Techno Press
Tp_Editing System.E (TES.E)
Login Search


sem
 
CONTENTS
Volume 46, Number 1, April10 2013
 

Abstract
In this study, the modified finite element- transfer matrix methods are proposed for free vibration analysis of asymmetric structures, the bearing system of which consists of shear wall-frames. In the study, a multi-storey structure is divided into as many elements as the number of storeys and storey masses are influenced as separated at alignments of storeys. The shear walls and frames are assumed to be flexural and shear cantilever beam structures. The storey stiffness matrix is obtained by formulating the governing equation at the center of mass for the shear walls and the frames in the i.th floor. The system transfer matrix is constructed in the dimension of 6x6 by transforming the obtained stiffness matrix. Thus, the dimension, which is 12nx12n in classical finite elements, is reduced to the dimension of 6x6. To study the suitability of the method, the results are assessed by solving two examples taken from the literature.

Key Words
modified finite element-transfer matrix; vibration; asymmetric; wall-frame

Address
Kanat B. Bozdogan: Department of Civil Engineering, Kirklareli University, Kirklareli, Turkey

Abstract
The optimum design of base isolation system considering model parameter uncertainty is usually performed by using the unconditional response of structure obtained by the total probability theory, as the performance index. Though, the probabilistic approach is powerful, it cannot be applied when the maximum possible ranges of variations are known and can be only modelled as uncertain but bounded type. In such cases, the interval analysis method is a viable alternative. The present study focuses on the bounded optimization of base isolation system to mitigate the seismic vibration effect of structures characterized by bounded type system parameters. With this intention in view, the conditional stochastic response quantities are obtained in random vibration framework using the state space formulation. Subsequently, with the aid of matrix perturbation theory using first order Taylor series expansion of dynamic response function and its interval extension, the vibration control problem is transformed to appropriate deterministic optimization problems correspond to a lower bound and upper bound optimum solutions. A lead rubber bearing isolating a multi-storeyed building frame is considered for numerical study to elucidate the proposed bounded optimization procedure and the optimum performance of the isolation system.

Key Words
stochastic earthquake; Base Isolation; bounded uncertainty; optimization

Address
Bijan Kumar Roy: Department of Civil Engineering, Bengal Engineering and Science University, Shibpur, India; University Institute of Technology, Burdwan University, Burdwan-713104, West Bengal, India
Subrata Chakraborty: Department of Civil Engineering, Bengal Engineering and Science University, Shibpur, India

Abstract
An extremum method is presented to predict the wrinkling characteristics of the inflated cone in bending. The wrinkling factor is firstly defined so as to obtain the wrinkling condition. The initial wrinkling location is then determined by searching the maximum of the wrinkling factor. The critical wrinkling load is finally obtained by determining the ratio of the wrinkling moment versus the initial wrinkling location. The extremum method is proposed based on the assumption of membrane material of beam wall, and it is extended to consider beam wall with thin-shell material in the end. The nondimensional analyses show that the initial wrinkling location is closely related to the taper ratio. When the taper ratio is higher than the critical value, the initial wrinkles will be initiated at a different location. The nondimensional critical wrinkling load nonlinearly increases as the taper ratio increases firstly, and then linearly increases after the critical taper ratio. The critical taper ratio reflects the highest load-carrying efficiency of the inflated cone in bending, and it can be regarded as a measure to optimize the geometry of the inflated cone. The comparative analysis shows fairly good agreement between analytical and numerical results. Over the whole range of the comparison, the mean differences are lower than 3%. This gives confidence to use extremum method for bending-wrinkling analysis of inflated conical cantilever beam.

Key Words
inflated conical cantilever beam; wrinkling; membrane; thin-shell; load-carrying efficiency

Address
Changguo Wang: Center for Composite Materials, Harbin Institute of Technology, Harbin, 150080 China; National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, Harbin Institute of Technology, Harbin, 150080 China
Zhenyong Du: Center for Composite Materials, Harbin Institute of Technology, Harbin, 150080 China
Huifeng Tan: National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, Harbin Institute of Technology, Harbin, 150080 China


Abstract
Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

Key Words
integral Abutment; bridge; uncertainty; load model; Monte Carlo

Address
WooSeok Kim: Civil Engineering, Chungnam National University, Daejeon 305-764, Korea
Jeffrey A. Laman: Civil and Environmental Engineering, Pennsylvania State University, University Park, PA 16801, U.S.A.

