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CONTENTS
Volume 22, Number 5, December10 2016
 

Abstract
While extensive efforts have been made in the past to develop finite element models (FEMs) for concrete-filled steel tubular columns (CFSTCs), these models may not be suitable to be used in some cases, especially in view of the utilisation of high strength steel and high strength concrete. A method is presented herein to predict the complete stress-strain curve of concrete subjected to tri-axial compressive stresses caused by axial load coupled with lateral pressure due to the confinement action in square and rectangular CFSTCs with normal and high strength materials. To evaluate the lateral pressure exerted on the concrete in square and rectangular shaped columns, an accurately developed FEM which incorporates the effects of initial local imperfections and residual stresses using the commercial program ABAQUS is adopted. Subsequently, an extensive parametric study is conducted herein to propose an empirical equation for the maximum average lateral pressure, which depends on the material and geometric properties of the columns. The analysis parameters include the concrete compressive strength (f’c = 20 - 110 N/mm2), steel yield strength (fy = 220 - 850 N/mm2), width-to-thickness (B/t) ratios in the range of 15-52, as well as the length-to-width (L/B) ratios in the range of 2-4. The predictions of the behaviour, ultimate axial strengths, and failure modes are compared with the available experimental results to verify the accuracy of the models developed. Furthermore, a design model is proposed for short square and rectangular CFSTCs. Additionally, comparisons with the prediction of axial load capacity by using the proposed design model, Australian Standard and Eurocode 4 code provisions for box composite columns are carried out.

Key Words
composite columns; flexural stiffness; reliability analysis

Address
(1) Farhad Aslani:
School of Civil, Environmental and Mining Engineering, The University of Western Australia, Crawley, WA 6009, Australia;
(2) Farhad Aslani, Brian Uy, Ziwen Wang:
Centre for Infrastructure Engineering and Safety, The University of New South Wales, Sydney NSW 2052, Australia;
(3) Brian Uy:
School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia;
(4) Vipul Patel:
School of Engineering and Mathematical Sciences, College of Science, Health and Engineering, La Trobe University, Bendigo, VIC 3552, Australia.

Abstract
This work investigates a thermomechanical bending analysis of functionally graded sandwich plates by proposing a novel quasi-3D type higher order shear deformation theory (HSDT). The mathematical model introduces only 5 variables as the first order shear deformation theory (FSDT). Unlike the conventional HSDT, the present one presents a novel displacement field which includes undetermined integral variables. The mechanical properties of functionally graded layers of the plate are supposed to change in the thickness direction according to a power law distribution. The core layer is still homogeneous and made of an isotropic ceramic material. The governing equations for the thermomechanical bending investigation are obtained through the principle of virtual work and solved via Navier-type method. Interesting results are determined and compared with quasi-3D and 2D HSDTs. The influences of functionally graded material (FGM) layer thickness, power law index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are discussed.

Key Words
sandwich plate; thermomechanical; analytical modeling; functionally graded material; stretching effect

Address
(1) Abdeldjalil Benbakhti, Noureddine Retiel:
Faculté des Sciences et de la Technologie, Département de Génie Mécanique, University Abdelhamid Ibn Badis, Mostaganem, 27000, Algérie;
(2) Mohamed Bachir Bouiadjra:
Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes, Faculté de Technologie, Département de génie civil, Algeria;
(3) Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria.

