Beam FEM Research Articles

The Influence of corrosion on the stresses in members of open deck railway bridges

Nowadays, many old riveted railway bridges, mainly their members of the open deck, are corroded. The paper demonstrates the influence of corrosion on a stringer beam and on a cross-girder beam of a particular steel truss railway bridge in Slovakia. This is an important step in the assessment of the loading capacity and the residual lifetime of this bridge. A simple beam FEM model was refined by modelling the investigated members as plate elements. In such a way the real boundary conditions of the members were modelled most realistically by keeping the model as simple as possible at the same time. The stresses in the members were first calculated with the original cross-sectional dimensions and the results were compared with the real measured corroded cross-sections. A future corrosion rate was estimated and calculation of this case was also performed. The influence of stringer to cross-beam rigidity, the size of 2D FEM elements, and the steel material model (linear, bilinear with 1% hardening) were investigated too.

Seismic Performance Analysis of a Multi-Span Continuous Girder Bridge under Multi-Excitation

Although the seismic response analysis under the multi-excitation was widely focused on the long-span flexible bridges, it is still necessary to pay more attention to this point of continuous girder bridges since the dynamic behavior of this type of bridges are different with either long-span bridges or simple support bridges. Based on the nonlinear dynamic time history analysis, a four-span continuous beam FEM was built, and the effect of excitation types and structure size on seismic response was studied. And results indicate that the structural performance of continuous girder bridges is sensitive with the space correlation of different location of seismic excitation. So its necessary to consider the space effect of excitation while carrying out a seismic design of continuous beam.

A Double Thick Beam FEM with Explosion Resistance Dynamics Analysis Based on Spline Wavelets in Underground Structure

Isoparametric B-spline wavelet functions can provide excellent approximation for smooth functions. In this paper, the response of composite laminated plate subjected to explosions is analyzed by using a double thick beam FEM mode based on the spline wavelet function. This mode, which can be considered in the distribution of normal stress and transverse shear stress simultaneously, is very important in the analysis of thick plate or blast-damage mechanism. The mode in analyzing underground structure and earth medium respond has the advantage of high precision and fast constringency and is easy to establish a element displacement function. The comparison between simulative and experimental results shows the effectiveness and precision of this method.

Reduced Modeling for Turbine Rotor-Blade Coupled Bending Vibration Analysis

In a traditional turbine-generator set, rotor shaft designers and blade designers have their own models and design process which neglects the coupled effect. Since longer blade systems have recently been employed (Saito et al. 1998, “Development of a 3000 rpm 43-in. last stage blade with high efficiency and reliability,” International Joint Power Generation Conference, pp. 89–96.) for advanced turbine sets to get higher output and efficiency, additional consideration is required concerning rotor bending vibrations coupled with a one-nodal (k = 1) blade system. Rotor-blade coupled bending conditions generally include two types so that the parallel and tilting modes of the shaft vibrations are respectively coupled with in-plane and out-of-plane modes of blade vibrations with a one-nodal diameter (k = 1). This paper proposes a method to calculate the natural frequency of a shaft blade coupled system. According to this modeling technique, a certain blade mode is reduced to a single mass system, which is connected to the displacement and angle motions of the shaft. The former motion is modeled by the m-k system to be equivalent to the blade on the rotating coordinate. The latter motion is commonly modeled in discrete form using the beam FEM on an inertia coordinate. Eigenvalues of the hybrid system covering both coordinates provide the natural frequency of the coupled system. In order to solve the eigenfrequencies of the coupled system, a tracking solver method based on sliding mode control concept is used. An eight-blade system attached to a cantilever bar is used for an example to calculate a coupled vibration with a one-nodal diameter between the blade and shaft.

タービンの翼軸連成曲げ振動解析向け等価質点モデル化

In a traditional turbine-generator set, rotor shaft designers and blade designers have their own models and design process which neglects the coupled effect. Since longer blade systems have recently been employed[1] for advanced turbine sets to get higher output and efficiency, additional consideration is required concerning rotor bending vibrations coupled with a one-nodal (k = 1) blade system. Rotor-blade coupled bending conditions generally include two types so that the parallel and tilting modes of the shaft vibrations are respectively coupled with in-plane and out-of-plane modes of blade vibrations with a one-nodal diameter (k = 1). This paper proposes a method to calculate the natural frequency of a shaft blade coupled system. According to this modeling technique, a certain blade mode is reduced to a single mass system, which is connected to the displacement and angle motions of the shaft. The former motion is modeled by the m-k system to be equivalent to the blade on the rotating coordinate. The latter motion is commonly modeled in discrete form using the beam FEM on an inertia coordinate. Eigenvalues of the hybrid system covering both coordinates provide the natural frequency of the coupled system. In order to solve the eigenfrequencies of the coupled system, a tracking solver method based on sliding mode control concept is used. An eight-blade system attached to a cantilever bar is used for an example to calculate a coupled vibration with a one-nodal diameter between the blade and shaft.Copyright © 2011 by ASME

Constraint Analysis on the Steel Mid Tower of a Tri Tower Suspension Bridge

A certain project of tri-tower suspension bridge of which the main span was 1080m was taken as a case study of the mid tower stability. A 3D beam FEM model has been carried out to investigate the global mechanical behavior of the bridge in which the internal force response to several different typical load cases were specifically concerned. Moreover, the cable spring stiffness to the mid tower was defined as the ratio of the initial horizontal forces acting on the top end of mid tower to the corresponding horizontal displacement. And the effect of this equivalent spring stiffness on the stability performance of the mid tower was compared to other tow constraint conditions to the tower including free constraint and pin constraint. The comparison showed that the cable equivalent stiffness was 4342kN/m when living load was acting along the whole main girder of the bridge while this value varied with different load cases. The difference between the effect caused by the cable spring stiffness and the free constraint was small indicating that the stability of the mid tower was not sensitive to the cable constraint. In addition, with the increase of the equivalent spring stiffness, the longitudinal buckling eigenvalue also became larger and gradually approached the condition of pin constraint.

Stability problems of steel structures in the presence of stochastic and fuzzy uncertainty

General ideas and problems of probability approach and its utilization in the verification of structural design procedures of EUROCODES are mentioned. The paper is aimed at the probability study of the ultimate limit state of a steel compressed member designed economically according to EUROCODE 3. The theoretical failure probability (reliability index) vs. ratio of permanent to variable load action is calculated by means of the Monte Carlo simulation method. The misalignment of the failure probability according to EN1990 is analysed. Initial imperfections are generally considered as random variables and random fields. The non-linear beam FEM is used. The influence of initial curvature shape and size variability of the member axis on the variability of load-carrying capacity is investigated. The probabilistic analysis is supplemented with the fuzzy analysis of the influence of uncertainties on the failure probability.

Report on first masing and single-mode locking in a prebunched beam FEM oscillator

The effects of electron beam prebunching on the radiation buildup process in a free electron maser oscillator operating in a collective-Raman regime and oscillating in the frequency range of 4 to 5 GHz are studied. An electron beam is prebunched, accelerated to 70 keV, transported through a drift region, and injected into a linearly polarized wiggler in which FEL interaction takes place. Single-frequency selection and locking due to electron beam prebunching is demonstrated; we show that the electron beam prebunching can be used to force the oscillator to achieve steady-state single-mode operation and to select the oscillator frequency to be any of the resonator natural frequencies of the cavity in net gain bandwidth. An appreciable speed-up of the oscillation buildup due to prebunching was also observed.