bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Live Load Distribution Factor Equation for Girder Bridges
Authors: Suksawang Nakin , Nassif Hani H.
Published: February 2008

Live load distribution factor (LDF) equations are among the most important bridge design calculations because they provide the distributed moment and forces, which are needed for designing new or for evaluating existing bridges. The AASHTO load and resistance factor design specification is the current standard for bridge design. It uses a power function containing parameters that are often unknown when bridges are being designed and thereby allows the design procedure to be iterative. This iterative design procedure is perceived by many practicing engineers as impractical and has raised questions regarding the desired level of simplicity in bridge design calculations. Therefore, simpler but more accurate LDF equations are needed. An experimental program to evaluate the behavior of girder bridges was launched. The program consisted of live load testing of actual girder bridges. A parametric study was carried out by using a detailed three-dimensional finite element analysis to determine how sensitive various bridge parameters are to the LDF. On the basis of the parametric study, new simplified LDF equations are proposed for various types of girder bridges, including steel, prestressed, and spread box girder bridges. The equation format is simplified as a function of two bridge parameters only (girder spacing and span length) while an equal level of accuracy is maintained. Results are compared with those from other available equations and are shown to have excellent correlation with the more exact finite element method.
Structured Public Involvement in Context-Sensitive Large Bridge Design Using Casewise Visual Evaluation
Authors: Bailey Keiron , Grossardt Ted , Ripy John , Toole Laura , Williams J. B. , Dietrick John
Published: February 2008

Subject to engineering constraints, bridges should present a pleasing visual aspect to their user communities. The research team extended its structured public involvement (SPI) protocol using casewise visual evaluation (CAVE) to the field of context-sensitive large-scale bridge design. The context-sensitive design process was used for Section 2 of the Louisville Southern Indiana Ohio River Bridges project. Key design parameters including bridge type, height, symmetry, complexity, and tunnel effect (superstructure shape) were identified by bridge designers. During a 3-month period, an SPI protocol was used to determine community preferences from Kentucky and Indiana participants. Group preferences were gathered rapidly, anonymously, and fairly from a focus group by using electronic polling technology to evaluate potential designs. A preference model was built by using CAVE, and a range of nonlinear preference variations relative to the design parameters was investigated. The favorable public evaluation results of the SPI process using CAVE are presented, and the reasons for its high performance are discussed. Emphasis is placed on the need for a close collaboration between bridge designers and public involvement specialists. The project demonstrates how an analytic approach to public involvement that integrates technology into the dialogic relationship between designers and the public allows for the achievement of inclusive, successful context-sensitive design even for large, complex infrastructure projects.
Repair and Retrofit Anchorage Designs for Two Texas Bridge Rails
Authors: Williams William
Published: February 2008

A project was focused on developing alternative rail anchorage systems for the Texas Department of Transportation's T501 and T203 bridge rail systems. The project considered only epoxy adhesive anchoring systems for each of these railings for use in repair and retrofit situations. Full-scale testing was performed on both rail types, and strength data were obtained with instrumented strain gauges on the rail anchorage for both rail types. These data were analyzed and used to develop alternate rail anchorage systems for both T501 and T203 bridge rails. Long-term durability of epoxy anchoring systems was also considered. The retrofit-repair strengths from the dynamic and static testing for both the T501 and the T203 compared closely to the dynamic and static strengths of the current strengths capacities. In summary, the strengths of the retrofit designs were close to and in some tests exceeded the calculated capacities of the bridge rails. The static strengths were close to the dynamic 50-ms average strengths recorded from the bogie testing. The new retrofit-repair designs developed and tested for this project are recommended for implementation for use on any new or existing bridge projects. The use of the Hilti RE 500 adhesive anchoring system was successful in achieving the strengths needed to adequately anchor the retrofit-repair reinforcement for both the T501 and the T203 bridge rails. The information learned from this project can be used to retrofit and repair other bridge rail designs in the future.
Load and Resistance Factor Design of Integral Bent Caps
Authors: Zayati Foued , Ibrahim Ahmed M. M. , Hida Susan
Published: February 2008

Cast-in-place concrete box girder highway bridges with integral bent cap substructures are the preferred bridge type in California. In the AASHTO LRFD Bridge Design Specifications, two methods are available for the design of integral bent caps: the sectional method for flexural members and the strut and tie method (STM) for flexural and deep members. Although many bent caps are considered deep beams according to the AASHTO load and resistance factor design provisions, practicing engineers elect to use the sectional method exclusively for design because of its familiarity and the lack of guidance for using STM. Design examples that used STM have been published, but none of these examples deals with integral bent caps. When applying STM to integral bent caps, several issues, unique to this geometry, need to be addressed. These issues are discussed, and three different integral bent cap design examples are presented. The design of the three bent cap examples was also carried out by using the sectional method. The application of the sectional method to integral bent caps presented its own issues. These issues are discussed, and the results of both methods are compared.
Alternative Reinforcing Details in Dapped Ends of Precast Concrete Bridge Girders
Authors: Herzinger Rainer , Elbadry Mamdouh
Published: February 2008