Abstract
The purpose of this paper is to compare the structural responses obtained from the stochastic analysis of a suspension bridge subjected to uniform and partially correlated seismic ground motions, using different spatial correlation functions commonly used in the earthquake engineering. The spatial correlation function employed in this study consists of a term that characterizes the loss of coherency. To account for the spatial variability of ground motions, the widely used four loss of coherency models in the literature has been taken into account in this study. Because each of these models has its own characteristics, it is intended to determine the sensitivity of a suspension bridge due to these losses of coherency models which represent the spatial variability of ground motions. Bosporus Suspension Bridge connects Europe to Asia in Istanbul is selected as a numerical example. The bridge has steel towers that are flexible, inclined hangers and a steel box-deck of 1074 m main span, with side spans of 231 and 255 m on the European and Asian sides, respectively. For the ground motion the filtered white noise model is considered and applied in the vertical direction, the intensity parameter of this model is obtained by using the S16E component of Pacoima Dam record of 1971 San Fernando earthquake. An analytically simple model called as filtered white noise ground motion model is chosen to represent the earthquake ground motion. When compared with the uniform ground motion case, the results obtained from the spatial variability models with partial correlation outline the necessity to include the spatial variability of ground motions in the stochastic dynamic analysis of suspension bridges. It is observed that while the largest response values are obtained for the model proposed by Harichandran and Vanmarcke, the model proposed by Uscinski produces the smallest responses among the considered partially correlated ground motion models. The response values obtained from the uniform ground motion case are usually smaller than those of the responses obtained from the partially correlated ground motion cases. While the response values at the flexible parts of the bridge are totally dominated by the dynamic component, the pseudo-static component also has significant contributions for the response values at the rigid parts of the bridge. The results also show the consistency of the spatial variability models, which have different characteristics, considered in this study.

Key Words
coherency; spatial variability; geometric nonlinearity; stochastic response; suspension bridge

Address
(1) Süeyman Adanur, Ahmet C. Altunışık:
Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey;
(2) Kurtuluş Soyluk:
Department of Civil Engineering, Gazi University, Ankara, Turkey;
(3) A. Aydın Dumanoğlu:
Karadeniz Technical University, Trabzon, Turkey.

Abstract
The use of high-strength concrete (HSC) in precast concrete segmental bridges (PCSBs) can minimize the superstructure geometry and reduce beam weight, which can accelerate the construction speed. Dry joints between the segments in PCSBs introduce discontinuity and require special attention in design and construction. Cracks in dry joints initiate more easily than those in epoxy joints in construction period or in service. Due to the higher rupture strength of HSC, the higher cracking resistance can be achieved. In this study, shear behavior of dry joints in PCSBs was investigated by experiments, especially focusing on cracking resistance and shear strength of HSC dry joints. It can be concluded that the use of HSC can improve the cracking resistance, shear strength, and ductility of monolithic, single-keyed and three-keyed specimens. The experimental results obtained from tests were compared with the AASHTO 2003 design provisions. The AASHTO 2003 provision underestimates the shear capacity of single-keyed dry joint C50 and C70 HSC specimens, underestimates the shear strength of three-keyed dry joint C70 HSC specimens, and overestimates the shear capacity of three-keyed dry joint C50 HSC specimens.

Key Words
dry joint; high-strength concrete (HSC); precast concrete segmental bridges (PCSBs); shear strength

Address
(1) Haibo Jiang, Ying Chen, Tianlong Wang, Zhuangcheng Fang:
School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou Higher Education Mega Center, Guangzhou, China;
(2) Airong Liu:
Guangzhou University-Tamkang University Joint Research Center for Engineering Structure Disaster Prevention and Control, Guangzhou University, Guangzhou Higher Education Mega Center, Guangzhou, China.

Abstract
This paper presents the dynamic characteristics analysis of the purlin-sheet roofs by the random vibration theories. Results show that the natural vibration frequency of the purlin-sheet roof is low, while the frequencies and mode distributions are very intensive. The random vibration theory should be used for the dynamic characteristics of the roof structures due to complex vibration response. Among the first 20th vibration modes, the first vibration mode is mainly the deformations of purlins, while the rest modes are the overall deformations of the roof. In the following 30th modes, it mainly performs unilateral local deformations of the roof. The frequency distribution of the first 20th modes varies significantly while those of the following 30th modes are relatively sensitive. For different parts, the contributions of vibration modes on the vibration response are different. For the part far from the roof ridge, only considering the first 5th modes can reflect the wind-induced vibration response. For the part near the ridge, at least the first 12 modes should be considered, due to complex vibration response. The wind vibration coefficients of the upwind side are slightly higher than that of the leeward side. Finally, the corresponding wind vibration coefficient for the purlin-sheet roof is proposed.

Key Words
purlin sheet roof; random vibration theory; dynamic characteristic; wind-induced vibration coefficient

Address
(1) Yingying Zhang:
State Key Laboratory for GeoMechanics and Deep Underground Engineering, Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering, China University of Mining and Technology, Xuzhou Jiangsu, 221116, China;
(2) Xiaoguang Song:
Shandong Academy of building research, Jinan Shandong, 250031, China;
(3) Qilin Zhang:
College of Civil Engineering, Tongji University, Shanghai 200092, China.

