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CONTENTS
Volume 56, Number 5, December10 2015
 

Abstract
There is a growing trend of considering uncertainty in optimization process since last few decades. In this regard, Robust Design Optimization (RDO) scheme has gained increasing momentum because of its virtue of improving performance of structure by minimizing the variation of performance and ensuring necessary safety and feasibility of constraint under uncertainty. In the present study, RDO of reinforced concrete folded plate and shell structure has been carried out incorporating uncertainty in the relevant parameters by Monte Carlo Simulation. Folded plate and shell structures are among the new generation popular structures often used in aesthetically appealing constructions. However, RDO study of such important structures is observed to be scarce. The optimization problem is formulated as cost minimization problem subjected to the force and displacements constraints considering dead, live and wind load. Then, the RDO is framed by simultaneously optimizing the expected value and the variation of the performance function using weighted sum approach. The robustness in constraint is ensured by adding suitable penalty term and through a target reliability index. The RDO problem is solved by Sequential Quadratic Programming. Subsequently, the results of the RDO are compared with conventional deterministic design approach. The parametric study implies that robust designs can be achieved by sacrificing only small increment in initial cost, but at the same time, considerable quality and guarantee of the structural behaviour can be ensured by the RDO solutions.

Key Words
robust design optimization; Monte Carlo simulation; folded plate structure; reinforced concrete shell; target reliability; parameter uncertainty

Address
Soumya Bhattacharjya, Subhasis Chakraborti and Subhashis Das: Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, West Bengal, India

Abstract
According to former studies, the mechanical properties of reinforced concrete filled tubular steel (RCFT) columns differed greatly from that of concrete filled steel tubular (CFT) columns because of interaction of inserted reinforcement in RCFT. Employing an experiment-based verification policy, a general FE nonlinear analysis model was developed to analyze the mechanical behavior and failure mechanism of RCFT columns under uniaxial compression. The reasonable stress-strain relationships were suggested for confined concrete, reinforcements and steel tube in the model. The mechanism for shear failure of concrete core was found out in the numerical simulation, and a none-conventional method and equation for evaluating the confinement effect of RCFT were proposed.

Key Words
RCFT; CFT; nonlinear analysis; confinement effect; shear failure

Address
Alifujiang Xiamuxi and Jiang Yu: College of Architecture and Civil Engineering, Xinjiang University, Urumqi 830047, China

Akira Hasegawa: Department of Civil Engineering and Architecture, Hachinohe Institute of Technology, Hachinohe, Japan

Abstract
This paper presents the design of reinforced concrete combined footings of trapezoidal form subjected to axial load and moments in two directions to each column using a new model to consider soil real pressure acting on the contact surface of the footing; such pressure is presented in terms of an axial load, moment around the axis \"X\" and moment around the axis \"Y\" to each column. The classical model considers an axial load and moment around the axis \"X\" (transverse axis) applied to each column, and when the moments in two directions are taken into account, the maximum pressure throughout the contact surface of the footing is considered the same. The main part of this research is that the proposed model considers soil real pressure and the classical model takes into account the maximum pressure, and also is considered uniform. We conclude that the proposed model is more suited to the real conditions and is more economical.

Key Words
footings design; trapezoidal combined footings; moments; bending shear; punching shear

Address
Arnulfo Luevanos Rojas: Faculty of Engineering, Science and Architecture, Juárez University of Durango State, Av. Universidad S/N, Fracc. Filadelfia, CP 35010, Gómez Palacio, Durango, México

Abstract
The stochastic finite element method is employed to obtain a stochastic dynamic model of angled beams subjected to impact loads when uncertain material properties are described by random fields. Using the perturbation technique in conjunction with a precise time integration method, a random analysis approach is developed for efficient analysis of random elastic waves. Formulas for the mean, variance and covariance of displacement, strain and stress are introduced. Statistics of displacement and stress waves is analyzed and effects of bend angle and material stochasticity on wave propagation are studied. It is found that the elastic wave correlation in the angled section is the most significant. The mean, variance and covariance of the stress wave amplitude decrease with an increase in bend angle. The standard deviation of the beam material density plays an important role in longitudinal displacement wave covariance.