Abstract
In order to identify damage of highway bridges rapidly, a method for damage identification using dynamic response of bridge induced by moving vehicle and static test data is proposed. To locate damage of the structure, displacement energy damage index defined from the energy of the displacement response time history is adopted as the indicator. The displacement response time histories of bridge structure are obtained from simulation of vehicle-bridge coupled vibration analysis. The vehicle model is considered as a four-degree-of-freedom system, and the vibration equations of the vehicle model are deduced based on the D\'Alembert principle. Finite element method is used to discretize bridge and finite element model is set up. According to the condition of displacement and force compatibility between vehicle and bridge, the vibration equations of the vehicle and bridge models are coupled. A Newmark-B algorithm based professional procedure VBAP is developed in MATLAB, and used to analyze the vehicle-bridge system coupled vibration. After damage is located by employing the displacement energy damage index, the damage extent is estimated through the least-square-method based model updating using static test data. At last, taking one simply supported bridge as an illustrative example, some damage scenarios are identified using the proposed damage identification methodology. The results indicate that the proposed method is efficient for damage localization and damage extent estimation.

Key Words
bridge; analysis of vehicle-bridge coupled vibration; static test; damage identification; energy index

Address
Jinsong Zhu and Qiang Yi: School of Civil Engineering, Tianjin University, Tianjin 300072, China; Key Laboratory of Coast Civil Structure Safety (Ministry of Education), Tianjin University, Tianjin 300072, China

Abstract
This paper proposes a novel iterative procedure for the design of planar reinforced concrete structures in which the reinforcement is designed for stresses calculated in a nonlinear finite element analysis. The procedure is intended as an alternative to strut and tie modeling for the design of complex structures like deep beams with openings. Practical reinforcement arrangements are achieved by grouping the reinforcement into user defined horizontal and vertical bands. Two alternative strategies are proposed for designing the reinforcement which are designated A and B. Design constraints are specified in terms of permissible stresses and strains in the reinforcement and strains in the concrete. A case study of a deep beam with an opening is presented to illustrate the method. Comparisons are made between design strategies A and B of which B is shown to be most efficient. The resulting reinforcement weights are also shown to compare favorably with those previously reported in the literature.

Key Words
reinforced concrete; D regions; automated design of reinforcement; nonlinear analysis; plane stress; strut and tie modeling

Address
Hamidreza Amini Najafian and Robert L. Vollum: Department of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, UK

Abstract
An experimental study has been carried out on square plain concrete (PC) and reinforced concrete (RC) columns strengthened with carbon fiber-reinforced polymer (CFRP) sheets. A total of 78 specimens were loaded to failure in axial compression and investigated in both axial and transverse directions. Slenderness of the columns, number of wrap layers and concrete strength were the test parameters. Compressive stress, axial and hoop strains were recorded to evaluate the stress-strain relationship, ultimate strength and ductility of the specimens. Results clearly demonstrate that composite wrapping can enhance the structural performance of square columns in terms of both maximum strength and ductility. On the basis of the effective lateral confining pressure of composite jacket and the effective FRP strain coefficient, new peak stress equations were proposed to predict the axial strength and corresponding strain of FRP-confined square concrete columns. This model incorporates the effect of the effective circumferential FRP failure strain and the effect of the effective lateral confining pressure. The results show that the predictions of the model agree well with the test data.

Key Words
CFRP; square column; confinement; strength; ductility; slenderness

Address
Riad Benzaid: L.G.G., Jijel University-B.P. 98, Cite Ouled Issa, Jijel, 18000, Algeria
Habib Abdelhak Mesbah: L.G.C.G.M., INSA of Rennes, University of Rennes 1, France

Abstract
In this paper, two new methods called Improved Amplitude-Frequency Formulation (IAFF) and Energy Balance Method (EBM) are applied to solve high nonlinear oscillators. Two cases are given to illustrate the effectiveness and the convenience of these methods. The results of Improved Amplitude-Frequency Formulation are compared with those of EBM. The comparison of the results obtained using these methods reveal that IAFF and EBM are very accurate and can therefore be found widely applicable in engineering and other science. Finally, to demonstrate the validity of the proposed methods, the response of the oscillators, which were obtained from analytical solutions, have been shown graphically and compared with each other.

Key Words
Improved Amplitude-Frequency Formulation (IAFF); Energy Balance Method (EBM); Nonlinear Oscillators

Address
I. Pakar and M. Bayat: Department of Civil Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com