Abstract
The paper presents an innovative steel moment frame with the replaceable reinforced concrete wall panel (SRW) structural system, in which the replaceable concrete wall can play a role to increase the overall lateral stiffness of the frame system. Two full scale specimens composed of the steel frames and the replaceable reinforced concrete wall panels were tested under the cyclic horizontal load. The failure mode, load-displacement response, deformability, and the energy dissipation capacity of SRW specimens were investigated. Test results show that the two-stage failure mode is characterized by the sequential failure process of the replaceable RC wall panel and the steel moment frame. It can be found that the replaceable RC wall panels damage at the lateral drift ratio greater than 0.5%. After the replacement of a new RC wall panel, the new specimen maintained the similar capacity of resisting lateral load as the previous one. The decrease of the bearing capacity was presented between the two stages because of the connection failure on the top of the replaceable RC wall panel. With the increase of the lateral drift, the percentage of the lateral force and the overturning moment resisted by the wall panel decreased for the reason of the reduction of its lateral stiffness. After the failure of the wall panel, the steel moment frame shared almost all the lateral force and the overturning moment.

Key Words
steel moment frame; replaceable wall panel; cyclic test; seismic behavior; two-stage failure

Address
School of Civil Engineering, Chang'an University, Xi'an 710061, China.

Abstract
Rectangular concrete-filled steel tubular columns with unequal wall thickness were investigated in the paper. The physical centroid, the centroidal principal axes of inertia, and the section core were given. The generalized bending formula and the generalized eccentric compression formula were deduced, and the equation of the neutral axis was also provided. The two rectangular concrete-filled steel tubular stub specimens subjected to the compression load on the physical centroid and the geometric centroid respectively were tested to verify the theoretical formulas.

Key Words
CFST; asymmetric cross section; physical centroid; generalized bending formula; generalized eccentric compression formula; cross section core

Address
(1) Yang Zhang, Chen-Jiang Yu, Guang-Yuan Fu, She-Xu Zhao, Si-Ping Li:
Department of Engineering Mechanics, Shanghai Jiao Tong University, Shanghai 200240, P.R. China;
(2) Yang Zhang:
School of Civil Engineering, Nanyang Institute of Technology, Nanyang 473004, P.R. China;
(3) Bing Chen:
Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China.

Abstract
This paper investigates the transverse impact response for ultra lightweight cement composite (ULCC) filled pipe-in-pipe structures through a parametric study using both a validated finite element procedure and a validated theoretical model. The parametric study explores the effect of the impact loading conditions (including the impact velocity and the indenter shape), the geometric properties (including the pipe length and the dimensions of the three material layers) as well as the material properties (including the material properties of the steel pipes and the filler materials) on the impact response of the pipe-in-pipe composite structures. The global impact responses predicted by the FE procedure and by the theoretical model agree with each other closely. The parametric study using the theoretical approach indicates the close relationships among the global impact responses (including the maximum impact force and the maximum global displacement) in specimens with the equivalent thicknesses, proposed in the theoretical model, for the pipe-in-pipe composite structures. In the pipe-in-pipe composite structure, the inner steel pipe, together with the outer steel pipe, imposes a strong confinement on the infilled cement composite and enhances significantly the composite action, leading to improved impact resistance, small global and local deformations.

Key Words
impact response; steel-concrete composite; dynamic analysis; sandwich composite; ultralightweight cement composite

Address
Department of Civil and Environmental Engineering, Centre for Offshore Research and Engineering, National University of Singapore, Singapore 117576.

