Vertical Curve Research Articles

Driver speed selection and crash risk: Insights from the naturalistic driving study

IntroductionThis study investigates how speed limits affect driver speed selection, as well as the related crash risk, while controlling for various confounding factors such as traffic volumes and roadway geometry. Data from a naturalistic driving study are used to examine how driver speed selection varies among freeways with different posted speed limits, as well as how the likelihood of crash/near-crash events change with respect to mean speed and standard deviation. MethodRegression models are estimated to assess three measures of interest: the average speed of vehicles during the time preceding crash/near-crash and baseline (i.e., normal) driving events; the variation in travel speeds leading up to each event as quantified by the standard deviation in speeds over this period; and the probability of a specific event resulting in a crash/near-crash based on speed selection and other factors. ResultsSpeeds were relatively stable across levels-of-service A and B, within a range of 1.5mph on average. Speeds were marginally lower (3.3mph) on freeways posted at 65mph versus 70mph. In comparison, speeds were approximately 10.2 to 13.4mph lower on facilities posted at 55mph or 60mph. Speeds were shown to be 2.5mph lower in rainy weather and 11mph lower under snow or sleet. ConclusionsSignificant correlation was observed with respect to speed selection behavior among the same individuals. Mean speeds are shown to increase with speed limits. However, these increases are less pronounced at higher speed limits. Drivers tend to reduce their travel speeds in presence of junctions and work zones, under adverse weather conditions, and particularly under heavy congestion. Crash risk increased with the standard deviation in speed, as well as on vertical curves and ramp junctions, and among the youngest and oldest age groups of drivers.

Inter shear transfer of unbonded prestressing precast segmental bridge column dry joints

The shear performance of precast segmental bridge column (PSBC) epoxy-free dry joints was investigated. Ten PSBC dry joint specimens were tested under monotonic direct shear loading. The design parameters include sectional shape, with or without shear keys, key number and geometry, and confining stress. The shear resistance-relative vertical displacement curves were recorded. The damage patterns and failure mechanism of tested specimens were analyzed. Shear strength formulas for prismatic, castellated, and flat dry joint were derived through data regression. The applicability of proposed formulas together with those from literature was investigated. Finally a finite element (FE) model was calibrated to study the friction contribution to shear capacity at various confining stresses.

Dynamics of soil water reservoir of wheat field in rain-fed area of the Loess Tableland, China

Soil reservoir is the basis of stable grain production and sustainable development in dry farming area. Based on the long-term field experiment, this paper investigated the changes of soil moisture in wheat field located in the rain-fed Changwu Tableland, and analyzed the interannual and annual variation characteristics and dynamics trends of soil reservoir from 2012 to 2015. The results showed that the vertical distribution curves of average soil water content were double peaks and double valleys: first peak and valley occurred in the 10-20 and 50 cm soil layer, respectively, while for the second peak and valley, the corresponding soil layer was the 100 and 280 cm soil layer. Soil reservoir did not coincide with precipitation for all yearly precipitation patterns but lagged behind. Yearly precipitation patterns had a great influence on the interannual and annual dynamic changes of soil reservoir. Compared with rainy year, the depth of soil moisture consumption decreased and supplementary effect of precipitation on soil moisture became obvious under effects of drought year and normal year. In rainy year, soil reservoir had a large surplus (84.2 mm), water balance was compensated; in normal year, it had a slight surplus (9.5 mm), water balance was compensated; while in drought year, it was slightly deficient (1.5 mm), water balance was negatively compensated. The dynamics of soil water in winter wheat field in the rain-fed Changwu Tableland could be divided into four periods: seedling period, slow consumption period, large consumption period, and harvest period, the order of evapotranspiration was large consumption period> seedling period> harvest period> slow consumption period.

Comparison of Biomechanical Characteristics on Barefoot Running and Shod Running

Background Compared with the rearfoot strike pattern of shod running, barefoot running with a forefoot strike pattern will change the kinematics and kinetic parameters. This paper analyses the biomechanical differences between barefoot running and shod running and aims to provide a reference for barefoot training and the prevention of sports injury. Methods Three-dimensional force plate test and three-dimensional video analysis. Results Kinetic characteristics: The F-t curve by the force plate test shows that barefoot running has a smooth curve with a single peak while the F-t curve of shod running has a double peak on the vertical direction curve. The maximum ground reaction force in the vertical direction of barefoot running is significantly less than shod running. Kinematics characteristics: Compared with shod running, barefoot running has a faster step frequency, a shorter stride length, a shorter foot-to-ground contact time. The smaller stride length means barefoot running has a bigger ankle plantar flexion, which shows barefoot running can reduce sports injuries.