Key Words
elastic wave; stochastic finite element; angled beam; impact; random parameter; uncertainty

Address
Changqing Bai: State Key Laboratory of Mechanical Structure Strength and Vibration/ School of Aerospace, Xi\'an Jiaotong University, Xi\'an 710049, China
Hualin Ma: China Construction Technology Group limited Company, Lanzhou 730080, China
Victor P.W. Shim: Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore

Abstract
When the temperature of a structure varies, there is a tendency to produce changes in the shape of the structure. The resulting actions may be of considerable importance in the analysis of the structures having non-prismatic members. The computation of design forces for the non-prismatic beams having symmetrical parabolic haunches (NBSPH) is fairly difficult because of the parabolic change of the cross section. Due to their non-prismatic geometrical configuration, their assessment, particularly the computation of fixed-end horizontal forces and fixed-end moments becomes a complex problem. In this study, the efficiency of the Artificial Neural Networks (ANN) and Adaptive Neuro Fuzzy Inference Systems (ANFIS) in predicting the design forces and the design moments of the NBSPH due to temperature changes was investigated. Previously obtained finite element analyses results in the literature were used to train and test the ANN and ANFIS models. The performances of the different models were evaluated by comparing the corresponding values of mean squared errors (MSE) and decisive coefficients (R2). In addition to this, the comparison of ANN and ANFIS with traditional methods was made by setting up Linear-regression (LR) model.

Key Words
non-prismatic member; finite element analysis; parabolic haunch; artificial neural networks, adaptive neuro fuzzy inference systems

Address
S. Bahadir Yüksel and Alpaslan Yarar: Department of Civil Engineering, Selcuk University, 42075 Konya, Turkey

Abstract
An analytical-computational method along with finite element analysis (FEA) has been employed to analyse the dynamic behaviour of deteriorated structures excited by time- varying mass. The present analysis is focused on the comparative study of a double cracked beam with inclined edge cracks and transverse open cracks subjected to traversing mass. The assumed computational method applied is the fourth order Runge-Kutta method. The analysis of the structure has been carried out at constant transit mass and speed. The response of the structure is determined at different crack depth and crack inclination angles. The influence of the parameters like crack depth and crack inclination angles are investigated on the dynamic behaviour of the structure. The results obtained from the assumed computational method are compared with those of the FEA for validation and found good agreements with FEA.

Key Words
cracked beam; inclined edge crack; crack inclination angles; crack depth

Address
Shakti P. Jena, Dayal R. Parhi and Devasis Mishra: Department of Mechanical Engineering, NIT, Rourkela, India

Abstract
Spherical reticulated shells are widely applied in structural engineering due to their good bearing capability and attractive appearance. Parametric modeling of spherical reticulated shells is the basis of internal analysis and optimization design. In the present study, generation methods of nodes and the corresponding connection methods of rod elements are proposed. Modeling programs are compiled by adopting the ANSYS Parametric Design Language (APDL). A shape optimization method based on the two-stage algorithm is presented, and the corresponding optimization program is compiled in FORTRAN environment. Shape optimization is carried out based on the objective function of the minimum total steel consumption and the restriction condition of strength, stiffness, slenderness ratio, stability. The shape optimization of four typical Schwedler spherical reticulated shells is calculated with the span of 30 m~80 m and rise to span ratio of 1/7~1/2. Compared with the shape optimization results, the variation rules of total steel consumption along with the span and rise to span ratio are discussed. The results show that: (1) The left and right rod-Schwedler spherical reticulated shell is the most optimized and should be preferentially adopted in structural engineering. (2) The left diagonal rod-Schwedler spherical reticulated shell is second only to left and right rod regarding the mechanical behavior and optimized results. It can be applied to medium and small-span structures. (3) Double slash rod-Schwedler spherical reticulated shell is advantageous in mechanical behavior but with the largest total weight. Thus, this type can be used in large-span structures as far as possible. (4) The mechanical performance of no latitudinal rod-Schwedler spherical reticulated shell is the worst and with the second largest weight. Thus, this spherical reticulated shell should not be adopted generally in engineering.

