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CONTENTS
Volume 49, Number 1, January10 2014
 

Abstract
A seismic evaluation is made of the response to horizontal ground shaking of cantilever retaining walls using the finite element model in three dimensional space whose verification is provided analytically through the modal analysis technique in case of the assumptions of fixed base, complete bonding behavior at the wall-soil interface, and elastic behavior of soil. Thanks to the versatility of the finite element model, the retained medium is then idealized as a uniform, elastoplastic stratum of constant thickness and semi-infinite extent in the horizontal direction considering debonding behavior at the interface in order to perform comprehensive soil-structure interaction (SSI) analyses. The parameters varied include the flexibility of the wall, the properties of the soil medium, and the characteristics of the ground motion. Two different finite element models corresponding with flexible and rigid wall configurations are studied for six different soil types under the effects of two different ground motions. The response quantities examined incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that the wall flexibility and soil properties have a major effect on seismic behavior of cantilever retaining walls and should be considered in design criteria of cantilever walls. Furthermore, the results of the numerical investigations are expected to be useful for the better understanding and the optimization of seismic design of this particular type of retaining structure.

Key Words
wall flexibility; soil-structure interaction; backfill-wall interaction; dynamic analysis

Address
Tufan Cakir: Department of Civil Engineering, Gumuşhane University, 29000 Gumuşhane, Turkey

Abstract
In this article, using finite element method of analysis (FEM), behavior of the endplate moment connection subjected to axial force and bending moment is investigated. In the FEM model, all the nonlinear characteristics such as material, geometry, as well as contact have been included. First, in order to verify the numerical model of the connection, an analysis of the endplate moment connection conducted without the application of the axial force. Results obtained from FEM indicating a close and good correlation with the experimental results. Then to investigate the influence of the axial forces, the connections subjected to axial forces as well as the bending moment are analyzed. To observe the overall effect of these actions, the momentaxial force interaction diagrams are drawn. It is observed that the presence of axial force even in a small value can change the behavior of the connection significantly. It is also shown that the axial forces can alter the failure mode of the connection; and therefore it could result in a different than the predicted moment capacity of the connection.

Key Words
moment connection; endplate; axial loading; finite element method; extended connection

Address
Mehdi Ghassemieh, Ali Akbar Gholampour : School of Civil Engineering, University of Tehran, Tehran, Iran
Iman Shamim : Department of Civil Engineering and Applied Mechanics, McGill University, Canada

Abstract
The main objective of this article is the exploitation of a stochastic hybrid mesh-free method based on stochastic generalized finite difference (SGFD), Newmark finite difference (NFD) methods and Monte Carlo simulation for thermoelastic wave propagation and coupled thermoelasticity analysis based on GN theory (without energy dissipation). A thick hollow cylinder with Gaussian uncertainty in mechanical properties is considered as an analyzed domain for the problem. The effects of uncertainty in mechanical properties with various coefficients of variations on thermo-elastic wave propagation are studied in details. Also, the time histories and distribution on thickness of cylinder of maximum, mean and variance values of temperature and radial displacement are studied for various coefficients of variations (COVs).

Key Words
second sound; stochastic generalized finite difference (SGFD) method; thermal shock; coupled thermoelasticity; Gaussian uncertainty

Address
Seyed Mahmoud Hosseini : Industrial Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, PO Box: 91775-1111, Mashhad, Iran
Farzad Shahabian : Civil Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, PO Box: 91775-1111, Mashhad, Iran

Abstract
This paper reports on the development of a minimum cost design model and its application for obtaining economic designs for reinforced High Strength Concrete (HSC) T-sections in bending under ultimate limit state conditions. Cost objective functions, behavior constraint including material nonlinearities of steel and HSC, conditions on strain compatibility in steel and concrete and geometric design variable constraints are derived and implemented within the Conjugate Gradient optimization algorithm. Particular attention is paid to problem formulation, solution behavior and economic considerations. A typical example problem is considered to illustrate the applicability of the minimum cost design model and solution methodology. Results are confronted to design solutions derived from conventional design office methods to evaluate the performance of the cost model and its sensitivity to a wide range of unit cost ratios of construction materials and various classes of HSC described in Eurocode2. It is shown, among others that optimal solutions achieved using the present approach can lead to substantial savings in the amount of construction materials to be used. In addition, the proposed approach is practically simple, reliable and computationally effective compared to standard design procedures used in current engineering practice.

Key Words
cost optimization; high strength concrete (HSC) T-sections; ultimate limit state (ULS); eurocode2 (EC-2); nonlinear programming; conjugate gradient algorithm

Address
B. Tiliouine and F. Fedghouche : Ecole Nationale Polytechnique, Departement de Genie-Civil, Laboratoire de Genie Sismique et de Dynamique des Structures, 10 Avenue, H. Badi, BP 182, El-Harrach, 16200, Algiers, Algeria

Abstract
Corrosion is one of the primary reasons why structures have limited durability. The present investigation is carried out to study the behavior of RC (Reinforced Concrete) structural members subjected to corrosion. Experimental investigations were carried out on National Bureau of Standard (NBS), RC beam specimens made of Ordinary Portland Cement (OPC) concrete. Load versus deflection behaviour was studied for different levels of corrosion i.e., 2.5%, 5%, 7.5% and 10%. It is observed that for every percentage increase in corrosion level, there is about 1.6% decrease in load carrying capacity. Also as the amount of corrosion increases there is a reduction in bond stress.