Integrated facies modeling in unconventional reservoirs using a frequentist approach: Example from a South Texas field

Modeling of rock types or facies in unconventional reservoirs presents numerous challenges that are not encountered in conventional reservoirs. Because the exploitation of unconventional reservoirs frequently relies on the use of large numbers of long, data-poor horizontal wells, routine tasks in conventional reservoirs, such as petrophysical analyses and rock-physics diagnostics, become problematic in unconventional reservoirs due to insufficient data. Similarly, the inability to generate synthetic seismograms in the horizontal section of the wells makes seismic well ties and time-depth conversions more difficult. Our approach for facies modeling in unconventional reservoirs attempts to overcome these challenges by using the abundant log information available along the vertical pilot well to extract discrete facies indicators (facies flags) from logging-while-drilling information along the horizontals. After performing a time-depth conversion constrained by geosteering information, we estimate facies probabilities using facies flags and prestack elastic inversion results also extracted along the horizontals. As opposed to the Bayesian formalism commonly used for facies probabilities estimation, our frequentist approach estimates probabilities directly from proportions derived from crossplots of inverted elastic properties without using the Bayes formula. No prior information is required. The margin of error in the probabilities is also estimated by applying a well-known formula used to estimate the margin of error in opinion polls. Finally, we use seismic probability results to select only points with high probability and high reliability, which are treated as hard constraints for stochastic facies modeling. The selection of the seismic constraints is also weighted by the vertical facies trend expected for the area of interest. Our final facies model closely follows horizontal and vertical well facies data, vertical proportion curves, and selected seismic constraints. The application of the methodology is illustrated in a carbonate-rich, unconventional reservoir in South Texas.

Holding capacity of dynamically installed anchors in normally consolidated clay under inclined loading

This paper describes a design framework for inclined tensile loading capacity (holding capacity) of dynamically installed anchors in soft clay. Centrifuge model test and numerical results indicate that, while ultimate inclined holding capacity increases with a loading angle smaller than 45° (to the vertical at anchor padeye), anchor failure is controlled predominantly by the ultimate vertical holding capacity, which can be predicted using the American Petroleum Institute method put forth in 2007 with interface friction ratio of 0.25–0.34 and 0.60–0.82 for short- and long-term conditions, respectively. For a loading angle larger than about 65°, anchor failure is controlled largely by the ultimate horizontal holding capacity. It is proposed herein that the ultimate lateral holding capacity can be estimated by generalizing Broms’ method put forth in 1964 for lateral anchor capacity to variable cross section; thereby allowing anchor geometry to be considered in a rational manner. Good agreement can be obtained between the estimated ultimate horizontal holding capacity and that computed using the finite element method by using a lateral resistance of 10.5su, where suis the undrained shear strength. For a loading angle between 45° and 65°, there is significant interaction between vertical and horizontal failure modes. This allows a normalized horizontal–vertical interaction curve to be defined by fitting data from this and previous studies.

Optimum Analysis and Design of Curved Concrete Dams

This research presents an efficient strategy to find optimum analysis and shape design for arch dams. Where the design geometry is built using (Solid Work Program), which is considered as one of important programs for analysis and design of complex structures. A finite element method is used to analyze the arch dam body, which is proved to be an important method for analysis and gives accurate results according to previous researches. The design of the basic shape of the dam has been done by using horizontal curve and vertical curve equations. After conducting the analysis and design of the initial model by (SolidWork) program, it was transferred to the second phase. This is the shape optimization process by using (Genetic Algorithm) in (Matlab) program. This method is an efficient method for all optimization problems in different branches. The objective function in this research is the minimum volume of the dam, which leads to minimum weight design. There are many constraint controls the selecting of optimum shape. In this work, geometrical and structural constraints are considered. At this stage, to calculate the volume of the dam body, integration method is used to convert the volume in terms of the design variables (tc1, tc2, and tc3) which represent the thickness of the dam at three levels. Then this equation has been moved to (Genetic Algorithm tools) using (m-file) to complete the optimization process. The results show that the best design shape of the dam is with thicknesses (5.5m, 13.3m, and 19.8m) with a final optimal volume of53.75% less than the initial model and the stress is still less than the allowable limits

