Elisa D. Sotelino

Effect of transition zone on elastic moduli of concrete materials

Abstract This paper proposes a composite model for evaluation of the elastic moduli of concrete materials. Concrete or mortar is assumed to have three phases, namely: aggregate, matrix and transition zone. Analytical solutions for effective elastic moduli of the proposed composite model are presented. The effect of the elastic moduli and volume fraction of the transition zone on overall elastic moduli of concrete or mortar is investigated. A procedure is also suggested to determine the elastic moduli of the transition zone knowing the overall elastic moduli of concrete or mortar.

An object-oriented programming framework for the parallel dynamic analysis of structures

Abstract This work addresses the time history analysis of structures subjected to dynamic loads using high performance computing environments. Structural mechanics, parallel computing, and object-oriented programming methodologies are integrated to design and implement frameworks for parallel and sequential transient finite element analysis ( TFE++ and PTFE++ ). The object-oriented approach is employed to facilitate extensibility, reusability, maintainability and simplicity of the resulting software. Parallel processing concepts and algorithms are used in the design of PTFE++ . An application has been developed to demonstrate the developed frameworks. It has been found that PTFE++ provides an efficient way to analyze large structural systems.

Fiber Heat Transfer Element for Modeling the Thermal Response of Structures in Fire

This paper introduces a novel type of heat transfer finite element that can be used to model the three-dimensional thermal response of structural beams and columns subjected to elevated temperatures associated with fire. The element is a three-node heat transfer element that uses a fiber discretization to account for both transverse and longitudinal temperature variations in a structural member. This fiber heat transfer element is purposely formulated to be compatible with any fiber beam-column finite element in a sequentially coupled thermal-mechanical analysis of a structural frame subjected to fire. The element is implemented in ABAQUS using a user-defined element subroutine. To demonstrate the capabilities of the fiber heat transfer element, analyses are performed on members with various types of thermal boundary conditions. Results indicate that the fiber heat transfer element offers excellent accuracy with minimal computational expense, making the fiber heat transfer element a valuable tool for modeling the behavior of frame structures in fire.

Distributed finite element computations using object-oriented techniques

An object-oriented parallel finite element framework has been developed to facilitate rapid prototyping of a wide variety of parallel finite element computations. Parallel computing and object-oriented technologies are integrated to achieve efficiency in both computation and software development. The paper presents various reusable and extensible components that constitute the parallel finite element architecture.

The generalized method for structural dynamics applications

A new single-step time-integration method for solving structural dynamics problems, termed generalized method, has been developed. Most of the existing single-step solution algorithms are special cases of this method. The derivation of the generalized method starts with the Taylor series approximations of the displacement, velocity, and acceleration between two time-stations. Equilibrium is satisfied in a weighted-average sense over the time-step by means of a weak form of the Galerkin procedure. The displacement, velocity, and acceleration are updated using the truncated Taylor series expressions. Numerical tests have been carried out to demonstrate the validity of the developed method.

A message-passing class library C++ for portable parallel programming

An object-oriented message-passing class library in C++, called PPI++, for portable parallel programming has been developed. PPI++ (parallel portability interface in C++) is designed to serve as a stable (unchanging) interface between the client parallel code and the rapidly evolving distributed computing environments. By taking advantage of encapsulation, inheritance, and polymorphism supported by C++, PPI++ provides a clean and consistent programming interface, which helps improve the clarity and expressiveness of client parallel codes and hides implementation details and complexity from the user to ease parallel programming tasks. In addition, the use of strong type-checking in C++ allows the detection of potential misuses of the library at compile time, and thus promotes code reliability. This paper describes the object-oriented design and implementation of PPI++. Evaluation of PPI++ on important performance issues, such as portability, ease-of-use, extensibility, and efficiency, is also discussed.

A Parallel Matrix Class Library in C++ for Computational Mechanics Applications

The object–oriented design and implementation of a matrix class library in C++ for parallel computing is described. The main goal of this library is to support the management of matrix data in a distributed environment and the parallel solution of linear systems of algebraic equations typical of computational mechanics applications. By using the object–oriented paradigm, a clean and consistent interface to the library is provided, and the implementation details are hidden from the user. These features improve the clarity and expressiveness of the client code and consequently ease the task of parallel programming. The library was developed and tested originally using a network of Sun Sparc 10 workstations. Test examples subsequently were run on the Intel Paragon XP/S. In these examples, the portability of the library among different distributed environments was demonstrated, and some preliminary performance studies of the library were carried out. Finally, the utilization of the class library in parallel finite–element computations is discussed. It is shown that the present library greatly simplifies the implementation of matrix operations intrinsic to parallel finite–element applications.

A concurrent explicit-implicit algorithm in structural dynamics

Abstract A concurrent explicit-implicit algorithm for time integration of the differential equations arising from a finite element discretization is described. The first step of the method consists of partitioning the finite element mesh into subdomains. As a consequence of this partition, the nodes in the resulting mesh form two distinct sets: interior nodes and interface nodes. Once these sets of nodes are identified, the method proceeds by integrating the interface nodes explicitly, and the interior nodes implicitly. Since the interior nodes in a specific subdomain are not shared by any other subdomain, they can be integrated independently. As a direct consequence, concurrency is introduced. Thus, this method is very well suited for implementation in parallel computers. In addition to this feature, the concurrent explicit-implicit algorithm is also expected to speed up computations, even on a sequential computer, by reducing the equation solving effort. Some considerations on the conversion of an originally sequential finite element analysis program to implement this method is given. Numerical examples are presented to illustrate the method.

Analysis of Steel Structures in Fire with Force-Based Frame Elements

This paper considers the extension of the force-based element formulation to simulate the nonlinear, temperature-dependent response of structural frames exposed to fire. The two-dimensional formulation presented here accounts for thermal expansion, temperature-dependent material properties, and residual stresses. The element utilizes a fiber discretization to simulate the gradual plastification of the section. Geometric nonlinearities are included through coordinate transformations of the corotational reference frame. Analyses of benchmark experimental tests demonstrate that the force-based element formulation is computationally stable and provides accurate results for structures exposed to fire. In addition, comparisons to traditional displacement-based elements indicate that the force-based element may offer improved computational efficiency because fewer elements are needed per member.

Object-oriented parallel programming tools for structural engineering applications

Abstract The principal objective of this work is to develop portable and extensible programming tools for the development of object-oriented parallel finite element codes for structural engineering applications. An object-oriented parallel portability interface for message-passing operations has been designed and implemented. An existing object-oriented matrix library is currently being extended to support the management of distributed matrix data and parallel solution of linear systems of algebraic equations. By taking advantage of C++ object-oriented programming, both the class libraries provide clean and consistent user interfaces, which not only help to improve the clarity and expressiveness of the client parallel codes, but also hide implementation details and complexity from the user to ease parallel programming tasks. In this paper, the object-oriented design and implementation of the class libraries are discussed. The libraries were first developed and tested using a network of Sun SPARC 10 workstations. Application examples were then studied on two commercial parallel computers: the IBM SP1 and the Intel Paragon XP/S 10, for evaluation of the portability and efficiency of the present class libraries.