Dimitris C. Rizos

Coupled BEM-FEM solutions for direct time domain soil-structure interaction analysis

Abstract A coupled BEM–FEM methodology is presented for 3D wave propagation and soil–structure interaction analysis in the direct time domain. The employed boundary element method (BEM) uses a new generation of the Stokes fundamental solutions that utilize the B-Spline family of polynomials. A standard finite element methodology for dynamic analysis along with direct integration in time is coupled to the BEM through a staggered solution approach. Each method provides initial conditions to the other at the beginning of each time step. Formulation and computational aspects of the proposed coupling scheme are discussed. A number of numerical examples are presented for the validation and demonstration of the general nature of the proposed methodology.

An advanced direct time domain BEM formulation for general 3-D elastodynamic problems

A new advanced time domain BEM formulation is presented for the study of general 3-D elastodynamic problems. The proposed method is based on the infinite space Stokes fundamental solutions, which, for the first time, are written in terms of body forces in the form of higher order B-spline time distributions. Higher order spatial and temporal discretization schemes are applied to the boundary integral equations of the elastodynamic system yielding a time marching solution for the characteristic response of the system due to an excitation with a B-spline distribution in time. This characteristic response due to a B-spline excitation forms the basis, within the framework of a general B-spline superposition scheme, for the calculation of the responses of the same elastodynamic system due to any transient forcing function.

Simulation of earthquake ground motions by a deterministic approach

Abstract A numerical method is presented for the computation of artificial earthquake records consistent with any arbitrarily specified target response spectra or power spectral density requirements. The proposed algorithm does not create new time histories but rather modifies, on the basis of an iterative deterministic approach, existing records to fit specific design requirements. The efficiency of the algorithm and the accuracy of the fitting process are substantially improved on the basis of a predictor–corrector type approach. The associated integrated computer code can, among its many other features, produce artificial earthquake records consistent with a number of compatible target response spectra at various damping levels, perform quadratic baseline correction, and calculate correlation factors for up to three earthquake records.

Transfer Length Probabilistic Model Updating in High Performance Concrete

A High Strength Reduced Modulus High Performance Concrete (HSRM-HPC) is being developed for the construction of railroad ties. This new material has the potential to produce ties with a longer life span than those built from traditional concrete because the reduced Young’s modulus could avoid stress concentrations. Railroad ties are commonly fabricated as prestressed concrete elements. The transfer length is an important parameter on these structural elements because the rail is placed toward the ends of the element. This paper uses Bayesian model updating to infer the transfer length with limited experimental data from a test performed in one prestressed beam. The material characteristics, experimental setup, and transfer length model are described in detail. Results show histograms of the transfer length obtained from the models considered.

Finite Element Model of High Strength Reduced Modulus High Performance Concrete

High Performance Concrete (HPC) with early strength development is the material of choice in the fabrication of prestressed concrete railroad ties. The higher strength of HPC results in significantly higher values of the Elastic Modulus and increases the brittleness and the rigidity of the material, leading to premature cracking and the deterioration of the railroad ties. A High-Strength Reduced-Modulus High Performance Concrete (HSRM-HPC) material has been developed by the authors and used in the fabrication of prototype concrete ties. Detailed models based on the Finite Element Method of the HSRM-HPC have been developed to simulate the ASTM-C469 tests for elastic modulus. The HSRM-HPC constituent materials, i.e. aggregates and cement mortar, have been explicitly modeled and assigned properties determined experimentally. Aggregates size and distribution is modeled using a combination of probabilistic distributions consistent with the results of an experimental sieve analysis. Details of the development of each model are discussed. The models are verified with experimental data. Assessment studies have been performed in order to optimize the models with respect to efficiency, the quality of the results and computational times.Copyright

Time Domain B-Spline BEM Methods for Wave Propagation in 3-D Solids and Fluids Including Dynamic Interaction Effects of Coupled Media

This chapter summarizes the theoretical developments of the author’s research team during the last 15 years in the area of a new family of direct time domain Boundary Element Methods that are based on the B-Spline fundamental solutions for wave propagation in solid and fluid media, and the resulting methodologies for solving problems involving dynamic interaction of coupled media. Special element types have been developed to accommodate rigid assemblages and fluid-solid interfaces and are summarized herein. Coupling procedures of the proposed BEM methods with the FEM are also outlined. A number of examples reported in the literature by the author and his coworkers are included at the end of the chapter.

Estimating Net Changes in Life-Cycle Emissions from Adoption of Emerging Civil Infrastructure Technologies

Abstract There is a net emissions change when adopting new materials for use in civil infrastructure design. To evaluate the total net emissions change, one must consider changes in manufacture and associated life-cycle emissions, as well as changes in the quantity of material required. In addition, in principle one should also consider any differences in costs of the two designs because cost savings can be applied to other economic activities with associated environmental impacts. In this paper, a method is presented that combines these considerations to permit an evaluation of the net change in emissions when considering the adoption of emerging technologies/materials for civil infrastructure. The method factors in data on differences between a standard and new material for civil infrastructure, material requirements as specified in designs using both materials, and price information. The life-cycle assessment approach known as economic input-output life-cycle assessment (EIO-LCA) is utilized. A brief background on EIO-LCA is provided because its use is central to the method. The methodology is demonstrated with analysis of a switch from carbon steel to high-performance steel in military bridge design. The results are compared with a simplistic analysis that accounts for the weight reduction afforded by use of the high-performance steel but assuming no differences in manufacture.

Software Development for Berthing Analysis and Structural Loading on Waterfront Facilities

Accurate and efficient determination of fender forces during berthing maneuvers is of prime interest in the naval industry. The physical problem involves dynamic interaction of fluids and structures within moving frames of reference and is nonlinear by nature. While rigorous models based on Finite Element analysis show superior accuracy, they are computationally expensive and are not suitable for production type activities. Impulse response techniques of the linearized system have shown acceptable accuracy as compared to experimental measurements. This work discusses the software BeAn, which is suitable for the calculation of fender forces and vessel motion during berthing operations. The solution methodologies are briefly introduced, the structure of the software is discussed and validation of the software is presented. Applications of the software have demonstrated its efficiency, versatility, speed and ease of use. These attributes make BeAn and ideal tool for production type activities.