Browsing by Subject "slab-on-grade"

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    Dynamic Analysis of Slab-on-Grade Systems: Forward and Backcalculation Analyses
    (2017-12) Booshehrian, Abbas
    The problem of calculating the response of a slab-on-grade is of interest for analysis and design of industrial floors, nuclear plants, mat and raft foundations, and pavement systems. These structures are often subjected to complicated external dynamic excitations such as earthquakes, impacts, and moving loads, resulting in a challenging load-structure system to simulate. For design and evaluation purposes, deflection-based non-destructive testing such as falling weight deflectometer (FWD) is often utilized to obtain the design properties of these structures. Typically, this is done in two stages: I) forward analysis in which a mathematical model is used to generate the response of the system to a known FWD load, given the structural properties, and II) inverse analysis (a.k.a. backcalculation) in which a numerical scheme is used to indicate the structural properties, given the response of the system to the known FWD load. The objective of this study was to develop a computational method based on the plate-ona-foundation approach to model and characterize the slab-on-grade structures subjected to a short-duration dynamic axisymmetric pressure induced by FWD. The advantage of this approach is that it is simple, efficient, and applicable to both elastic and viscoelastic slabs. Furthermore, this approach is compatible with the recently-developed analysis which estimates the excess vehicular fuel consumed due to the viscous deformation of the pavement under the moving load. Thereby, in addition to the applications for the design and analysis of structures, the backcalculated properties may be employed as inputs for realistic evaluation of the environmental impacts caused by the additional fuel use. To do so, an efficient numerical forward-solution in the time-domain was developed for the response of a thin and infinite viscoelastic Kirchhoff-Love plate resting on a foundation by making use of a Hankel transform in space and a finite difference method in time. Then, the shortcomings of the traditional foundation models, such as the Winkler, Pasternak, and Vlasov models, in capturing the dynamic behavior of the system were highlighted, and required modifications were made. Next, a gradient-based optimization scheme was employed in conjunction with the forward-solution to develop a fast and reliable dynamic backcalculation. To showcase the ability and applications of the developed analysis, multiple case studies were carried out using the data recorded by the FWDs tested on asphalt and concrete pavements. Finally, the traditional Vlasov foundation model was modified accordingly to accommodate the dynamics of the structure. This reinforced the analysis with the ability to characterize the foundation in addition to the top slab.