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CONTENTS
Volume 20, Number 1, January20 2016
 

Abstract
The strength and stiffness of the steel beams to concrete-filled tubular columns connections are significantly reduced if the thick-walled components are used. However, the thick-walled tubes used for columns can largely reduce the demand for space and increase the strength-to-weight ratio. This paper describes the cyclic performance of extended through-diaphragm connections between steel beams and thick-walled concrete-filled tubular columns improved with fillets around the diaphragm corners. Test on one full-scale connection was conducted to assess the seismic behavior of the connection in terms of strength, stiffness, ductility, deformation, energy dissipation, and strain distribution. It is shown that the fillets and extended through-diaphragm can alleviate the stress concentration in the connection and thus improve the seismic performance. The test results demonstrate that the through-diaphragm connections with thick-walled concrete-filled tubular columns can offer sufficient energy dissipation capacity and ductility appropriate for its potential application in seismic design.

Key Words
CFT column; extended through-diaphragm connection; thick-walled; cyclic loading; experimental behavior; seismic performance

Address
(1) Ying Qin:
School of Civil Engineering, Key Lab of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing, China;
(2) Zhihua Chen, Jingjing Bai:
Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, China;
(3) Zilin Li:
School of Civil Engineering, Tianjin Chengjian University, Tianjin, China.

Abstract
Cold-formed steel structures are increasingly attractive due to their benefits of good mechanical performance and constructional advantages. However, this type of construction is still not fully exploited as a result of the acknowledged difficulties involved in forming construction-efficient and cost-effective connections. Furthermore, there is a lack of information on the structural behavior of the cold-formed steel connections. In this study, the research on various cold-formed steel connections was comprehensively reviewed from both fundamental and structural points of view, based on the available experimental and analytical data. It reveals that the current design codes and guidelines for cold-formed steel connections tend to focus more on the individual bearing capacity of the fasteners rather than the overall structural behavior of the connections. Significant future work remains to be conducted on the structural performance of cold-formed steel connection. In addition, extensive previous research has been carried out to propose and evaluate an economical and efficient connection system that is obtained from the conventional connecting techniques used in the hot-rolled industry. These connecting techniques may not be suitable, however, as they have been adopted from hot-rolled steel portal frames due to the thinness of the sheet in cold-formed steels. The review demonstrates that with the increasing demand for cold-formed steel constructions throughout the world, it is crucial to develop an efficient connection system that can be prefabricated and easily assembled on site.

Key Words
connections; cold-formed steel; fundamental behavior; structural performance

Address
(1) Ying Qin:
School of Civil Engineering, Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing, China;
(2) Zhihua Chen:
Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, China.

Abstract
Polyurethane foam with low density used in sandwich panels is examined in the paper. A series of experiments was carried out to identify mechanical parameters of the foam. Various experimental methods were used for determining the shear modulus, namely a four and three point bending tests (the most common in engineering practice), a double-lap shear test and a torsion test. The behavior of PU in axial compression and tension was also studied. The experiments revealed pronounced anisotropy of the PU foam. An orthotropic model is proposed. Limitations of application of isotropic model of PU in engineering practice is also discussed.

Key Words
polyurethane foam; anisotropy; sandwich panels; material model; experimental methods

Address
(1) Monika Chuda-Kowalska:
Institute of Structural Engineering, Poznan University of Technology pl. Sklodowskiej-Curie 5, 60-965 Poznan, Poland;
(2) Andrzej Garstecki:
Stanislaw Staszic University of Applied Sciences in Pila, ul. Podchorazych 10, 64-920 Pila, Poland.

Abstract
The predominant type of buckling that I-steel concrete composite beams experience in the negative moment area is distortional buckling. The key factors that affect distortional buckling are the torsional and lateral restraints by the bottom flange. This study thoroughly investigates the equivalent lateral and torsional restraint stiffnesses of the bottom flange of an I-steel concrete composite beam under negative moments. The results show a coupling effect between the applied forces and the lateral and torsional restraint stiffnesses of the bottom flange. A formula is proposed to calculate the critical buckling stress of the I-steel concrete composite beams under negative moments by considering the lateral and torsional restraint stiffnesses of the bottom flange. The proposed method is shown to better predict the critical bending moment of the I-steel composite beams. This article introduces an improved method to calculate the elastic foundation beams, which takes into account the lateral and torsional restraint stiffnesses of the bottom flange and considers the coupling effect between them. The results show a close match in results from the calculation method proposed in this paper and the ANSYS finite element method, which validates the proposed calculation method. The proposed calculation method provides a theoretical basis for further research on distortional buckling and the ultimate resistance of I-steel concrete composite beams under a variable axial force.

Key Words
steel concrete composite beams; distortional buckling; rotational restraint stiffness; lateral restraint stiffness; elastic foundation beam method

Address
(1) Wangbao Zhou, Shujin Li:
School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan, 430070, China;
(2) Zhi Huang, Lizhong Jiang:
School of Civil Engineering, Central South University, Changsha, 410075, China.