The ends of precast girders often have a reduced depth over short lengths in the form of dapped ends. Girders with dapped ends normally are used in parking structures and pedestrian bridges. Because of the reduced depth at the girder ends, the shear stresses are high, and, therefore, the design of dapped ends requires special consideration. Dapped ends typically are reinforced with conventional stirrups and longitudinal reinforcing bars, which require hooks and bends and even welded plates to ensure sufficient anchorage. The efficiency of use of studs with single or double heads for reinforcing dapped ends is investigated. Strut-and-tie models are used to develop different layouts of the reinforcement. Two analytical methods based on the shear friction and diagonal bending theories are used to determine the location of the critical crack at failure and to examine the effectiveness of the reinforcement layouts. An experimental program is conducted on a series of dapped-end beams to corroborate the analytical study. The use of studs in dapped-end zones is shown to provide an efficient and reliable solution that prevents premature failure caused by inadequate anchorage of conventional reinforcement.
Multiple Presence Statistics for Bridge Live Load Based on Weigh-in-Motion Data
Authors: Gindy Mayrai , Nassif Hani H.
Published: February 2008

A study was done to determine truck load spectra for bridges in New Jersey with emphasis on multiple truck presence statistics. Truck weight data were collected by the New Jersey Department of Transportation from 25 weigh-in-motion sites throughout the state between 1993 and 2003 (with some gaps). The sites encompass a variety of site-specific conditions, including truck volume, road and area type, and number of lanes. For each truck, the recorded parameters include the time of passage, speed, travel lane, number of axles, and axle loads and spacings. Of particular interest are the frequency and correlation among trucks simultaneously occurring on a bridge either as following, side by side, or staggered. This multiple presence directly affects simulation, future extrapolation of live load effects, and code calibration. In fact, the case of two trucks occurring side by side has been considered the governing case for the design of bridges during the development and calibration of the AASHTO LRFD Bridge Design Specifications. However, until recently, multiple presence statistics have been based on few observations of truck traffic at a small number of sites. Statistics are presented for various truck loading cases, and the effects of truck volume, area type, road type, and bridge span length on such statistics are examined. It is observed that truck volume and bridge span length have a significant effect on the frequency of multiple truck presence, whereas area and road type have only slight effect. It is also observed that the rate of increase in the percent occurrence of following loading events is lower for bridge span lengths of up to 100 ft (30 m) as compared with longer spans, whereas for staggered loading patterns the opposite is true. The frequency of side-by-side trucks was found to remain relatively constant with respect to span length.
Bridge Displacement Estimates from Measured Acceleration Records
Authors: Gindy Mayrai , Nassif Hani H. , Velde Jana
Published: February 2008

Girder displacement is an important component of bridge design and evaluation because it is directly related to bridge stiffness and flexibility. The complex interaction between vehicle and bridge dynamics will result in vibration and deflection greater than that under equivalent static loading. However, field measurement of girder displacement generally is non-trivial. Different sensors and instrumentation systems can be used to measure bridge displacement. Some of these provide direct measurements, whereas others indirectly provide displacement through measurements of the angle of rotation, velocity, or acceleration of the girder. Indirect methods, however, require additional signal processing analyses to remove the effect of small errors in recordings caused by sensor drift, unknown initial bridge conditions, and signal noise. These errors become sufficiently large through successive integrations and greatly distort the integrated velocity and displacement signals. Two correction methods are examined, namely, the velocity estimation method and the linear baseline correction method (BCM), for minimizing such errors in obtaining displacements indirectly from acceleration records. Independently measured girder acceleration and displacement records from a three-span continuous bridge under controlled live load testing are used to evaluate the accuracy of each method. It is found that the linear BCM results in a corrected displacement profile that more reasonably approximates the measured trace under various loading patterns. The choice of integration boundaries is also shown to affect the accuracy of both methods. An objective approach based on the energy content of the signal is proposed.
Impact Echo Data Analysis Based on Hilbert-Huang Transform
Authors: Algernon Daniel , Wiggenhauser Herbert
Published: February 2008

