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CONTENTS
Volume 52, Number 2, October25 2014
 

Abstract
A four-noded curved shell finite element for the geometrically non-linear analysis of beams curved in plan is introduced. The structure is conceived as a sequence of macro-elements (ME) having the form of transversal segments of identical topology where each slice is formed using a number of the curved shell elements which have 7 degrees of freedom (DOF) per node. A curved box-girder beam example is modelled using various meshes and linear analysis results are compared to the solutions of a well-known computer program SAP2000. Linear and non-linear analyses of the beam under increasing uniformly distributed loads are also carried out. In addition to box-girder beams, the proposed element can also be used in modelling open-section beams with curved or straight axes and circular plates under radial compression. Buckling loads of a circular plate example are obtained for coarse and successively refined meshes and results are compared with each other. The advantage of this element is that curved systems can be realistically modelled and satisfactory results can be obtained even by using coarse meshes.

Key Words
curved shell finite element; second-order effect; buckling

Address
Ulku H. Calik-Karakose, Engin Orakdogen, Ahmet I. Saygun: Department of Civil Engineering, Faculty of Civil Engineering, Istanbul Technical University, 34469 Maslak, İstanbul, Turkey
Harm Askes: Department of Civil and Structural Engineering, University of Sheffield, Sir Frederick Mappin Building Mappin Street, Sheffield, S1 3JD, U.K.

Abstract
Non-stationary random vibration of linear structures with uncertain parameters is investigated in this paper. A time-domain explicit formulation method is first presented for dynamic response analysis of deterministic structures subjected to non-stationary random excitations. The method is then employed to predict the random responses of a structure with given values of structural parameters, which are used to fit the conditional expectations of responses with relation to the structural random parameters by the response surface technique. Based on the total expectation theorem, the known conditional expectations are averaged to yield the random responses of stochastic structures as the total expectations. A numerical example involving a frame structure is investigated to illustrate the effectiveness of the present approach by comparison with the power spectrum method and the Monte Carlo simulation method. The proposed method is also applied to non-stationary random seismic analysis of a practical arch bridge with structural uncertainties, indicating the feasibility of the present approach for analysis of complex structures.

Key Words
non-stationary random vibration; stochastic structures; time-domain; explicit formulation

Address
Cheng Su: School of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510640, P.R. China; State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510640, P.R. China
Rui Xu: of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510640, P.R. China

Abstract
An accurate finite element (FE) model of a structure is essential for predicting reliably its dynamic characteristics. Such a model is used to predict the effects of structural modifications for dynamic design of the structure. These modifications may be imposed by design alterations for operating reasons. Most of the model updating techniques neglect damping and so these updated models can\'t be used for accurate prediction of vibration amplitudes. This paper deals with the basic formulation of damped finite element model updating method and its use for structural dynamic modifications. In this damped damped finite element model updating method, damping matrices are updated along with mass and stiffness matrices. The damping matrices are updated by updating the damping coefficients. A case involving actual measured data for the case of F-shaped test structure, which resembles the skeleton of a drilling machine is used to evaluate the effectiveness of damped FE model updating method for accurate prediction of the vibration levels and thus its use for structural dynamic modifications. It can be concluded from the study that damped updated FE model updating can be used for structural dynamic modifications with confidence.

Key Words
damping identification; model updating; structural dynamic modifications

Address
Vikas Arora: Department of Technology and Innovation, University of Southern Denmark, Campusvej 55, Odense 5230, Denmark

Abstract
In this paper, Simple Adaptive Control (SAC) method is used to mitigate the detrimental effects of earthquakes on MR-damper equipped structures. Acceleration Feedback (AF) is utilized since measuring the acceleration response of structures is known to be reliable and inexpensive. The SAC is simple, fast and as an adaptive control scheme, is immune against the effects of plant and environmental uncertainties. In the present study, in order to translate the desired control force into an applicable MR damper command voltage, a neural network inverse model is trained, validated and used through the simulations. The effectiveness of the proposed AF-based SAC control system is compared with optimal H2/LQG controllers through numerical investigation of a three-story model building. The results indicate that the SAC controller is substantially effective and reliable in both undamaged and damaged structural states, specifically in reducing acceleration responses of seismically excited buildings.