Key Words
bond stress; OPC concrete; corrosion rate; durability

Address
Akshatha Shetty, Katta Venkataramana and K.S. Babu Narayan : Department of Civil Engineering, National Institute of Technology, Karnataka Surathkal, 575025, India

Abstract
The study deals with physical modeling of space frame- pile foundation and soil system using finite element models. The superstructure frame is analyzed using complete three -dimensional finite element method where the component of the frame such as slab, beam and columns are descretized using 20 node isoparametric continuum elements. Initially, the frame is analyzed assuming the fixed column bases. Later the pile foundation is worked out separately wherein the simplified models of finite elements such as beam and plate element are used for pile and pile cap, respectively. The non-linear behaviour of soil mass is incorporated by idealizing the soil as non-linear springs using p-y curve along the lines similar to that by Georgiadis et al. (1992). For analysis of pile foundation, the non-linearity of soil via p-y curve approach is incorporated using the incremental approach. The interaction analysis is conducted for the parametric study. The non-linearity of soil is further incorporated using iterative approach, i.e., secant modulus approach, in the interaction analysis. The effect the various parameters of the pile foundation such as spacing in a group and configuration of the pile group is evaluated on the response of superstructure owing to non-linearity of the soil. The response included the displacement at the top of the frame and bending moment in columns. The non-linearity of soil increases the top displacement in the range of 7.8 %- 16.7%. However, its effect is found very marginal on the absolute maximum moment in columns. The hogging moment decreases by 0.005% while sagging moment increases by 0.02%.

Key Words
soil-structure interaction; non-linearity of soil; p-y curve; configuration of pile groups; top displacement; bending moment

Address
H.S. Chore : Department of Civil Engineering, Datta Meghe College of Engineering, Sector-3, Airoli, Navi Mumbai- 400 708, India
R.K. Ingle : Department of Applied Mechanics, Visvesvaraya National Institute of Technology (VNIT), Nagpur- 440 010, India
V.A. Sawant : Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee- 247 667, India

Abstract
The stochastic response surface method (SRSM) and the response surface method (RSM) are often used for structural reliability analysis, especially for reliability problems with implicit performance functions. This paper aims to compare these two methods in terms of fitting the performance function, accuracy and efficiency in estimating probability of failure as well as statistical moments of system output response. The computational procedures of two response surface methods are briefly introduced first. Then their capabilities are demonstrated and compared in detail through two examples. The results indicate that the probability of failure mainly reflects the accuracy of the response surface function (RSF) fitting the performance function in the vicinity of the design point, while the statistical moments of system output response reflect the accuracy of the RSF fitting the performance function in the entire space. In addition, the performance function can be well fitted by the SRSM with an optimal order polynomial chaos expansion both in the entire physical and in the independent standard normal spaces. However, it can be only well fitted by the RSM in the vicinity of the design point. For reliability problems involving random variables with approximate normal distributions, such as normal, lognormal, and Gumbel Max distributions, both the probability of failure and statistical moments of system output response can be accurately estimated by the SRSM, whereas the RSM can only produce the probability of failure with a reasonable accuracy.

Key Words
structural reliability; stochastic response surface method; response surface method; polynomial chaos expansion; performance function; probability of failure

Address
Shui-Hua Jiang, Dian-Qing Li, Chuang-Bing Zhou : State Key Laboratory of Water Resources and Hydropower Engineering Science, Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering (Ministry of Education), Wuhan University, Wuhan, P.R. China
Li-Min Zhang : Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

Abstract
In order to investigate the characteristics of torsional wind loads on rectangular tall buildings, five models with different rectangular cross-sections were tested in a boundary wind tunnel. Based on the test results, the RMS force coefficients, power spectrum densities as well as vertical correlation functions of torsional wind loads were analyzed. Formulas that took the side ratio as parameters were proposed to fit the test results above. Comparisons between the results calculated by the formulas and the wind tunnel measurements were made to verify the reliability of the proposed formulas. An simplified expression to evaluate the dynamic torsional wind loads on rectangular tall buildings in urban terrain is presented on basis of the above formulas and has been proved by a practical project. The simplified expressions as well as the proposed formulas can be applied to estimate wind-induce torsional response on rectangular tall buildings in the frequency domain.

Key Words
rectangular tall buildings; wind tunnel test; RMS torque coefficients; power spectrum density; vertical correlation function; torsional wind loads

Address
Yi Li : College of Civil Engineering, Hunan University, Changsha, 410082 Hunan, China
J.W. Zhang, Q.S. Li : Department of Civil and Architectural Engineering, City University of Hong Kong, Kowloon, Hong Kong


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