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Volume 27, Number 5, June10 2018

Mechanical shear connectors are commonly used to transfer longitudinal shear forces across the steel-concrete interface in composite beams. Steel pipe as a new shear connector is proposed in this research and its performance to achieve composite strength is investigated. Experimental monotonic push-out tests were carried out for this connector. Then, a nonlinear finite element model of the push-out specimens is developed and verified against test results. Further, the finite element model is used to investigate the effects of pipe thickness, length and diameter on the shear strength of the connectors. The ultimate strengths of these connectors are reported and their respective failure modes are discussed. This paper comprises of the push-out tests of ten specimens on this shear connector in both the vertical and horizontal positions in different reinforced concretes. The results of experimental tests are given as load-deformation plots. It is concluded that the use of these connectors is very effective and economical in the medium shear demand range of 150-350 KN. The dominant failure modes observed were either failure of concrete block (crushing and splitting) or shear failure of pipe connector. It is shown that the horizontal pipe is not as effective as vertical pipe shear connector and is not recommended for practical use. It is shown that pipe connectors are more effective in transferring shear forces than channel and stud connectors. Moreover, based on the parametric study, a formula is presented to predict the pipe shear connectors' capacity.

Key Words
push-out test; pipes; shear connectors; reinforced concrete; composite beams; monotonic loading

(1) Saeed Nasrollahi, Shervin Maleki:
Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
(2) Mahdi Shariati:
Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran;
(3) Aminaton Marto:
Malaysia-Japan International Institute of Technology (MJIIT), Universiti Teknologi Malaysia Kuala Lumpur, Malaysia;
(4) Majid Khorami:
Facultad de Arquitectura y Urbanismo, Universidad Tecnológica Equinoccial, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador.

This study presents a novel method of improving the strength and stiffness of cold-formed steel (CFS) beams. Flexural members are primary members in most of the structures. Hence, there is an urgent need in the CFS industry to look beyond the conventional CFS beam sections and develop novel techniques to address the severe local buckling problems that exist in CFS flexural members. The primary objective of this study was to develop new CFS composite beam sections with improved structural performance and economy. This paper presents an experimental study conducted on different CFS composite beams with simply supported end conditions under four point loading. Material properties and geometric imperfections of the models were measured. The test strengths of the models are compared with the design strengths predicted by using Australian/New Zealand Standard for cold-formed steel structures. Furthermore, to ensure high precision testing, a special testing rig was also developed for testing of long span beams. The description of test models, testing rig features and test results are presented here. For better interpretation of results, a comparison of the test results with a hot rolled section is also presented. The test results have shown that the proposed CFS composite beams are promising both in terms of better structural performance as well as economy.

Key Words
failure modes; cold-formed steel composite beams; structural behavior; timber packing; critical load

(1) M. Adil Dar:
Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India;
(2) N. Subramanian:
Consulting Engineer, Maryland, USA;
(3) M. Anbarasu:
Department of Civil Engineering, Government College of Engineering Salem, Tamilnadu, India;
(4) A.R. Dar:
Department of Civil Engineering, National Institute of Technology Srinagar, J&K, India;
(5) James B.P. Lim:
Department of Civil & Environmental Engineering, University of Auckland, New Zealand.

A 1/3 composite cylindrical shell with a central rectangular opening was axially compressed experimentally, and its critical buckling load and displacement, and strains were measured. A finite element model (FEM) of the shell with Hashin failure criteria was established to analyze its buckling and post-buckling behaviors by nonlinear Newton-Raphson method. The geometric imperfection sensitivity and the effect of side supported conditions of the shell were investigated. It was found that the Newton-Raphson method can be used to analyze the buckling and post-buckling behaviors of the shell. The shell is not sensitive to initial geometric imperfection. And the support design of the shell by side stiffeners is a good way to obtain the critical buckling load and simplify the experimental fixture.

Key Words
composite shell; opening; post-buckling; Newton-Raphson method; FEM; axial compression

(1) Yihao Ma, Xiaoquan Cheng, Xin Guo, Jie Zhang:
School of Aeronautic Science and Engineering, Beihang University, Beijing, 100191, China;
(2) Xiaoquan Cheng:
Key Laboratory of Aircraft Advanced Design Technology (Beihang University), Ministry of Industry and Information Technology, Beijing, 100191, China;
(3) Zhaodi Wang, Yahong Xu:
Institute 306 of the 3rd Academy of CASIC, Beijing, 100074, China.

The objective of this work is to analyze large deflections of a fiber reinforced composite cantilever beam under point loads. In the solution of the problem, finite element method is used in conjunction with two dimensional (2-D) continuum model. It is known that large deflection problems are geometrically nonlinear problems. The considered non-linear problem is solved considering the total Lagrangian approach with Newton-Raphson iteration method. In the numerical results, the effects of the volume fraction and orientation angles of the fibre on the large deflections of the composite beam are examined and discussed. Also, the difference between the geometrically linear and nonlinear analysis of fiber reinforced composite beam is investigated in detail.

Key Words
large deflection analysis; fiber reinforced composite beam; total Lagragian; Finite Element Method

Department of Civil Engineering, Bursa Technical University, Yıldırım Campus, Yıldırım, Bursa 16330, Turkey.

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

Key Words
CFDST columns; longitudinal stiffeners; transverse ring stiffeners; cyclic loading; hysteresis; pinching; ductility; dissipated energy

Civil Engineering Department, Urmia University of Technology, Urmia, Iran.

