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CONTENTS
Volume 60, Number 1, October10 2016
 

Abstract
In this study, the supersonic panel flutter of doubly curved composite sandwich panels with variable thickness is considered under aerothermoelastic loading. Considering different radii of curvatures of the face sheets in this paper, the thickness of the core is a function of plane coordinates (x,y), which is unique. For the first time in the current model, the continuity conditions of the transverse shear stress, transverse normal stress and transverse normal stress gradient at the layer interfaces, as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the sandwich panel are satisfied. The formulation is based on an enhanced higher order sandwich panel theory and the vertical displacement component of the face sheets is assumed as a quadratic one, while a cubic pattern is used for the in-plane displacement components of the face sheets and the all displacement components of the core. The formulation is based on the von Karman nonlinear approximation, the one-dimensional Fourier equation of the heat conduction along the thickness direction, and the first-order piston theory. The equations of motion and boundary conditions are derived using the Hamilton principle and the results are validated by the latest results published in the literature.

Key Words
aerothermoelastic loading; doubly curved sandwich panels; variable thickness; enhanced higher order sandwich panel theory; piston theory

Address
Mostafa livani, Keramat MalekzadehFard and Saeed Shokrollahi: Space Research Institute, MalekAshtar University of Technology, Tehran-Karaj Highway, Tehran, Iran

Abstract
In this paper two procedures for determination of the elastic curve of the simply and multiple supported beams are developed. Determination of the elastic curve is complex as it requires to solve a strong nonlinear differential equation with given boundary conditions. For numerical solution the initial guess of the slope at the end of the beam is necessary. Two procedures for obtaining of the initial guess are developed: one, based on transformation of the supported beam into a clamped-free one, and second, on the linearization of the problem. Procedures are applied for calculating of elastic curve of a simply supported beam and a beam with three supports. Obtained results are compared. Advantages and disadvantages of both methods are discussed. It is proved that both suggested procedures give us technically accurate results.

Key Words
elastic curve; supported beam; initial guess for slope

Address
István Bíró: University of Szeged, Faculty of Engineering, Mars tér 7, H-6724 Szeged, Hungary
Livija Cveticanin: University of Novi Sad, Faculty of Technical Sciences, Trg D. Obradovica 6, 21000 Novi Sad, Serbia; Obuda University, Donát Bánki Faculty, Népszinház u. 8, H-1081 Budapest, Hungary

Abstract
During the recent years, resistance mechanisms of reinforced concrete (RC) buildings against progressive collapse are investigated extensively. Although a general agreement is observed about their qualitative behavior in technical literature, there is not such a comprehensive point of view regarding the quantitative methods for predicting collapse resistance of RC members. Therefore, in the present study a simplified theoretical method is developed in order to predict general behavior of RC frames under the column removal scenario. In the introduced method, the robustness of the frame is extracted based on the capacity of the beams. The proposed method expresses ultimate arching and catenary capacities of the beams and also obtains the corresponding vertical displacements. Based on the calculated capacities, the introduced method also provides a quantitative assessment of structural robustness and determines whether or not the collapse occurs. The capability of the method is evaluated using experimental results in the literature. The evaluation study indicates that the proposed theoretical procedure can establish a reliable foundation for progressive collapse assessment of RC frame structures.

Key Words
progressive collapse analysis; RC beam; RC frame; compressive arch action; catenary action; structural robustness

Address
Reza Abbasnia, Foad Mohajeri Nav, Nima Usefi and Omid Rashidian: Civil Engineering Department, Iran University of Science and Technology, Narmak, Tehran, Iran

Abstract
A large number of welded steel moment-resisting framed (SMRF) structures failed due to brittle fracture induced by ductile fracture at beam-to-column connections during 1994 Northridge earthquake and 1995 Kobe (Hyogoken-Nanbu) earthquake. Extensive research efforts have been devoted to clarifying the mechanism of the observed failures and corresponding countermeasures to ensure more ductile design of welded SMRF structures, while limited research on the failure analysis of the ductile cracking was conducted due to lack of computational capacity and proper theoretical models. As the first step to solve this complicated problem, this paper aims to establish a straightforward procedure to simulate ductile cracking of welded joints under monotonic tension. There are two difficulties in achieving the aim of this study, including measurement of true stress-true strain data and ductile fracture parameters of different subzones in a welded joint, such as weld deposit, heat affected zone and the boundary between the two. Butt joints are employed in this study for their simple configuration. Both experimental and numerical studies on two types of butt joints are conducted. The validity of the proposed procedure is proved by comparison between the experimental and numerical results.

Key Words
ductile fracture; true stress-true strain; butt weld; cracking; structural steel

Address
Liang-Jiu Jia: Research Institute of Structural Engineering and Disaster Reduction, College of Civil Engineering, Tongji University, Shanghai, 200092, China
Toyoki Ikai: Department of Civil Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-Ku,
Nagoya, 468-8502, Japan
Lan Kang: School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, 510640, China
Hanbin Ge and Tomoya Kato: Department of Civil Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-Ku,
Nagoya, 468-8502, Japan

Abstract
In this paper, the normalized variable V=(log N-B)(log Ao-C), as derived from the probabilistic S-N field of Castillo and Canteli, is taken as a reference for calculation of damage accumulation and probability of failure using the Miner number in scenarios of variable amplitude loading. Alternative damage measures, such as the classical Miner and logarithmic Miner, are also considered for comparison between theoretical lifetime prediction and experimental data. The suitability of this approach is confirmed for it provides safe lifetime prediction when applied to fatigue data obtained for riveted joints made of a puddle iron original from the Fão bridge, as well as for data from experimental programs published elsewhere carried out for different materials (aluminium and concrete specimens) under distinct variable loading histories.

