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CONTENTS
Volume 48, Number 1, October10 2013
 

Abstract
The seismic response of RC space frame structures with isolated footing resting on a shallow soil stratum on rock is presented in this paper. Homogeneous soil stratum of different stiffness in the very soft to stiff range is considered. Soil, footing and super structure are considered to be the parts of an integral system. A finite element model of the integrated system is developed and subjected to scaled acceleration time histories recorded during two different real earthquakes. Dynamic analysis is performed using mode superposition method of transient analysis. A parametric study is conducted to investigate the effect of flexibility of soil in the dynamic behaviour of low- rise building frames. The time histories and Fourier spectra of roof displacement, base shear and structural response quantities of the space frame on compliant base are presented and compared with the fixed base condition. Results indicate that the incorporation of soil flexibility is required for the realistic estimate of structural seismic response especially for single storey structures resting on very soft soil.

Key Words
seismic response; transient analysis; natural period; soil flexibility; Fourier spectra; base shear

Address
B.R. Jayalekshmi, V.G. Deepthi Poojary, Katta Venkataramana and R. Shivashankar: Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal Srinivasnagar, Karnataka – 575 025, India

Abstract
In the present paper, a coaxial rotating smeared crack model is proposed for mass concrete in three-dimensional space. The model is capable of applying both the constant and variable shear transfer coefficients in the cracking process. The model considers an advanced yield function for concrete failure under both static and dynamic loadings and calculates cracking or crushing of concrete taking into account the fracture energy effects. The model was utilized on Koyna Dam using finite element technique. Damwater and dam-foundation interactions were considered in dynamic analysis. The behavior of dam was studied for different shear transfer coefficients considering/neglecting fracture energy effects. The results were extracted at crest displacement and crack profile within the dam body. The results show the importance of both shear transfer coefficient and the fracture energy in seismic analysis of concrete dams under high hydrostatic pressure.

Key Words
concrete gravity dam; smeared crack model; shear transfer coefficient; fracture energy

Address
Mohammad Amin Hariri-Ardebili: Department of Civil, Environmental and Architectural Engineering, University of Colorado at Boulder, ECCE 168, UBC 80309-0428, Boulder, CO, USA
Seyed Mahdi Seyed-Kolbadi and Hasan Mirzabozorg: Department of Civil Engineering, K. N. Toosi University of Technology, Vali-asr St., 15875-4416, Tehran, Iran

Abstract
Initiation and growth of delamination is a great concern of designers of composite structures. Interface elements with de-cohesive constitutive law in the content of continuum damage mechanics can be used to predict initiation and growth of delamination in single and mixed mode conditions. In this paper, an interface element based on the cohesive zone method has been developed to simulate delaminatoin growth of post-buckled laminate under fatigue loading. The model was programmed as the user element and user material by the \"User Programmable Features\" in ANSYS finite element software. The interface element is a three-dimensional 20 node brick with small thickness. Because of mixed-mode condition of stress field at the delamination-front of post-buckled laminates, a mixed-mode bilinear constitutive law has been used as user material in this model. The constitutive law of interface element has been verified by modelling of a single element. A composite laminate with initial delamination under quasi-static compressive Loading available from literature has been remodeled with the present approach. Moreover, it will be shown that, the closer the delamination to the free surface of laminate, the slower the delamination growth under compressive fatigue loading. The effects of laminate configuration on delamination growth are also investigated.

Key Words
interface element; buckling; laminated composites; fatigue; finite element method

Address
Hossein Hosseini-Toudeshky and M. Saeed Goodarzi: Department of Aerospace Engineering, Amirkabir University of Technology, No. 424, Hafez Ave, Tehran, Iran
Bijan Mohammadi: School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran

Abstract
It is still inadequate for investigating the highly nonlinear and complex mechanical behaviors of single-layer latticed domes by only performing a force-based demand-capacity analysis. The energy-based balance method has been largely accepted for assessing the seismic performance of a structure in recent years. The various factors, such as span-to-rise ratio, joint rigidity and damping model, have a remarkable effect on the load-carrying capacity of a single-layer latticed dome. Therefore, it is necessary to determine the maximum load-carrying capacity of a dome under extreme loading conditions. In this paper, a mechanical model for members of the semi-rigidly jointed single-layer latticed domes, which combines fiber section model with semi-rigid connections, is proposed. The static load-carrying capacity and seismic performance on the single-layer latticed domes are evaluated by means of the mechanical model. In these analyses, different geometric parameters, joint rigidities and roof loads are discussed. The buckling behaviors of members and damage distribution of the structure are presented in detail. The sensitivity of dynamic demand parameters of the structures subjected to strong earthquakes to the damping is analyzed. The results are helpful to have a better understanding of the seismic performance of the single-layer latticed domes.