Emerging Numerical-Modeling Technique To Evaluate Asphaltene-Inhibitor Efficiency During Entire Field Life

Summary This work sought to establish a robust asphaltene flow-assurance engineering with asphaltene inhibitor to mitigate the risk of asphaltene precipitation in tubing. For this purpose, the best candidate was selected through the asphaltene dispersant test (ADT). Furthermore, its inhibiting efficiency was evaluated by generating a numerical model. The purpose of this evaluation was to predict how its efficiency varied during entire field life in which production conditions changed in early and late life. Through the two-stage ADT, the best inhibitor IB-23 was selected from a total of nineteen samples. The IB-23 revealed a high inhibiting efficiency of more than 80% at 200 ppm concentration, and maintained its efficiency more than 70% even at 10 ppm. Currently, any commercial software is not available for the modeling of asphaltene inhibitor caused by confidentiality for inhibitor physical data. This study achieved modeling of inhibiting efficiency by treating an inhibitor as a pseudoresin and/or pseudocomponent. It could be defined with limited physical data that were available in a publicly accessible material-safety data sheet (MSDS). The numerical model was generated with a cubic-plus-association (CPA) equation of state (EOS) together with the conventional fluid characterization to characterize the asphaltene crudes. This paper demonstrates that the numerical model expressed the inhibiting efficiency as a size-reduction of asphaltene-precipitation envelope (APE) and a decrease in the amount of asphaltene precipitated. The model validity was checked by comparing with experimentally measured weight data of asphaltene deposits during the ADT. Assuming natural depletion, the APEs were compared with a variation of vertical lifting curves (VLCs) in tubing. Two VLCs were assumed to represent early and late field conditions (i.e., high wellhead/reservoir pressures and depleted ones). The no-inhibitor case revealed that precipitating risk existed over most of the tubing section. In contrast, the inhibitor-dosed case could significantly reduce the risks in the early stage in particular. Even in the late stage, the risks could be minimized because the interception of VLC on the APE became shorter than that of the no-inhibitor case. Asphaltene inhibitor is a typical countermeasure; however, most of the applications offer only temporary relief. Through an entire field life, the production conditions vary such as pressure decline, gas/oil ratio (GOR) increase, and others. Accordingly, the efficiency of the inhibitor, initially selected as the best, fades away. Then, another screening would be required to select an alternative one that can adapt effectiveness to the new operating condition. This paper contributes to estimating its inhibiting efficiency during a whole field life.

Kinesiophobia is Strongly Associated with Altered Loading after an ACL Reconstruction: Implications for Re-injury Risk