Abstract
This paper proposes an extension of the Improved Forced Based Design procedure to 3D steel structures. The Improved Forced Based Design (IFBD) procedure consists of a more rational sequence of the design checks proposed in Eurocode 8 and involves a more realistic selection of the behaviour factor instead of selecting an empirical value based on the ductility class and lateral resisting system adopted. The design procedure was tested on a group of four 3D steel structures, composed by moment-resisting frames with three storeys height and the same plan configuration in all storeys. The plan configuration was defined in order to target lateral restrained or unrestrained systems as well as plan regular or irregular structures. The same group of structures was also designed according to the force-based process prescribed in Eurocode 8. The member sizes obtained through the two approaches were compared and the seismic performance was assessed through nonlinear static and time-history analyses. The limit states referred to structural and non-structural damage, considering the two levels design approach, which are the serviceability and the ultimate limit states, were examined. The results obtained reveal that the IFBD leads to more economical structures that still comply with the performance requirements prescribed in Eurocode 8.

Key Words
3D steel structures; forced-based design; behaviour factor; moment resisting frames; Eurocode 8

Address
(1) R. Peres, R. Bento:
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal;
(2) J.M. Castro:
Faculdade de Engenharia da Universidade do Porto, Porto, Portugal.

Abstract
Concrete-filled double skin steel tube (CFDST) beam-columns are widely used in industrial plants, subways, high-rise buildings and arch bridges. The CFDST columns have the same advantages as traditional CFT members. Moreover, they have lighter weight, higher bending stiffness, better cyclic performance, and have higher fire resistance capacities than their CFT counterparts. The scope of this study is to develop finite element models that can predict accepted capacities of double skin concrete-filled tube columns under the combined effect of axial and bending actions. The analysis results were studied to determine the distribution of stresses among the different components and the effect of the concrete core on the outer and inner steel tube. The developed models are first verified against the available experimental data. Accordingly, an extensive parametric study was performed considering different key factors including load eccentricity, slenderness ratio, concrete compressive strength, and steel tube yield strength. The results of the performed parametric study are intended to supplement the experimental research and examine the accuracy of the available design formulas.

Key Words
beam-columns; concrete-filled tube; double-skin; parametric study

Address
Structural Engineering Department, Cairo University, Gamaa Street, Giza, Egypt.

Abstract
This paper presents the cost optimization of a composite I beam floor system, designed to be made from a reinforced concrete slab and steel I sections. The optimization was performed by the mixed-integer non-linear programming (MINLP) approach. For this purpose, a number of different optimization models were developed that enable different design possibilities such as welded or standard steel I sections, plastic or elastic cross-section resistances, and different positions of the neutral axes. An accurate economic objective function of the selfmanufacturing costs was developed and subjected to design, resistance and deflection (in)equality constraints. Dimensioning constraints were defined in accordance with Eurocode 4. The Modified Outer-Approximation/ Equality-Relaxation (OA/ER) algorithm was applied together with a two-phase MINLP strategy. A numerical example of the optimization of a composite I beam floor system, as presented at the end of this paper, demonstrates the applicability of the proposed approach. The optimal result includes the minimal produced costs of the structure, the optimal concrete and steel strengths, and dimensions.

Key Words
composite structures; cost optimization; structural optimization; mixed-integer non-linear programming; MINLP

Address
University of Maribor, Faculty of Civil Engineering, Transportation Engineering and Architecture, Smetanova 17, 2000 Maribor, Slovenia.

Abstract
In this paper, the 3D stress state and inter-laminar stresses in a rotating thin laminated cylinder shell are studied. The thickness of the cylinder is supposed to be thin and it is made of laminated composite material and can have general layer stacking. The governing equations of the cylindrical shell are obtained by employing the Layerwise theory (LWT). The effect of rotation is considered as rotational body force which is induced due to the rotation of the cylinder about its axis. The Layerwise theory (LWT), is used to discrete the partial differential equations of the problem to ordinary ones, in terms of the displacements of the mathematical layers. By applying the Free boundary conditions the solution of the governing equations is completed and the stress state, the inter-laminar stresses, and the edge effect in the rotating cylindrical shells are investigated in the numerical results. To verify the results, LWT solution is compared with the results of the FEM solution and good agreements are achieved. The inter-laminar normal and shear stresses in rotating cylinder are studied and effects of layer stacking and angular velocity is investigated in the numerical results.

Key Words
rotating cylindrical shell; inter-laminar stresses; layerwise theory; laminated composite

Address
Advanced Materials and Computational Mechanics Lab., Department of Mechanical Engineering, University of Zanjan, University Blvd, P.O Box 45371-38791, Zanjan, Iran.

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