Key Words
single-layer latticed dome; seismic performance; damping; semi-rigid connection; stability

Address
Huidong Zhang: School of Civil Engineering, Tianjin Chengjian University, No.26 JinJing Road, XiQing District, Tianjin 300384, China
Qinghua Han: School of Civil Engineering, Tianjin University, No.92 WeiJin Road, NanKai District, Tianjin 300072, China

Abstract
The paper presents the formulation of 3-nodal line semi-analytical Mindlin-Reissner finite strip in the buckling analysis of thin-walled members, which are subjected to arbitrary loads. The finite strip is simply supported in two opposite edges. The general loading and in-plane rotation techniques are used to develop this finite strip. The linear stiffness matrix and the geometric stiffness matrix of the finite strip are given in explicit forms. To validate the proposed model and study its performance, numerical examples of some thin-walled sections have been performed and the results obtained have been compared with finite element models and the published ones.

Key Words
finite strip; buckling analysis; arbitrary load; general loading condition; Mindlin plate theory; Mindlin-Reissner finite strip

Address
Bui H. Cuong: Department of Civil and Industrial Building, National University of Civil Engineering, 55 Giai Phong Street, Ha noi, Vietnam

Abstract
An optimization work was developed in this work to provide design information for sandwich beam in civil engineering applications. This research is motivated by the wide-range applications of sandwich structures such as; slab, beam, girder, and railway sleeper. The design of a sandwich beam was conducted by using analytical and numerical optimization. Both analytical and numerical procedures consider the optimum design with structure mass objective minimization. Allowable deflection was considered as design constraints. It was found that the optimized core to the skins mass ratio is affected by the skin to core density and elastic modulus ratios. Finally, the optimum core to skin mass ratio cannot be constant for different skin and core materials.

Key Words
sandwich beam; mass; analytical; numerical; optimization

Address
Ziad K. Awad: Civil Engineering Department, College of Engineering, University of Mosul, Iraq

Abstract
This paper studies the static and dynamic characteristics of composite plates subjected to an arbitrary periodic load in hygrothermal environments. The material properties of composite plates are depended on the temperature and moisture. The governing equations of motion of Mathieu-type are established by using the Galerkin method with reduced eigenfunction transforms. A periodic load is taken to be a combination of axial pulsating load and bending stress in the example problem. The regions of dynamic instability of laminated composite plates are determined by solving the eigenvalue problems based on Bolotin\'s method. The effects of temperature rise and moisture concentration on the dynamic instability of laminated composite plates are investigated and discussed. The influences of various parameters on the instability region and dynamic instability index are also investigated. The numerical results reveal that the influences of hygrothermal effect on the dynamic instability of laminated plates are significant.

Key Words
dynamic instability; hygrothermal effect; laminated plates; Galerkin method; bolotin

Address
Hai Wang: Mechanical Engineering, Ming Chi University of Technology,Tai-Shan 24301, Taiwan
Chun-Sheng Chen: Mechanical Engineering, Lunghwa University of Science and Technology, Gui-Shan 33306, Taiwan
Chin-Ping Fung: Mechanical Engineering, Oriental Institute of Technology, Pan-Chiao 22061, Taiwan

Abstract
This paper intends to present an application of isogeometric analysis in crack problems. An isogeometric formula is developed based on NURBS basis functions - enriched and adopted via X-FEM enrichment functions. The proposed method which is represented by the combination of the two above-mentioned methods, first by using NURBS functions models the geometry exactly and then by defining level set function on domain, identifies available discontinuity in elements. Additional DOFs are allocated to elements containing the crack and X-FEM enrichment functions enrich approximate solution. Moreover, a subelement refinement technique is used to improve the accuracy of integration by the Gauss quadrature rule. Finally, several numerical examples are illustrated to demonstrate the effectiveness, robustness and accuracy of the proposed method during calculation of crack parameters.

Key Words
isogeometric analysis; XFEM; crack analysis; NURBS; enrichment functions

Address
S. Shojaee: Department of Civil Engineering, Shahid Bahonar University, Kerman, Iran
M. Ghelichi: Department of Civil Engineering, Graduate University Of Technology, Kerman, Iran
E. Izadpanah: Department of Civil Engineering, Shahid Bahonar University, Kerman, Iran


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