Impact echo is an acoustic method based on the use of transient stress waves generated by an elastic impact; it is used for nondestructive testing of concrete structures. In practical applications, the signals obtained often are superimposed by further mechanical vibrations and the so-called geometry effects, which are caused mainly by surface waves. Because of attenuation in the concrete as well as the divergence of the acoustical waves, impact echo signals are transient. As a result, the frequency content changes over time. Normally the analysis is carried out on the Fourier power spectrum of the signal. However, the Fourier spectrum is still affected by the mentioned effects and has well-known deficiencies for short transient signals within longer time sweeps. Application of the Hilbert-Huang transform is presented as a refined method for the time-frequency analysis of nonstationary impact echo data. The basic properties of the method and its practical application for time-frequency analysis of impact echo data, signal filtering, and pattern identification are presented.
Sensitivity Studies of Grout Defects in Posttensioned Bridge Ducts Using Impact Echo Scanning Method
Authors: Tinkey Yajai , Olson Larry D.
Published: February 2008

Findings are presented from an NCHRP Innovations Deserving Exploratory Analysis Program project, Nondestructive Evaluation Method for Determination of Internal Grout Conditions Inside Bridge Posttensioning Ducts Using Rolling Stress Waves for Continuous Scanning. The study involved a defect sensitivity study of an impact echo scanner to detect and image discontinuities in posttensioned ducts of a mock-up U-shaped bridge girder and a mock-up slab. Various sizes of ducts were included in this study as well as various sizes of void defects. A detailed sensitivity study of nondestructive grout defect detection with impact echo scanning of eight ducts 4 in. in diameter with constructed defects was the main focus in the study. Comparisons of the impact echo defect interpretation and the actual design conditions of the ducts inside the bridge girder or slab are presented. The impact echo results are presented three-dimensionally by using thickness surface plots to provide improved visualization and interpretation of the internal grout to void defect conditions inside the ducts of the girder. The impact echo tests were performed with a scanner, which greatly facilitates the impact echo test process by allowing for rapid, near continuous testing and true scanning capabilities to test concrete structures. The general background of the impact echo technique and the impact echo scanner is summarized. Descriptions of two mock-up specimens used in the experiment and the discussion of the results from the impact echo scanner are presented.
Reaction Distribution in Highly Skewed Continuous Steel Girder Bridge
Authors: Badwan Inmar Z. , Liang Robert Y.
Published: February 2008

A field live load test and a finite element method (FEM) analysis performed on an existing 60° skew, three-span continuous steel girder bridge are presented. The live load testing program with nonstandard truck load was carried out to allow for assessing the adequacy of existing structures and pier support to carry an HS25 standard load. In particular, it was of interest to evaluate the effect of bridge skew on the distribution of reaction forces at interior piers. The measured bridge response under the live load was used to develop and calibrate a FEM model by using the ANSYS computer program. The calibrated FEM model was then used to predict bridge response under an HS25 load. For all load cases investigated, the FEM results showed that distribution of vertical reaction forces on the interior piers was nonuniform. The analysis results indicated that higher reaction forces were experienced by piers on the side of the bridge closer to the obtuse corner than on the side near the acute corner. The importance of using actual field measured test data to develop and calibrate a realistic FEM model is demonstrated.
Factors Affecting Stress Crack Resistance of Corrugated High-Density Polyethylene Pipe
Authors: Hsuan Y. Grace , Gurian Patrick , Zhang Jingyu
Published: February 2008

In the AASHTO M294 specification for high-density polyethylene corrugated pipe, the stress crack resistance (SCR) property is determined on the basis of the performance of virgin pipe resins. The specification requires pipe resins to have a failure time greater than 24 h by using the notched constant ligament stress test. However, SCR of the finished pipe can be significantly different than that of the corresponding resin because of the effects of additives such as carbon black, regrind, and manufacturing processing. As part of the NCHRP 4-26 project, the effects of carbon black, percentage of regrind material, and pipe processing on SCR were evaluated. Twenty-four pipes and 13 resins from five manufacturers were tested. For the majority of resins, carbon black decreased SCR of the resin. The effect of regrind on SCR varied substantially from pipe to pipe; however, increasing the regrind from 10% to 20% did not show significant changes. The manufacturing process was found to have the greatest effect on the reduction of SCR. The influencing factors and 95% confidence interval were established between pipe resin and pipe plaque and between pipe liner and pipe plaque. The proposed minimum failure times for SCR of virgin resin, pipe plaque, and pipe liner are 33, 24, and 18 h, respectively. The data indicate that pipes with qualified resin may not necessarily pass the pipe liner proposed value. Thus, an SCR specification on pipe liner is more critical than a virgin resin.
Soil-Structure Interaction and Imperfect Trench Installations for Deeply Buried Corrugated Polyvinyl Chloride Pipes
Authors: Kang Junsuk , Parker Frazier , Yoo Chai H.
Published: February 2008

