Analysis Of Large Structural Systems Research Articles

A systematic wave-based method for analysis of large planar frame structures based on Timoshenko waveguide theory

This paper presents a new hybrid analytical/numerical systematic approach for continuous modeling of wave propagation in planar structural systems. To do so, a structure is considered as a number of waveguide elements that are connected to each other through different types of discontinuities. The wave propagation in waveguides is modeled using advanced Timoshenko beam theory to account for the rotary inertia, which provides accurate results for high-frequency excitations. The refraction matrices for different types of discontinuities such as change of material and cross section, various types of boundary conditions, and two- and three-member joints are presented using the existing literature, and the refraction matrices for a right-angled four-member joint is derived analytically for the first time. To provide a robust methodology for the analysis of large structural systems, a general new assembly procedure is introduced that is capable of assembling all of the propagation and refraction matrices in a single global system matrix. To insure the validity of the proposed methodology, detailed numerical examples are provided and their results are verified with finite element numerical method.

Reliability analysis of large structural systems

Brute force Monte Carlo simulation methods can, in principle, be used to calculate accurately the reliability of complicated structural systems, but the computational burden may be prohibitive. A new Monte Carlo based method for estimating system reliability that aims at reducing the computational cost is therefore proposed. It exploits the regularity of tail probabilities to set up an approximation procedure for the prediction of the far tail failure probabilities based on the estimates of the failure probabilities obtained by Monte Carlo simulation at more moderate levels. In this paper, the usefulness and accuracy of the estimation method is illustrated by application to a particular example of a structure with several thousand potentially critical limit state functions. The effect of varying the correlation of the load components is also investigated.

Stochastic analysis of large structural systems under fully non-stationary input

Dynamic analysis of large linear systems is usually performed adopting the well-known modal analysis along with modal truncation of higher modes. However, in the case in which the contribution of higher modes is not negligible, modal correction methods have to be introduced to improve the accuracy of the dynamic response either in the case of deterministic or stochastic excitation. Aim of this paper is to propose a new computationally competitive method for the stochastic analysis of large linear system vibrating under fully non-stationary Gaussian excitations. The method is based on the extension of the mode-acceleration method and its variant, the stochastic mode-acceleration method, for the evaluation of the non-geometric spectral moments of the non-stationary response. Numerical results from the study of a large MDoF structure show the accuracy and the efficiency of the proposed technique.

Combined Approximations for Efficient Probalistic Analysis of Structures

Real-life analysis and design problems involve uncertainties. Quantification of the uncertainties in a system's response is important and requires a probabilistic analysis of the system. A main challenge in probabilistic analysis of large structural systems is the high computational effort due to the multiple repeated analyses involved. The combined approximations (CA) method, which combines the strengths of both local and global approximations, can be used for efficient probabilistic analysis of structures. The CA method is a combination of binomial series (local) approximations (also called Neumann expansion approximations) and reduced basis (global) approximations. An efficient method is presented for probabilistic analysis of structural systems using the CA method. The effectiveness of this method is demonstrated on analysis of mistuned bladed disk assemblies and systems with progressive collapse using Monte Carlo simulation. It is shown that the method can predict accurately the probability distribution function of the responses of these systems at a considerably lower cost than a method using finite element analysis in each cycle of Monte Carlo simulation.

Fast Transient Analysis for Locally Nonlinear Structures by Recursive Block Convolution

The transient analysis of large structural systems with localized nonlinearities is a computationally demanding process, inhibiting dynamic redesign and optimization. A previously developed integral equation formulation for transient structural synthesis has demonstrated the ability to solve large locally nonlinear transient problems in a fraction of the time required by traditional direct integration methods, with equivalent or better accuracy. A recursive block-by-block convolution algorithm is developed for the solution of the governing integral equation that further reduces the solution time required. A computing time comparison of single-block versus multiple-block solutions is provided.

Use of Special Ritz Vectors in Dynamic Substructure Analysis

A numerical method is presented for the dynamic response analysis of large structural systems that are modeled as substructures. The method is similar to the component mode synthesis technique; however, the generation of the substructure modes is very efficient since the eigenvectors of the substructures are not evaluated. In addition, the characteristics of the loading are used in the algorithm, which can result in improved accuracy with the use of fewer vectors. The purpose of the method is to efficiently evaluate the dynamic displacements and forces within complex structures subjected to a particular type of loading. The technique does produce approximate modeshapes and frequencies; however, this is not the basic purpose of the method. The efficiency and accuracy of the method has previously been demonstrated for the direct dynamic analysis of complete structures. In this paper the method is extended to systems of substructures in which local substructure Ritz vectors are used to reduce the number of d...

