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CONTENTS
Volume 56, Number 6, December25 2015
 

Abstract
Upgrading or strengthening of existing reinforced concrete (RC) infrastructure is an emerging demand nowadays. Near Surface Mounted (NSM) technique is very promising approach for flexural strengthening of RC members. However, premature failure such as concrete cover separation failure have been a main concern in utilizing this technique. In this study, U-wrap end anchorage with carbon fiber reinforced polymer (CFRP) fabrics is proposed to eliminate the concrete cover separation failure. Experimental programs were conducted to the consequence of U-wrap end anchorage on the flexurally strengthened RC beams with NSM- steel. A total of eight RC rectangular beam specimens were tested. One specimen was kept unstrengthened as a reference; three specimens were strengthened with NSM-steel bars and the remaining four specimens were strengthened with NSM-steel bars and U-wrap end anchorage using CFRP fabrics. A 3D non-linear finite element model (FEM) was developed to simulate the flexural response of the tested specimens. It is revealed that NSM-steel (with and without end-anchors) significantly improved the flexural strength; moreover decreased deflection and strains compared with reference specimen. Furthermore, NSM-steel with end anchorage strengthened specimens revealed the greater flexural strength and improve failure modes (premature to flexure) compared with the NSM-steel without end anchorage specimens. The results also ensured that the U-wrap end anchorage completely eliminate the concrete cover separation failure.

Key Words
polymer composites; flexural strengthening; finite element modeling; NSM-steel; debonding; end anchorage; CFRP fabrics

Address
Md. Akter Hosen, Mohd Zamin Jumaat, A. B. M. Saiful Islam, Mohamed Kamruzzaman, Md. Nazmul Huda and Mahmudur Rahman Soeb: Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia

Abstract
The nonlinear numerical analysis of the impact response of reinforced concrete/mortar beam incorporated with the updated Lagrangian method, namely the Smoothed Particle Hydrodynamics (SPH) is carried out in this study. The analysis includes the simulation of the effects of high mass low velocity impact load falling on beam structures. Three material models to describe the localized failure of structural elements are: (1) linear pressure-sensitive yield criteria (Drucker-Prager type) in the pre-peak regime for the concrete/mortar meanwhile, the shear strain energy criterion (Von Mises) is applied for the steel reinforcement (2) nonlinear hardening law by means of modified linear Drucker-Prager envelope by employing the plane cap surface to simulate the irreversible plastic behavior of concrete/mortar (3) implementation of linear and nonlinear softening in tension and compression regions, respectively, to express the complex behavior of concrete material during short time loading condition. Validation upon existing experimental test results is conducted, from which the impact behavior of concrete beams are best described using the SPH model adopting an average velocity and erosion algorithm, where instability in terms of numerical fragmentation is reduced considerably.

Key Words
erosion; impact loading; modified Drucker-Prager; RC beam; smoothed particle hydrodynamics

Address
S.N. Mokhatar: Jamilus Research Center, Faculty of Civil and Environmental Engineering, University Tun Hussein Onn Malaysia, 86400, Batu Pahat, Johor, Malaysia
Y. Sonoda: Structural Analysis Laboratory, Department of Civil Engineering, Kyushu University, Motooka 744, Nishi-ku, Fukoka, Japan
A.B.H. Kueh and Z.M. Jaini: Construction Research Centre, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia

Abstract
In this paper, a new approach based on the continuum model is proposed to estimate the main cable tension force of suspension bridges from measured natural frequencies. This approach considered the vertical vibration of a main cable hinged at both towers and supported by an elastic girder and hangers along its entire length. The equation reflected the relationship between vibration frequency and horizontal tension force of a main cable was derived. To avoid to generate the additional cable tension force by sagextensibility, the analytical solution of characteristic equation for anti-symmetrical vibration mode of the main cable was calculated. Then, the estimation of main cable tension force was carried out by antisymmetric characteristic frequency vector. The errors of estimation due to characteristic frequency deviations were investigated through numerical analysis of the main cable of Taizhou Bridge. A field experiment was conducted to verify the proposed approach. Through measuring and analyzing the responses of a main cable of Taizhou Bridge under ambient excitation, the horizontal tension force of the main cable was identified from the first three odd frequencies. It is shown that the estimated results agree well with the designed values. The proposed approach can be used to conduct the long-term health monitoring of suspension bridges.