The imperfect trench installation method has been used to reduce earth pressure on buried rigid pipes by inducing positive soil arching over the pipe. Because they are relatively flexible, corrugated thermoplastic pipes induce a small amount of positive soil arching. Therefore, there has been little research on the effects of imperfect trench installation on flexible pipes, such as those fabricated with corrugated thermoplastic. A study was done of the soil-structure interaction for corrugated poly-vinyl chloride (PVC) pipes and the efficiency of the imperfect trench method for their installation. The soil-structure model was simulated with the Duncan soil model and Selig soil parameters by using the finite element method. The geometry of a soft zone was optimized to maximize the earth load reduction effects for imperfect trench installations. The optimization process was based on parametric studies of the geometry and location of the soft zone, combined with bedding and sidefill treatments to reduce earth pressures. Predictor equations for earth load, maximum stress, and deflection of corrugated PVC pipes were formulated that incorporate the proposed optimum soft zone geometry and installation techniques. Parametric studies revealed that the optimum geometry of the soft zone in the proposed imperfect trench installations could reduce the maximum wall stress in corrugated PVC pipes by 85%.
Longitudinal Progression of Burst Head during Pipe Bursting
Authors: Nkemitag Michael , Moore Ian D.
Published: February 2008

Axisymmetric finite element analysis is used to model the forward movement of the burst head along the pipe axis during static pipe bursting. The modeling procedures are described, including treatment of the mixed boundary condition at the interface between the bursting head and the surrounding material, along which radial displacements are imposed to match the cavity expansion as the rigid burst head displaces the surrounding ground, and friction is also modeled. Calculations are reported for the four pipe bursting configurations considered in an earlier laboratory study. Comparisons of calculated and measured values of pulling force reveal that the new finite element procedure provides effective measurements of the resistance of the burst head to forward progression and the total force required to pull the bursting head and new pipe through the old pipe system. The numerical procedure could be used in future studies to estimate pulling force requirements for specific projects, considering the burial depth, soil material, degree of pipe upsize, and specific geometry of the pipe bursting head.
Guideline for Interpreting AASHTO Specifications to Design or Evaluate Buried Structures with Comprehensive Solution Methods
Authors: Katona Michael G. , McGrath Timothy J.
Published: February 2008

Design engineers and consultants are required to satisfy the criteria set forth in the AASHTO LRFD Bridge Design Specifications when designing buried culverts within the national transportation infrastructure. Adherence to the specifications is especially difficult when an engineer uses a comprehensive solution method such as a finite element program to predict the deformations and internal forces of the culvert-soil system. Part of the difficulty is in knowing how to apply factored loads as well as to determine their values. A more difficult problem is to assess whether the culvert is structurally safe according to the AASHTO LRFD specifications. Said another way, the design criteria and the corresponding factored capacities as written in the specifications are less than well defined. A succinct interpretation is presented of the AASHTO specification for load and resistance factor design (LRFD) for buried structures with regard to factored loads and design criteria. Tabularized values are provided for load factors and load modifiers to quantify dead loads, earth loads, and live loads, which are required for a LRFD analysis to produce the factored demands. Also presented are tabularized descriptions of the design criteria and the corresponding factored capacities, which are defined and quantified for corrugated metal, reinforced concrete, and plastic pipe materials. For some culverts, the design criteria have been generalized to provide sufficient information that is compatible with comprehensive analysis methods. Although intended especially for design engineers who use comprehensive analysis tools, the information presented is also useful and educational for engineers who use the simplified design solutions in the AASHTO LRFD specifications.
Quadrimaran Ferries
Authors: Hockberger William A.
Published: February 2008

The ideal marine vessel would be fast, reliable, comfortable, safe, economical, environmentally friendly, and operable even in shallow water. However, some of these characteristics conflict with each other; this conflict makes it almost impossible to obtain them all to a satisfactory degree in a single package. The Quadrimaran is a new vessel design that appears to combine more of these characteristics than any other design now available. It achieves this level of functionality by violating some long-held ideas about how vessels should be designed. Although the design may be suitable for large freight carriers, for now it makes sense to focus on smaller sizes; ferries are an excellent application. Several related applications (e.g., emergency relief) can benefit greatly from the Quadrimaran's particular characteristics.
Stated Preference Technique for Analysis of Container Port Competition
Authors: Hao Xu
Published: February 2008

