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CONTENTS
Volume 18, Number 3, September 2004
 

Abstract
Defective metallic components and structures are being repaired with bonded composite patches to improve overall mechanical and fatigue properties. In this study, fatigue crack growth tests were conducted on pre-cracked 7075/T6 Aluminum substrates with and without bonded Boron/epoxy patches. A considerable increase in the fatigue life and a decrease in the stress intensity factor (SIF) were observed as the number of patch plies increased. The experimental results demonstrate that the patch configurations and patch thickness can enhance fatigue life by order of magnitude. Quantitative comparisons between analytical and experimental data were made, and the analytical model based on a modified Rose\'s analytical solution appears to best estimate the fatigue life.

Key Words
bonded repair; composite patch; fatigue life; crack growth rate; aluminum alloy; defective structure.

Address
Q. Y. Wang; Department of Civil Engineering & Mechanics, Sichuan University, Chengdu, 610065, China
N. Kawagoishi and Q. Chen; Department of Mechanical Engineering, Kagoshima University, Kagoshima, 890-0065, Japan
R. M. Pidaparti; Department of Mechanical Engineering, Purdue University, Indianapolis, IN 46202, USA

Abstract
Structural acceleration regulation is a means of managing structural response energy and enhancing the performance of civil structures undergoing large seismic events. A quadratic output regulator that minimizes a measure including the total structural acceleration energy is developed and tested on a realistic non-linear, semi-active structural control case study. Suites of large scaled earthquakes are used to statistically quantify the impact of this type of control in terms of changes in the statistical distribution of controlled structural response. This approach includes the impulses due to control inputs and is shown to be more effective than a typical displacement focused control approach, by providing equivalent or better performance in terms of displacement and hysteretic energy reductions, while also significantly reducing peak story accelerations and the associated damage and occupant injury. For earthquake engineers faced with the dilemma of balancing displacement and acceleration demands this control approach can significantly reduce that concern, reducing structural damage and improving occupant safety.

Key Words
structural acceleration; quadratic regulator; semi-active control; civil structures; near-field earthquakes; LQRy.

Address
J. Geoffrey Chase; University of Canterbury, Department of Mechanical Engineering, Private Bag 4800, Christchurch, New Zealand
Luciana R. Barroso; Texas A&M University, Department of Civil Engineering, College Station, TX 77843, U.S.A.
Stephen Hunt; University of Canterbury, Department of Mechanical Engineering, Private Bag 4800,Christchurch, New Zealand

Abstract
An artificial neural network (ANN) application is presented for flexural and axial vibration analysis of elastic beams with various support conditions. The first three natural frequencies of beams are obtained using multi layer neural network based back-propagation error learning algorithm. The natural frequencies of beams are calculated for six different boundary conditions via direct solution of governing differential equations of beams and Rayleigh

Key Words
artificial neural networks; natural frequencies; axial and flexural vibration; elastic beams.

Address
Omer Civalek; Akdeniz University, Engineering Faculty, Civil Engineering Dept.,
Division of Mechanics, Antalya, Turkey

Abstract
A four-point bending RC beam strengthened with FRP plate is investigated based on the theory of elasticity. Taking the adhesive layer into account but ignoring some secondary parameters, the analytical solutions of the normal stress and shear stress on concrete-adhesive interface are obtained and discussed. Besides, the pure bending region of the beam is analyzed and the ultimate load of the beam is predicted. The results obtained in the present paper agree very well with both the results of FEM and the experimental findings.

Key Words
FRP plate; adhesive layer; reinforced beam; ultimate load; composites.

Address
Minglan Peng and Zhifei Shi; School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China

Abstract
The vibration control problem of structures with random parameters is discussed, which is approximated by a deterministic one. A method for calculating the standard deviations of eigenvalues of the closed-loop systems is presented by using the random perturbation. The method presented in this paper will not require the distribution function of the random parameters of the systems other than their means and variances. Similarly, the distribution function of the random eigenvalues will not be computed other than their means and variances. The standard deviations of eigenvalues of the uncertain closed-loop systems can be used to estimate the stability robustness. The present method is applied to a vibration control system to illustrate the application. The numerical results show that the present method is effective.

Key Words
uncertain systems; vibration active control; random parameters; standard deviations of eigenvalues of the closed-loop systems.

Address
Su Huan Chen, Chun Liu and Yu Dong Chen;
Department of Mechanics, Jilin University, Nanling Campus, Changchun 130025, P. R. China

Abstract
Rocking response of rigid bodies with rectangular footprint, freely standing on horizontal rigid plane is studied analytically. Bodies are subjected to simulated single component of horizontal earthquakes. The effect of baseline correction, applied to simulated excitations, on the rocking response is first examined. The sensitiveness of rocking motion to the details of earthquakes and geometric properties of rigid bodies is investigated. Due to the demonstrated sensitivity of rocking response to these factors, prediction of rocking stability must be made in the framework of probability theory. Therefore, using a large number of simulated earthquakes, the effects of duration and shape of intensity function of simulated earthquakes on overturning probability of rigid bodies are studied. In the case when a rigid body is placed on any floor of a building, the corresponding probability is compared to that of a body placed on the ground. For this purpose, several shear frames are employed. Finally, the viability of the energy balance equation, which was introduced by Housner in 1963 and widely used by nuclear power industry to estimate the rocking stability of bodies, is evaluated. It is found that the equation is robust. Examples are also given to show how this equation can be used.

Key Words
rigid body; rocking response; simulated earthquakes; energy balance equation.

Address
Kamil Aydin; Erciyes University, Faculty of Engineering, Dept. of Civil Engineering, 38039 Kayseri, Turkey

Abstract
The present study provides a relatively simple and accurate analytical model for the prediction of time-dependent stresses and curvatures of cracked R.C. sections under working loads. A more simplified solution is also provided. The proposed models are demonstrated by considering a numerical example and conducting a parametric study on the effects of relevant R.C. design parameters. In contrary to tension reinforcement, the compression reinforcement is found to contribute significantly in reducing tensile stresses in tension steel and in reducing the total section curvatures. The good accuracy of the proposed approximate solution opens a new vision towards a simple yet accurate model for the prediction of time-dependent effects in R.C. structures.

Key Words
racking; curvatures; reinforced concrete; stresses; time-dependent behavior.

Address
Rajeh Z. Al-Zaid; Civil Engineering Department, College of Engineering, P.O. Box 800, King Saud University, Riyadh 11421, Saudi Arabia

Abstract
Based on the basic equations of elasticity, free-edge effects on stresses in cross-ply laminated plates are found by using the state space method. The laminates are subjected to uniaxial-uniform extension plate, which is a typical example of general plane strain problem. The study takes into account material constants of all individual material layers and the state equation of a laminate is solved analytically in the through thickness direction. By this approach, a composite plate may be composed of an arbitrary number of orthotropic layers, each of which may have different material properties and thickness. The solution provides a continuous displacement and inter-laminar stress fields across all material interfaces and an approxiamte prediction to the singularity of stresses occurring in the boundary layer region of a free-edge. Numerical solutions are obtained and compared with the results obtained from an alternative numerical method.

Key Words
laminated plates; uniform extension; free edge effects; state equation; analytical solution.

Address
Hongyu Sheng; Institute of Civil Engineering, Hefei University of Technology, Hefei, 230009, P. R. China
Jianqiao Ye; School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, UK


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