Key Words
tension force; main cable; suspension bridge; continuum model; anti-symmetrical vibration

Address
Jun Wang, Weiqing Liu, Lu Wang and Xiaojian Han: College of Civil Engineering, Nanjing Tech University, Nanjing, China

Abstract
In this study, a non-stationary random earthquake Clough-Penzien model is used to describe earthquake ground motion. Using stochastic direct integration in combination with an equivalent linear method, a solution is established to describe the non-stationary response of lead-rubber bearing (LRB) system to a stochastic earthquake. Two parameters are used to develop an optimization method for bearing design: the post-yielding stiffness and the normalized yield strength of the isolation bearing. Using the minimization of the maximum energy response level of the upper structure subjected to an earthquake as an objective function, and with the constraints that the bearing failure probability is no more than 5% and the second shape factor of the bearing is less than 5, a calculation method for the two optimal design parameters is presented. In this optimization process, the radial basis function (RBF) response surface was applied, instead of the implicit objective function and constraints, and a sequential quadratic programming (SQP) algorithm was used to solve the optimization problems. By considering the uncertainties of the structural parameters and seismic ground motion input parameters for the optimization of the bearing design, convex set models (such as the interval model and ellipsoidal model) are used to describe the uncertainty parameters. Subsequently, the optimal bearing design parameters were expanded at their median values into first-order Taylor series expansions, and then, the Lagrange multipliers method was used to determine the upper and lower boundaries of the parameters. Moreover, using a calculation example, the impacts of site soil parameters, such as input peak ground acceleration, bearing diameter and rubber shore hardness on the optimization parameters, are investigated.

Key Words
seismic isolated structure; optimal design; lead-core rubber bearing (LRB); stochastic analysis; convex sets

Address
Fan Jian and Long Xiaohong: School of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Wuhan, China
Zhang Yanping: School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, China

Abstract
This study focuses on the load carrying capacity and the force transfer mechanism of multi-hole perfobond shear connectors in steel-concrete composite structure. The behavior of multi-hole perfobond shear connector is more complicated than single-hole connector cases. 2 groups push-out tests were conducted. Based on the test results, behavior of the connection was analyzed and the failure mechanism was identified. Simplified iterative method and analytic solution were proposed based on force equilibrium for analyzing multi-hole perfobond shear connector performance. Finally, the sensitivity of design parameters of multi-hole perfobond shear connector was investigated. The results of this research showed that shear force distribution curve of multi-hole perfobond shear connector is near catenary. Shear forces distribution were determined by stiffness ratio of steel to concrete member, stiffness ratio of shear connector to steel member, and number of row. Efficiency coefficient was proposed to should be taking into account in different limit state.

Key Words
steel-concrete composite structure; perfobond shear connectors; push-out tests; mechanical behavior; simplified calculation

Address
Xing Wei and Lin Xiao: School of Civil Engineering, Southwest Jiaotong University, Chengdu, China
Shiling Pei: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, USA

Abstract
In this study, free vibration analysis of an edge cracked multilayered symmetric sandwich beams made of functionally graded materials are investigated. Modelling of the cracked structure is based on the linear elastic fracture mechanics theory. Material properties of the functionally graded beams change in the thickness direction according to the power and exponential laws. To represent functionally graded symmetric sandwich beams more realistic, fifty layered beam is considered. Composition of each layer is different although each layer is isotropic and homogeneous. The considered problem is carried out within the Timoshenko first order shear deformation beam theory by using finite element method. A MATLAB code developed to calculate natural frequencies for clamped and simply supported conditions. The obtained results are compared with published studies and excellent agreement is observed. In the study, the effects of crack location, depth of the crack, power law index and slenderness ratio on the natural frequencies are investigated.

Key Words
functionally graded materials; cracked beam; free vibration; FEM

Address
Yusuf Cunedioglu: Mechanical Engineering Department, Faculty of Engineering, Nigde University, 51245, Campus, Nigde, Turkey

Abstract
An effective method to calculate aerodynamic loads and aeroelastic responses of large wind turbine tower-blade coupled structures in yaw condition is proposed. By a case study on a 5 MW large wind turbine, the finite element model of the wind turbine tower-blade coupled structure is established to obtain the modal information. The harmonic superposition method and modified blade-element momentum theory are used to calculate aerodynamic loads in yaw condition, in which the wind shear, tower shadow, tower-blade modal and aerodynamic interactions, and rotational effects are fully taken into account. The mode superposition method is used to calculate kinetic equation of wind turbine tower-blade coupled structure in time domain. The induced velocity and dynamic loads are updated through iterative loop, and the aeroelastic responses of large wind turbine tower-blade coupled system are then obtained. For completeness, the yaw effect and aeroelastic effect on aerodynamic loads and wind-induced responses are discussed in detail based on the calculating results.