Objectives:The effect of kinesiophobia (fear of movement) following an anterior cruciate ligament (ACL) reconstruction has recently received greater attention. Elevated kinesiophobia as measured on the Tampa Scale of Kinesiophobia (TSK) has been previously found to be associated with poorer outcomes. However, the effect of kinesiophobia in ACL reconstructed patients on high impact and challenging tasks associated with re injury risk such as jumping has not been investigated. Establishing the relationship between kinesiophobia and jump landing mechanics could result in the development of specific treatments to reduce fear of movement and improve jump landing mechanics after ACL reconstruction, resulting in a diminished re-injury risk. Therefore, the purpose of this study is to define the relationship between landing mechanics (axial loading rates and impact forces) with the TSK score in patients 6 months after ACL reconstruction.Methods:Twenty subjects, 6 months post ACL reconstruction, who had completed post-operative physical therapy, and were cleared by their physician to begin return to sport drills participated in the study. Subjects completed an instrumented drop vertical landing assessment with the ground reaction forces recorded while the subjects performed a drop vertical jump task off a 30.48 cm high box. Three trials were taken and the data were analyzed using custom Labview code and Visual 3D software during the period of time from foot contact until initial impact peak. The average loading rate was defined as the linear portion of the vertical ground reaction curve between 20-80% of foot contact to initial impact peak. Subjects also completed the TSK questionnaire. Associations between loading rate and vertical impact peak to the TSK scale were made with Pearson correlation coefficients with significant relationships defined as p<0.05.Results:20 subjects (11 female, 9 male, Ages 19 ± 3.3 yrs, H 1.73 ± 0.11 m, M 69.1 ± 12.2 kg) with bone patellar bone autografts completed the study. The mean loading rate was 56.96 ± 18.6 %bodyweight/sec, initial impact peak 0.88 ± 0.24 %bodyweight, and TSK value was 33.1 ± 6.8. There was a significant negative association between poorer responses on the TSK scale and initial impact peak forces (r=-0.624, p=0.003) but not average loading rate (r=-0.243, p=-0.302) (Figure 1).Conclusion:We found greater kinesiophobia to be associated with a lower weight-bearing in the ACL reconstructed limb. Potentially, subjects who are afraid of loading their reconstructed limb transfer weight to the uninjured limb, increasing the demand placed upon that limb. The greater forces that the contra lateral limb must absorb may in part be related to the elevated risk of injury associated with the non injured limb. The lack of relationship to loading rate suggests kinesiophobia is more related to the magnitude of the load and not the subject’s ability to control the load. These results suggest that in patients with elevated kinesiophobia, cognitive training may be needed before initiating movement retraining or other exercises to improve landing mechanics. Additional prospective studies are needed to assess if these relationships improve over time and determine the optimal time to intervene to reduce subsequent injury risk.

Early Objective Clinical Testing Predicts Jump Landing Mechanics Following an ACL Reconstruction: Impact for the Clinician and Return to Play Testing

Objectives:Currently, objective functional assessments are performed at the time of return to play following an anterior cruciate ligament (ACL) reconstruction. While informative, by that time the majority of organized rehabilitation has been completed, leaving little time for clinicians to address remaining impairments. Further, few objective tests have been compared to faulty movement mechanics. Identifying objective clinical tests that can be administered early during recovery from an ACL reconstruction which predict long term joint mechanics would provide sufficient time to address the underlying deficits prior to return to play testing. Thus, the purpose of this study was to determine if objective clinical tests (60 second single leg step down test and quadriceps strength) administered 3 months after surgery predicted jump landing mechanics of the knee (knee extension moment, average loading rate, vertical impact peak) at 6 months following an ACL reconstruction.Methods:29 subjects completed objective clinical testing at 3 months post operatively that included the 60 second single leg step down test and an assessment of isometric knee strength. To perform the 60 second single leg step down test, subjects performed a single leg squat by touching their heel on a scale with less than 10% of their bodyweight as many times as they could for 60 seconds while standing on an 8-inch box. Isometric knee extension strength was assessed with a hand held dynamometer secured to a table. The subject performed 4 isometric maximum isometric contractions for 5 seconds. At 6 months, performed a instrumented drop vertical landing jumping. Three trials were taken and the data were analyzed using custom Labview and Visual 3D code. The average loading rate was defined as the linear portion of the vertical ground reaction curve between 20-80% of foot contact to initial impact peak. Associations between quadriceps strength and the timed single leg step down test to knee extensor moment, average loading rate, and vertical impact peak were then made with Pearson correlation coefficients.Results:29 subjects (15 male and 14 female, Ages 20.2 ± 4.7 yrs, 24 bone patellar bone vs 5 hamstring autografts, H 1.75 ± 0.12 m, M 72.2 ± 12.1 kg) completed the study. The mean quadriceps strength was 23.3 ± 10.2 N, timed single leg step down test 20 ± 11 step downs, knee extensor moment 1.32 ± 0.54 Nm/kg, loading rate was 64.5 ± 23.6 %bodyweight/sec, and vertical impact peak 0.97 ± 0.36 %bodyweight. We found significant positive associations between 3 month quadriceps strength and knee extensor moment (r=0.442, p=0.016), average vertical loading rate (r=0.426, p=0.021), and vertical impact peak (r=0.619, p=0.000) (Figure 1). We found no significant associations between 3 month single leg step down performance and landing mechanics.Conclusion:We show the ability of a early, quick, clinically-feasible method of assessing quadriceps strength to predict joint mechanics during a drop vertical jump 6 months after ACL reconstruction. This assessment can be used to screen individuals at much earlier time point who need additional focused treatment to improve their outcomes prior to return to play testing. Further, they can give the orthopedic surgeon additional data to educate the patient and family about the need to not return to higher level activities too early and reinforces the need to be compliant with rehabilitation in order to maximize results at the time individuals begin return to sport drills.

