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CONTENTS
Volume 18, Number 4, April 2015
 

Abstract
This paper focuses on the strengthening methods used for improving the compression behaviors of perforated box-section walls as provided in the anchorage zones of steel pylons. Rectangular plates containing double-row continuous elliptical holes are investigated by employing the boundary condition of simple supporting on four edges in the out-of-plane direction of plate. Two types of strengthening stiffeners, named flat stiffener (FS) and longitudinal stiffener (LS), are considered. Uniaxial compression tests are first conducted for 18 specimens, of which 5 are unstrengthened plates and 13 are strengthened plates. The mechanical behaviors such as stress concentration, out-of-plane deformation, failure pattern, and elasto-plastic ultimate strength are experimentally investigated. Finite element (FE) models are also developed to predict the ultimate strengths of plates with various dimensions. The results of FE analysis are validated by test data. The influences of non-dimensional parameters including plate aspect ratio, hole spacing, hole width, stiffener slenderness ratio, as well as stiffener thickness on the ultimate strengths are illustrated on the basis of numerous parametric studies. Comparison of strengthening efficiency shows that the continuous longitudinal stiffener is the best strengthening method for such perforated plates. The simplified formulas used for estimating the compression strengths of strengthened plates are finally proposed.

Key Words
steel pylon; double cable planes; perforated plate; elliptical hole; strengthening method; uniaxial compression

Address
(1) Bin Cheng, Jianlei Wang:
Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;
(2) Jie Wu:
College of Civil Engineering, Tongji University, Shanghai 200092, China;
(3) Bin Cheng:
State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.

Abstract
Self-compacting Concrete Filled steel Tubes (SCFT), which combines the advantages of steel and concrete materials, can be applied to strengthen the RC columns. In order to investigate the eccentric loading behavior of the strengthened columns, this paper presents an experimental and numerical investigation on them. The experimental results showed that the use of SCFT is interesting since the ductility and the bearing capacity of the RC columns are greatly improved. And the performance of strengthened columns is significantly affected by four parameters: column section type (circular and square), wall thickness of the steel tube, designed strength grade of strengthening concrete and initial eccentricity. In the numerical program, a generic fiber element model which takes in account the effect of confinement is developed to predict the behavior of the strengthened columns subjected to eccentric loading. After the fiber element analysis was verified against experimental results, a simple design formula based on the model is proposed to calculate the ultimate eccentric strength. Calibration of the calculated results against the test results shows that the design formula closely estimates the ultimate capacities of the eccentrically compressed strengthened columns by 5%.

Key Words
RC columns; strengthening; concrete-filled steel tube (CFT); eccentric strength

Address
School of Civil Engineering, Wuhan University, Wuhan City, Hubei Province, 430072, China.

Abstract
Up to now, Japan has more than 200 corrugated steel web composite beam bridges which are under construction and have been constructed, and China has more than 30 corrugated steel web composite beam bridges. The bridge type includes the simply supported beam, continuous beam, continuous rigid frame and cable stayed bridge etc. The section form has developed to the single box and multi-cell box girder from the original single box and single chamber. From the stress performance and cost saving, the span range of 50~150 m is the most competitive. At present, the design mostly adopts the computational analytical method combining the spatial bar system model, plane beam grillage model and solid model. However, the spatial bar system model is short of the refinement analysis on the space effect, such as the shear lag effect, effective distribution width problem, and eccentric load factor problem etc. Due to the similarity of the plane beam grillage method in the equivalence principle, it cannot accurately reflect the shearing stress distribution and local stress of the top and bottom plates of the box type composite beam. The solid model is very difficult to combine with the overall calculation. Moreover, the spatial grid model can achieve the refinement analysis, with the integrity of the analysis and the comprehensiveness of the stress checking calculation, and can make up the deficiency of the analytical method currently. Through the example verification of the solid model and spatial grid model, it can be seen that the calculation results for the stress and the displacement of two models are almost consistent, indicating the applicability and precision of the spatial grid model.

Key Words
corrugated steel web; composite beam bridge; solid model; spatial grid model; refinement

Address
Department of Bridge Engineering, Tongji University, Shanghai 200092, P.R. China.

Abstract
The continuous composite I-girder should have a sufficient rotation capacity (or ductility) to redistribute the negative bending moment into an adjacent positive bending moment region. However, it is generally known that the ductility of the high strength steel is smaller than that of conventional steel, and application of high strength steel can cause ductility problems in a negative moment region of the I-girder. In this study, moment redistribution of the continuous composite I-girder with high strength steel was studied, where high strength steel with yield stress of 690 MPa was considered (the ultimate stress of the steel was 800 MPa). The available and required rotation capacity of the continuous composite I-girder with high strength steel was firstly derived based on the stress-strain curve of high strength steel and plastic analysis, respectively. A large scale test and a series of non-linear finite element analysis for the continuous composite I-girder with high strength steel were then conducted to examine the effectiveness of proposed models and to investigate the effect of high strength steel on the inelastic behavior of the negative bending moment region of the continuous composite I-girder with high strength steel. Finally, it can be found that the proposed equations provided good estimation of the requited and available rotation capacity of the continuous composite I-girder with high strength steel.