Rate‐Type Concrete Creep Law with Reduced Time

For creep analysis of large structural systems, the linear aging integral‐type creep law needs to be converted to a rate‐type form which consists of a system of first‐order linear differential equations with age‐dependent coefficients. The system may be visualized by the Kelvin chain model with age‐dependent elastic moduli and viscosities. In the existing formulation, the independent variable is actual time. It is shown that, by using as the independent variable a certain reduced time which increases with time at a gradually declining rate, one reduces the number of differential equations needed to describe creep within the given time range, thereby making numerical structural analysis more efficient. An algorithm for identifying the material parameters from given creep data, based on minimization of a sum of squared deviations, is also presented. Thermodynamic restrictions on the material coefficients are analyzed. Finally, the capability of closely approximating available creep data is demonstrated.

Weekly singular integral for creep rate of concrete

Despite decades of intensive research, an entirely satisfactory constitutive relation for creep in concrete is still unavailable, even for working stress levels [I]. The rate-type creep laws with internal variables [2], although rather effective for numerical creep analysis of large structural systems, seem to be incapable of describing the aging phenomena without at least partially violating some thermodynamic requirements [2]. This suggests that, for a complete description of creep in concrete, an integral-type law might be inevitable.

Dynamic analysis of large structural systems with local nonlinearities

In many types of structures that exhibit significant nonlinearity during dynamic response the nonlinear stiffness property is confined to a few predetermined localities. This physical characteristic may be exploited by making use of substructure concepts in the dynamic response analysis. The elastic components may be represented by a small matrix of stiffness coefficients coupling them to the nonlinear elements, and only the properties of the few nonlinear elements need be modified during the response analysis. Both direct and indirect techniques for taking advantage of localized nonlinearity are reviewed here. In the direct methods the equations of motion are integrated by step-by-step procedures. Various methods of reducing the effective number of degrees of freedom are discussed. In the indirect methods the response to simple loadings is determined, and the response to the prescribed loading is obtained by superposition. A technique for applying superposition to the linear portion of the structure while treating the nonlinear region by a step-by-step procedure is described.

Computation of age-dependent relaxation spectra

A computer algorithm for the computation of discrete age-dependent relaxation spectra of concrete from creep or relaxation test data is presented and a full FORTRAN IV listing is given. The algorithm is base on a previously outlined method, consisting in the expansion of relaxation curves in series of real exponentials on the basis of a least square criterion. This method is refined herein by imposing suitable smoothing conditions upon the spectra in order to reduce spurious sensitivity of results to small changes in given creep data. Two variants are given; in one the spectrum is approximated as a cubic polynomial in the logarithm of age and the logarithm of the relaxation time, while in the other one a cubic polynomial in the logarithm of age alone is used. Numerical examples show that given smooth creep data can be recovered from the spectra with a negligible error, which demonstrates that the spectra fully characterize creep properties. Apart from being a fundamental characteristic of creep, the relaxation spectra convert a hereditary creep law into a history independent rate-type form, which is requisite for creep analysis of large structural systems.

Dynamic Analysis of Large Structural Systems

The techniques used in predicting the time history response of structural systems subjected to a dynamic environment have seen major modifications in the last 10 years. The increased capabilities of digital computers have been the impetus for improved numerical techniques and computer codes. Direct decomposition methods for the solution of linear equations have replaced iterative techniques like relaxtaion and Gauss-Seidel. Eigenvalue and eigenvector extraction methods like inverse iterations, Q/R, L/R, and A/P have received a great deal of attention, and many standard computer codes utilizing these methods are available. The present generation of computers offers the user a large variety of hardware and software options. The CDC 6600 with a 60-bit word and 130 000 core words is an ideal machine for large dynamics analysis programs, while the IBM-360 series with a 32-bit word size is inadequate and double precision must be used. Computer programs such as STARDYNE, NASTRAN, SAMIS, and SRUDL are capable of solving dynamic structural problems with thousands of degrees of freedom. It is important for the analyst to understand their capabilities and shortcomings in order to make effective use of them.

Computer analysis of large structural systems.

Numerical procedure for structural systems analysis, discussing computer application to hydrodynamic, electric, magnetic, thermodynamic, elastostatic and elastodynamic problems

The Analysis of Large Structural Systems

The Analysis of Large Structural Systems