Key Words
seismic control; acceleration feedback; simple adaptive control; MR dampers; neural networks

Address
F. Amini and M. Javanbakht: Department of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

Abstract
In this paper the progressive collapse resisting capacity of steel moment frames with MR dampers is evaluated, and a preliminary design procedure for the dampers to prevent progressive collapse is suggested. Parametric studies are carried out using a beam-column subassemblage with varying natural period, yield strength, and damper force. Then the progressive collapse potentials of 15-story steel moment frames installed with MR dampers are evaluated by nonlinear dynamic analysis. The analysis results of the model structures showed that the MR dampers are effective in preventing progressive collapse of framed structures subjected to sudden loss of a first story column. The effectiveness is more noticeable in the structure with larger vertical deflection subjected to larger inelastic deformation. The maximum responses of the structure installed with the MR dampers designed to meet a given target dynamic response factor generally coincided well with the target value on the conservative side.

Key Words
MR dampers; moment frames; progressive collapse; nonlinear dynamic analysis

Address
Jinkoo Kim: Department of Architectural Engineering, Sungkyunkwan University, Suwon, Korea
Seungjun Lee: Samsung Engineering and Construction, Ltd., Seoul, Korea
Kyung-Won Min: Department of Architectural Engineering, Dankook University, Yongin, Korea

Abstract
A two-step procedure to detect and quantify damages in structures from changes in curvature mode shapes is presented here. In the first step the maximum difference in curvature mode shapes of the undamaged and damaged structure are used for visual identification of the damaged internal-substructure. In the next step, the identified substructures are searched using unified particle swarm optimization technique for exact identification of damage location and amount. Efficiency of the developed procedure is demonstrated using beam like structures. This methodology may be extended for identifying damages in general frame structures.

Key Words
damage assessment; inverse problem; curvature mode shape; stiffness reduction factor

Address
Bharadwaj Nanda, Damodar Maity: Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India
Dipak Kumar Maiti: Department of Aerospace Engineering, Indian Institute of Technology, Kharagpur, India

Abstract
In this paper, linear buckling analysis of a curved sandwich beam with a flexible core is investigated. Derivation of equations for face sheets is accomplished via the classical theory of curved beam, whereas for the flexible core, the elasticity equations in polar coordinates are implemented. Employing the von-Karman type geometrical non-linearity in strain-displacement relations, nonlinear governing equations are resulted. Linear pre-buckling analysis is performed neglecting the rotation effects in pre-buckling state. Stability equations are concluded based on the adjacent equilibrium criterion. Considering the movable simply supported type of boundary conditions, suitable trigonometric solutions are adopted which satisfy the assumed edge conditions. The critical uniform load of the beam is obtained as a closed-form expression. Numerical results cover the effects of various parameters on the critical buckling load of the curved beam. It is shown that, face thickness, core thickness, core module, fiber angle of faces, stacking sequence of faces and openin angle of the beam all affect greatly on the buckling pressure of the beam and its buckled shape.

Key Words
sandwich curved beam; buckling; flexible core; critical load

Address
A. Poortabib and M. Maghsoudi: Space Research Institute, Tehran 15914, Iran

Abstract
This study presents a hunting search based optimum design algorithm for engineering optimization problems. Hunting search algorithm is an optimum design method inspired by group hunting of animals such as wolves, lions, and dolphins. Each of these hunters employs hunting in a different way. However, they are common in that all of them search for a prey in a group. Hunters encircle the prey and the ring of siege is tightened gradually until it is caught. Hunting search algorithm is employed for the automation of optimum design process, during which the design variables are selected for the minimum objective function value controlled by the design restrictions. Three different examples, namely welded beam, cellular beam and moment resisting steel frame are selected as numerical design problems and solved for the optimum solution. Each example differs in the following ways: Unlike welded beam design problem having continuous design variables, steel frame and cellular beam design problems include discrete design variables. Moreover, while the cellular beam is designed under the provisions of BS 5960, LRFD-AISC (Load and Resistant Factor Design-American Institute of Steel Construction) is considered for the formulation of moment resisting steel frame. Levy Flights is adapted to the simple hunting search algorithm for better search. For comparison, same design examples are also solved by using some other well-known search methods in the literature. Results reveal that hunting search shows good performance in finding optimum solutions for each design problem.

