Yutaka Toi

Analysis of structurally discontinuous reinforced concrete building frames using the ASI technique

Abstract The Adaptively Shifted Integration (ASI) technique, which produces the highest computational efficiency in the finite element analyses of framed structures including static and dynamic collapse problems, is applied to structurally discontinuous problems of reinforced concrete building frames. A new numerical scheme based on the updated Lagrangian formulation (ULF) adaptation of the ASI technique is developed, by modeling the fracture of a section by a plastic hinge located at the exact position with a simultaneous release of resultant forces in the element. By using the algorithms described in this paper, the analyses became possible even by the conventional displacement-based finite element codes, and sufficiently reliable solutions for practical use have been obtained in the explosive demolition and seismic damage analyses of a five storied, five span RC building frame. The present technique can be easily implemented with minimum effort into the existing finite element codes utilizing the linear Timoshenko beam element.

Thermal Elasto-Viscoplastic Damage Behavior of Structural Members in Hot-Dip Galvanization

Continuum damage mechanics is applied to the prediction of the initiation of cracks on structural members in hot-dip galvanization. The elastoviscoplastic constitutive equation considering damage, in which most material parameters are temperature-dependent, is employed in the three-dimensional finite element analysis of the structural behavior in hot-dip galvanization. The material constants concerning damage are determined by the comparison of the finite element solutions with the bending test results for the stiffened plates in molten zinc in order to consider the effect of zinc-embrittlement of the material. Numerical study is conducted for the possibility of cracking near the holes for bolts on pylon members in hot-dip galvanization.

Finite element analysis of quasi-static and dynamic collapse behaviors of framed structures by the adaptively shifted integration technique

The adaptively shifted integration technique (abbreviated to the ASI technique) is applied to the dynamic collapse problems of framed structures including the quasi-static collapse under repeated loading. The unloading of materials plays an important role in these behaviors. In the present analysis using cubic beam elements, the reshifting of the integration points to the Gaussian points in the unloaded elements is conducted in order to attain higher accuracy for the material-unloading behavior. The solutions given by conventional method, the ASI technique with and without reshifting are compared to show the validity of the newly proposed computational algorithm.

Damage mechanics models for brittle microcracking solids based on three-dimensional mesoscopic simulations

Abstract Fracture behaviors of brittle polycrystalline solids such as ceramic materials are deeply related to microcracking. Continuum damage mechanics is considered a powerful theoretical framework to deal with brittle microcracking solids. However, it is fairly difficult to obtain analytically, as well as experimentally, evolution equations for microcracking and reduced elastic compliances of microcracked solids. In the present study, a three-dimensional mesoscopic simulation method using a discontinuum mechanics model is employed to obtain this information. Based on the results of mesoscopic simulations, improved damage mechanics models assuming anisotropy as well as isotropy are proposed. Some numerical studies have been conducted to confirm their validities.

Finite element crush analysis of framed structures

Abstract The present study is concerned with the development of a finite element algorithm for crush analysis of three-dimensional framed structures under quasi-static loading and its experimental verifications. Details of the incremental formulation by the updated Lagrangian approach is described, in which the linear Timoshenko beam element is employed with the shifted integration technique and with the elasto-plastic constitutive equation expressed in terms of resultant forces. The strain-hardening and the frictional contact are also taken into account in the present analysis. The results of finite element analyses are compared with the crush test results conducted for beams, columns and framed structures.

Discrete limit analysis of plate and shell structures

Abstract The Rigid Bodies-Spring Models previously proposed by the second author are applied to nonlinear analysis of general thin-walled structures. Both material and geometrical nonlinearities are taken into consideration in the analysis. Several numerical examples are shown in order to verify the validity of the present method.

A discrete method of limit analysis and its application to plastic stability problems of structural members

Abstract A method of discrete limit analysis which was proposed by Kawai in 1976 is extended to study structural behaviour of a set of solid blocks at the ultimate state of loading where the effect of finite rotation of these blocks should be taken into account. It is shown that Shanleys theory of plastic buckling can be simply demonstrated by using the present discrete models.

Development of Damage Assessment Method for Steel Structures Using Material-Structure Coupling Analysis

Once assessment of material failure characteristics is captured precisely in a unified way, it can be directly incorporated to the structural failure assessment under various loading environments, based on the theoretical backgrounds so called Local Approach to Fracture. The aim of this study is the development of an expert system applicable for the assessment of structural integrity throughout crack initiation and structural failure based on the Local Approach to Fracture. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, was developed and employed in the 3-D FEA code in order to numerically evaluate the material and/or structural responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations for each material, was implemented in an automatic system using genetic algorithm based on an inference system. The material constants selected from genetic search and constitutive equations are used directly in the failure assessment of material and/or structures. The performance of the developed system has been evaluated for the S-N relationship assessment of several materials as well as the crack initiation assessment of various weldments in steel structures.

Finite element crush analysis of structural components and experimental validations

The application of the non linear finite element method to the crushing problem for structural components and experimental validation is described. Lower order finite elements based on the reduced integration technique are employed with the updated lagrangian formulation in the developed computer codes. The tube components are analyzed under the following loading conditions: (i) circular tubes under lateral compression, (ii) square tubes under lateral compression, (iii) toroidal shells under lateral compression, (iv) circular tubes under axial compression, (v) square tubes under axial compression, (vi) circular tubes under lateral loading. The numerical results are compared with the results of the crush tests conducted by the authors (a).

Coupled Analysis of Induction Hardening Considering Induction Heating, Thermal Elasto-viscoplastic Damage, and Phase Transformation

The coupled computational procedure of the induction heating, the thermal conduction, the thermal elasto-viscoplastic damage, and the phase transformation analysis has been developed for the induction hardening analysis of steel machine parts. The validity of the proposed computational procedure has been illustrated by conducting the induction hardening analysis of a circular bar and a notched circular bar.