanistic-Empirical Procedure
Loulizi, Amara; Flintsch, Gerardo W.; McGhee, Kevin K. (Virginia Center for Transportation Innovation and Research, 2006-07-01)
This project evaluated the procedures proposed by the Mechanistic-Empirical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. Thirty-three cores were extracted from nine sites in Virginia to measure their dynamic moduli in the lab. Falling-weight deflectometer (FWD) testing was performed at the sites because the backcalculated moduli are needed for the Level 1 procedure. The resilient modulus was also measured in the lab because it is needed for the Level 2 procedure. A visual pavement rating was performed based on pavement condition because it is needed for the Level 3 procedure. The selected cores were tested for their bulk densities (Gmb) using the AASHTO T166 procedure and then for their dynamic modulus in accordance with the AASHTO TP62-03 standard test method. Then the cores were broken down and tested for their maximum theoretical specific gravity (Gmm) using the AASHTO T-209 procedure. Finally an ignition test was performed to find the percentage of binder and to reclaim the aggregate for gradation analysis. Volumetric properties were then calculated and used as input for the Witczak dynamic modulus prediction equations to find what the MEPDG calls the undamaged master curve of the HMA layer. The FWD data, resilient modulus data, and pavement rating were used to find the damaged master curve of the HMA layer as suggested for input Levels 1, 2, and 3, respectively. It was found that the resilient modulus data needed for a Level 2 type of analysis do not represent the entire HMA layer thickness, and therefore it was recommended that this analysis should not be performed by VDOT when implementing the design guide. The use of Level 1 data is recommended because FWD testing appears to be the only procedure investigated that can measure the overall condition of the entire HMA layer.

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