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CONTENTS
Volume 24, Number 4, July20 2017
 

Abstract
This paper highlights the experimental and numerical investigations performed on a tubular T-joint fabricated from circular hollow sections under axial compressive loads applied at the brace. Tests were performed on a reference joint and the joint wrapped with Carbon Fiber Reinforced Polymer (CFRP). The Nitowrap EP carbon fiber with Nitowrap 410 resin serve as a composite material is used for wrapping the T-joint. Schematic diagram of the fabricated tubular joint for the experimental test setup, along with the experimental and numerical results are presented. After performing these experiments, it has been demonstrated that the joint wrapped with CFRP has a better strength and lesser deflection than a reference joint. Finite element analysis carried out in Ansys reveals that the results were in good correlation with the experimental values.

Key Words
tubular joints; CFRP; Ansys; experimental investigation; finite element analysis

Address
Department of Civil Engineering, National Institute of Technology Calicut, Calicut-673601, India.


Abstract
With the increasing application of explosive composite structure in many engineering fields, its interface bonding state detection is more and more significant to avoid catastrophic accidents. However, this task still faces challenges due to the complexity of the bonding interface. In this paper, the concept of nonlinear output frequency response functions (NOFRFs) is introduced to detect the bonding state of explosive composite structure. The NOFRFs can describe the nonlinear characteristics of nonlinear vibrating system. Because of the presence of the bonding interface, explosive composite structure itself is a nonlinear system; when bonding interface of the structure is damaged, its dynamic characteristics show enhanced nonlinear characteristic. Therefore, the NOFRFs-based detection index is proposed as indicator to detect the bonding state of explosive composite pipes. The experimental results verify the effectiveness of the detection approach.

Key Words
bonding state detection; explosive composite structure; nonlinear output frequency response functions

Address
(1) School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049, China;
(2) State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an 710049, China.

Abstract
Of high strength bolts, the torque shear type bolt is known to be clamped normally when pin-tails are broken. Sometimes the clamping loads on slip critical connections considerably fluctuate from the required tension due to variation of torque coefficient. This is why the viscosity of lubricant affects the torque coefficient by temperature. In this study, the clamping tests of high strength bolts were performed independently at laboratory conditions and at outdoor environment. The temperatures of outdoor environment candidates were ranged from -11°C to 34°C for six years. The temperature at laboratory condition was composed from -10°C to 50°C at each 10°C interval. At outdoor environment conditions, the clamping load of high strength bolt was varied from 159 to 210 kN and the torque value was varied from 405 to 556 Nm. The torque coefficients at outdoor environment were calculated from 0.126 to 0.158 when tensions were measured from 179 to 192 kN by using tension meter. The torque coefficients at outdoor environment conditions were analyzed as the range from 0.118 to 0.152. From these tests, the diverse equations of torque coefficient, tension dependent to temperature can be acquired by statistic regressive analysis. The variable of torque coefficient at laboratory conditions is 0.13% per each 1°C when it reaches 2.73% per each 1°C at outdoor environment conditions. When the results at laboratory conditions and at outdoor environment were combined to get the revised equations, the change in torque coefficient was modified as 0.2% per each 1°C and the increment of tension was adjusted as 1.89 % per each 1°C.

Key Words
high strength bolt; torque; tension; torque-coefficient; estimation

Address
(1) Hwan-Seon Nah:
Smart Energy Lab., Korea Electric Power Corporation Research Institute, 65 Munji-Ro Yusung-Gu, Daejon, 305-380, Korea;
(2) Sung-Mo Choi:
The University of Seoul, Department of Architectural Engineering, 163 Siripdaero, Dongdaemun-gu, Seoul, 130-743, Korea.

Abstract
This paper presents an experimental study on damage evolution laws of solid-web steel reinforced concrete (SRC) T-shaped columns along the direction of the web under various loadings. Ten specimens with a scale ratio of 1/2 and a shear span ratio of 2.5 were designed and fabricated. The influences of various parameters, including the axial compression ratio, steel ratio, and loading mode, were examined. The mechanical performances including load-displacement curve and energy dissipation capacity under the monotonic and low cyclic loadings were analyzed. Compared with the monotonic loading, bearing capacity, ultimate deformation capacity, and energy dissipation capacity of the specimens decrease to some extent with the increase of the displacement amplitude and the number of loading cycle. The results show that the damage process of the SRC T-shaped column can be divided into five stages, namely non-damage, slight-damage, steadily-developing-damage, severedamage and complete-damage. Finally, based on the Park-Ang model, a modified nonlinear damage model which combines the maximum deformation with hysteretic energy dissipation is proposed by taking into account the dynamic influence of the aforementioned parameters. The results show that the modified model in this paper is more accurate than Park-Ang model and can better describe the damage evolution of SRC T-shaped columns.