With the development of container port services and inland logistics, the differences between regional container terminals are gradually diminishing while the competitiveness among ports is increasing. As a result, port choice is becoming an important aspect of port transportation demand behavior. A framework based on the stated preference technique is developed for the analysis of container port competition and the feasibility of hub port implementation in China. This framework is applied to an analysis of container terminal competitiveness in the coastal provinces of eastern China, including terminals in Dalian, Guangzhou, Ningbo, Qingdao, Shanghai, Shenzhen, and Tianjin. A pilot survey conducted at Dalian Container Terminal (which is located near several similar-scale container terminals) aimed at identifying the main attributes that importers and exporters of containerized cargos consider when choosing ports of service; results of the survey are presented. The main attributes were the goal of a factor analysis experiment conducted to reduce the number of attributes considered in applying the stated preference technique.
Waterways Curriculum
Authors: Eidson William C.
Published: February 2008

The waterways curriculum—a strategic framework for presenting marine industry concepts to school-aged children—is outlined. Through a national structure, the marine industry will have the opportunity to develop a fun and exciting educational program. The waterways curriculum framework comprises several key components to create flexibility and thereby reach more participants. Educational materials are categorized by age groupings (cohorts) and school grade levels (modules) to allow the age-appropriate presentation of materials to participants. The waterways curriculum also includes four presentation pathways to facilitate its use in various settings: school programs, community outreach (youth organizations), on-site teaching (field trips), and expositions (e.g., boat shows). By offering consistent materials that cover a broad range of marine topics for each category and age level, the waterways curriculum will provide participants an opportunity to explore the marine industry in a fun and challenging way. After the framework is outlined, examples of potential materials and activities for use in the waterways curriculum are highlighted, as well as existing resources and possible partnerships for the program development team to explore. A turnkey program is not included; instead, the focus is on the starting points for delivering marine topics to youth. Ample opportunities exist for future development of the waterways curriculum by marine professionals and educational specialists. With the combined efforts of industry and academic leaders, the waterways curriculum can inspire youth to explore opportunities in the marine transportation industry.
Variation of Crack Width over Time in Continuously Reinforced Concrete Pavement
Authors: Nam Jeong-Hee , Kim Dong-Ho , Choi Seongcheol , Won Moon C.
Published: February 2008

The primary objective of this paper is to present the findings of field studies that investigated variations in crack widths over time in three continuously reinforced concrete pavement projects in Texas. Also presented are crack width variations through the slab depth. Vibrating wire gauges were installed at three slab depths—top, middle, and bottom—during concrete placement. Transverse cracks were induced at the locations of the gauges, and concrete strains were measured. The ages of the projects varied from 11 months to 2 years, 10 months. Significant variations existed in crack widths along the slab depth. Crack widths were largest at the top and smallest at the bottom. In the test sections of this study, crack widths at the middepth were about three-quarters of those at the top. Crack widths at the top and middepth were a direct function of temperature variations in the concrete at those depths. However, there was a poor correlation between concrete temperatures and crack widths at the bottom. There was clear evidence that moisture variations in concrete have substantial effects on concrete volume changes and crack widths. An immediate decrease in crack widths was observed after rains. Crack widths decreased over time within the time frame of this study. This finding is not consistent with the current theory on crack width variations over time, and further study is currently under way at the University of Texas at Austin to identify the causes. The findings will be reported as they become available.
Experimental and Analytical Investigations of Mechanistic Effects of Dowel Misalignment in Jointed Concrete Pavements
Authors: Prabhu Milind , Varma Amit H. , Buch Neeraj
Published: February 2008

This paper presents the results of experimental and analytical investigations on the effects of dowel misalignment on the joint opening behavior and distress in concrete pavement joints. It focuses on the development of three-dimensional (3-D) finite element models for computing the complex stress states and resulting damage in concrete pavement joints with misaligned dowels and, through experimental results, their validation. The concrete pavement is modeled by using a damage–plasticity material model, which uses concepts of damage–plasticity formulation in compression and cracking combined with damage elasticity in tension. The longitudinal bond between the steel dowel and the concrete is modeled in two parts. First, the longitudinal bond resulting from chemical adhesion, mechanical interlock, and static friction (in the aligned state) is modeled by means of spring elements. The nonlinear force–deformation relationship for the spring elements is derived from specific experimental results. Second, the longitudinal bond resulting from transverse interaction between steel dowels and the concrete pavement is modeled by surface-to-surface contact interaction elements and associated friction models. The 3-D finite element models are validated by the results of experimental investigations. These validated models provide significant insight into the 3-D stress states and principal stresses that develop in concrete pavement joints with misaligned dowels. They are used to evaluate analytically the effects of misalignment type, magnitude, uniformity, and distribution on the 3-D stress states and resulting damage in concrete pavements.
Fracture Behavior of Functionally Graded Concrete Materials for Rigid Pavements
Authors: Roesler Jeffery , Paulino Glaucio , Gaedicke Cristian , Bordelon Amanda , Park Kyoungsoo
Published: February 2008

