Kenji Himeno

Evaluation of Sidewalk Unevenness Based on Wheelchair Traveling Resistance

Differences in the levels and the transverse and longitudinal gradients on sidewalks can seriously hinder the mobility of wheelchair users. On sidewalks where such differences and gradients are minor, the mobility of wheelchair users can be seriously hindered by surface unevenness in the case of rough sidewalks. This paper analyzes the longitudinal profiles of sidewalks in service and torque data for traveling wheelchairs with the goal of proposing a method for evaluating the surface unevenness of sidewalks based on the travel resistance imposed on wheelchairs. A test track with variable gradients and unevenness was traveled by panel members, who were then asked to rate the subjective discomfort of the test track. The study revealed a strong correlation between the surface unevenness values calculated by the proposed method and the discomfort rating offered by the panel members.

CURLING STRESS EQUATION FOR TRANSVERSE JOINT EDGE OF A CONCRETE PAVEMENT SLAB BASED ON FINITE-ELEMENT METHOD ANALYSIS

In the design of concrete pavement, curling stresses caused by the temperature difference between the top and bottom surfaces of the slab should be calculated at the transverse joint edge in some cases. However, no such equation has been developed in the past. Accordingly, a curling stress equation was developed based on stress analysis using the finite-element method (FEM). In this FEM analysis, a concrete pavement and its transverse joint were expressed by means of a thin plate-Winkler foundation model and a spring joint model, respectively. Multiregression analysis was applied to the results of the FEM numerical calculation and, consequently, a curling stress equation was obtained. After comparing the calculated results of the equation with curling stress equations developed in the past, it was confirmed that the equation was valid and practical.

A Study of Longitudinal Crack Which Occurs to the Surface of Asphalt Pavement by Wheel Tracking Test

It is known that asphalt pavement is subject to longitudinal cracking that begin at the surface and propagate downward. The main mechanism involved is considered to be bending-induced tensile strain away from the tire or shear-induced near-surface tensile strain at the tire edge. It is difficult to specify the location where such cracks occur because vehicles do not follow precisely the same path. Some cracks might form beneath the tire of a vehicle. However, no reliable method has yet been established. The purpose of the present study was to identify the mechanism involved in longitudinal cracking in asphalt mixtures using an improved wheel tracking test. By varying the temperature and loading conditions, it was determined that cracking occurred beneath the tire. The cracks had similar shapes to the longitudinal cracks that occur in road surfaces. The bottom surface of the asphalt showed no evidence of cracking. To determine the reason for this, stress relaxation in an asphalt mixture was investigated using compression tests. As the results, the stress-relaxation performance of an asphalt mixture becomes higher as temperature increases. Moreover the compressive stress was reduced immediately to about half of its maximum value. This suggests that if the compressive stress in the surface layer is released, the residual strain in the binder course layer would act as a tensile strain, which gives rise to the formation of cracks.

Structural evaluation of pavement using surface wave and portable FWD tests

SASW has been well known as one of nondestructive testing methods for pavements. This method makes use of the dispersion characteristics to estimate the thickness and modulus of pavement layers. It is difficult to obtain accurate dispersion curves even if the analytical surface wave fields are used, where only the stiffness proportional damping is considered. However, the good agreement of dispersion curves has been found for the analytical surface wave fields if Rayleigh damping is adopted in the numerical simulation. In this paper, a dynamic general FEM software was developed to inverse the layer moduli and Rayleigh damping coefficient of the tested pavement structure using the portable FWD data. It shows that the predicted dispersion curves are well approximately to ones obtained from experimental SASW.

Airport pavement roughness evaluation based on aircraft response

Runway roughness affects primarily ride quality and dynamic wheel loads. The forces applied onto the airport pavement by aircraft vary instantaneously above and blow the static weight, which in turn increase the runway roughness. One method to effectively assess the ride quality of the airport runway is to measure its longitudinal profile and numerical simulate aircraft response performing a takeoff, landing or taxiing on that profile data. In this study the aircraft responses excited as the aircraft accelerates or moves at a constant speed on the runway during takeoff and taxi are computed by using the improved computer program TAXI. This procedure is capable of taking into account both the effects of discrete runway bumps and runway roughness. Thus, sections of significant dynamic response can be determined, and the maintenance and rehabilitation works for airport runways will be conducted.

EVALUATION OF OPEN GRADED ASPHALT MIXTURES BY IMAGE ANALYSIS OF CROSS SECTIONS

A fundamental investigation was made on void structures of porous and coarse graded asphalt mixtures to combine their geometrical and physical characteristics. The voids in the mixture were visualized by filling them up with colored epoxy resin. The mixture was then cut after hardening and the sections were carefully imaged by a scanner connected to a personal computer system.Every pixel of the scanned image of each section was digitized into three values and geometrical distributions of void, mineral aggregate, and binder are characterized as well as each content is quantified. It was found that each mixture has its own specific characteristics in images in cross sections, which is presumably related to its mixture properties.