The effect of crash characteristics on cyclist injuries: An analysis of Virginia automobile-bicycle crash data

This paper examines bicyclist, automobile driver, vehicle, environmental, and roadway characteristics that influence cyclist injury severity in order to determine which factors should be addressed to mitigate the worst bicyclist injuries. An ordered probit model is used to examine single bicycle-single vehicle crashes from Virginia police crash report data from 2010 to 2014. Five injury severity levels are considered: fatalities, severe injuries, minor or possible injuries, no apparent injuries, and no injury. The results of this study most notably found automobile driver intoxication to increase the probability of a cyclist fatality six fold and double the risk of a severe injury, while bicyclist intoxication increases the probability of a fatality by 36.7% and doubles the probability of severe injury. Additionally, bicycle and automobile speeds, obscured automobile driver vision, specific vehicle body types (SUV, truck, and van), vertical roadway grades and horizontal curves elevate the probability of more severe bicyclist injuries. Model results encourage consideration of methods to reduce the impact of biking and driving while intoxicated such as analysis of bicycling under the influence laws, education of drunk driving impacts on bicyclists, and separation of vehicles and bicycles on the road. Additionally, the results encourage consideration of methods to improve visibility of bicyclists and expectation of their presence on the road.

Axial Uplift Behavior of Belled Piers in Sloping Ground

Belled piers are frequently utilized for self-supporting transmission line towers, and the uplift loading is normally the controlling design load. However, belled piers placed in sloping ground have less uplift resistance than the same foundations built on flat ground. This study elucidates the uplift behavior of axially uplift-loaded belled piers in sloping ground. Two full-scale belled piers were constructed in a loess slope having an inclination of 20° with the horizontal, and pullout load testing was conducted for each belled pier. Both the site conditions and the load tests were documented comprehensively. The uplift load versus vertical shaft-head displacement curve of the belled piers in sloping ground exhibited an initial linear region, a curvilinear transition, and a final linear region, which is similar to that of a typical uplift or compression load–displacement curve for level ground. However, the shaft-head displacement at the lower sloping side was larger than that at the upper sloping side. Therefore, the shaft head rotated in the uplift loading direction, and the instantaneous rotation angle increased with the applied load. Unlike the level ground case, the uplift failure of the belled piers in sloping ground initiated from the edge of the bell at the lower sloping side and propagated into the slope surface as the soils deformed and pushed laterally toward the lower sloping side. The failure cracks on the ground surface were not symmetric and developed mainly on the lower sloping side. A comparison of the elastic limit load and the interpreted failure load of the two belled piers revealed that additional embedment of the foundation in sloping ground can achieve an increase in uplift resistance to match the level ground uplift capacity.

Reservoir characterization and multiscale heterogeneity modeling of inclined heterolithic strata for bitumen-production forecasting, McMurray Formation, Corner, Alberta, Canada

