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Wu K.-F.,National Chiao Tung University | Thor C.P.,Turner Fairbank Highway Research Center
Transportation Research Record | Year: 2015

Many factors are associated with crash risk, but their contribution to the progression of a crash is often unclear. Research on and understanding of the crash sequence are needed. One of the advantages of studying crash sequence is to identify the causative chain of crashes and, subsequently, the identification of effective countermeasures that may feasibly mitigate crash risk. An analogy to epidemiological studies is particularly useful: although researchers confirm that many factors are associated with an increase in the probability of myocardial infarction, there is still a need to research the disease process, the physiological process that promotes disease growth, and the possible interventions to treat or even prevent the disease. This study used data from the Integrated Vehicle-Based Safety System program. Two freeway rear-end events, including one crash and one near crash, with similar crash sequences were studied. The crash sequences of the two events were as follows: (a) the drivers maintained a temporal headway of less than 1 s at the beginning; (b) the traffic flow conditions were likely to cause misjudgments by the drivers and result in glances in inappropriate directions; (c) when the drivers were distracted, the leading vehicle decelerated; (d) the drivers did not decelerate accordingly and had their feet on the accelerator pedal; and (e) one event resulted in a crash and the other in a near crash. This study highlighted an approach for comparing and dissecting the differences in the crash sequence that led to the different outcomes.

Wang D.,Turner Fairbank Highway Research Center | Roesler J.R.,University of Illinois at Urbana - Champaign
International Journal of Pavement Engineering | Year: 2014

This paper presents an analytical solution for prediction of the one-dimensional (1D) time-dependent temperature profile in a multi-layered rigid pavement system. Temperature at any depth in a rigid pavement system can be estimated by using the proposed solution with limited input data, such as pavement layer thicknesses, material thermal properties, measured air temperatures and solar radiation intensities. This temperature prediction problem is modelled as a boundary value problem governed by the classic heat conduction equations, and the air temperatures and solar radiation intensities are considered in the surface boundary condition. Interpolatory trigonometric polynomials, based on the discrete least squares approximation method, are used to fit the measured air temperatures and solar radiation intensities during the time period of interest. The solution technique employs the complex variable approach along with the separation of variables method. A FORTRAN program was coded to implement the proposed 1D analytical solution. Field model validation demonstrates that the proposed solution generates reasonable temperature profile in the concrete slab for a four-layered rigid pavement system during two different time periods of the year. © 2012 Taylor and Francis.

Li X.-J.,Turner Fairbank Highway Research Center | Marasteanu M.O.,University of Minnesota
Proceedings of the Society for Experimental Mechanics, Inc. | Year: 2010

This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results, also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length. © Society for Experimental Mechanics 2009.

Li X.,Turner Fairbank Highway Research Center | Marasteanu M.,University of Minnesota
Engineering Fracture Mechanics | Year: 2010

The fracture process zone (FPZ) is a key factor to mechanistically characterize material fracture. This study investigates the FPZ of asphalt mixture at low temperature. The fracture process under a semi-circular bend (SCB) test of seven asphalt mixtures that represent a combination of different factors was monitored using an acoustic (AE) system with eight piezoelectric sensors. The size of FPZ was estimated by locating micro-cracks that correspond to 95% AE energy before peak load in the vicinity of the initial crack tip. The experimental data illustrates the significant influence of test temperature on the behavior of the asphalt mixture. Comparison results showed that the size of the FPZ significantly depends on air voids and aggregate type, but is less depend on the asphalt content. It was found that at a very low temperature, different loading rates produced very close FPZ, both for the width and length. No obvious difference was observed on the width of the FPZ for the three different initial notch lengths, whereas the length of the FPZ was found significantly increases with the decrease of the notch length. The size of FPZ was also numerically estimated for one case with the cohesive zone model (CZM) calibrated by experimental data from the same SCB test. The FPZ size obtained with both methods agrees reasonably with each other. © 2010 Elsevier Ltd.

Park E.S.,Texas A&M University | Carlson P.J.,Texas A&M University | Porter R.J.,University of Utah | Andersen C.K.,Turner Fairbank Highway Research Center
Accident Analysis and Prevention | Year: 2012

Although it is generally expected that wider lines will have a positive effect on vehicle safety, there have not been any convincing evidence based on the crash data analysis, partly because of the lack of relevant data. In this paper, the safety effect of wider edge lines was examined by analyzing crash frequency data for road segments with and without wider edge lines. The data from three states, Kansas, Michigan, and Illinois, have been analyzed. Because of different nature of data from each state, a different statistical analysis approach was employed for each state: an empirical Bayes, before-after analysis of Kansas data, an interrupted time series design and generalized linear segmented regression analysis of Michigan data, and a cross sectional analysis of Illinois data. Although it is well-known that causation is hard to establish based on observational studies, the results from three extensive statistical analyses all point to the same findings. The consistent findings lend support to the positive safety effects of wider edge lines installed on rural, two-lane highways. © 2012 Elsevier Ltd. All rights reserved.

Maya L.F.,Turner Fairbank Highway Research Center | Zanuy C.,Technical University of Madrid | Albajar L.,Technical University of Madrid | Lopez C.,CSIC - Eduardo Torroja Institute for Construction Science | Portabella J.,Prainsa
Construction and Building Materials | Year: 2013

Interest in precast construction system has been growing due to the emphasis on improving work zone safety, reducing construction time and environmental impact, while maintaining quality. This experimental study aimed to develop a method to connect precast elements avoiding the use of complex reinforcing details and inefficient construction processes. For that purpose, the outstanding properties of ultra high performance fibre reinforced concretes (UHPFRC) were used to develop continuity connections between precast elements. A two-stage experimental program was defined to study the behaviour of precast elements connected using short reinforcement splice lengths. In the first experimental stage, flexural beam tests were carried out to assess the use of short reinforcement splice lengths in continuity connections. In the second experimental stage, an alternative beam-column connection for precast construction using UHPFRC was proposed and tested. The configuration proposed avoids the interference between longitudinal and transversal reinforcement, reduces the in situ work and makes it possible to define an efficient and safe construction process. © 2013 Elsevier B.V.

