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CONTENTS
Volume 25, Number 4, March10 2007
 

Abstract
A pilot study has been conducted to guide the development of a finite element modeling formulation for the analysis of architectural glass curtain walls under in-plane lateral load simulating earthquake effects. This pilot study is one aspect of ongoing efforts to develop a general prediction model for glass cracking and glass fallout for architectural glass storefront and curtain wall systems during seismic loading. For this study, the ANSYS finite element analysis program was used to develop a model and obtain the stress distribution within an architectural glass panel after presumed seismic movements cause glass-to-frame contact. The analysis was limited to static loading of a dry-glazed glass curtain wall panel. A mock-up of the glass curtain wall considered in the analysis with strain gages mounted at select locations on the glass and the aluminum framing was subjected to static loading. A comparison is made between the finite element analysis predicted strain and the experimentally measured strain at each strain gage location.

Key Words
curtain walls; architectural glass; seismic evaluation; finite element analysis; static test

Address
A.M. Memari, A. Shirazi and P.A. Kremer; Department of Architectural Engineering, The Pennsylvania State University, 104 Engineering Unit A, University Park, PA 16802, U.S.A.

Abstract
The contact problem for an elastic layer resting on an elastic half plane is considered according to the theory of elasticity with integral transformation technique. External loads P and Q are transmitted to the layer by means of two dissimilar rigid flat punches. Widths of punches are different and the thickness of the layer is h. All surfaces are frictionless and it is assumed that the layer is subjected to uniform vertical body force due to effect of gravity. The contact along the interface between elastic layer and half plane will be continuous, if the value of load factor, , is less than a critical value, cr. However, if tensile tractions are not allowed on the interface, for  >cr the layer separates from the interface along a certain finite region. First the continuous contact problem is reduced to singular integral equations and solved numerically using appropriate Gauss-Chebyshev integration formulas. Initial separation loads, cr, initial separation points, xcr, are determined. Also the required distance between the punches to avoid any separation between the punches and the layer is studied and the limit distance between punches that ends interaction of punches, is investigated. Then discontinuous contact problem is formulated in terms of singular integral equations. The numerical results for initial and end points of the separation region, displacements of the region and the contact stress distribution along the interface between elastic layer and half plane is determined for various dimensionless quantities.

Key Words
continuous contact; discontinuous contact; separation; elastic layer; rigid punch; asymmetric loading; integral equation; elasticity

Address
Talat Sukru Ozsahin; Civil Engineering Department, Karadeniz Technical University, Trabzon, Turkey

Abstract
A four-node hybrid stress element for analysing orthotropic folded plate structures is presented. The formulation is based on Hellinger-Reissner variational principle. The element is developed by combining a hybrid plane stress element and a hybrid plate element. The proposed element has six degree of freedom per node and permits an easy connection to other type of elements. An equilibrated stress field in each element and inter element compatible boundary displacement field are assumed independently. Static and free vibration analyses of folded plates are carried out on numerical examples to show that the validity and efficiency of the present element.

Key Words
folded plate; assumed stress hybrid element; finite element; static analysis; free vibration

Address
Kutlu Darilmaz; Department of Civil Engineering, Istanbul Technical University 34469, Maslak, Istanbul, Turkey

Abstract
By using the incremental form of the endochronic theory of plasticity, a model of material function is proposed in this paper to investigate plastic behavior. By comparing the stress-strain hysteresis loop, the theory is shown to agree well with the experimental results, especially in the evolution of peak stress values of SAE 4340 steel loaded by cyclic loading with various amplitudes. Depending on the choice of material parameters, the present model can substantially result in six categories of material function, each of which can behave differently with respect to an identical deformation history. In addition, the present model of material function is shown to be capable of describing the behavior of erasure of memory of materials, as experimentally observed by Lamba and Sidebottom (1978).

Key Words
endochronic theory; cyclic loading conditions; material function; erasure of memory

Address
Wei-Ching Yeh; Department of Mechanical Engineering, National Central University, Chung-Li, 32054, Taiwan, R.O.C.
Hsi-Yen Lin; Patent Division III, Intellectual Property Office, Ministry of Economic Affairs, R.O.C.
Jhen-Bo Jhao; Department of Mechanical Engineering, National Central University, Chung-Li, 32054, Taiwan, R.O.C.

Abstract
As the LNG (Liquefied Natural Gas) tank contains cryogenic liquid, realistic thermal analyses are of a primary importance for a successful design. The structural details of the LNG tank are so complicated that some strategies are necessary to reasonably predict its temperature distribution. The proposed heat transfer model can consider the beneficial effects of insulation layers and a suspended deck on temperature distribution of the outer concrete tank against cryogenic conditions simply by the boundary conditions of the outer tank model. To this aim, the equilibrium condition or heat balance in a steady state is utilized in a various way, and some aspects of heat transfer via conduction, convection and radiation are implemented as necessary. Overall thermal analysis procedures for the LNG tank are revisited to examine some unjustifiable assumptions of conventional analyses. Concrete and insulation properties under cryogenic condition and a reasonable conversion procedure of the temperature-induced nonlinear stress into the section forces are discussed. Numerical examples are presented to verify the proposed schemes in predicting the actual temperature and stress distributions of the tank as affected by the cryogenic LNG for the cases of normal operation and leakage from the inner steel tank. It is expected that the proposed schemes enable a designer to readily detect the effects of insulation layers and a suspended deck and, therefore, can be employed as a useful and consistent tool to evaluate the thermal effect in a design stage of an LNG tank as well as in a detailed analysis.

Key Words
LNG storage tank; cryogenic temperature; heat transfer analysis; thermal stress; leakage; insulations

Address
Se-Jin Jeon, Byeong-Moo Jin and Young-Jin Kim; DAEWOO E&C, Institute of Construction Technology, 60 Songjook-dong, Jangan-gu, Suwon, Kyonggi 440-210, South Korea
Chul-Hun Chung; Department of Civil and Environmental Engineering, Dankook University, San 8, Hannam-dong, Youngsan-gu, Seoul 140-714, South Korea

Abstract
Two methods were developed for analyzing problems with two adjacent sub-domains modeled by different kinds of elements in finite element method. Each sub-domain can be defined independently without the consideration of equivalent division with common nodes used for the interface. These two methods employ an individual interface to accomplish the compatibility. The MLSA method uses the moving least square approximation which is the basic formulation for Element Free Galerkin Method to formulate the interface. The displacement field assumed by this method does not pass through nodes on the common boundary. Therefore, nodes can be chosen freely for this method. The results show that the MLSA method has better approximation than traditional methods.

Key Words
compatibility; sub-domain; element free; moving least square; finite element; beam; plane stress

Address
Chan-Ping Pan; Department of Construction Engineering, National Taiwan University of Science and Technology, Taiwan
Hsing-Chih Tsai; Ecological and Hazard Mitigation Engineering Research Center, National Taiwan University of Science and Technology, Taiwan

Abstract
The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading P(t) = Ps + Pd cost is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at  = m + n, ( is the excitation frequency and m and n are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at  = 21, where 1 is the fundamental frequency, other cases of  = m + n, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

Key Words
parametric instability; combination resonance; the method of multiple scales; finite element method; tensile non-uniform edge loading; damping

Address
Ratnakar. S. Udar and P. K. Datta; Department of Aerospace Engineering, Indian Institute of Technology, Kharagpur-721302, India


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