Key Words
schwedler spherical reticulated shell; APDL; parametric modeling; shape optimization

Address
J. Wu, X.Y. Lu, S.C. Li and Y.G. Xue: Geotechnical and Structural Engineering Research Center, Shandong University, Ji\'nan 250061, Shandong, China; Institute of Engineering Mechanics, Shandong Jianzhu University, Ji\'nan 250101, Shandong, China
X.Y. Lu: Institute of Engineering Mechanics, Shandong Jianzhu University, Ji\'nan 250101, Shandong, China
S.C. Li, Z.H. Xu, L.P. Li: Geotechnical and Structural Engineering Research Center, Shandong University, Ji\'nan 250061, Shandong, China
D.L. Zhang: Shandong Agriculture and Engineering University, Ji\'nan 250100, Shandong, China
Y.G. Xue: Geotechnical and Structural Engineering Research Center, Shandong University, Ji\'nan 250061, Shandong, China

Abstract
In this paper, the modified form of shear deformation plate theories is proposed. First, the displacement field geometry of classical and the first order shear deformation theories are compared with each other. Using this comparison shows that there is a kinematic relation among independent variables of the first order shear deformation theory. So, the modified forms of rotation functions in shear deformation theories are proposed. Governing equations for rectangular and circular thick laminated plates, having been analyzed numerically so far, are solved by method of separation of variables. Natural frequencies and mode shapes of the plate are determined. The results of the present method are compared with those of previously published papers with good agreement obtained. Efficiency, simplicity and excellent results of this method are extensible to a wide range of similar problems. Accurate solution for governing equations of thick composite plates has been made possible for the first time.

Key Words
classical theory; first order shear deformation; modified form; laminated plate; vibration; accurate solution

Address
Mohammad Asadi Dalir and Alireza Shooshtari: Mechanical Engineering Department, Bu-Ali Sina University, 65175-4161 Hamedan, Iran

Abstract
In this paper the effects of fling-step and forward-directivity on the seismic performance of steel eccentrically braced frames (EBFs) are addressed. Four EBFs with various numbers of stories (4-, 8-,12- and 15-story) were designed for an area with high seismic hazard. Fourteen near-fault ground motions including seven with forward-directivity and seven with fling-step effects are selected to carry out nonlinear time history (NTH) analyses of the frames. Furthermore, seven more far-field records were selected for comparison. Findings from the study reveal that the median maximum links rotation of the frames subjected to three set of ground motions are in acceptable range and the links completely satisfy the requirement stated in FEMA 356 for LS performance level. The arrival of the velocity pulse in a near-fault record causes few significant plastic deformations, while many reversed inelastic cycles result in low-cycle fatigue damage in far-fault records. Near-fault records in some cases are more destructive and the results of these records are so dispersed, especially the records having fling-step effects.

Key Words
seismic performance; eccentrically braced frame; near-fault earthquake; fling-step; forwarddirectivity

Address
Reyhaneh Eskandari and Davoud Vafaei: Department of Civil Engineering, Chabahar Maritime University, Chabahar, Iran

Abstract
This paper presents a novel method based on sensitivity of structural response for identifying both the system parameters and input excitation force of a bridge. This method, referred to as \"Adjoint Variable Method\", is a sensitivity-based finite element model updating method. The computational cost of sensitivity analyses is the main concern associated with damage detection by these methods. The main advantage of proposed method is inclusion of an analytical method to augment the accuracy and speed of the solution. The reliable performance of the method to precisely indentify the location and intensity of all types of predetermined single, multiple and random damages over the whole domain of moving vehicle speed is shown. A comparison study is also carried out to demonstrate the relative effectiveness and upgraded performance of the proposed method in comparison to the similar ordinary sensitivity analysis methods. Moreover, various sources of error including the effects of noise and primary errors on the numerical stability of the proposed method are discussed.

Key Words
simultaneous damage detection; sensitivity; model updating; Ill posed problem; Inverse problem; regularization; noise

Address
Reza Abbasnia, Akbar Mirzaee and Mohsenali Shayanfar: Department of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran, Islamic Republic of Iran


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