Key Words
wind turbine tower-blade coupled structure; aerodynamic loads; aeroelastic effect; yaw effect; parameter analysis

Address
S.T. Ke and T.G. Wang: Jiangsu Key Laboratory of Hi-Tech Research for Wind Turbine Design, Nanjing University of Aeronautics and Astronautics, Yudao Road 29, Nanjing 210016, China
Y.J. Ge: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Siping Road 1239, Shanghai 200092, China
Y. Tamura: Center of Wind Engineering Research, Tokyo Polytechnic University, 1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan

Abstract
The influence of hygrothermal effects on the vibration frequency and buckling load of a shear deformable composite plate with arbitrary initial stresses was investigated. The governing equations of the effects of humid, thermal and initial stresses are established using the variational method. The material properties of the composite plate are affected by both temperature and moisture. The initial stress is taken to be a combination of uniaxial load and pure bending in a hygrothermal environment. The influence of various parameters, such as the fiber volume fraction, temperature, moisture concentration, length/thickness ratios, initial stresses and bending stress ratio on the vibration and stability of the response of a laminated plate are studied in detail. The behavior of vibration and stability are sensitive to temperature, moisture concentration, fiber volume fraction and initial stresses.

Key Words
hygrothermal effect; laminated plates; initial stress

Address
Hai Wang: Department of Mechanical Engineering, Ming Chi University of Technology, Tai-Shan 24301, Taiwan
Chun-Sheng Chen: Department of Mechanical Engineering, Lunghwa University of Science and Technology, Gui-Shan 33306, Taiwan
Chin-Ping Fung: Department of Mechanical Engineering, Oriental Institute of Technology, Pan-Chiao 22061, Taiwan

Abstract
Structural robustness has become an important design variable. However, based on the existing definitions of structural robustness it is often difficult to analyse and evaluate structural robustness, and sometimes not efficient since they mix structural robustness with several other structural variables. This paper concerns the development of a new structural robustness definition, and structural robustness and structural fragility indices. The basis for the development of the new indices is the analysis of the damage energy of structural systems for a given hazard scenario and involves a criterion to define an \"unavoidable collapse\" state. Illustrative examples are given detailing the steps and calculations needed to obtain values for both the structural robustness and the structural fragility indices. Finally, this paper presents the main advantages of the newly proposed definition and indices for the structural risk analysis over existing traditional methods.

Key Words
structural robustness; structural fragility; structural collapse; energy analysis; falsework

Address
Joao Andre: Department of Structures, National Laboratory for Civil Engineering, Av. Brasil, 101, 1700-066 Lisbon, Portugal
Robert Beale: Department of Mechanical Engineering and Mathematical Sciences, Oxford Brookes University, Wheatley Campus, OX33 1HX Oxford, UK
Antonio M. Baptista: Department of Structures, National Laboratory for Civil Engineering, Av. Brasil, 101, 1700-066 Lisbon, Portugal

Abstract
Jute rope is one of the most popular materials used for composites in various industries and in civil engineering. This experimental study investigated two types of jute rope with different diameters for jute rope composite plates to determine the best combination of jute rope and carbon fiber in terms of ratio and physical and mechanical properties. Eight combinations of carbon fiber and jute rope with different percentages of carbon fiber were analyzed. Tensile tests for the jute rope composite plate and hybrid jute rope composite were conducted, and the mechanical and physical properties of the specimens were compared. Thereafter, the ideal combinations of jute rope with an optimum percentage of carbon fiber were identified and recommended. These particular combinations had tensile strengths that were 2.23 times and 1.76 times higher than other varieties in each type.

Key Words
carbon fibre; hybrid; polymer-matrix composites; mechanical properties; jute rope

Address
Karim Nouri and Md. Ashraful Alam: Department of Civil Engineering, Faculty of Engineering, University Tenaga Nasional, Malaysia
Mohammad Mohammadhassani: Department of Civil Engineering, Faculty of Engineering, Shiraz University, Shiraz, Iran
Mohd Zamin Bin Jumaat: Department of Civil Engineering, Faculty of Engineering, University of Malaya, Malaysia
Amir Hosein Abna: Department of Civil Engineering, Faculty of Engineering, Shiraz University, Shiraz, Iran


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