Currently, in concrete pavements, a single concrete mixture design and structural surface layer are selected to resist mechanical loading without an attempt to affect concrete pavement shrinkage, ride quality, or noise attenuation adversely. An alternative approach is to design sublayers within the concrete pavement surface that have specific functions and thus to achieve higher performance at a lower cost. The objective of this research was to address the structural benefits of functionally graded concrete materials (FGCMs) for rigid pavements by testing and modeling the fracture behavior of different combinations of layered plain concrete materials and concrete materials reinforced with synthetic fibers. The three-point bending-beam test was used to obtain the softening behavior and fracture parameters of each FGCM. The peak loads and initial fracture energy between the plain, fiber-reinforced, and FGCMs were similar; this signified similar crack initiation. The total fracture energy clearly indicated the improvements in fracture behavior of FGCM relative to full-depth plain concrete. The fracture behavior of FGCM depended on the position of the fiber-reinforced layer relative to the starter notch. The fracture parameters of both the fiber-reinforced and plain concrete were embedded into a finite element–based cohesive zone model. The model successfully captured the experimental behavior of the FGCMs and now can be implemented to predict the fracture behavior of proposed FGCM configurations and structures such as rigid pavements. This integrated approach (testing and modeling) is promising and demonstrates the viability of FGCM for designing layered concrete pavement systems.
Determination of In-Place Hot-Mix Asphalt Layer Modulus for Rehabilitation Projects by a Mechanistic–Empirical Procedure
Authors: Loulizi Amara , Flintsch Gerardo W. , McGhee Kevin
Published: February 2008

This paper summarizes the findings of a project that evaluated the procedures proposed by the Mechanistic–Empirical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. A total of 33 cores were extracted from nine sites in Virginia to measure their dynamic moduli in the lab. Falling weight deflectometer (FWD) testing and visual pavement rating were performed at the sites, and the resilient modulus was measured in the laboratory. Selected cores were tested for their bulk densities and then for their dynamic moduli. The cores were broken down and tested for their maximum theoretical specific gravity. 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 (as proposed in Chapter 2 of the MEPDG) does not represent the entire HMA layer thickness, and therefore it was recommended that this analysis should not be performed. 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.
Development of a Simplified Design Procedure for Determining Layer Thickness in Long-Life Pavements
Authors: Lee Hyun Jong , Park Hee Mun , Lee Jung Hun
Published: February 2008

This study is a part of the research for developing the technologies of long-life pavements having a design life of more than 40 years. The objective of this study was to develop a simplified design procedure for determining the layer thickness needed for long-life pavements. High modulus asphalt binder for the intermediate layer was introduced and applied in this procedure. To develop the models for predicting the critical pavement responses, a synthetic database was established through use of a finite element program with various combinations of layer thickness and modulus. The synthetic database includes structural and material information, surface deflection, and critical pavement responses. From the developed synthetic database, this paper suggests the minimum layer thickness and modulus value—based on the concept of limited strain level—for long-life pavements. This study also determined experimentally the fatigue endurance limit of asphalt mixtures used in this study. A long-life pavement should have an intermediate layer with a thickness greater than 175 mm (6.89 in.), and an asphalt mix with a modulus greater than 3.5 GPa (507 ksi) should be used. Measured strain values from the accelerated pavement testing and field test sections have been used to validate the proposed design procedure. The validation study has shown that the use of a high modulus asphalt mix is capable of reducing the tensile strain at the bottom of the asphalt concrete layer and layer thickness significantly. The validation study has also shown that the proposed procedure can predict the measured strain values from the test sections within an acceptable level.
Windows-Based Top-Down Cracking Design Tool for Florida
Authors: Wang Jianlin , Birgisson Bjorn , Roque Reynaldo
Published: February 2008

Top-down cracking has been found to be a predominant mode of distresses of asphalt pavements in Florida. Therefore, it is important to accommodate top-down cracking in the design of asphalt mixtures and pavement structures. After a multiyear study on top-down cracking supported by the Florida Department of Transportation, the University of Florida developed a top-down cracking model based on hot-mix asphalt fracture mechanics. This paper presents the implementation of the Florida cracking model into a mechanistic–empirical (M-E) flexible pavement design framework. Based on the energy ratio concept, a new M-E pavement design tool for top-down cracking has been developed. In the Level 3 M-E design, a series of semiempirical models were developed for estimation of time-dependent material properties. With incorporation of the material properties models, the design tool is capable of performing pavement thickness design as well as pavement life prediction for top-down cracking in Florida. The thickness design is optimized for different traffic levels, mixture types, and binder selections, and the optimization is an automated process. This design tool has been packed into Windows-based software, making it convenient to use for pavement design engineers.
Development and Significance of Statewide Volume Adjustment Factors in Mechanistic–Empirical Pavement Design Guide
Authors: Tran Nam H. , Hall Kevin D.
Published: February 2008