Key Words
steel reinforced concrete (SRC); T-shaped column; damage evolution; damage model; experimental study; various loadings

Address
College of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China.


Abstract
As a thin-walled structure, local joint flexibility (LJF) in a tubular structure is prominent, and it may produce significant effect on the static performance for the overall structure. This study presents a simplified analytical model to analyze the static behavior for a steel tubular structure with LJF. The presented model simplifies a tubular structure into a frame model consisted of beam elements with considering the LJFs at the connections between any two elements. Theoretical equations of the simplified analytical model are deduced. Through comparison with 3-D finite element results of two typical planar tubular structures consisted of T- and Y-joints respectively, the presented method is proved to be accurate. Furthermore, the effect of LJF on the overall performance of the two tubular structures (including the deflection and the internal forces) is also investigated, and it is found from analyses of internal forces and deformation that a rigid connection assumption in a frame model by using beam elements in finite element analysis can provide unsafe and inaccurate estimation.

Key Words
tubular structure; local joint flexibility (LJF); simplified analytical model; theoretical equations; static behavior

Address
(1) Yamin Wang, Yongbo Shao:
School of Mechatronic Engineering, Southwest Petroleum University, Chengdu 610500, P.R. China;
(2) Yifang Cao:
Center for Infrastructure Engineering, School of Computing, Engineering and Mathematics, Western Sydney University, NSW 2751, Australia.

Abstract
In Y-shaped eccentrically braced frame fabricated with high strength steel (Y-HSS-EBF), link uses conventional steel while other structural members use high strength steel. Cyclic test for a 1:2 length scaled one-bay and one-story Y-HSSEBF specimen and shake table test for a 1:2 length scaled three-story Y-HSS-EBF specimen were carried out to research the seismic performance of Y-HSS-EBF. These include the failure mode, load-bearing capacity, ductility, energy dissipation capacity, dynamic properties, acceleration responses, displacement responses, and dynamic strain responses. The test results indicated that the one-bay and one-story Y-HSS-EBF specimen had good load-bearing capacity and ductility capacity. The threestory specimen cumulative structural damage and deformation increased, while its stiffness decreased. There was no plastic deformation observed in the braces, beams, or columns in the three-story Y-HSS-EBF specimen, and there was no danger of collapse during the seismic loads. The designed shear link dissipated the energy via shear deformation during the seismic loads. When the specimen was fractured, the maximum link plastic rotation angle was higher than 0.08 rad for the shear link in AISC341-10. The Y-HSS-EBF is a safe dual system with reliable hysteretic behaviors and seismic performance.

Key Words
dynamic properties; eccentrically braced frames (EBFs); high strength steel (HSS); seismic performance; experimental study

Address
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, P.R. China.


Abstract
This paper presents a series of ultimate and fatigue experimental investigation on concrete-filled rectangular hollow section (CRHS) X joints with Perfobond Leister rib (PBR) under tension. A total of 15 specimens were fabricated, in which 12 specimens were tested under ultimate tension and 3 specimens were investigated in fatigue test. Different parameters including PBR stiffening, brace-to-chord ratio (β) and inclined angle (&$952;) were considered in the test. Each joint was tested to failure under tension load. Obtained from test result, PBR was found to improve the tension strength and fatigue durability of CRHS joint substantially. Concrete dowel consisted by PBR and concrete inside the chord stiffened the joint, which leaded to a combination failure mode of punching shear and chord plastification of CRHS joint under tension. Finite element analysis validated the compound failure mode. Stress concentration on typical spot of CRHS joint was mitigated by PBR which was observed from fatigue test. Initial fatigue crack presented in CRHS joint with PBR also differentiated with the counterpart without PBR.

Key Words
concrete-filled rectangular joint; perfobond leister rib; experimental investigation; fatigue; concrete dowel

Address
(1) Yongjian Liu, Lei Jiang:
School of Highway, Chang'an University, Xi'an 710064, China;
(2) Zhihua Xiong, Yuncheng Feng:
CCCC First Highway Consultants Co., Ltd., Xi'an 710075, China.