In this article a four unknown quasi-3D shear deformation theory for the bending analysis of functionally graded (FG) plates is developed. The advantage of this theory is that, in addition to introducing the thickness stretching impact (

Key Words
quasi 3D theory; bending; functionally graded plate

(1) Nabil Hebbar, Mohamed Bourada, Mohamed Sekkal, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Mohamed Sekkal, Abdelouahed Tounsi:
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria;
(3) Abdelouahed Tounsi:
Civil and Environmental Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia;
(4) S.R. Mahmoud:
Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia.

The requirement to safe and economical buildings caused to the exploitation of nonlinear capacity structures and optimization of them. This requirement leads to forming seismic design method based on performance. In this study, concentrically braced frames (CBFs) have been optimized at the immediate occupancy (IO) and collapse prevention (CP) levels. Minimizing structural weight is taken as objective function subjected to performance constraints on inter-story drift ratios at various performance levels. In order to evaluate the seismic capacity of the CBFs, pushover analysis is conducted, and the process of optimization has been done by using Bee Algorithm. Results indicate that performance based design caused to have minimum structural weight and due to increase capacity of CBFs.

Key Words
performance-based design; CBF; optimization; bee colony algorithm; pushover

(1) Iman Mansouri:
Department of Civil Engineering, Birjand University of Technology, Birjand, Iran;
(2) Sanaz Soori:
Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran;
(3) Hamed Amraie:
Islamic Azad University-Roudehen Branch, Roudehen, Iran;
(4) Jong Wan Hu:
Department of Civil and Environmental Engineering, Incheon National University, Incheon 22012, South Korea;
(5) Jong Wan Hu:
Incheon Disaster Prevention Research Center, Incheon National University, Incheon 22012, South Korea;
(6) Shahrokh Shahbazi:
TAAT Investment Group, Tehran, Iran.

Performance-Based Plastic Design (PBPD) method has been recently developed to evaluate the behavior of structures in different performance levels. The PBPD method utilizes a base shear force and a lateral load pattern that are estimated based on energy and yielding mechanism concepts. Using of current lateral force pattern results in weak structural members in upper stories of a structure so that the values of the story drift in these stories are larger than the target drift, particularly in high-rise buildings. Therefore, such distribution requires modifications to overcome this drawback. This paper proposes a modified lateral load pattern for steel Eccentrically Braced Frames (EBFs) based on parametric study. In order toachieve the modified load pattern, a group of 26 EBFs has been analyzed under a set of 20 earthquake ground motions. Additionally, results of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis in order to derive the new load pattern. To prove the efficiency of present study, three EBFs as examples were designed by modified pattern and current PBPD distribution. Inelastic dynamic analyses results showed that the story drifts using modified lateral load pattern were well within the target values in comparison with current pattern in PBPD, particularly where the effect of the height is significant. The modified load pattern reduces the possibility of underdesigning in upper levels and overdesigning in lower levels of the frames.

Key Words
performance-based plastic design; lateral load pattern; eccentrically braced frames; energy balance; steel building

Department of Civil Engineering, Shahid Bahonar University of Kerman, P.O. Box 76175-133, Kerman, Iran.

This study investigated the seismic performance of a hybrid damper composed of a steel slit plate and friction pads, and an optimum retrofit scheme was developed based on life cycle cost. A sample hybrid damper was tested under cyclic loading to confirm its validity as a damping device and to construct its nonlinear analysis model. The effectiveness of the optimum damper distribution schemes was investigated by comparing the seismic fragility and the life cycle costs of the model structure before and after the retrofit. The test results showed that the damper behaved stably throughout the loading history. Numerical analysis results showed that the slit-friction hybrid dampers optimally distributed based on life cycle cost proved to be effective in minimizing the failure probability and the repair cost after earthquakes.

Key Words
steel slit dampers; friction dampers; seismic retrofit; optimum design; life cycle cost

Department of Civil and Architectural Engineering, Sungkyunkwan University, Suwon, Republic of Korea.

Through extensive research, there exist a new type of connection between railway bridge girders and steel-concrete composite panels. In addition to conventional shear connectors, newly developed blind bolts have been recently adopted for retrofitting. However, the body of knowledge on their influence and application to railway structures has not been thoroughly investigated. This study has thus placed a particular emphasis on the application of blind bolts on the Sydney Harbour Bridge as a feasible alternative constituent of railway track upgrading. Finite element modeling has been used to simulate the behaviours of the precast steel-concrete panels with common types of bolt connection using commercially available package, ABAQUS. The steel-concrete composite track slabs have been designed in accordance with Australian Standards AS5100. These precast steel-concrete panels are then numerically retrofitted by three types of most practical bold connections: head studded shear connector, Ajax blind bolt and Lindapter hollow bolt. The influences of bolt connections on load and stress transfers and structural behaviour of the composite track slabs are highlighted in this paper. The numerical results exhibit that all three bolts can distribute stresses effectively and can be installed on the bridge girder. However, it is also found that Lindapter hollow bolts are superior in minimising structural responses of the composite track slabs to train loading.

Key Words
steel-concrete composites; railway track slabs; track support structures; modular precast composites; bolt connections

(1) Olivia Mirza:
School of Computing, Engineering & Mathematics, University of Western Sydney, Kingswood, NSW 2747 Australia;
(2) Sakdirat Kaewunruen:
Birmingham Centre for Railway Research and Education, School of Civil Engineering, The University of Birmingham, Edgbaston, B15 2TT, UK.

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