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CONTENTS
Volume 38, Number 3, February10 2021
 

Abstract
In order to study the interfacial bond-slip behavior of steel reinforced recycled concrete (SRRC) under cyclic loading, thirteen specimens were designed and tested under cyclic loading and one under monotonic loading. The test results indicated that the average bond strength of SRRC decreased with the increasing replacement ratio of recycled concrete, whereas the bond strength increased with an increase in the concrete cover thickness, the volumetric stirrup ratio, and the strength of recycled concrete. The ultimate bond strength of the cyclically-loaded specimen was significantly (41%) lower than that of the companion monotonically-loaded specimen. The cyclic phenomena also showed that SRRC specimens went through the non-slip phase, initial slip phase, failure phase, bond strength degradation phase and residual phase, with all specimens exhibiting basically the same shape of the bond-slip curve. Additionally, the paper presents the equations that were developed to calculate the characteristic bond strength of SRRC, which were verified based on experimental results.

Key Words
steel reinforced recycled concrete (SRRC); bond-slip behavior; cyclic loading; bond strength; replacement ratio of recycled concrete

Address
Rui Ren, Liangjie Qi, Jianyang Xue and Xiguang Liu: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China;
Key Lab of Structural Engineering and Earthquake Resistance, Ministry of Education (XAUAT), Xi'an 710055, China
Xin Zhang: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi;an 710055, China
Hui Ma: School of Civil Engineering and Architecture, Xi'an University of Technology, Xi'an 710048, China
Togay Ozbakkaloglu: Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA


Abstract
This paper presents a displacement-based numerical methodology following the Euler-Bernoulli theory to simulate the 2 nonlinear behavior of steel structures. It is worth emphasizing the adoption of co-rotational finite element formulations considering large displacements and rotations and an inelastic material behavior. The numerical procedures proposed considers plasticity concentrated at the finite elements nodes, and the simulation of the steel nonlinear behavior is approached via the Strain Compatibility Method (SCM), where the material constitutive relation is used explicitly. The SCM is also applied in determining the sections bearing capacity. Moreover, the present numerical approach is not limited to a specific structural member cross-sectional typology, with the residual stress models introduced explicitly in subareas of steel cross-sections generated by a 2D discretization. Finally, results consistent with the literature and with low processing time are presented.

Key Words
co-rotational approach; concentrated plasticity; SCM; various steel sections

Address
Jessica L.Silva, Lidiane R.R.M. Deus and Ricardo A.M. Silveira: Department of Civil Engineering, Federal University of Ouro Preto, Campus Universitário,
Morro do Cruzeiro, 35400-000, Brazil
Igor J.M. Lemes: Department of Engineering, Federal University of Lavras, Campus Universitário, Kennedy, 37200-900, Brazil


Abstract
In this study, the fatigue property of U rib-to-crossbeam connections in orthotropic steel bridge (OSB) crossbeams under heavy traffic vehicle load was investigated considering the effects of in-plane shear stress. The applicability of an improved structural stress (ISS) method was validated for the fatigue behavior analysis of nonwelded arc-shaped cutout regions in multiaxial stress states. Various types of fatigue testing specimens were compared for investigating the equivalent structural stress, fatigue crack initiation positions, and failure modes with the unified standards. Furthermore, the implications of OSB crossbeams and specified loading cases are discussed with respect to the improved method. The ISS method is proven to be applicable for analyzing the fatigue property of nonwelded arc-shaped cutout regions in OSB crossbeams. The used method is essential for gaining a reliable prediction of the most likely failure modes under a specific heavy traffic vehicle load. The evaluated results using the used method are proven to be accurate with a slighter standard deviation. We obtained the trend of equivalent structural stress in arc-shaped cutout regions and validated the crack initiation positions and propagation directions by comparing them with the fatigue testing results. The implications of crossbeam spans on fatigue property are less significant than the effects of crossbeams.

Key Words
orthotropic steel bridges; heavy traffic vehicle load; in-plane shear structural stress; improved structural stress

Address
Haibo Yang and Hongliang Qian: School of civil engineering, Harbin Institute of Technology, Harbin, China, 150000
Ping Wang: School of Ocean Engineering, Harbin Institute of Technology at Weihai, Weihai, China, 264200

Abstract
An equivalent single-layer theory (EST) is put forward for analyzing free vibrations of steel-concrete composite beams (SCCB) based on a higher-order beam theory. In the EST, the effect of partial interaction between sub-beams and the transverse shear deformation are taken into account. After using the interlaminar shear force continuity condition and the shear stress free conditions at the top and bottom surface, the displacement function of the EST does not contain the first derivatives of transverse displacement. Therefore, the C0 interpolation functions are just demanded during its finite element implementation. Finally, the EST is validated by comparing the results of two simply-supported steel-concrete composite beams which are tested in laboratory and calculated by ANSYS software. Then, the influencing factors for free vibrations of SCCB are analyzed, such as, different boundary conditions, depth to span ratio, high-order shear terms, and interfacial shear connector stiffness.