Key Words
fatigue; cumulative damage; Miner

Address
Sergio Blasón and Alfonso Fernández-Canteli: Engineering Faculty of Gijón, University of Oviedo, Campus de Viesques, 33203 Gijón, Spain
José A.F.O. Correia, Abílio M.P. De Jesus and Rui A.B. Calçada: Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal


Abstract
Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.

Key Words
tube hydroforming; pulsating; stress-strain relationship; free hydraulic bulging

Address
Lianfa Yang, Ninghua Wang and Yulin He: Faculty of Mechanical & Electrical Engineering, Guilin University of Electronic Technology, Guilin 541004, Guangxi, P.R. China

Abstract
Two new elements with six degrees of freedom are proposed by applying the equilibrium conditions and strain-displacement equations. The first element is formulated for the infinite ratio of beam radius to thickness. In the second one, theory of the thick beam is used. Advantage of these elements is that by utilizing only one element, the exact solution will be obtained. Due to incorporating equilibrium conditions in the presented formulations, both proposed elements gave the precise internal forces. By solving some numerical tests, the high performance of the recommended formulations and also, interaction effects of the bending and axial forces will be demonstrated. While the second element has less error than the first one in thick regimes, the first element can be used for all regimes due to simplicity and good convergence. Based on static responses, it can be deduced that the first element is efficient for all the range of structural characteristics. The free vibration analysis will be performed using the first element. The results of static and dynamic tests show no deficiency, such as, shear and membrane locking and excessive stiff structural behavior.

Key Words
free vibration analysis; closed-form stiffness matrix; curved beam; equilibrium conditions; strain-displacement relationships; thin beam; Finite Element Method (FEM); thick beam

Address
Mohammad Rezaiee-Pajand and Niloofar Rajabzadeh-Safaei: Department of Civil Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Iran

Abstract
Tuned Liquid Dampers (TLDs) provide low damping when it comes to deep water condition, and that not all water depth is mobilized in energy dissipation. This research focussed on a method to improve the efficiency of TLDs with deep water condition. Several bottom-mounted baffles were installed inside a TLD and the dynamic characteristics of modified TLDs together with their effect on the vibration control of a SDOF structure were studied experimentally. A series of free vibration and harmonic forced vibration tests were carried out. The controlling parameter in the conducted tests was the Vertical Blocking Ratio (VBR) of baffles. Results indicated that increase in VBR decreases the natural frequency of TLD and increases its damping ratio. It was found that the VBR range of 10% to 30% reduced response of the structure significantly. The modified TLD with the VBR of 30% showed the best performance when reduction in structural responses under harmonic excitations were compared.

Key Words
tuned liquid damper; bottom baffles; deep water; vibration control of structures; harmonic excitation

Address
Hossein Shad, Azlan Adnan and Hamid Pesaran Behbahani: Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310, Johor, Malaysia
Mohammadreza Vafaei: Center for Forensic Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310, Johor, Malaysia

Abstract
Structure-dependent integration methods seem promising for structural dynamics applications since they can integrate unconditional stability and explicit formulation together, which can enable the integration methods to save many computational efforts when compared to an implicit method. A newly developed structure-dependent integration method can inherit such numerical properties. However, an unusual overshooting behavior might be experienced as it is used to compute a forced vibration response. The root cause of this inaccuracy is thoroughly explored herein. In addition, a scheme is proposed to modify this family method to overcome this unusual overshooting behavior. In fact, two improved formulations are proposed by adjusting the difference equations. As a result, it is verified that the two improved formulations of the integration methods can effectively overcome the difficulty arising from the inaccurate integration of the steady-state response of a high frequency mode.

Key Words
overshoot; forced vibration response; local truncation error; high frequency modes; structure-dependent integration method

Address
Shuenn-Yih Chang, Tsui-Huang Wu and Ngoc-Cuong Tran: Department of Civil Engineering, National Taipei University of Technology, NTUT Box 2653, Taipei 106, Taiwan, Republic of China

Abstract
Nowadays using Carbon Fiber Reinforced Polymer (CFRP) has been expanded in strengthening steel structures. Given that few studies have taken about strengthening of steel hollow pipe sections using CFRP, in present study, the effects of CFRP sheets using two layers as well as in combination with additional reinforcing strips has been assessment. Strengthening of five specimens was carried out in laboratory tests. As well as numerical simulation was performed for all specimens by Finite Element Method (FEM) using ABAQUS software and high correlation between the results of numerical models with experimental data indicate the power of FEM in this field. The results of both laboratory and simulated specimens showed that load-bearing capacity of circular cross-sections can be significantly increased using CFRP retrofitting technique. Also, application of additional CFRP reinforcing strips and layers caused more strength for the strengthened specimens.

Key Words
retrofitting; steel hollow pipe section; transverse load; CFRP

Address
Kambiz Narmashiri and Ghadir Mehramiz: Department of Civil Engineering, College of Engineering, Zahedan Branch, Islamic Azad University, Zahedan, Iran


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