A new Mechanistic–Empirical Pavement Design Guide (MEPDG) has been developed under NCHRP Project 1-37A. Pavement design procedures recommended for use in MEPDG represent a significant departure from current procedures. The MEPDG requires new traffic inputs for estimating the magnitude, configuration, and frequency of the loads that are applied throughout the pavement design life. The Arkansas State Highway and Transportation Department (AHTD) sponsored research in which one objective was development of statewide truck traffic volume adjustment factors, including class and monthly and hourly distribution factors, and evaluating significance of the developed inputs in the MEPDG. The AHTD provided classification data collected at 55 weigh-in-motion (WIM) sites from 2003 through 2005. Because of missing and inaccurate classification data at several WIM sites, only 23 sites provided classification data suitable for this study. On the basis of selected data, statewide monthly, hourly, and class distribution factors were developed for Arkansas. Analyses using the MEPDG showed the state-specific class distribution factors to have a significant effect on predicted pavement performance, compared with predictions generated by using default distribution values. However, the effect of using state-specific monthly and hourly distribution factors on predicted pavement performance rather than default values was not significant. Therefore, it is recommended that the state-specific class distribution factors be used with the default monthly and hourly distribution factors in the MEPDG. In addition, periodic review and update of statewide class distribution factors, as necessary, are recommended.
Development and Influence of Statewide Axle Load Spectra on Flexible Pavement Performance
Authors: Tran Nam H. , Hall Kevin D.
Published: February 2008

The Mechanistic–Empirical Pavement Design Guide (MEPDG) developed under NCHRP Project 1-37A requires new inputs for traffic characterization. One important traffic input is axle load distribution factors, or axle load spectra. These spectra represent the percentage of the total axle applications within each load interval for single, tandem, tridem, and quad axles. The Arkansas State Highway and Transportation Department sponsored research to develop statewide axle load spectra and evaluate the significance of the developed inputs in the MEPDG. Of 25 weigh-in-motion sites selected for this study, only 10 stations provided good weight data for development of statewide axle load spectra. On the basis of the available weight data, statewide axle load spectra for single, tandem, and tridem axles were developed. However, the data contained few quad axles; therefore, statewide quad-axle load spectra were not generated. A sensitivity analysis related to the axle load spectra showed a significant difference in predicted pavement performance resulting from the statewide and MEPDG default axle load spectra. Therefore, the state-specific axle load spectra are recommended for implementation of the MEPDG in Arkansas and updated periodically unless no significant changes are observed in the future.
Assessment of in Situ Dielectric Constant of Pavement Materials
Authors: Evans Robert , Frost Matthew , Stonecliffe-Jones Martyn , Dixon Neil
Published: February 2008

The use of ground-penetrating radar (GPR) for pavement investigation has developed rapidly over the past 20 years. The technique involves recording the passage of electromagnetic pulses transmitted into the pavement structure. GPR has enhanced and improved the range and certainty of information that can be obtained from pavement investigations. Analysis of data can provide information on layer depths, material condition, moisture, voiding, reinforcement, and location of other features. The dielectric constant is a material property that affects the speed and reflection amplitude of electromagnetic GPR pulses. Accurate determination or estimation of the dielectric constant is required for accurate analysis of pavement material information from GPR data. Typical pavement materials will have a bulk dielectric constant used in analysis that is the result of both the material constituents (binder, aggregate, etc.) and condition (moisture content, amount of voiding, etc.). This paper aims to provide a review and assessment of in situ dielectric constants of bituminous pavement materials determined from analysis of GPR data. The results of a large number of in situ pavement investigations, on a range of bituminous materials of varying condition, are reported. Dielectric constants from analysis of GPR investigations are determined and compared with existing data, and the effect of material condition and properties are discussed and assessed. The paper concludes that improved assessment of the in situ dielectric constant can be conducted and provide enhanced information from radar data analysis if consideration of material condition is made when selecting the values used in the analysis.
Potential Impact of Housing Policy on Transportation Infrastructure in Chinese Cities
Authors: Deng Yi , Liu Rongfang (Rachel)
Published: February 2008