Key Words
rotation capacity; ductility; continuous I-girder; composite I-girder; high strength steel

Address
(1) Hyun Sung Joo, Hak-Eun Lee:
School of Civil, Environmental & Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-701, South Korea;
(2) Jiho Moon:
New Transportation Research Center, Korea Railroad Research Institute (KRRI), Uiwang-si, Gyeonggi-do, South Korea;
(3) Ik-Hyun Sung:
Department of Civil Engineering, Hanseo University, Chungcheongnam-do 356-706, South Korea.

Abstract
This paper aims to present an alternative analytical method for transient vibration analysis of doubly-curved laminated shells subjected to dynamic loads. In the method proposed, the governing differential equations of laminated shell are derived using the dynamic version of the principle of virtual displacements. The governing equations of first order shear deformation laminated shell are obtained by Navier solution procedure. Time-dependent equations are transformed to the Laplace domain and then Laplace parameter dependent equations are solved numerically. The results obtained in the Laplace domain are transformed to the time domain with the help of modified Durbin's numerical inverse Laplace transform method. Verification of the presented method is carried out by comparing the results with those obtained by Newmark method and ANSYS finite element software. Also effects of number of laminates, different material properties and shell geometries are discussed. The numerical results have proved that the presented procedure is a highly accurate and efficient solution method.

Key Words
doubly-curved laminated shell; transient vibration analysis; inverse laplace transform; analytic solution

Address
Department of Civil Engineering, Adiyaman University, 02040 Adiyaman, Turkey.

Abstract
This paper investigates the vibration phenomenon of a nanobeam subjected to a time-dependent heat flux. Material properties of the nanobeam are assumed to be graded in the thickness direction according to a novel exponential distribution law in terms of the volume fractions of the metal and ceramic constituents. The upper surface of the functionally graded (FG) nanobeam is pure ceramic whereas the lower surface is pure metal. A nonlocal generalized thermoelasticity theory with dual-phase-lag (DPL) model is used to solve this problem. The theories of coupled thermoelasticity, generalized thermoelasticity with one relaxation time, and without energy dissipation can extracted as limited and special cases of the present model. An analytical technique based on Laplace transform is used to calculate the variation of deflection and temperature. The inverse of Laplace transforms are computed numerically using Fourier expansion techniques. The effects of the phase-lags (PLs), nonlocal parameter and the angular frequency of oscillation of the heat flux on the lateral vibration, the temperature, and the axial displacement of the nanobeam are studied.

Key Words
thermoelasticity; DPL model; FG nanobeam; nonlocal Euler-Bernoulli theory; heat flux

Address
(1) Ashraf M. Zenkour:
Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia;
(2) Ashraf M. Zenkour:
Department of Mathematics, Faculty of Science, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt;
(3) Ahmed E. Abouelregal:
Department of Mathematics, Faculty of Science, Mansoura University, Mansoura 35516, Egypt;
(4) Ahmed E. Abouelregal:
Department of Mathematics, College of Science and Arts, Aljouf University, Al-Qurayat, Saudi Arabia.

Abstract
This paper presents a new cost-effective hybrid GFRP-Concrete deck system that the GFRP panel serves as both tensile reinforcement and stay-in-place form. In order to understand the fatigue behavior of such hybrid deck, fatigue test on a full-scale specimen under sagging moment was conducted, and a series of static tests were also carried out after certain repeated loading cycles. The fatigue test results indicated that such hybrid deck has a good fatigue performance even after 3.1 million repeated loading cycles. A three-dimensional finite element model of the hybrid deck was established based on experimental work. The results from finite element analyses are in good agreement with those from the tests. In addition, flexural fatigue analysis considering the reduction in flexural stiffness and modulus under cyclic loading was carried out. The predicted flexural strength agreed well with the analytical strength from finite element simulation, and the calculated fatigue failure cycle was consistent with the result based on related S-N curve and finite element analyses. However, the flexural fatigue analytical results tended to be conservative compared to the tested results in safety side. The presented overall investigation may provide reference for the design and construction of such hybrid deck system.