Abstract
The stud is one of the most frequently used shear connectors which are important to the steel-concrete composite action. The static and fatigue behavior of stud in the steel fiber reinforced concrete (SFRC) were particularly concerned in this study through the push-out tests and analysis. It was for the purpose of investigating and explaining a tendency proposed by the current existing researches that the SFRC may ameliorate the shear connector's mechanical performance, and thus contributing to the corresponding design practice. There were 20 test specimens in the tests and 8 models in the analysis. According to the test and analysis results, the SFRC had an obvious effect of restraining the concrete damage and improving the stud static performance when the compressive strength of the host concrete was relatively low. As to the fatigue aspect, the steel fibers in concrete also tended to improve the stud fatigue life, and the favorable tensile performance of SFRC may be the main reason. But such effect was found to vary with the fatigue load range. Moreover, the static and fatigue test results were compared with several design codes. Particularly, the fatigue life estimation of Eurocode 4 appeared to be less conservative than that of AASHTO, and to have higher safety redundancy than that of JSCE hybrid structure guideline.

Key Words
stud shear connector; steel fiber reinforced concrete (SFRC); stud mechanical performance; fatigue life

Address
(1) Chen Xu, Qingtian Su:
Department of Bridge Engineering, College of Civil Engineering, Tongji University, 1239 Siping Rd, Shanghai, China;
(2) Hiroshi Masuya:
Department of Environmental Design, Institute of Science and Engineering, Kanazawa University, Kakumamachi, Kanazawa, Japan.

Abstract
In this paper, full-scale loading tests were performed on a rectangular segmental tunnel lining, which was assembled by steel composite segments, to investigate its load-bearing structural behavior and failure mechanism. The tests were also used to confirm the composite effect by adding concrete inside to satisfy the required performance under severe loading conditions. The design of the tested rectangular segmental lining and the loading scheme are also described to better understand the bearing capacity of this composite lining structure. It is found that the structural ultimate bearing capacity is governed by the bond capacity between steel plates and the tunnel segment. The failure of the strengthened lining is the consequence of local failure of the bond at waist joints. This led to a fast decrease of the overall stiffness and eventually a loss of the structural integrity.

Key Words
rectangular tunnel lining; composite segment; full-scale test; failure mechanism; ultimate bearing capacity

Address
(1) Xian Liu:
College of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai,
China;
(2) Xinyu Hu:College of Urban Construction and Safety Engineering, Shanghai Institute of
Technology, 100 Haiquan Road, Shanghai, China;
(3) Linxing Guan, Wei Sun:Shanghai Municipal Engineering Design Institute (Group) Co. Ltd., 901 North Zhongshan no.2 Road, Shanghai, China.

Abstract
This paper deals with nonlinear dynamic stability of embedded piezoelectric nano-composite separators conveying pulsating fluid. For presenting a realistic model, the material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The separator is reinforced with single-walled carbon nanotubes (SWCNTs) which the equivalent material properties are obtained by mixture rule. The separator is surrounded by elastic medium modeled by nonlinear orthotropic visco Pasternak foundation. The separator is subjected to 3D electric and 2D magnetic fields. For mathematical modeling of structure, three theories of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT) are applied. The differential quadrature method (DQM) in conjunction with Bolotin method is employed for calculating the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the dynamic instability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that the magnetic and electric fields as well as SWCNTs as reinforcer are very important in dynamic instability analysis of structure.

Key Words
piezoelectric separators; viscoelastic; SSDT; DQM; orhtotropic viscoelastic medium

Address
(1) H. Rahimi Pour, A. Ghorbanpour Arani, Gh. Sheikhzadeh:
Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran;
(2) A. Ghorbanpour Arani:
Institute of Nanoscience & Nanotechnology, University of Kashan, Kashan, Iran.

Abstract
The goal of this study is to investigate structural analysis and behaviors of an innovative aerial work platform truss frame whose ductility is improved by using high strength-steel UL-700. The present space truss frame can move or stop through tunnels for maintenance constructions by automatic facilities and workmanship within standardized limited building lines of tunnel. Most of all, this method overcomes problematic, which is to block cars during construction periods, seriously, of typical methods like as using truck and scaffolds for tunnel maintenance. According to evaluated appropriate design results of space truss frames of numerical examples by using a commercial MIDAS GEN program, it is verified that design parameters such as layered size, cross-sectional size, and steel material of the present space truss frame are determined to depend on characteristics such as lanes or shape of road tunnels.

Key Words
road tunnel; maintenance; aerial work platform; blocking transportations; MIDAS GEN; UL-700

Address
Department of Architectural Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul, 143-747, Republic of Korea.



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