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Volume 28, Number 3, February20 2008

Information on the distribution of the basic random variable is essential for the accurate analysis of structural reliability. The usual method for determining the distributions is to fit a candidate
distribution to the histogram of available statistical data of the variable and perform approximate goodness-of-fit tests. Generally, such candidate distribution would have parameters that may be evaluated from the statistical moments of the statistical data. In the present paper, a cubic normal distribution, whose parameters are determined using the first four moments of available sample data, is investigated. A parameter table based on the first four moments, which simplifies parameter estimation, is given. The simplicity, generality, flexibility and advantages of this distribution in statistical data analysis and its significance in structural reliability evaluation are discussed. Numerical examples are presented to demonstrate these advantages.

Key Words
structural reliability; probability distributions; statistical moments; data fitting, fourthmoment reliability index.

Yan-Gang Zhao and Zhao-Hui Lu: Dept. of Architecture and Civil Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, 466-8555, Japan

In this paper, linear elastic isotropic structures under the effects of both stochastic operators and stochastic excitations are studied. The analysis utilizes the spectral stochastic finite elements (SSFEM) with its two main expansions namely; Neumann and Homogeneous Chaos expansions. The random excitation and the random operator fields are assumed to be second order stochastic processes. The
formulations are obtained for the system solution of the two dimensional problems of plane strain and plate bending structures under stochastic loading and relevant rigidity using the previously mentioned
expansions. Two finite element programs were developed to incorporate such formulations. Two illustrative examples are introduced: the first is a reinforced concrete culvert with stochastic rigidity
subjected to a stochastic load where the culvert is modeled as plane strain problem. The second example is a simply supported square reinforced concrete slab subjected to out of plane loading in which the slab
flexural rigidity and the applied load are considered stochastic. In each of the two examples, the first two statistical moments of displacement are evaluated using both expansions. The probability density function of the structure response of each problem is obtained using Homogeneous Chaos expansion.

Key Words
stochastic structures; stochastic finite elements method (SFEM); stochastic excitation; stochastic operators; neumann expansion; Homogeneous Chaos expansion.

O.H. Galal: Engineering Mathematics and Physics Department, Faculty of Engineering, Fayoum University, Egypt
W. El-Tahan: Structural Engineering Department, Faculty of Engineering, Cairo University, Egypt
M.A. El-Tawil and A.A. Mahmoud: Engineering Mathematics and Physics Department, Faculty of Engineering, Cairo University, Egypt

In the present paper a mechanical model to predict the compressive response of high strength short concrete columns with square cross-section confined by transverse steel is presented. The model allows one to estimate the equivalent confinement pressures exercised by transverse steel during the loading process taking into account of the interaction of the stirrups with the inner core both in the plane of the stirrups and in the space between two successive stirrups. The lateral pressure distributions at hoop levels are obtained by using a simple model of elastic beam on elastic medium simulating the interaction between stirrups and concrete core, including yielding of steel stirrups and damage of concrete core by means of the variation in the elastic modulus and in the Poisson?s coefficient. Complete stress-strain curves in compression of confined concrete core are obtained considering the variation of the axial forces in the leg of the stirrup during the loading process. The model was compared with some others presented in the literature and it was validated on the basis of the existing experimental data. Finally, it was shown that the model allows one to include the main parameters governing the confinement problems of high strength concrete members such as: - the strength of plain concrete and its brittleness; - the diameter, the pitch and the yielding stress of the stirrups; - the diameter and the yielding stress of longitudinal bars; - the side of the member, etc.

Key Words
compression; high strength concrete; confinement stress-strain curves.

G. Campione: Dipartimento di Ingegneria Strutturale e Geotecnica, Universita di Palermo Viale delle Scienze . 90128 Palermo, Italy

Seismic performance of coupling beams not designed for ductility is examined. Eight 1:4 scale coupling beam specimens, with seven reinforced concrete sections and one composite section, were tested under cycles of push-pull action. Characteristics of the specimens include moderate shear span ratio in the range of 2.5-3.5, high main reinforcement ratio at 3-4% and small to large stirrup spacing with 90-
degree hooks. All the reinforced concrete specimens failed in a brittle manner. Displacement ductility of specimens with large stirrup spacing (?140 mm) is in the range of 3 to 5. Seismic performance of the
specimens is also examined using the ultimate drift angle and the amount of energy dissipated. Correlating the test data, an empirical relationship is proposed to estimate the ultimate drift angle of a
class of coupling beams considered in the study not designed for ductility.

Key Words
reinforced concrete; coupling beams; seismic; shear; ultimate drift angle; ductility.

S.S.E. Lam: Dept. of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong
B. Wu: Dept. of Civil Engineering, South China University of Technology, Guangzhou, China
Z.Q. Liu: School of Civil Engineering, Harbin Institute of Technology, Harbin, China
Y.L. Wong: Dept. of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong

Continuous operation of test and measurement is a new operating technique in the petroleum exploitation, which combines perforation with test and measurement effectively. In order to measure the original pressure of stratum layer exactly and prevent testing instrument from being impaired or damaged, a suitable shock absorber is urgently necessary to research. Based on the attempt on the FEM analysis and experiment research, a new shock absorber is designed and discussed in this paper. 3D finite element model is established and simulated accurately by LS-DYNA, the effect and the dynamic character of the shock absorber impact by half sinusoidal pulse force under the main lobe frequency are discussed both on theoretics and experiment. It is shown that the new designed shock absorber system has good capability
of shock absorption for the impact load.

Key Words
shock absorber; disturbing force; groundsill; absorption coefficient; impact strength; main lobe frequency.

Yuanxun Wang and Peng Zhang: Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
Zhijian Cui: Huazhong University of Science and Technology, Wuhan, 430074, P.R. China
Xi?an Shiyou University, Xi?an, 710065, P.R. China
Chuanyao Chen: Huazhong University of Science and Technology, Wuhan, 430074, P.R. China


Key Words
buckling; perforated plates; linearly varying in-plane load; plates with cutouts; rectangular

M. Aydin Komur and Mustafa Sonmez: Dept. of Civil Engineering, School of Engineering, Aksaray University, 68100, Aksaray, Turkey

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