Study On The Dynamical Response Of Flexible Pavement Foundations Under Random Loads

As the development of road traffic, the over-load and over-limit phenomenon becomes extraordinarily common. The static method or quasi-static method to design freeway finds hard to meet the demand. It is imperative to have further study of vehicle-roadbed and road surface dynamic interaction mechanism. The dissertation targets on flexible pavement. By regarding vehicle-roadbed and road surface as synthesized system, deeper theoretic analysis and experimental research were made on some heated and difficult issues (description of road surface, determination of random dynamic load, dynamic response of roadbed and road surface etc.) about interaction between heavy-load vehicle and road surfaces in the freeway.1. Through the random excitation resource of vehicle induced vibration, i.e. exterior properties of road surface. The frequency domain method was applied to predict the PSD, and emphatically analyze the characteristics and regularity of unevenness of freeway surface. It concludes that vehicle dynamic loads induced by road surface random unevenness excitation are random spatio-changing loads. On account of that, quarter vehicle dynamic model was adopted while considering wheels' damping effect. Matlab program was used to model numerically the vehicle random dynamic load on the uneven road surface. Random dynamic load time-distance curve of vehicle model at any speed was described in the time domain. In the mean time, discussed were the relationship between vehicle random dynamic load and surface excitation frequency, vehicle speed, wavelength surface standard wavenumber spectral density, and clarified were the characteristics and regularity of surface random excitation input induced by vehicles.2. Based on physical mechanic properties of flexible road surface and with reference to pertinent files, transfer function matrix was adopted via theory of layered system after transformation through Fourier and Laplace integration; it predicts solution of dynamic equation of multiple viscoelastic system under moving harmonic loads. Due to the difficulties of analyzing viscoelastic, FEM numerical method applied in ANSYS was proposed as the way to analyze multiple-layered dynamic response.3. According to proposition of multiple-layered viscoelastic system of flexible roadbed and surface, 3-D dynamic FEM model of flexible roadbed and surface was established, and FEM was successfully applied to study the interaction between vehicles and roadbed and road surface. Further modeled and discussed was dynamic response under the single-wheel unit vehicles load (including vehicles' lateral pushing forces and tangential pushing forces) and other factors. Elaborated were the fatigueness-induced damage regularity and mechanism under vehicle dynamic load interaction of flexible roadbed and surface.4. Experiments were conducted on the ChangDe-ZhangJiajie newly-constructed freeway of dynamic response of each structural layer of flexible roadbed and surface under heavy-load vehicle. With consideration to impact of vehicle load, speed and freeway lane on the dynamic response regularity of roadbed and surface, analyzed were characteristics of frequency and PSD, and compared with road surface unevenness excitation characteristics. The results show that surface excitation, vehicle vibration, load input, dynamic response of roadbed and surface are cause-effect interdependent. Through quadratic orthogonally regression, established was numerical model of interaction between roadbed-surface dynamic response and speed, dynamic load, second effect of load and velocity-load. Thus it expounded the damage impact of each factors on surface structure.5. 1/2 truck model was established to reflect experimental vehicles properties. Normal form method was adopted to obtain solution to the vehicle model dynamic equation. Alter input of four-wheel load in the ANSYS 3D model to model roadbed and surface dynamic response, were compared numerical modeling results with experimental values, which shows that experimental value conforms to numerical solutions. Therefore, the viscoelastic 3D Finite model established in the dissertation is valid.