Yukio Kikuta

Time domain backcalculation of pavement

Falling weight deflectometor (FWD) has been frequently used to evaluate structural integrity of pavement. The device applies an impulsive force on the surface of pavement and measure surface deflections at several locations including the place of loading. Although the test is dynamic, the data is regarded as pseudo-static data. According to common practice, using the peak load and the corresponding peak deflections, layer moduli are estimated in a static domain such that the measured peak deflections coincide with the corresponding calculated deflections based on the assumption of the theory of linear elasticity. This paper presents a method to back calculate layer moduli in dynamic domain such that the histories of both measured and calculated responses corresponding to the impulsive force coincide. Pavement is modeled by an axisymmetric linear elastic system. FEM is utilized coupled with Ritz vector to reduce a matrix and thus to improve computational efficiency. The backcalculation algorithm used is the Gauss-Newton method coupled with a truncated singular value decomposition.

DYNAMIC BACKCALCULATION OF PAVEMENT STRUCTURE USING MULTIPLE SETS OF TIME-SERIES DATA

Backcalculation analysis is generally greatly affected by errors in the measured deflection data. An average of multiple deflection data sets corresponding to a standard load is normally used in static backcalculation in order to reduce the effects of these errors. However, this procedure can not be applied in case of time series data. A rather time consuming procedure is used, where backcalculation is performed using each deflection data set and then an average of the backcalculated pavement layer properties is determined. This paper proposes a new method where multiple sets of time series data can be used simultaneously in dynamic backcalculation to determine an average result. Computation time is similar to the case of one data set. Domain of analysis and the number of nodes are also examined.

COMPARATIVE STUDIES OF BACKCALCULATED RESULTS FROM FWDS WITH DIFFERENT LOADING DURATION

The falling weight deflectometer (FWD) test applies an impulsive force on the surface of pavement and measures surface deflections at several locations. FWDs produced at different manufacturers often differ in loading duration. The difference may affect backcalculation results because the FWD test is dynamic in nature, This paper investigates the effect of the difference on backcalculated layer moduli.

Influence of Seed Layer Moduli on Finite Element Method-Based Modulus Backcalculation Results

The determination of pavement layer moduli from falling weight deflec-tometer test data is known as backcalculation analysis. Generally, back-calculation analysis is unstable—greatly influenced by several causes of error. They may be categorized as modeling error in the forward analysis, deflection measurement error, or numerical computation error due to instability in the backcalculation procedure, for example. Because of these problems, the seed values selected for layer moduli greatly influence backcalculation results. To reduce the effects of measurement error, truncated singular-value decomposition is used for regularization. Variable scaling, often used in optimization algorithms, is implemented to improve numerical accuracy. A Ritz vector reduction method is used to solve a large system of dynamic equations in dynamic backcalculation efficiently, and various other means are introduced to decrease computational time. Recent updates of Dynamic Back Analysis for Layer Moduli software, first developed ...

DOMAIN OF ANALYSIS OF ELASTIC MULTILAYER SYSTEM MODELED BY FEM

Analysis of pavement structure is modeled by FEM. Results of analysis may be affected by the size of domain of analysis because FEM analysis is conducted in a limited domain instead of half-space domain. This paper investigates the proper size of analysis of FEM analysis. Backcalculating pavement layer moduli from FWD tests is based on a static analysis of impulse-type pavement response. This paper also investigates how factors such as loading time and loading pattern affect surface deflections.

Structural Optimization Under Complicated Loading

Authors will present a method to find an optimum design of structures under the condition of force free to change its direction. Furthermore the method is extended to the case of multiple forces allowed to move their directions. On top of finding optimum design, the method can obtain a set of the most unfavorable force direction. Design requirements considered are bounds on tensile and compressive stresses, buckling stress and displacement.