Key Words
hybrid bridge deck; fatigue behavior; model test; finite element analysis; flexural fatigue analysis

Address
(1) Haohui Xin, Yuqing Liu, Youyou Zhang:
Department of Bridge Engineering, Tongji University, Shanghai, China;
(2) Jun He:
School of Civil Engineering and Architecture, Changsha University of Science & Technology, Hunan, China;
(3) Haifeng Fan:
Composite Construction Laboratory CCLab, Swiss Federal Institute of Technology, BP Ecublens 1015 Lausanne, Switzerland.

Abstract
An equivalent friction element is proposed to simulate the friction in cable-strut joints. Equivalent stiffness matrixes and load vectors of the friction element are derived and are unified into patterns for FEM by defining a virtual node specially to store internal forces. Three approaches are described to verify the rationality of the new equivalent friction element: applying the new element in a cable-roller model, and numerical solutions match well with experimental results; applying the element in a continuous sliding cable model, and theoretical values, numerical and experimental results are compared; and the last is applying it in truss string structures, whose results indicate that there would be a great error if the cable of cable supported structures is simulated with discontinuous cable model which is usually adopted in traditional finite element analysis, and that the prestress loss resulted from the friction in cable-strut joints would have adverse effect on the mechanical performance of cable supported structures.

Key Words
equivalent friction element; equivalent stiffness; equivalent load; experiment; cable supported structure

Address
(1) School of Civil Engineering, Tianjin University, Tianjin, 300072, China;
(2) Key Laboratory of Coast Civil Structure and Safety, Ministry of Education, Tianjin University, Tianjin, 300072, China.

Abstract
To promote greater acceptance and use of composite RCS systems, a two-bay two-story frame specimen with improved composite RCS joint details was tested in the laboratory under reversed cyclic loading. The test revealed superior seismic performance with stable load versus story drift response and excellent deformation capacity for an inter-story drift ratio up to 1/25. It was found that the failure process of the frame meets the strong-column weak-beam criterion. Furthermore, cracking inter-story drift ratio and ultimate inter-story drift ratio both satisfy the limitation prescribed by the design code. Additionally, inter-story drift ratios at yielding and peak load stage provide reference data for Performance-Based Seismic Design (PBSD) approaches for composite RCS frames. An advantage over conventional reinforced concrete and steel moment frame systems is that the displacement ductility coefficient of the RCS frame system is much larger. To conclude, the test results prove that composite RCS frame systems perform satisfactorily under simulated earthquake action, which further validates the reliability of this innovative system. Based on the test result, some suggestions are presented for the design of composite RCS frame systems.

Key Words
composite structure; RCS; composite joint; capacity; ductility; seismic response

Address
College of Civil Engineering, Xi'an University of Architecture & Technology, 13 Yanta Road, Xi'an, Shaanxi Province, 710055, China.

Abstract
The method of cross-section analysis for different sections in a structural frame has been widely investigated since the 1960s for determination of sectional capacities of beam-columns. Many handcalculated equations and design graphs were proposed for the specific shape and type of sections in precomputer age decades ago. In design of many practical sections, these equations may be uneconomical and inapplicable for sections with irregular shapes, leading to the high construction cost or inadequate safety. This paper not only proposes a versatile numerical procedure for sectional analysis of beam-columns, but also suggests a method to account for residual stress and geometric imperfections separately and the approach is applied to design of high strength steels requiring axial force-moment interaction for advanced analysis or direct analysis. A cross-section analysis technique that provides interaction curves of arbitrary welded sections with consideration of the effects of residual stress by meshing the entire section into small triangular fibers is formulated. In this study, two doubly symmetric sections (box-section and H-section) fabricated by high-strength steel is utilized to validate the accuracy and efficiency of the proposed method against a hand-calculation procedure. The effects of residual stress are mostly not considered explicitly in previous works and they are considered in an explicit manner in this paper which further discusses the basis of the yield surface theory for design of structures made of high strength steels.

Key Words
cross-sectional analysis; high-strength steel; residual stress

Address
(1) Tian-Ji Li, Si-Wei Liu, Siu-Lai Chan:
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China;
(2) Tian-Ji Li:
College of Civil Engineering, Tongji University, Shanghai, China.

Abstract
Ultra-lightweight cement composite (ULCC) with a compressive strength of 60 MPa and density of 1,450 kg/m3 has been developed and used in the steel-concrete-steel (SCS) sandwich structures. This paper investigates the structural performances of SCS sandwich composite beams with ULCC as filled material. Overlapped headed shear studs were used to provide shear and tensile bond between the face plate and the lightweight core. Three-dimensional nonlinear finite element (FE) model was developed for the ultimate strength analysis of such SCS sandwich composite beams. The accuracy of the FE analysis was established by comparing the predicted results with the quasi-static tests on the SCS sandwich beams. The FE model was also applied to the nonlinear analysis on curved SCS sandwich beam and shells and the SCS sandwich beams with J-hook connectors and different concrete core including ULCC, lightweight concrete (LWC) and normal weight concrete (NWC). Validations were also carried out to check the accuracy of the FE analysis on the SCS sandwich beams with J-hook connectors and curved SCS sandwich structure. Finally, recommended FE analysis procedures were given.