Bitumen reservoirs dominated by inclined heterolithic stratification (IHS) formed in large point bars of the Aptian (Lower Cretaceous) McMurray Formation in the northwestern part of the Corner oil sand lease (Alberta, Canada) were investigated to establish their value. Hybrid production technologies were applied to thin pay, typified by homogeneous reservoir sand units thicker than 5 m at the base overlain by IHS (so-called ‘thin pay’), as well as IHS-dominated reservoirs in which the IHS extends down to the base of the reservoir. High-resolution seismic data and well data (core, dipmeter, HMI) were used to map four facies associations, comprising a total of 16 sedimentary facies, as well as various fluid contacts to assist in reservoir characterization and risk assessment. The conceptual depositional model was based on the analysis of the migration and re-orientation history of the IHS-dominated point bars reflecting lateral accretion, downstream migration, rotation and relocation of the bars. Multiple reactivation events, which control the heterolithic nature and reservoir quality of the deposits, create developable “pools”.Seven electrofacies (with generally increasing mud content) were defined and used as input to construct vertical proportion curves that relate the electrofacies distribution to geomodel statistics in the main reservoir zone. At the electrofacies scale, numerical effective porosity-permeability models were created using micromodeling and minimodeling concepts. The geometrical shape of the electrofacies in the geomodel was investigated using non-stationary Truncated Gaussian (TG) facies simulation to enforce the stacking patterns. Each geomodel area was characterized using one variogram to efficiently compute the horizontal and vertical variogram ranges and average azimuths. Sequential Gaussian simulation (SGS) was used to map the distribution of key petrophysical parameters such as effective porosity, effective water saturation and Vshale. Empirically derived saturation versus elevation profiles for each electrofacies were included in the modeling. The distributions from the micro- and mini-modeling were introduced using probability field (P-field) simulation. To investigate the amount of connected resources (the degree of connectivity of good sand as well as IHS) were extractable flow simulation studies were performed at the pad scale. In preparation for reservoir simulation, connectivity calculations within the local pool geomodel realizations were tailored for the reservoir heterogeneities (i.e., IHS) that are expected to have a major impact on the specific thermal and gravity drainage extraction processes. The geomodel realizations were ranked by expected pseudo-dynamic behaviour with connected exploitable pay as a critical parameter.

Global phase portraits of a degenerate Bogdanov-Takens system with symmetry (Ⅱ)

The degenerate Bogdanov-Takens system $\dot x = y-(a_1x+a_2x^3),~\dot y = a_3x+a_4x^3$ has two normal forms, one of which is investigated in [Disc. Cont. Dyn. Syst. B (22)2017,1273-1293] and global behavior is analyzed for general parameters. To continue this work, in this paper we study the other normal form and perform all global phase portraits on the Poincaré disc. Since the parameters are not restricted to be sufficiently small, some classic bifurcation methods for small parameters, such as the Melnikov method, are no longer valid. We find necessary and sufficient conditions for existences of limit cycles and homoclinic loops respectively by constructing a distance function among orbits on the vertical isocline curve and further give the number of limit cycles for parameters in different regions. Finally we not only give the global bifurcation diagram, where global existences and monotonicities of the homoclinic bifurcation curve and the double limit cycle bifurcation curve are proved, but also classify all global phase portraits.

Bionic Design for Reducing Adhesive Resistance of the Ridger Inspired by a Boar's Head.

The main feature of the boar's head used to root around for food is the front part, which is similar to the ridger in terms of function, load, and environment. In this paper, the boar's head was selected as the biological prototype for developing a new ridger. The point cloud of the head was captured by a 3D scanner, and then, the head surface was reconstructed using 3D coordinates. The characteristic curves of the front part of the boar's head were extracted, and then, five cross-sectional curves and one vertical section curve were fitted. Based on the fitted curves, five kinds of bionic ridgers were designed. The penetrating resistances of the bionic ridgers and traditional ridger were tested at different speeds in an indoor soil bin. The test results showed that bionic ridger B had the best penetrating resistance reduction ratio of 16.67% at 4.2 km/h velocity. In order to further evaluate the performance of the best bionic ridger (bionic ridger B), both the bionic ridger and traditional ridger were tested in a field under the same working conditions. The field results indicate that the bionic ridger reduces penetrating resistance by 6.91% compared to the traditional ridger, and the test results validate that the bionic ridger has an effect on reducing penetrating resistance.

Longitudinal distribution of extreme pressures in a hydraulic jump downstream of a stepped spillway

ABSTRACT The overflow system of a dam safely controls the water level of a reservoir. The design of these structures should predict the damage caused by the action of the turbulent flow to which they are subject to. The combination formed by a stepped spillway followed by a stilling basin promotes a considerable portion of the energy dissipation in the actual chute of the stepped spillway but it is not sufficient to completely avoid the risk of damaging the basin. In this paper, we analyze the longitudinal distribution of extreme pressures in a stilling basin downstream of a stepped spillway. The study was based on the instant pressure data from the tests carried out in a physical model in the Laboratório de Obras Hidráulicas in IPH/UFRGS. Thus, it was found that the pressure behavior is similar to that observed in studies involving smooth chute spillways, except in the area surrounding the base of the stepped spillway, where high pressure fluctuations may occur. This happens as a result of the impact caused by the flow in the dissipation structure, which is not observed downstream of smooth chute spillways due to the existence of a vertical concordance curve between the spillway and the stilling basin.

