Mitao Ohga

Structural analysis by a combined boundary element-transfer matrix method

Abstract The combined finite element-transfer matrix method has the advantage of reducing the size of a matrix to less than that obtained by the ordinary finite element method. The analytical procedure in this method for bending and buckling problems are described, and techniques for treating the structure with intermediate conditions are proposed. Various numerical examples of these problems are shown to demonstrate the efficiency and accuracy of this method. The results from these examples agree well with those obtained by the finite element method and others.

Transient analysis of plates by a combined finite element-transfer matrix method

Abstract The combined use of the finite element and transfer matrix is applied to the transient analyses of the structures under various excitations. An approximation is also introduced in the equations of motion for the case of in-plane excitations in order to reduce computational efforts. Furthermore, the technique of exchanging the state vectors is, in this paper, proposed to avoid the propagation of round off errors occurred in recursive multiplications of the transfer and point matrices, and the Newmark β method is employed for time integrations. Some numerical examples are presented to demonstrate the accuracy as well as the capability of the proposed method for transient analyses of the plates under out-of-plane and in-plane excitations.

Prediction of residual strength of corroded tensile steel plates

Recently, the damage due to deterioration of materials in many old steel bridge structures, which causes unavoidable strength reduction, is becoming a serious problem in Japan and all over the world. Therefore the remaining load-carrying capacities must be carefully evaluated in order to understand the feasibility of those steel structures for the current usage and to evaluate the necessity of retrofitting of selected corroded members to strengthen the existing structure. This paper proposes a new method to calculate the remaining yield and tensile strengths by using a concept of representative effective thickness (teff) with the correlation of initial thickness (t0) and the maximum corroded depth (tc,max), based on the results of many tensile coupon tests of actual corroded plates. Further, the feasibility of establishing of an analytical methodology to predict the residual strength capacities of a corroded steel member with fewer number of measuring points is also discussed.

Bending analysis of plates with variable thickness by boundary element-transfer matrix method

Abstract The combined boundary element-transfer matrix method is proposed for plate bending problems. In this method, a transfer matrix is obtained, from the sytem of equations derived by the procedure based on the boundary element method. This method permits the use of large number of elements, without getting involved with large matrices. A much smaller computer is therefore sufficient. Some numerical examples are presented to demonstrate the accuracy as well as the capability of the proposed method for solutions of plate bending problems.

Analysis of folded plate structures by a combined boundary element-transfer matrix method

Abstract A structural analysis method based on a combined use of the boundary element and transfer matrix methods is proposed for static problems of folded plate structures. A transfer matrix is, in this paper, evaluated by assembling of those for in-plane and plate bending problems, which are derived from the systems of equations based on the ordinary boundary element method for in-plane and plate bending problems, respectively. This method, therefore, permits the use of a large number of elements, without getting involved with large matrices. Some numerical examples of plates and folded plate structures subjected to various loads are proposed and their results are compared with those obtained by the finite element method.

Buckling mode shapes of thin-walled members

Abstract An analytical procedure to estimate not only the elastic buckling loads but also buckling mode shapes by transfer matrix method is presented. The transfer matrix is derived from the differential equations for the plate subjected to axial load. The buckling coefficients and buckling mode shapes of the L-, U-, H- and box-section members are presented for various aspect ratios and the efficiency of this method is investigated.

Structural Appraisal-based Different Approach to Estimate the Remaining Fatigue Life of Railway Bridges

The current fatigue life estimation methods of railway bridges are generally based on combinations of measured strain histories, Miner’s rule, and railway code provided fatigue curve. Even though the past measured strain histories are available for major bridges, most of the old bridges do not have past strain measurements. Furthermore, in case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of its omission of load sequence effect. These reasons hinder the usage of current methods to estimate the realistic remaining fatigue life of most of the existing railway bridges. Therefore, a new method is presented in this article to estimate remaining fatigue life of riveted railway bridges. The method mainly consists of predicted stress histories, recently developed sequential law and fully known Wöhler curve. Here, it is essential to use the fully known Wöhler curve as the related fatigue curve. Hence, the technique, which utilizes transfer of the partially known Wöhler curve to fully known curve, is also discussed in this article. Further, this method describes a reasonably accurate procedure to obtain the past stress histories from present day measured strains. Initially, the article describes the proposed method for remaining fatigue life estimation. Then the sequential law and associated fully known S-N curve determination procedure are verified by comparing theoretical fatigue life, damage behavior with real fatigue life and damage behavior of few materials. Finally, the remaining fatigue life of an existing railway bridge is estimated. Hence, validity and merits of the proposed method is confirmed by comparing the results with previous method-based fatigue lives.

Ermittlung der Beultraglasten ausgesteifter Schalen mit Hilfe von Übertragungsmatrizen

ÜbersichtBei Beultraglastsberechnungen von ausgesteiften Kreiszylinderschalen unter Axialbelastung im plastischen Bereich werden das Deformationsverfahren und das Eigenwertverfahren mit Hilfe von übertragungsmatrizen verwendet, wobei die Übertragungsmatrix im Deformationsverfahren aus der nach der Finite-Element-Methode gewonnenen Steifigkeitsmatrix hergeleitet wird. Bei gleichzeitiger Berücksichtigung der Vorverformungen und der Restspannungen bzw. bei alleiniger Berücksichtigung der Restspannungen werden Rechenergebnisse von längsausgesteiften Schalen nach beiden Verfahren vorgelegt und verglichen.SummaryThe deformation and eigenvalue method using the transfer matrix are applied to ultimate strength analyses of axially compressed, stiffened cylindrical shells in the plastic range. The transfer matrix in the deformation method is obtained by suitable transformation of the stiffness matrix used in the finite element method, and the transfer matrix in the eigenvalue method is described by the linearized differential equation of shells. In the deformation method geometrical imperfections and residual stresses are taken into consideration, while in the eigenvalue method the former are not considered. The numerical results of stiffened shells obtained by both methods are illustrated and compared with each other.

Buckling analysis of thin-walled members with closed cross sections

Abstract In this paper, an analytical procedure for the elastic buckling problems of thin-walled members with closed cross sections by the transfer matrix method is presented. The transfer matrix is obtained from the differential equations for a plate subjected to axial load, and the extended transfer matrix for closed cross sections is derived from that for branched panels. The analytical local and overall elastic buckling loads for thin-walled members with closed cross sections can be obtained simultaneously. Furthermore, a technique to estimate the buckling mode shapes of these members is also shown. To investigate the accuracy and efficiency of this method, some numerical examples are presented.

Natural frequencies and mode shapes of thin-walled members

Abstract An analytical procedure to estimate both the natural frequencies and mode shapes of thin-walled members is presented using the transfer matrix method. The transfer matrix is derived from the differential equations of the plate panel of thin-walled members. The proposed method gives exact natural frequencies and mode shapes of thin-walled members. Thus the vibration phenomenon of such members can be clarified exactly. Some numerical examples are presented to illustrate the accuracy and efficiency of the proposed method.