Moving Wheel versus Impact Deflections and Their Use in Pavement Evaluation

Traffic speed deflection devices (TSDDs) have been developed since around 2000 to allow for safe and efficient structural evaluation of highway networks. One barrier to TSDD implementation is the inherent differences in deflections produced by moving truck loads and by falling weight deflectometer (FWD), the current deflection testing standard. To better understand the differences in data produced by the two devices, FHWA sponsored research into one particular TSDD, the rolling wheel deflectometer (RWD). The study utilized the finite layer program ViscoWave to model both FWD and RWD loads to demonstrate the effect of their inherent differences on pavement deflections and other simulated parameters. In addition, ViscoWave was used to generate theoretical FWD and RWD deflections for a diverse set of pavement structures and subgrade conditions. The resulting deflections were used to develop correlations between the two devices, which were validated with side-by-side FWD and RWD field tests performed on 23 sites. The research determined that the differences between FWD and RWD deflections vary depending on pavement factors and loading characteristics. The two devices produced similar deflections on thicker, stiffer, lower-deflection pavements, while the FWD produced relatively higher deflections on thinner, weaker, higher-deflection pavements. Therefore, use of common FWD data analysis programs will produce different results, such as layer moduli, for TSDD devices. Advanced analysis routines capable of modeling the TSDD’s moving load and loading configurations are needed.

Phát triển chương trình tính toán kết cấu mặt đường nhựa theo phương pháp phân lớp hữu hạn

Phương pháp phần tử hữu hạn (FE) đã được sử dụng rộng rãi trong việc mô phỏng và dự báo sự xuống cấp của kết cấu mặt đường nhựa. Tuy nhiên, mô hình khối ba chiều (3D) trong các hệ thống phần mềm thương mại như ABAQUS hay phần mềm mã nguồn mở như Cast3M đòi hỏi tài nguyên và thời gian tính toán lớn. Để giải quyết vấn đề này, các mô hình đơn giản hóa được quan tâm phát triển cho các mục tiêu cụ thể. Trong nghiên cứu này, lý thuyết cơ bản về phương pháp phân lớp hữu hạn (Finite Layer Method) được trình bày và là cơ sở phát triển mã nguồn FastKM bằng ngôn ngữ lập trình Python và giao diện người dùng cho phép mô phỏng bài toán kết cấu mặt đường nhựa nhiều lớp. Kết quả nhận được là đồ thị và biểu đồ màu thể hiện chuyển vị, ứng suất, biến dạng của kết cấu. Tiếp đó, một kết cấu mặt đường nhựa điển hình được mô phỏng trên 3 phần mềm là CAST3M, ABAQUS và FastKM theo với 3 phương pháp phân tích khác nhau là LET (Layer Elastic Theory), FEM (Finite Element Method) và phân lớp hữu hạn FLM (Finite Layer Method) nhằm kiểm chứng tính chính xác cũng như so sánh thời gian tính toán giữa các mô hình. Phần mềm FastKM sử dụng phương pháp FLM cho kết quả chính xác tương đương với mô hình phần tử hữu hạn 3D trên Abaqus và thời gian tính toán nhanh hơn hai phương pháp còn lại.

INJECTION OF SULFUR DIOXIDE IN A FINITE LAYER, INITIALLY SATURATED WITH METHANE AND WATER

Based on the presented mathematical model, the process of injection of liquid sulfur dioxide into a reservoir of finite length initially saturated with methane and water, accompanied by the formation of sulfur dioxide gas hydrate, is studied. It is shown that the process of formation of sulfur dioxide gas hydrate at certain values of the temperature of injected sulfur dioxide and the permeability of the formation can be accompanied by the formation of a zone saturated with methane and its gas hydrate. The influence of formation parameters and injected sulfur dioxide on the features of the process offormation of gas hydrate is studied. It is shown that if the formation of sulfur dioxide hydrate is accompanied by the formation of a zone containing methane and its gas hydrate, then this region degenerates over time into the frontal surface of the phase transition. A critical diagram is constructed that separates these two modes.

Model of Soil-structure Interaction of Objects Resting on Finite Depth Soil Layers for Seismic Design

In case of seismic design of structures the deformability and damping of the soil should be considered, which can be performed in several ways. The infinite soil half space can be approximated with the cone model, which gives constant values for the spring stiffnesses and dashpot characteristics, and an additional mass element for rocking motion. To approximate the dynamic impedance function of a soil layer more complex models were also applied. Most of the methods do not take into account the finite dimensions of the soil, which results significantly different behavior than spring-dashpot systems. To consider the effect of a finite layer a new simple model based on a physical approach is given for the horizontal excitation of strip foundations. Numerical verification is presented, and the parameter range is determined, where the application of the new model is recommended, since applying a spring-dashpot model results in significant errors.

Thermoelastic Stress and Deformation Analyses of Functionally Graded Doubly Curved Shells

In this paper, the authors develop Reissner’s mixed variational theorem (RMVT)-based finite layer methods for the three-dimensional (3D) coupled thermoelastic analysis of simply supported, functionally graded, doubly curved (DC) shells with temperature-independent material properties. A two-phase composite material is considered to form the shell, and its material properties are assumed to obey a power–law distribution of the volume fractions of the constituents through the thickness direction of the shell. The effective material properties are estimated using the Mori–Tanaka scheme. The accuracy and convergence rate of these RMVT-based finite layer methods are validated by comparing their solutions with the quasi 3D and accurate two-dimensional solutions available in the literature.

On the Refined Conjectures on Fitting Ideals of Selmer Groups of Elliptic Curves with Supersingular Reduction

In this paper, we study the Fitting ideals of Selmer groups over finite subextensions in the cyclotomic $\mathbb{Z}_p$-extension of $\mathbb{Q}$ of an elliptic curve over $\mathbb{Q}$. Especially, we present a proof of the “weak main conjecture” à la Mazur and Tate for elliptic curves with good (supersingular) reduction at an odd prime $p$. We also prove the “strong main conjecture” suggested by the second named author under the validity of the $\pm $-main conjecture and the vanishing of a certain error term. The key idea is the explicit comparison among “finite layer objects”, “$\pm $-objects”, and “fine objects” in Iwasawa theory. The case of good ordinary reduction is also treated.

Who Says Backcalculation Is Only about Layer Moduli?

In this study, an existing finite layer algorithm for dynamic analysis of pavement structure was enhanced to incorporate the nonlinear behavior of unbound pavement materials. The nonlinear (stress-dependent) modulus was approximated in the vertical direction, which is similar to the approach used with multi-layered elastic and viscoelastic analysis methods for incorporating material nonlinearity. First, the enhanced finite layer algorithm was used to backcalculate the layer thickness, unit weight, Poisson’s ratio, and damping ratio in addition to the linear (viscoelastic and elastic) modulus of all layers. Then, the parameters backcalculated from the linear analysis were used to estimate the seed values for the subsequent nonlinear analysis in which the stress-dependent moduli of the unbound layers were backcalculated. Deflection data from two field sections (with thick and thin asphalt concrete layer) were used for demonstration. The results showed excellent agreement between the measured and backcalculated deflection time histories. In addition, it was found that the use of backcalculated parameters for the thickness, unit weight, Poisson’s ratio, and damping resulted in lower errors for both the linear and nonlinear analyses. Furthermore, the results of the backcalculation indicated that the material nonlinearity was more pronounced for the thin pavement, in which case the backcalculation error may be reduced further by incorporating the stress-dependent modulus.