Key Words
structural optimization; cellular beams; steel frames; welded beam design problem; hunting search algorithm; Levy flights

Address
Erkan Dogan: Department of Civil Engineering, Faculty of Engineering, Celal Bayar University, 45160, Manisa, Turkey

Abstract
Two-layer coupled or composite beams with discrete shear connectors of finite dimensions are commonly encountered in pre-fabricated construction. This paper presents the development of simplified closed-form solutions for such type of coupled beams for practical applications. A new coupled beam element is proposed to represent the unconnected segments in the beam. General solutions are then developed by an inductive method based on the results from the finite element analysis. A modification is subsequently considered to account for the effect of local deformations. For typical cases where the local deformation is primarily concerned about its distribution over the depth of the coupled beam, empirical modification factors are developed based on parametric calculations using finite element models. The developed analytical method for the coupled beams in question is simple, sufficiently accurate, and suitable for quick calculation in engineering practice.

Key Words
prefabrication; modular structures; coupled beam; discrete shear connection; composite effect; simplified solution

Address
Tianxin Zheng: Department of Civil Engineering, University of Nottingham Ningbo, Ningbo, China
Yong Lu and Asif Usmani: Institute for Infrastructure and Environment, School of Engineering, The University of Edinburgh, The King

Abstract
In this study an innovative method of earthquake-resistant strengthening of reinforced concrete structures is presented for the first time. Strengthening according to this new method consists of the construction of steel fiber high-strength concrete jackets without conventional reinforcement which is usually applied in the construction of conventional reinforced concrete jackets (i.e., longitudinal reinforcement, stirrups, hoops). The proposed in this study innovative steel fiber high-strength or ultra highstrength concrete jackets were proved to be much more effective than the reinforced concrete jackets and the FRP-jackets when used for the earthquake-resistant strengthening of reinforced concrete structural members.

Key Words
steel fiber high-strength concrete; reinforced concrete jackets; beam-column joints; columns; cyclic loads

Address
Alexander-Dimitrios G. Tsonos: Department of Civil Engineering, Aristotle University of Thessaloniki, GR-54124, Thessaloniki, Greece

Abstract
In this paper, a new meta-heuristic algorithm named Ranked Particles Optimization (RPO), is presented. This algorithm is not inspired from natural or physical phenomena. However, it is based on numerous researches in the field of meta-heuristic optimization algorithms. In this algorithm, like other meta-heuristic algorithms, optimization process starts with by producing a population of random solutions, Particles, located in the feasible search space. In the next step, cost functions corresponding to all random particles are evaluated and some of those having minimum cost functions are stored. These particles are ranked and their weighted average is calculated and named Ranked Center. New solutions are produced by moving each particle along its previous motion, the ranked center, and the best particle found thus far. The robustness of this algorithm is verified by solving some mathematical and structural optimization problems. Simplicity of implementation and reaching to desired solution are two main characteristics of this algorithm.

Key Words
meta-heuristic optimization algorithm; Ranked Particles Optimization; RPO; particle; ranked center

Address
A. Kaveh and A. Nasrollahi: Centre of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran

Abstract
This paper presents detailed analysis of the internal forces of interior beam-column joints of reinforced concrete (RC) frames under seismic action, identifies critical joint sections, proposes consistent definitions of average joint shear stress and average joint shear strain, derives formulas for calculating average joint shear and joint torque, and reports simplified analysis of the effects of joint shear and torque on the flexural strengths of critical joint sections. Numerical results of internal joint forces and flexural strengths of critical joint sections are presented for a pair of concentric and eccentric interior connections extracted from a seismically designed RC frame. The results indicate that effects of joint shear and torque may reduce the column-to-beam flexural strength ratios to below unity and lead to \"joint-yielding mechanism\" for seismically designed interior connections. The information presented in this paper aims to provide some new insight into the seismic behavior of interior beam-column joints and form a preliminary basis for analyzing the complicated interaction of internal joint forces.

Key Words
axial strength; beam columns; flexural strength; interaction; joints; reinforced concrete; seismic behavior; shear; torsion

Address
Hua Zhou: Hainan University, 58 Renmindadao, Haikou, Hainan, 570228, PRC; APCE Design Group Limited, 2nd Floor, Tower A, 19 Yusha Road, Haikou, Hainan, 570125, PRC
Jiangli Zhang: Hainan University, 58 Renmindadao, Haikou, Hainan, 570228, PRC


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