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CONTENTS
Volume 62, Number 1, April10 2017
 

Abstract
This paper describes laboratory tests carried out to evaluate the influence of class F fly ash (FA) on fracture toughness of plain concretes, specified at the third model fracture. Composites with the additives of: 0%, 20% and 30% siliceous FA were analysed. Fracture toughness tests were performed on axial torsional machine MTS 809 Axial/Torsional Test System, using the cylindrical specimens with dimensions of 150/300 mm, having an initial circumferential notch made in the half-height of cylinders. The studies examined effect of FA additive on the critical stress intensity factor KIIIc. In order to determine the fracture toughness KIIIc a special device was manufactured.The analysis of the results revealed that a 20% FA additive causes increase in KIIIc, while a 30% FA additive causes decrease in fracture toughness. Furthermore, it was observed that the results obtained during fracture toughness tests are convergent with the values of the compression strength tests.

Key Words
concrete; siliceous fly ash; fracture toughness, third model fracture

Address
Grzegorz Ludwik Golewski: Department of Structural Engineering, Faculty of Civil Engineering and Architecture, Lublin University of Technology, Nadbystrzycka 40 Str., 20-618, Lublin, Poland

Abstract
The base force element method (BFEM) is a new finite element method. In this paper, a degenerated 4-mid-node plane element from concave polygonal element of BFEM was proposed. The performance of this quadrilateral element with 4 mid-edge nodes in the BFEM on complementary energy principle is studied. Four examples of linear elastic analysis for plane frame structure are presented. The influence of aspect ratio of the element is analyzed. The feasibility of the 4 mid-edge node element model of BFEM on complementary energy principles researched for plane frame problems. The results using the BFEM are compared with corresponding analytical solutions and those obtained from the standard displacement finite element method. It is revealed that the BFEM has better performance compared to the displacement model in the case of large aspect ratio.

Key Words
base force element method; complementary energy principle; plane frame; aspect ratio; finite element method

Address
Yijiang Peng, Yaqiong Bai and Qing Guo: Key Laboratory of Urban Security and Disaster Engineering, Ministry of Education, Beijing University of Technology,Beijing ,100124, China

Abstract
Engineered Cementitious Composite (ECC) is a special class of the new generation of high performance fiber reinforced cementitious composites (HPFRCC) featuring high ductility with relatively low fiber content. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of slag and aggregate size and amount, by employing nonlinear finite element method. The validity of the models was verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method, nonlinear parametric study was then conducted to evaluate the influence of the ECC aggregate content (AC), ECC compressive strength (fECC), maximum aggregate size (Dmax) and slag amount (ϕ) parameters on the flexural stress, deflection, load and strain of ECC beams. The simulation results indicated that when increase the slag and aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of slag and aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 61.55%, 725%, and 879%, respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy.

Key Words
engineered cementitious composite (ECC); flexural behavior; ductility; finite element modelling; parametric study

Address
Hind M. Kh, Mustafa Özakça and Talha Ekmekyapar: Department of Civil Engineering, University of Gaziantep, 27310 Gaziantep, Turkey

Abstract
We present in this paper a finite element formulation for nonlinear torsional analysis of 3D beams with arbitrary composite cross-sections. Since the proposed formulation employs a continuum mechanics based beam element with kinematics enriched by the extended St. Venant solutions, it can precisely account higher order warping effect and its 3D couplings. We propose a numerical procedure to calculate the extended St. Venant equation and the twisting center of an arbitrary composite cross-section simultaneously. The accuracy and efficiency of the proposed formulation are thoroughly investigated through representative numerical examples.

Key Words
nonlinear analysis; finite element method; beam; composite; torsion; warping

Address
Kyungho Yoon: Department of Mechanical and Aerospace Engineering, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Republic of Korea
Do-Nyun Kim: Department of Mechanical and Aerospace Engineering, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Republic of Korea; Institue of Advanced Machines and Design, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Republic of Korea
Phill-Seung Lee: Department of Mechanical Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

Abstract
In this study, the failure behavior of composite material in the biaxial and off-axis loading is studied based on a computational micromechanical model. The model is developed so that the combination of mechanical and thermal loading conditions can be considered in the analysis. The modified generalized plane strain assumption of the theory of elasticity is used for formulation of the micromechanical modeling of the problem. A truly meshless method is employed to solve the governing equation and predict the distribution of micro-stresses in the selected RVE of composite. The fiber matrix interface is assumed to be perfect until the interface failure occurs. The biaxial and off-axis loading of the SiC/Ti and Kevlar/Epoxy composite is studied. The failure envelopes of SiC/Ti and Kevlar/Epoxy composite in off-axis loading, biaxial transverse-transverse and axialtransverse loading are predicted based on the micromechanical approach. Various failure criteria are considered for fiber, matrix and fiber-matrix interface. Comparison of results with the available results in the litreture shows excellent agreement with experimental studies.

