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CONTENTS
Volume 13, Number 5, May 2002
 

Abstract
This study lays emphasis on the development of efficient analytical models for a multistory structure with wings, including the in-plane deformation of floor slabs. For this purpose, a multistory structure with wings is regarded as the combination of multistory structures with rectangular plan and their junctions. In addition, a multistory structure with a rectangular plan is considered to be an assemblage of two-dimensional frames and floor slabs connecting two adjacent frames at each floor level. This modeling, concept can be easily applied to multistory structures with plans in the shape of L, T, Y, U, H, etc. To represent the in-plane deformation of floor slabs efficiently, a two-dimensional frame and the floor slab connecting two adjacent frames at each floor level are modeled as a stick model with two degrees of freedom per floor and a stiff beam with shear deformations, respectively. Three models are used to investigate the effect of in-plane deformation of the floor slab at the junction of wings on the seismic behavior of structures. Based on the comparison of dynamic analysis results obtained using the proposed models and three-dimensional finite element models, it could be concluded that the proposed models can be used as an efficient tool for an approximate analysis of a multistory structure with wings.

Key Words
multistory structure with wings, analytical models, 3-D finite element models, junction of wings, L-shaped plan, seismic behavior, flexible wings

Address
Moon SK, Kyungsan Univ, Dept Civil Engn, Kyungsan 712715, South Korea
Kyungsan Univ, Dept Civil Engn, Kyungsan 712715, South Korea
Sung Kyun Kwan Univ, Dept Architectural Engn, Suwon 440746, South Korea

Abstract
The structural dynamic optimization problem based on probability is studied. Considering the randomness of structural physical parameters and the given constraint values, we develop a dynamic optimization mathematical model of engineering structures with the probability constraints of frequency, forbidden frequency domain and the vibration mode. The sensitivity of structural dynamic characteristics based on probability is derived. Two examples illustrate that the optimization model and the method applied are rational and efficient.

Key Words
engineering structures, dynamic characteristics, frequency and mode, probability constraints, dynamic sensitivity, optimization design

Address
Chen JJ, Xidian Univ, Dept Elect Mech Engn, Xian 710071, Peoples R China
Xidian Univ, Dept Elect Mech Engn, Xian 710071, Peoples R China

Abstract
Recently we formulated a 2D hybrid stress element from the 3D Hellinger-Reissner principle for the analysis of thick bodies that are symmetric to the thickness direction. Polynomials have typically been used for all the displacement and stress fields. Although the element predicted the dominant stress and all displacement fields accurately, its prediction of the out-of-plane shear stresses was affected by the very high order terms used in the polynomials. This paper describes an improved formulation of the 2D element using Fourier series expansion for the out-of-plane displacement and stress fields. Numerical results illustrate that its predictions have markedly improved.

Key Words
hybrid stress element, out-of-plane fields, plane deformation, Fourier-series expansion, 3-D elastic theory

Address
Feng ML, Univ Cent Queensland, Fac Engn & Phys Syst, Rockhampton MC, Qld 4702, Australia
Univ Cent Queensland, Fac Engn & Phys Syst, Rockhampton MC, Qld 4702, Australia
Univ Sci & Technol China, Dept Modern Mech, Hefei 230026, Peoples R China

Abstract
In this study, the analysis of high-speed vehicle-bridge interactions by a simplified 3-dimensional finite element model is performed. Since railroads are constructed mostly as double tracks, there exists eccentricity between the vehicle axle and the neutral axis of cross section of a railway bridge. Therefore, for the more efficient and accurate vehicle-bridge interaction analysis, the analysis model should include the eccentricity of axle loads and the effect of torsional forces acting on the bridge. The investigation into the influences of eccentricity of the vehicle axle loads and vehicle speed on vehicle-bridge interactions are carried out for two cases. In the first case, only one train moves on its track and in the other case, two trains move respectively on their tracks in the opposite direction. From the analysis results of an existing bridge, the efficiency and capability of the simplified 3-dimensional model for practical application can be also verified.

Key Words
railway bridge, vehicle-bridge interaction analysis, double tracks, eccentricity of vehicle axle loads, influence of eccentricity, influence of vehicle speed

Address
Song MK, Korea Adv Inst Sci & Technol, Dept Civil & Environm Engn, Taejon 305701, South Korea
Korea Adv Inst Sci & Technol, Dept Civil & Environm Engn, Taejon 305701, South Korea

Abstract
This paper considers the buckling and post-buckling behavior of empty metal storage tanks under wind load. The structures of such tanks may be idealized as cantilever cylindrical shells, and the structural response is investigated using a computational model. The modeling employs a doubly curved finite element based on a theory by Simo and coworkers, which is capable of handling large displacements and plasticity. Buckling results for tanks with four different geometric relations are presented to consider the influence of the ratios between the radius and the height of the shell (R/L), and between the radius and the thickness (R/t). The studies aim to clarify the differences in the shells regarding their imperfection-sensitivity. The results show that thin-walled short tanks, with R/L = 3, display high imperfection sensitivity, while tanks with R/L = 0.5 are almost insensitive to imperfections. Changes in the total potential energy of tanks that would buckle under the same high wind pressures are also considered.