Abstract
In steel and concrete composite girders, the load transfer between the steel beam and the concrete slab is commonly ensured by installing shear connectors. In this paper, to investigate the nonlinear behavior of perfobond connectors, a total of 60 push-out specimens were fabricated and tested with the variables for the hole diameter, the concrete strength, the thickness of concrete slab, the diameter, strength and existence of perforating rebar, the thickness, height and distance of perfobond ribs. The failure mode and the load-slip behavior of perfobond connectors were obtained. A theoretical model was put forward to express the load-slip relationship. Analytical formulas of shear capacity and peak slip were also proposed considering the interaction between the concrete dowel and the perforating rebar. The calculation results of the proposals agreed well with the experimental values.

Key Words
composite bridge; perfobond connector; push-out test; load-slip behavior; theoretical model

Address
(1) Shuangjie Zheng, Yuqing Liu:
Department of Bridge Engineering, Tongji University, Shanghai, China;
(2) Shuangjie Zheng, Teruhiko Yoda, Weiwei Lin:
Department of Civil and Environmental Engineering, Waseda University, Tokyo, Japan.

Abstract
Two-dimensional elastoplastic finite element formulation is employed to investigate the load- carrying capacity degradation of reinforced concrete piers wrapped with steel plates due to occurrence of corrosion at the pier base. By comparing with experimental results, the employed finite element analysis method is verified to be accurate. After that, a series of parametric studies are conducted to investigate the effect of corrosion ratio and corrosion mode of steel plates located near the base of in-service pier P2 on load-carrying capacity of the piers. It is observed that the load-carrying capacity of the piers decreases with the increase in corrosion ratio of steel plates. There exists an obvious linear relationship between the load-carrying capacity and the corrosion ratio in the case of even corrosion mode. The degradation of load-carrying capacity resulted from the web\'s uneven corrosion mode is more serious than that under even corrosion mode, and the former case is more liable to occur than the latter case in actual engineering application. Finally, the failure modes of the piers under different corrosion state are discussed. It is found that the principal tensile strain of concrete and yield range of steel plates are distributed within a wide range in the case of slight corrosion, and they are concentrated on the column base when complete corrosion occurs. The findings obtained from the present study can provide a useful reference for the maintenance and strengthening of the in-service piers.

Key Words
bridge engineering; reinforced concrete pier; wrapped steel plate; corrosion ratio; corrosion mode; load-carrying capacity degradation

Address
(1) Shengbin Gao:
Department of Civil Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China;
(2) Toyoki Ikai, Hanbin Ge:
Department of Civil Engineering, Meijo University, Nagoya, 468-8502, Japan;
(3) Jie Ni:
The IT Electronic 11th Design & Research Institute, Shanghai, 200233, China.

Abstract
Steel shear wall system has been used in recent years in tall buildings due to its appropriate behavior advantages such as stiffness, high strength, economic feasibility and high energy absorption capability. Coupled steel plate shear walls consist of two steel shear walls that are connected to each other by steel link beam at each floor level. In this article the frames of 3, 10, and 15 of (C-SPSW) floor with rigid connection were considered in three different lengths of 1.25, 2.5 and 3.75 meters and link beams with plastic section modulus of 100% to the panel beam at each floor level and analyzed using three pairs of accelerograms based on nonlinear dynamic analysis through ABAQUS software and then the performance of walls and link beams at base shear, drift, the period of structure, degree of coupling (DC) and dissipated energy evaluated. The results show that the (C-SPSW) system base shear increases with a decrease in the link beam length, and the drift, main period and dissipated energy of structure decreases. Also the link beam length has different effects on parameters of coupling degrees.

Key Words
coupled steel plate shear wall; link beam; nonlinear dynamic analysis; plastic section modulus

Address
Faculty of Civil Engineering, Semnan University, Semnan, P.O. Box 35195-363, Iran.


Abstract
Composite column design is strongly influenced by the computation of the critical buckling load, which is very sensitive to the effective flexural stiffness (EI) of the column. Because of this, the behaviour of a composite column under lateral loading and its response to deflection is largely determined by the EI of the member. Thus, prediction models used for composite member design should accurately mirror this behaviour. However, EI varies due to several design parameters, and the implementation of high-strength materials, which are not considered by the current composite design codes of practice. The reliability of the design methods from six codes of practice (i.e., AS 5100, AS/NZS 2327, Eurocode 4, AISC 2010, ACI 318, and AIJ) for composite columns is studied in this paper. Also, the reliability of these codes of practice against a serviceability limit state criterion are estimated based on the combined use of the test-based statistical procedure proposed by Johnson and Huang (1997) and Monte Carlo simulations. The composite columns database includes 100 tests of circular concrete-filled tubes, rectangular concrete-filled tubes, and concrete-encased steel composite columns. A summary of the reliability analysis procedure and the evaluated reliability indices are provided. The reasons for the reliability analysis results are discussed to provide useful insight and supporting information for a possible revision of available codes of practice.