Key Words
an equivalent single-layer theory; steel-concrete composite beams; C0 interpolation functions; free vibrations; finite element method

Address
Kai Q. Sun, Nan Zhang and Xiao Liu: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
State Key Laboratory for Track Technology of High-Speed Railway, Beijing 100081, China
Yan X. Tao: Railway Engineering Research Institute, China Academy of Railway Sciences Corporation Limited, Beijing 100081, China;
State Key Laboratory for Track Technology of High-Speed Railway, Beijing 100081, China



Abstract
The aim of this paper is to analyze the nonlinear bending of functionally graded (FG) curved nanobeams reinforced by carbon nanotubes (CNTs) in thermal environment. Chen-Yao' s surface elastic theory and geometric nonlinearity are also considered. The nanobeams are subjected to uniform loadings and placed on three-parameter substrates. The Euler-Lagrange equations are employed to deduce the equations of equilibrium. Then, the asymptotic solutions and boundary value problems are analytically determined by utilizing the two-step perturbation technique. Finally, the effects of the surface parameters, geometric factors, foundation stiffness, volume fraction, thermal effects and layout type of CNTs on the nonlinear bending of the nanobeams are discussed.

Key Words
curved nanobeams; snap-bucking; surface energy density; carbon nanotube-reinforced nanocomposites; thermal effects

Address
Yuan Yuan Zhang, Yu X. Wang and Huo M. Shen: School of Mechanics and Engineering, Southwest Jiaotong University, China
Xin Zhang:Department of Mechanical Engineering, Northwestern University, USA
Gui-Lin She: School of mechanical engineering, Chongqing University, Chongqing 400044, China

Abstract
The mechanical behavior of the outer square inner circular concrete-filled dual steel tubular (SCCFT) stub columns under axial compression is investigated by means of experimental research, numerical analysis and theoretical investigation. Parameters such as diameter ratio, concrete strength and steel ratio were discussed to identify their influence on the mechanical properties of SCCFT short columns on the basis of the experimental investigation of seven SCCFT short columns. By establishing a finite element model, nonlinear analysis was performed to discuss the longitudinal and transverse stress of the dual steel tubes. The longitudinal stress characteristics of the core and sandwich concrete were also analyzed. Furthermore, the failure sequence was illustrated and the reasonable cross-section composition of SCCFT stub column was proposed. A formula to predict the axial load capacity of SCCFT stub column was advanced and verified by the results from experiment and the finite element.

Key Words
SCCFT stub column; diameter ratio; finite element analysis (FEA); failure sequence; ultimate loading capacity; theoretical formula

Address
Fa-xing Ding and Liping Wang: School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P.R. China;
Engineering Technology Research Center for Prefabricated Construction Industrialization of Hunan
Wenjun Wang and Yi-Sun: School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P.R. China
Province, Changsha, 410075, P. R. China
Xue-mei Liu: Department of Infrastructure Engineering, The University of Melbourne, Parkville, VIC 3010, Australia


Abstract
To achieve a rational detail of the girder-abutment joints in composite integral bridges, and validate the performance of the joints with perfobond connectors, this paper proposes two innovative types of I-shaped steel girder-concrete abutment joints with perfobond connectors intended for the most of bearing capacity and the convenience of concrete pouring. The major difference between the two joints is the presence of the top flange inside the abutments. Two scaled models were investigated with tests and finite element method, and the damage mechanism was revealed. Results show that the joints meet design requirements no matter the top flange exists or not. Compared to the joint without top flange, the initial stiffness of the one with top flange is higher by 7%, and the strength is higher by 50%. The moment decreases linearly in both types of the joints. At design loads, perfobond connectors take about 70% and 50% of the external moment with and without top flange respectively, while at ultimate loads, perfobond connectors take 53% and 26% of the external moment respectively. The ultimate strengths of the reduced sections are suggested to be taken as the bending strengths of the joints.

Key Words
fully integral abutment bridge (FIAB); girder-abutment joint; bearing capacity; composite girder; experimental test

Address
Chen Liang and Yuqing Liu: Department of Bridge Engineering, Tongji University, Shanghai, China
Changjun Zhao, Bo Lei and Jieliang Wu: Zhejiang Provincial Institute of Communications Planning, Design & Research, Zhejiang, China

Abstract
Micro-electro-mechanical systems (MEMS) are widely employed in sensors, biomedical devices, optic sectors, and micro-accelerometers. New reinforcement materials such as carbon nanotubes as well as graphene platelets provide stiffer structures with controllable mechanical specifications by changing the graphene platelet features. This paper deals with buckling analyses of functionally graded graphene platelets micro plates with two piezoelectric layers subjected to external applied voltage. Governing equations are based on Kirchhoff plate theory assumptions beside the modified couple stress theory to incorporate the micro scale influences. A uniform temperature change and external electric field are regarded along the micro plate thickness. Moreover, an external in-plane mechanical load is uniformly distributed along the micro plate edges. The Hamilton's principle is employed to extract the governing equations. The material properties of each composite layer reinforced with graphene platelets of the considered micro plate are evaluated by the Halpin–Tsai micromechanical model. The governing equations are solved by the Navier's approach for the case of simply-supported boundary condition. The effects of the external applied voltage, the material length scale parameter, the thickness of the piezoelectric layers, the side, the length and the weight fraction of the graphene platelets as well as the graphene platelets distribution pattern on the critical buckling temperature change and on the critical buckling in-plane load are investigated. The outcomes illustrate the reduction of the thermal buckling strength independent of the graphene platelets distribution pattern while meanwhile the mechanical buckling strength is promoted. Furthermore, a negative voltage, -50 Volt, strengthens the micro plate stability against the thermal buckling occurrence about 9% while a positive voltage, 50 Volt, decreases the critical buckling load about 9% independent of the graphene platelet distribution pattern.

Key Words
graphene platelets; modified couple stress theory; piezoelectric layer; closed/open circuit; buckling analysis

Address
Fatemeh Abbaspour and Hadi Arvin: Faculty of Engineering, Shahrekord University, Shahrekord, Iran


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