Techno Press


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CONTENTS
Volume 40, Number 1, October10 2011
 

Abstract
Ambient vibration tests were carried out to evaluate the dynamic properties of an asymmetric steel building with semi-rigid connections. The test case has many non-structural elements, constructed in the city of Tehran (Iran). The tests were conducted to obtain natural frequencies, mode shapes and damping ratio of the structure and then Fourier transform were used to analyze the velocity records obtained from the tests. The first and second natural periods of the building were obtained as 1.37 s and 1.28 s through the test and damping ratio for the first mode was calculated as 0.047. However, Natural periods obtained from finite element model have higher values from those gained from ambient vibration. Then the model was calibrated by modeling of the in-fill masonry panels at their exact locations and considering the boundary conditions by modeling two blocks near the block No. 3, but the differences were existed. These differences may be due to some hidden stiffness of nonstructural elements in the low range of elastic behavior, showing the structure stiffer than it is in reality.

Key Words
ambient vibration; dynamic characteristics; natural frequency; mode shape; steel building

Address
H. Shakib: School of Civil Engineering, Tarbiat Modares University, Tehran, Iran
N. Parsaeifard: International Institute of Earthquake Engineering and Seismology, Tehran, Iran

Abstract
An effective method for detection linear flaws in plate structures via two-dimensional discrete wavelet transform is proposed in this study. The proposed method was applied to a four-fixed supported rectangular plate containing damage with arbitrary length, depth and location. Numerical results identifying the damage location are compared with the actual results to demonstrate the effectiveness of the proposed method. Also, a wavelet-based method presented for de-noising of mode shape of plate. Finally, the performance of the proposed method for de-noising and damage identification was verified using experimental data. Comparison between the location detected by the proposed method, and the plate

Key Words
damage detection; de-noising; plate; wavelet transform; damage location

Address
A. Bagheri: Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
G. Ghodrati Amiri, M. Khorasani and H. Bakhshi: Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science & Technology, PO Box 16765-163, Narmak, Tehran 16846, Iran

Abstract
Under large storm loads sections of a long pipeline on the seabed can be uplifted. Numerically this loss of contact is extremely difficult to simulate, but accounting for uplift and any subsequent recontact behaviour is a critical component in pipeline on-bottom stability analysis. A simple method numerically accounting for this uplift and reattachment, while utilising efficient force-resultant models, is provided in this paper. While force-resultant models use a plasticity framework to directly relate the resultant forces on a segment of pipe to the corresponding displacement, their historical development has concentrated on precisely modelling increasing capacity with penetration. In this paper, the emphasis is placed on the description of loss of penetration during uplifting, modelled by \'strainsoftening\' of the force-resultant yield surface. The proposed method employs uplift and reattachment criteria to determine the pipe uplift and recontact. The pipe node is allowed to become free, and therefore, the resistance to the applied hydrodynamic loads to be redistributed along the pipeline. Without these criteria, a localised failure will be produced and the numerical program will terminate due to singular stiffness matrix. The proposed approach is verified with geotechnical centrifuge results. To further demonstrate the practicability of the proposed method, a computational example of a 1245 m long pipeline subjected to a large storm in conditions typical of offshore North-West Australia is discussed.

Key Words
pipeline; soil-structure interaction; centrifuge test; calcareous sand; force-resultant model; plasticity

Address
Yinghui Tian and Mark J. Cassidy: Centre for Offshore Foundation Systems, The University of Western Australia,
35 Stirling Highway, Crawley WA 6009, Australia

Abstract
An analytical method is presented to investigate electromagnetothermoelastic behaviors of a hollow sphere composed of functionally graded piezoelectric material (FGPM), placed in a uniform magnetic field, subjected to electric, thermal and mechanical loads. For the case that material properties obey an identical power law in the radial direction of the FGPM hollow sphere, exact solutions for electric displacement, stresses, electric potential and perturbation of magnetic field vector in the FGPM hollow sphere are determined by using the infinitesimal theory of electromagnetothermoelasticity. Some useful discussion and numerical examples are presented to show the significant influence of material inhomogeneity. The aim of this research is to understand the effect of composition on electromagnetothermoelastic stresses and to design optimum FGPM hollow spheres.