Key Words
micromechanics of failure; off-axis loading; biaxial loading; meshless methods; failure envelope

Address
Isa Ahmadi: Advanced Materials and Computational Mechanics Lab., Department of Mechanical Engineering, University of Zanjan, University Blvd, 45371-38791, Zanjan, Iran

Abstract
An effective design approach for Multiple Tuned Mass Dampers (MTMDs) in pedestrian bridges was proposed by utilizing the transfer function to obtain each TMD\'s optimum stiffness and damping. A systematic simulation of pedestrian excitations was described. The motion equation of a typical MTMD system attached to a Multi-degree-of-freedom (MDOF) system was presented, and the transfer function from the input pedestrian excitations to the output acceleration responses was defined. By solving the minimum norm of the transfer function, the parameters of the MTMD which resulted in the minimum overall responses can be obtained. Two applications of lightly damped pedestrian bridges attached with MTMD showed that MTMDs designed through this method can significantly reduce the structural responses when subjected to pedestrian excitations, and the vibration control effects were better than the MTMD when it was considered as being composed of equal number and mass ratios of TMDs designed by classical Den Hartog method.

Key Words
multiple tuned mass dampers; pedestrian bridge; optimization design; vibration control; pedestrian excitation

Address
Zheng Lu, Peizhen Li: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China; Research Institute of Structural Engineering and Disaster Reduction, Tongji University, Shanghai 200092, China
Xiaoyi Chen: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, Shanghai 200092, China
Xiaowei Li: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, Shanghai 200092, China; Tongji Architectural Design (Group) Co., Ltd (TJAD), Shanghai 200092, China

Abstract
The free vibration analysis of fluid conveying Timoshenko pipeline with different boundary conditions using Differential Transform Method (DTM) and Adomian Decomposition Method (ADM) has not been investigated by any of the studies in open literature so far. Natural frequencies, modes and critical fluid velocity of the pipelines on different supports are analyzed based on Timoshenko model by using DTM and ADM in this study. At first, the governing differential equations of motion of fluid conveying Timoshenko pipeline in free vibration are derived. Parameter for the nondimensionalized multiplication factor for the fluid velocity is incorporated into the equations of motion in order to investigate its effects on the natural frequencies. For solution, the terms are found directly from the analytical solution of the differential equation that describes the deformations of the cross-section according to Timoshenko beam theory. After the analytical solution, the efficient and easy mathematical techniques called DTM and ADM are used to solve the governing differential equations of the motion, respectively. The calculated natural frequencies of fluid conveying Timoshenko pipelines with various combinations of boundary conditions using DTM and ADM are tabulated in several tables and figures and are compared with the results of Analytical Method (ANM) where a very good agreement is observed. Finally, the critical fluid velocities are calculated for different boundary conditions and the first five mode shapes are presented in graphs.

Key Words
adomian decomposition method; critical fluid velocity; differential transform method; fluid conveying pipeline; free vibration; natural frequencies

Address
Baran Bozyigit, Yusuf Yesilce and Seval Catal: Department of Civil Engineering, Dokuz Eylul University, 31560, Buca, Izmir, Turkey

Abstract
Utilizing composite members in structures has been considered by many researchers in the past few decades. Using FRP can be very effective owing to its excessively high-tensile strength, which compensate concrete weak performance in tension. In this research, the studied composite beam includes a GFRP semi-confined trapezoidal section covered by GFRP and concrete layers. To assess the bearing capacity, a finite-element model of a composite beam subjected to displacement control loading has been developed and the results were validated using experimental results found throughout the literature. Several parameters affecting the bending performance and behavior of the semi-confined beam have been investigated in this study. Some of these parameters included the thickness of GFRP trapezoidal section members, concrete layer thickness, GFRP layer thickness and the confinement degree of the beam. The results revealed that the beam confinement had the highest effect on the bearing capacity due to prevention of separation of concrete from GFRP which causes the failure of the beam. From the results obtained, an optimal model of primary beam section has been introduced, which provides a higher bearing capacity with the same volume of materials used in the original beam section.