Key Words
composite columns; flexural stiffness; reliability analysis

Address
(1) Farhad Aslani, Ryan Lloyd, Brian Uy:
Centre for Infrastructure Engineering and Safety, The University of New South Wales, Sydney NSW 2052, Australia;
(2) Won-Hee Kang:
Institute for Infrastructure Engineering, Western Sydney University, Penrith NSW 2751, Australia;
(3) Stephen Hicks:
Heavy Engineering Research Association, HERA House, P.O. Box 76-134, Manukau 2241, Aukland, New Zealand.

Abstract
The paper presents comprehensive quasi-static stability analysis results for a real funnel-flow cylindrical steel silo composed of horizontally corrugated sheets strengthened by vertical thin-walled column profiles. Linear buckling and non-linear analyses with geometric and material non-linearity were carried out with a perfect and an imperfect silo by taking into account axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. Finite element simulations were carried out with 3 different numerical models (single column on the elastic foundation, 3D silo model with the equivalent orthotropic shell and full 3D silo model with shell elements). Initial imperfections in the form of a first eigen-mode for different wall loads and from 꼒n-situ. measurements with horizontal different amplitudes were taken into account. The results were compared with Eurocode 3. Some recommendations for the silo dimensioning were elaborated.

Key Words
silo; corrugated sheet; columns; buckling; stability; numerical modelling; Eurocode; geodetic measurements

Address
Department of Civil and Environmental Engineering, Gda?k University of Technology, Narutowicza 11/12, 80-233 Gdańsk, Poland.


Abstract
This paper presents the details of Finite Element (FE) analysis carried out to determine the limiting deformation capacity and failure mode of Laced Steel-Concrete Composite (LSCC) beam, which was proposed and experimentally studied by the authors earlier (Anandavalli et al. 2012). The present study attains significance due to the fact that LSCC beam is found to possess very high deformation capacity at which range, the conventional laboratory experiments are not capable to perform. FE model combining solid, shell and link elements is adopted for modeling the beam geometry and compatible nonlinear material models are employed in the analysis. Besides these, an interface model is also included to appropriately account for the interaction between concrete and steel elements. As the study aims to quantify the limiting deformation capacity and failure mode of the beam, a suitable damage model is made use of in the analysis. The FE model and results of nonlinear static analysis are validated by comparing with the load-deformation response available from experiment. After validation, the analysis is continued to establish the limiting deformation capacity of the beam, which is assumed to synchronise with tensile strain in bottom cover plate reaching the corresponding ultimate value. The results so found indicate about 20° support rotation for LSCC beam with 45° lacing. Results of parametric study indicate that the limiting capacity of the LSCC beam is more influenced by the lacing angle and thickness of the cover plate.

Key Words
steel-concrete composite construction; shear connector; finite element analysis; concrete damage plasticity model; static response

Address
Academy of Scientific and Innovative Research; CSIR-Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai 600 113, India.


Abstract
Shear connectors are key components to ensure the efficient composite action and satisfactory transfer of shear forces at the steel–concrete interface in composite beams. Under hazardous circumstances, such as fire in a building, the performance of a composite beam significantly relies on the performance of shear connectors. Studies on the behavior of shear connectors subjected to elevated temperatures performed in the last decade are reviewed in this paper. The experimental testing of push-out specimens, the design approaches provided by researchers and different codes, the major failure modes, and the finite element modeling of shear connectors are highlighted. The critical research review showed that the strength of a shear connector decreases proportionally with the increase in temperature. Compared with the volume of work published on shear connectors at ambient temperatures, a few studies on the behavior of shear connectors under fire have been conducted. Several areas where additional research is needed are also identified in this paper.

Key Words
high temperatures; shear connectors; load-slip; composite beam; push-out

Address
Department of Civil Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia.

Abstract
In this study the finite element method is utilized to predict the deflection and vibration characteristics of rectangular plates made of saturated porous functionally graded materials (PFGM) within the framework of the third order shear deformation plate theory. Material properties of PFGM plate are supposed to vary continuously along the thickness direction according to the power-law form and the porous plate is assumed of the form where pores are saturated with fluid. Various edge conditions of the plate are analyzed. The governing equations of motion are derived through energy method, using calculus of variations while the finite element model is derived based on the constitutive equation of the porous material. According to the numerical results, it is revealed that the proposed modeling and finite element approach can provide accurate deflection and frequency results of the PFGM plates as compared to the previously published results in literature. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as porosity volume fraction, material distribution profile, mode number and boundary conditions on the natural frequencies and deflection of the PFGM plates in detail. It is explicitly shown that the deflection and vibration behaviour of porous FGM plates are significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FGM plates with porosity phases.

Key Words
porous materials; finite element analysis; higher order shear deformation plate theory; vibration; deflection; functionally graded material

Address
Mechanical Engineering Department, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran P.O.B. 16818-34149.


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