Key Words
functionally graded piezoelectric material (FGPM); hollow sphere; analytical method; electromagnetothermoelastic; perturbation of magnetic field vector

Address
Hong-Liang Dai and Yan-Ni Rao: State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body,
Hunan University, Changsha, 410082, China; Department of Engineering Mechanics, College of Mechanical & Vehicle Engineering, Hunan University, Changsha, 410082, China

Abstract
In this paper a simple mathematical model for approximate static analysis of combined system of framed tube, shear core and two outrigger-belt truss structures subjected to lateral loads is presented. In the proposed methodology, framed tube is modeled as a cantilevered beam with a box section and interaction between shear core and outrigger-belt truss system with framed tube is modeled using torsional springs placed at location of outrigger-belt truss; these torsional springs act in a direction opposite to rotation generated by lateral loads. The effect of shear lag on axial deformation in flange is quadratic and in web it is a cubic function of geometry. Here the total energy of the combined system is minimized with respect to lateral deflection and rotation in plane section. Solution of the resulting equilibrium equations yields the unknown coefficients of shear lag along with the stress and displacement distributions. The results of a numerical example, 50 storey building subjected to three different types of lateral loading obtained from SAP2000 are compared to those of the proposed method and the differences are found to be reasonable. The proposed method can be used during the preliminary design stages of a tall building and can provide a better understanding of the effects of various parameters on the overall structural behavior.

Key Words
tall building; framed tube; shear core; outrigger-belt truss; shear lag; static analysis

Address
Reza Rahgozar: Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
Ali Reza Ahmadi: Department of Civil and Mechanical Engineering, International Center for Science and High Technology, Mahan, Iran
Omid Hosseini and Mohsen Malekinejad: Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract
Integration of finite element analysis (FEA) software into various software platforms is commonly used in coupling systems such as systems involving structural control, fluid-structure, windstructure, soil-structure interactions and substructure method in which FEA is used for simulating the structural responses. Integrating an FEA program into various other software platforms in an efficient and simple way is crucial for the development and performance of the entire coupling system. The lack of simplicity of the existing integration methods makes this integration difficult and therefore entails the motivation of this study. In this paper, a novel practical technique, namely CS technique, is presented for integrating a general FEA software framework OpenSees into other software platforms, e.g., Matlab-Simulink

Key Words
coupling systems; OpenSees – Simulink; software integration; client-server techniques; soilstructure interaction; shake table modeling

Address
Quan Gu: Department of Civil Engineering, School of Architecture and Civil Engineering, Xiamen University, Xiamen, Fujian, 361005, P.R. China
Ozgur Ozcelik: Department of Civil Engineering, School of Engineering, Dokuz Eylul University, Buca/Izmir, 35160, Turkey

Abstract
The strengthening and rehabilitation of reinforced concrete structures with externally bonded carbon fibre reinforced polymer (FRP) laminates has shown excellent performance and, as a result, this technology is rapidly replacing steel plate bonding techniques. This paper addresses this issue, and presents results deals with the influence of external bonded CFRP-reinforcement on the time-dependent behavior of reinforced concrete beams. A total of eight reinforced concrete beams with cracked and uncracked section, with and without externally bonded CFRP laminates, were investigated for their creep and shrinkage behavior. All the beams considered in this paper were simply supported and subjected to a uniform sustained loading for the period of six months. The main parameters of this study are two types of sustained load and different degrees of strengthening scheme for both cracked and un-cracked sections of beams. Both analytical and experimental work has been carried out on strengthened beams to investigate the cracking and deflection performance. The applied sustained load was 56% and 38% of the ultimate static capacities of the un-strengthened beams for cracked and un-cracked section respectively. The analytical values based on effective modulus method (EMM) are compared to the experimental results and it is found that the analytical values are in general give conservative estimates of the experimental results. It was concluded that the attachment of CFRP composite laminates has a positive influence on the long term performance of strengthened beams.

Key Words
long-term deflection; cracked beam; CFRP laminates; sustained loading; creep and shrinkage

Address
Ehsan Ahmed and Habibur Rahman Sobuz: Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300, Kota Samarahan, Sarawak, Malaysia

Abstract
Closed form solutions for equilibrium and flexibility matrices of the Mindlin-Reissner theory based eight-node rectangular plate bending element (MRP8) using Integrated Force Method (IFM) are presented in this paper. Though these closed form solutions of equilibrium and flexibility matrices are applicable to plate bending problems with square/rectangular boundaries, they reduce the computational time significantly and give more exact solutions. Presented closed form solutions are validated by solving large number of standard square/rectangular plate bending benchmark problems for deflections and moments and the results are compared with those of similar displacement-based eight-node quadrilateral plate bending elements available in the literature. The results are also compared with the exact solutions.

Key Words
closed form solutions; flexibility matrix; equilibrium matrix; integrated force method; rectangular plate element

Address
H.R. Dhananjaya: Department of Civil Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia; Manipal Institute of Technology, Manipal-576 104, India
P.C. Pandey: Department of Civil Engineering, Indian Institute of Science, Bangalore-560012, India
J. Nagabhushanam: Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India
Ismail Othamon: Department of Civil Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia



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