Key Words
concrete; GFR; composite beam; finite-element; confinement

Address
Amir Masoud Hassanzadeh and Mehdi Dehestani: Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract
This paper presents an explicit analytical iteration method for form-finding analysis of suspension bridges. By extending the conventional analytical form-finding method predicated on the elastic catenary theory, two nonlinear governing equations are derived for calculating the accurate unstrained lengths of the entire cable systems both the main cable and the hangers. And for the gradient-based iteration method, the derivation of explicit calculation for the Jacobian matrix while solving the nonlinear governing equation enhances the computational efficiency. The results from sensitivity analysis show well performance of the explicit Jacobian matrix compared with the traditional finite difference method. According to two numerical examples of long span suspension bridges studied, the proposed method is also compared with those reported approaches or the fundamental criterions in suspension bridge structural analysis, which eventually confirms the accuracy and efficiency of the proposed approach.

Key Words
form-finding analysis; suspension bridge; analytical method; elastic catenary cable; finite element analysis

Address
Hongyou Cao, Yun-Lai Zhou: Department of Civil and Environmental Engineering, National University of Singapore, 117576, Singapore
Zhijun Chen: School of Civil Engineering & Mechanics, Huazhong University of Science & Technology, Wuhan, 4300743, China
Magd Abdel Wahab: Division of Computational Mechanics, Ton Duc Thang University, Ho Chi Minh City, Vietnam; Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam; Soete Laboratory, Faculty of Engineering and Architecture, Ghent University,Technologiepark Zwijnaarde 903, B-9052 Zwijnaarde, Belgium

Abstract
This paper discusses an experimental programme that was carried out to study the effects of specimen size-shape and type of moulds on the compressive strength of concrete. For this purpose, cube specimens with 150 mm dimensions, cylinder specimens with 150x300 mm dimensions, and prism specimens with 150x150x375 mm dimensions were prepared. The experimental programme was carried out with several concrete compositions belonging to strength classes C20/25, C25/30, C30/37, C40/50 and C60/75. Furthermore, the test results were curve-fitted using the least squares method to obtain the new parameters for the modified size effect law.

Key Words
compressive strength; size effect; specimen geometry; cure conditions

Address
Farhad Aslani: School of Civil, Environmental and Mining Engineering, The University of Western Australia, Crawley, WA 6009, Australia
Lino Maia, José Santos: CONSTRUCT-LABEST, Faculty of Engineering (FEUP), University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal; Faculty of Exact Sciences and Engineering, University of Madeira, Campus da Penteada, 9020-105 Funchal, Portugal

Abstract
This paper deals with critical buckling load optimization of symmetric angle-ply laminated stepped flat columns under axial compression load. The design objective is the maximization of the critical buckling load and the design variable is the fiber orientations in the layers of the laminates. The classical laminate plate theory is used for the finite element solution of the laminated stepped flat columns. The modified feasible direction (MFD) method is used for the optimization routine. For this purpose, a program based on FORTRAN is exploited. Finally, the optimization results are presented for width ratios (b/B), ratios of fillet radius (r1/r2), aspect ratios (L/B) and boundary conditions. The results are presented in graphical and tabular forms and the results are compared.

Key Words
laminated stepped columns; critical buckling load; modified feasible direction method; optimization

Address
Umut Topal: Department of Civil Engineering, Karadeniz Technical University, Faculty of Technology, 61830, Trabzon, Turkey

Abstract
The bi-material elastic system consisting of the circular hollow cylinder and the infinite elastic medium surrounding this cylinder is considered and it is assumed that on the inner free face of the cylinder a point-located axisymmetric time harmonic force, with respect to the cylinder\'s axis and which is uniformly distributed in the circumferential direction, acts. The shear-spring type imperfect contact conditions on the interface between the constituents are satisfied. The mathematical formulation of the problem is made within the scope of the exact equations of linear elastodynamics. The focus is on the frequency-response of the interface normal and shear stresses and the influence of the problem parameters, such as the ratio of modulus of elasticity, the ratio of the cylinder thickness to the cylinder radius, and the shear-spring type parameter which characterizes the degree of the contact imperfectness, on these responses. Corresponding numerical results are presented and discussed. In particular, it is established that the character of the influence of the contact imperfection on the frequency response of the interface stresses depends on the values of the vibration frequency of the external forces.

Key Words
forced vibration; frequency response; hollow cylinder; surrounding elastic medium; shear-spring type imperfection; underground structure

Address
Surkay D. Akbarov: Department of Mechanical Engineering, Yildiz Technical University, Istanbul, Turkey; Institute of Mathematics and Mechanics of NAS Azerbaijan, Baku, Azerbaijan
Mahir A. Mehdiyev: Institute of Mathematics and Mechanics of NAS Azerbaijan, Baku, Azerbaijan; Azerbaijan State Economics University, Department of Mathematics, Baku, Azerbaijan


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