Key Words
cement composite; finite element analysis; J hook connector; overlapped connector; sandwich structure

Address
Department of Civil and Environmental Engineering, National University of Singapore, E1A-07-03, One Engineering Drive 2, Singapore 117576.


Abstract
Concrete-filled tubes (CFT), formed by an outer steel tube filled with plain or reinforced concrete inside, have been increasingly used these recent decades as columns or beam-columns, especially for tall buildings in seismic areas due to their excellent structural response. This improved behavior is derived from the effect of confinement provided by the tube, since the compressive strength of concrete increases when being subjected to hydrostatic pressure. In circular CFTs under compression, the whole tube is uniformly tensioned due to the radial expansion of concrete. Contrarily, in rectangular and square-shaped CFTs, the lateral flanges become subjected to in-plane bending derived from this volumetric expansion, and this fact implies a reduction of the confinement effect of the core. This study presents a numerical analysis of different configurations of CFT stub columns with inner stiffening plates, limited to the study of the influence of these plates on the compressive behavior without eccentricity. The final purpose is to evaluate the efficiency in terms of strength and ductility of introducing stiffeners into circular and square CFT sections under large deformation axial loading.

Key Words
axial compression; concrete-filled steel tubes; numerical analysis; design codes; composite structures

Address
Technical University of Catalonia, Structures in Architecture, Av. Diagonal 649 Barcelona 08028, Spain.

Abstract
Concrete-filled circular t steel tubular joints (CFSTJs) in practice are frequently subjected to fluctuated loadings caused by wind, earthquake and so on. As fatigue crack is sensitive to such cyclic loadings, assessment on performance of CFSTJs with crack-like defect attracts more concerns because both high stress concentration at the brace/chord intersection and welding residual stresses along weld toe cause the materials in the region around the intersection to be more brittle. Once crack initiates and propagates along the weld toe, tri-axial stresses in high gradient around the crack front exist, which may bring brittle fracture failure. Additionally, the stiffness and the load carrying capacity of the CFSTJs with crack may decrease due to the weakened connection at the intersection. To study the behaviour of CFSTJs with initial crack, experimental tests have been carried out on three full-scale CFCST T-joints with same configuration. The three specimens include one uncracked joint and two corresponding cracked joints. Load-displacement and load-deformation curves, failure mode and crack propagation are obtained from the experiment measurement. According to the experimental results, it can be found that he load carrying capacity of the cracked joints is decreased by more than 10% compared with the uncracked joint. The effect of crack depth on the load carrying capacity of CFCST T-joints seems to be slight. The failure mode of the cracked CFCST T-joints represents as plastic yielding rather than brittle fracture through experimental observation.

Key Words
concrete-filled circular steel tubular T-joint (CFCST T-joint); experimental study; fatigue crack; residual static strength; failure mode

Address
School of Civil Engineering, Yantai University, Qingquan Road 32#, Laishan District, Yantai, Shandong Province, PR China, 264005.

Abstract
In this paper, a new nonlocal hyperbolic refined plate model is presented for free vibration properties of functionally graded (FG) plates. This nonlocal nano-plate model incorporates the length scale parameter which can capture the small scale effect. The displacement field of the present theory is chosen based on a hyperbolic variation in the in-plane displacements through the thickness of the nano-plate. By dividing the transverse displacement into the bending and shear parts, the number of unknowns and equations of motion of the present theory is reduced, significantly facilitating structural analysis. The material properties are assumed to vary only in the thickness direction and the effective properties for the FG nano-plate are computed using Mori-Tanaka homogenization scheme. The governing equations of motion are derived based on the nonlocal differential constitutive relations of Eringen in conjunction with the refined four variable plate theory via Hamilton\'s principle. Analytical solution for the simply supported FG nano-plates is obtained to verify the theory by comparing its results with other available solutions in the open literature. The effects of nonlocal parameter, the plate thickness, the plate aspect ratio, and various material compositions on the dynamic response of the FG nano-plate are discussed.

Key Words
nonlocal elasticity theory; nano-plates; free vibration; refined plate theory; functionally graded materials

Address
(1) Ismahene Belkorissat, Abdelouahed Tounsi, E.A. Adda Bedia:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Mohammed Sid Ahmed Houari, Abdelouahed Tounsi:
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, Algérie;
(3) S.R. Mahmoud:
Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia;
(4) S.R. Mahmoud:
Mathematics Department, Faculty of Science, University of Sohag, Egypt.

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