Stopping Sight Distance and Available Sight Distance: New Model and Reliability Analysis Comparison

Stopping sight distance (SSD) is an important design criterion used in the geometry of highways and streets. Design guidance implies that SSD is used to ensure safety along the roadway. This paper reviews SSD design criteria and develops an updated model to improve consistency between available sight distance and SSD criteria found in geometric design policy. A new variable, the distance from the front of the car to the driver’s eye ( Lfront-eye), is used in the updated model. Distributional values for Lfront-eye are determined. A method accounting for lighted (daytime and lighted nighttime) versus unlighted nighttime conditions is also discussed. A probabilistic analysis of vertical curve SSD uses Monte Carlo simulation. The results of this analysis are compared with the SSD model found in current geometric design policy. Possible values for Lfront-eye that can be used in design guidance are proposed. Potential issues that should be investigated in future work are discussed.

Assessment of the effects of expressway geometric design features on the frequency of accident crash rates using high-resolution laser scanning data and GIS

ABSTRACTAccurate information on accidents and on the relevant factors that affect them is critical for establishing the relationship between accident frequency and explanatory factors. In this study, we present a simplified method to extract road geometric features accurately from very high-resolution laser scanning data to analyze accident frequency on the North-South Expressway in Malaysia. Using expressway geometric features (i.e. horizontal and vertical alignments) extracted from laser scanning data and accident histories, this research first developed an APM based on geometric regression and a geographic information system (GIS). Then, an elasticity analysis was conducted to investigate the relationship between accident occurrence and road geometric design features. Results of the case study showed that the length of the road segments (mean = 0.014, elasticity = 0.122), the number of vertical curves in a road section (mean = 4.797, elasticity = 0.999), and the presence of a horizontal curve in a road segment (mean = 2.746, elasticity = 0.877), the average distance to the nearest access point (mean = -0.001, elasticity = −0.035), and AADT (mean = 3.01, elasticity = 0.881) determined accident occurrence, all at a significance level of 5%. This study shows that laser scanning systems can provide an easy and efficient method to collect transportation data, particularly those for accident analysis.

Stopping sight distance adequacy assessment on freeways: the case of left horizontal curves over crest vertical curves

ABSTRACT This paper investigates potential Stopping Sight Distance (SSD) violation on divided highways at left horizontal curves overlapped with crest vertical curves. The authors previously developed a SSD control methodology that relates the 3D configuration to the dynamics of a vehicle moving along the roadway. This methodology is applied for the assessment of critical design parameters related to both demanded and available SSD values. Initially, utilizing control geometric and driver – obstacle values adopted by AASHTO 2011 design policy, SSD inadequacy areas were revealed. Subsequently, on the basis of an explanatory modeling approach for a number of geometry parameters, evaluation of SSD sufficiency was carried out in terms of the probability of SSD inadequacy and the prediction of the object height in order to grant SSD adequacy (amended object height). These models may be useful to researchers and practitioners aiming to evaluate the interaction of the utilized design parameters in terms of SSD inadequacy.

Progressive Collapse Analysis of Concrete-filled Steel Tubular Column to Steel Beam Connections Using Multi-scale Model

The multi-scale model which combined the fiber beam element with the fine element was used to investigate the progressive collapse performance of steel beam to concrete-filled steel tubular (CFST) column connections. By using the nonlinear static analysis method and taking into account the influence of the adjacent framework of joints, the resistance of progressive collapse, the failure modes and the stress distribution revealed the resistance mechanism of these joints during the process of progressive collapse. And the vertical displacement time history curves of joints which displayed the progressive collapse resistance demands of these joints were obtained by using the nonlinear dynamic analysis method. The relationship between resistance capacity and resistance demand of these joints were obtained by analyzing the nonlinear static analysis results and the nonlinear dynamic analysis results. These analysis results showed that the frame structure with these joints which enabled to form the resistance mechanism and new alternate path of unbalanced loads can prevent the occurrence of progressive collapse after the failure of column connected to joints. And the adjacent framework can improve the ability of anti-progressive collapse of these joints.