Key Words
buckling, cylindrical shells, finite elements, postbuckling, tanks, total potential energy, wind load

Address
Godoy LA, Univ Puerto Rico, Dept Civil Engn, Puerto Rico, PR 00681 USA
Univ Puerto Rico, Dept Civil Engn, Puerto Rico, PR 00681 USA
Natl Univ Cordoba, Struct Dept, Cordoba, Argentina

Abstract
A dynamic elastic local buckling analysis is presented for a pile subjected to an axial impact load. The pile is assumed to be geometrically perfect. The interactions between the pile and the surrounding soil are taken into account. The interactions include the normal pressure and skin friction on the surface of the pile due to the resistance of the soil. The analysis also includes the influence of the propagation of stress waves through the length of the pile to the distance at which buckling is initiated and the mass of the pile. A perturbation technique is used to determine the critical buckling length and the associated critical time. As a special case, the explicit expression for the buckling length of a pile is obtained without considering soil resistance and compared with the one obtained for a column by means of an alternative method. Numerical results obtained show good agreement with the experimental results. The effects of the normal pressure and the skin friction due to the surrounding soil, self-weight, stiffness and geometric dimension of the cross section on the critical buckling length are discussed. The sudden change of buckling modes is further considered to show the \'snap-through\' phenomenon occurring as a result of stress wave propagation.

Key Words
dynamic buckling, pulse buckling, piles, high velocity impact, stress wave, perturbation, critical buckling length

Address
Yang J, Univ Leeds, Sch Civil Engn, Leeds LS2 9JT, W Yorkshire, England
Univ Leeds, Sch Civil Engn, Leeds LS2 9JT, W Yorkshire, England

Abstract
For the evaluation of the capability of a tubular member of an offshore structure to absorb the collision energy, a simple method can be employed for the collision analysis without performing the detailed analysis. The most common simple method is the rigid-plastic method. However, in this method any characteristics for horizontal movement and rotation at the ends of the corresponding tubular member are not included. In a real structural system of an offshore structure, tubular members sustain a certain degree of elastic support from the adjacent structure. End fixity has influences in the behaviors of a tubular member. Three-dimensional FEM analysis can include the effect of end fixity fully, however in viewpoints of the inherent computational complexities of the 3-D approach, this is not the recommendable analysis at the initial design stage. In this paper, influence of end fixity on the behaviors of a tubular member is investigated, through a new approach and other approaches. A new analysis approach that includes the flexibility of the boundary points of the member is developed here. The flexibility at the ends of a tubular element is extracted using the rational reduction of the modeling characteristics. The property reduction is based on the static condensation of the related global stiffness matrix of a model to end nodal points of the tubular element. The load-displacement relation at the collision point of the tubular member with and without the end flexibility is obtained and compared. The new method lies between the rigid-plastic method and the 3-demensional analysis. It is self-evident that the rigid-plastic method gives high strengthening membrane effect of the member during global deformation, resulting in a steeper slope than the present method. On the while, full 3-D analysis gives less strengthening membrane effect on the member, resulting in a slow going load-displacement curve. Comparison of the load-displacement curves by the new approach with those by conventional methods gives the figures of the influence of end fixity on post-yielding behaviors of the relevant tubular member. One of the main contributions of this investigation is the development of an analytical rational procedure to figure out the post-yielding behaviors of a tubular member in offshore structures.

Key Words
tubular member, end fixity, post-yielding, FEM analysis

Address
Cho KN, Hongik Univ, Dept Naval Architecture & Ocean Engn, Jochiwon 339701, Chungnam, South Korea
Hongik Univ, Dept Naval Architecture & Ocean Engn, Jochiwon 339701, Chungnam, South Korea

Abstract
In performing the dynamic analysis, the step size used in a step-by-step integration method might be much smaller than that required by the accuracy consideration in order to capture the rapid chances of dynamic loading or to eliminate the linearization errors. It was first found by Chen and Robinson that these difficulties might be overcome by integrating the equations of motion with respect to time once. A further study of this technique is conducted herein. This include the theoretical evaluation and comparison of the capability to capture the rapid changes of dynamic loading if using the constant average acceleration method and its integral form and the exploration of the superiority of the time integration to reduce the linearization error. In addition, its advantage in the solution of the impact problems or the wave propagation problems is also numerically demonstrated. It seems that this time integration technique can be applicable to all the currently available direct integration methods.

Key Words
time integration, smoothing effect, linearization errors

Address
Chang SY, Natl Taiwan Univ, Natl Ctr Res Earthquake Engn, Taipei 10764, Taiwan
Natl Taiwan Univ, Natl Ctr Res Earthquake Engn, Taipei 10764, Taiwan


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