Directive No. 165, a new directive from the Chinese central government–specifically, the Department of Construction–requires that 70% of new residential units be smaller than 90 m2, as of June 1, 2006. The directive raised great concerns after initial confusion and speculation, not only for land developers and consumers but also for urban and transportation planners. The intention of the new policy is clearly targeted to tame ever-rising housing prices and bring affordable housing to average citizens. However, it is questionable whether the policy at its face value can achieve those objectives. The policy's effect on land use, urban form, infrastructure, and eventually the housing market is as yet unknown. This paper focuses on the potential effect of the new housing policy on urban infrastructure, particularly transportation. On the basis of the historical urban development in China, Western experience, and current problems and issues encountered by most large metropolitan areas worldwide, the authors caution that the new housing policy may create an unexpected negative effect on transportation infrastructure and make the already congested roadways in most urban areas in China even worse. Some modifications or relevant strategies are needed to achieve the objective of housing affordability while not sacrificing quality of life. It is suggested that connections be made between housing development and urban infrastructure such as transportation, power, water, and comprehensive land use policies to achieve balanced growth and avoid potential social problems.
How Public Transportation's past is Haunting its Future in Bogotá, Colombia
Authors: Ardila Arturo
Published: February 2008

Bogotá, Colombia, is internationally known for recent innovations in public transportation, namely, the Transmilenio bus rapid transit system. Transmilenio carries close to 1.3 million trips per day, or 20% of bus trips in the city, on an 84-km network. Transmilenio's original plan called for implementing a system that covered the entire city, replacing the previous bus system. However, the institutional arrangement for service pro-vision in the traditional bus system is plagued with negative incentives that lead to poor-quality service, oversupply of buses, and inflated fares. In addition, the government agency in charge of controlling the traditional bus system is weak and lacks the authority to carry out the required policies. The result is a pervasive oversupply of buses despite Transmilenio's efforts to reduce it and powerful vested interests that have organized against the project. As a result, the analysis suggests that Transmilenio's original plan faces obstacles that can hamper the implementation of future stages because of the problems in the traditional mode. This paper analyzes Bogotá's current public transportation situation and seeks to draw lessons for cities in developing countries, particularly Latin America, that try to replicate Bogotá's reforms. Although the paper does not question Transmilenio's success, it does raise issues that need to be addressed to make bus rapid transit planning and public transit reform more effective.
Electric Two-Wheelers in China
Authors: Weinert Jonathan X. , Ma Chaktan , Yang Xinmiao , Cherry Christopher R.
Published: February 2008

Despite rapid economic growth in China during the past decade and the rise in personal car ownership, most Chinese still rely on two-wheeled vehicles (2WVs) or public transport for commuting. The majority of these 2WVs are bicycles. In recent years, concern about poor air quality in urban areas and rising energy costs have caused cities to ban gasoline-powered scooters in city centers. Simultaneously, a new 2WV mode emerged to fill the void: the electric bike (e-bike). This shift to e-bikes is occurring rapidly throughout China, especially in its cities. E-bike sales reached 10 million per year in 2005 as more bike and public transit users shifted to this mode. City planners and policy makers are undecided on how to plan for and regulate e-bikes because it is not yet clear what effect they will have on travel behavior, public transportation use, and safety. To begin to understand these effects, bike and e-bike users were surveyed in Shijiazhuang, a medium-size city with particularly high 2WV use, to identify differences in travel characteristics and attitudes. The following conclusions were reached (partial list): (a) e-bikes are enabling people to commute longer distances, with important implications for energy use, accessibility, and urban expansion of cities; (b) people underserved by public transportation are shifting to e-bikes; and (c) women feel safer crossing intersections on an e-bike compared with a regular bike, but they have strong reservations about increasing e-bike speed capability.
Projection of Chinese Motor Vehicle Growth, Oil Demand, and CO2 Emissions Through 2050
Authors: Huo Hong , Wang Michael , Johnson Larry , He Dongquan
Published: February 2008

During this study a methodology was developed to project growth trends of the motor vehicle population and associated oil demand and carbon dioxide (CO2) emissions in China through 2050. In particular, the numbers of highway vehicles, motorcycles, and rural vehicles were projected under three scenarios of vehicle growth by following different patterns of motor vehicle growth in Europe and Asia. Projections showed that by 2030 China could have more highway vehicles than the United States has today. Three scenarios of vehicle fuel economy were also developed on the basis of current and future policy efforts to reduce vehicle fuel consumption in China and in developed countries. With the vehicle population projections and potential vehicle fuel economy data, it was projected that in 2050 China's on-road vehicles could consume approximately 614 million to 1,016 million metric tons of oil (or 12.4 million to 20.6 million barrels per day) and emit 1.9 billion to 3.2 billion metric tons (or 2.1 billion to 3.5 billion tons) of CO2 each year. Although these projections by no means imply what will happen in the Chinese transportation sector by 2050, they do demonstrate that an uncontained growth in motor vehicles and only incremental efforts to improve fuel economy will certainly result in severe consequences for oil use and CO2 emissions in China.