Xue W.,Virginia Polytechnic Institute and State University | Weaver E.,Turner Fairbank Highway Research Center
Transportation Research Record | Year: 2011

FHWA conducted controlled loading tests on the US-23 test road in hot weather conditions in Ohio. The tests used four tire types in both dual and wide-base configurations, which were fitted on a single unit two-axle truck, maintaining a constant gross vehicle weight. Two pavement sections, one 8 in. (200 mm) and one 4 in. (100 mm) thick, were instrumented with strain gauge rosettes oriented vertically to measure strain traces induced from the passing wheel loads at three speeds and tire inflation pressures. Pavement temperature was monitored with depth during testing as well as wheel track offset distance from the strain sensors. Because of time constraints, only the sensors in the plane parallel to the direction of loading were analyzed, and response data were compared only with linear elastic pavement response models. The as-measured data were processed and evaluated for all rosettes oriented in the direction of loading. Stress relaxation modulus data were used to adjust the pavement modulus to a common temperature and loading time so all measured data could be compared at the same loading conditions. The WinLEA linear elastic model was used to determine the relationship of structural modulus to strain. Lateral offset distributions were determined from measured data to adjust all strains to the offset where maximum strain response is observed in the as-measured data. The adjustments were then applied to the as-measured strain data to make consistent comparisons between tires. Three of the four tire configurations produce nearly equivalent pavement response, which was attributed to similarities between the tire footprint widths.

Chen L.,Professional Service Industries Inc. | Graybeal B.A.,Turner Fairbank Highway Research Center
Journal of Bridge Engineering | Year: 2012

The concrete-damaged plasticity (CDP) model with proposed material properties replicated the observed deflection and strain responses of three experimentally tested I-girders and was determined to be consistent for different spans under both flexural and shear tests. In this study, the CDP model was further tested in modeling the behaviors of a prestressed second-generation ultrahigh-performance concrete (UHPC) pi-girder. The computational aspects include discussion of the various parameters that influenced the accuracy of the model and investigation of the scenarios regarding the limits that are useful for further optimization of the girder. The CDP model was reconfirmed to be consistent and reliable in replicating the observed structural response of both the UHPC pi-girder and a modified structural configuration referred to as the "UHPC pi-girder-with-joint. " The finite-element analysis modeling techniques developed herein are expected to be valuable in the future development of additional UHPC structural components. © 2012 American Society of Civil Engineers.

Li X.,Turner Fairbank Highway Research Center | Gibson N.,U.S. Federal Highway Administration
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2013

This study investigated the feasibility of performing dynamic modulus and fatigue performance tests using reduced scale specimens in an Asphalt Mixture Performance Tester. Ten different mixtures were characterized which had different nominal maximum aggregate sizes and were laboratory prepared or field cored from accelerated pavement test sections. Indirect tension dynamic modulus was included in the characterization of the field cored materials. An aspect ratio for 38 mm diameter specimens was recommended based on an exploratory portion of the study. The experimental results show that the modulus of the small scale specimens can be quite similar to the full size specimens and tends to be slightly softer at high temperature and low reduced frequencies. Phase angle is more comparable and, when different, tends to be slightly higher for the small scale specimens. Data analysis comparing the full size and small scale specimens revealed two out of three data quality indicators from small size dynamic modulus are as good as that of full size dynamic modulus. The third quality indicator was worse for about one third of the data points, but the majority of tests satisfied recommended values. The fatigue test results showed the modulus reduction at failure and endurance limit are comparable between full size and small scale specimens. There was no consistent trend where small scale was larger or smaller than full scale specimens in fatigue resistance and the ranking was mostly preserved between the two sized specimens. Overall, the small scale approach is very promising which can allow the field-compacted fatigue and stiffness characteristics of pavements to be assessed. The applications of this research are field validation of cracking tests, performance based quality assurance and forensic investigations. © 2013 Taylor & Francis.

Nicks J.E.,Turner Fairbank Highway Research Center | Esmaili D.,Turner Fairbank Highway Research Center | Adams M.T.,Turner Fairbank Highway Research Center
Geotextiles and Geomembranes | Year: 2016

This paper evaluates the results of 13 large scale Geosynthetic Reinforced Soil (GRS) column load tests, also known as performance tests (PT) or mini-pier tests, to study the effect of tensile strength (Tf), vertical reinforcement spacing (Sv), facing elements, and backfill properties on the deformations of GRS at 200 kPa, typical bridge bearing pressures, and also at 400 kPa. The results indicate that GRS performs well under service conditions. A semi-empirical expression is proposed for prescribed bearing pressures to limit vertical strain to 0.5% of the abutment height. In addition, recommendations for estimating lateral deformation for GRS bridge abutments are also provided. At 200 kPa surcharge for this series of tests, vertical settlements ranged from 8.3 to 33.9 mm (or from 0.4% to 1.7% axial strain); lateral deformations ranged from 3.0 mm to 10.1 mm (or 0.6%-2.0% lateral strain); and reinforcement strain ranged from less than 1% during construction to less than 3% during loading. The lateral deformation results indicate that the maximum displacement occurs in the top third region of the wall face. Comparing the vertical and lateral displacement data shows that most GRS models experienced negligible positive volume changes up to about 1% under typical bridge service loads. © 2016.

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