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Ding F.-X.,Central South University | Fu L.,Central South University | Yu Z.-W.,Central South University | Yu Z.-W.,National Engineering Laboratory for High Speed Railway Construction
Thin-Walled Structures | Year: 2017

Compressive tests of the CFST stub columns with artificial notches in the steel tubes were conducted in this paper to investigate the effects of the material imperfections of steel tubes on column performances. The load-strain responses, column strength and confining effects were discussed in detail. A parametric study, including the notch length, notch orientation, notch location and ductility, was also conducted. The results indicate that the notched CFST specimens have quite different failure modes from the intact CFST specimens. A notched CFST specimen may fail by bulging or closing of the notch, which was determined by the notch orientation. The results also show that the notched CFST specimens had lower mechanical performances than the intact CFST specimens because the notch steel tube could not offer sufficient confining effect on the concrete core inside it. Based on the experimental results, a practical calculation formula for the bearing capacity of notched CFST columns was proposed, which gave well agreement with the experimental results. © 2017

Zhou W.,Central South University | Zhou W.,National Engineering Laboratory for High Speed Railway Construction | Jiang L.,Central South University | Jiang L.,National Engineering Laboratory for High Speed Railway Construction
Steel and Composite Structures | Year: 2017

Cold-formed lipped channel columns (CFLCCs) have been widely used in light gauge steel constructions. The distortional buckling is one of the important buckling modes for CFLCCs and the distortional buckling critical load depends significantly on the rotational restrain stiffness generated by the web to the lipped flange. First, a simplified explicit expression for the rotational restraint stiffness of the lipped flange has been derived. Using the expression, the characteristics of the rotational restraint stiffness of the lipped flange have been investigated. The results show that there is a linear coupling relationship between the applied forces and the rotational restraint stiffness of the lipped flange. Based on the explicit expression of the rotational restraint stiffness of the lipped flange, a simplified analytical formula has been derived which can determine the elastic distortional buckling critical stress of the CFLCCs subjected to axial compression. The simplified analytical formula developed in this study has been shown to be accurate through the comparisons with results from the distortional buckling analyses using the ANSYS finite element software. The developed analytical formula is easy to apply, and can be used directly in practical design and incorporated into future design codes and guidelines. Copyright © 2017 Techno-Press, Ltd.

Ren W.-X.,Central South University | Ren W.-X.,National Engineering Laboratory for High Speed Railway Construction | Fang S.-E.,Fuzhou University | Deng M.-Y.,Zhengzhou Institute of Aeronautical Industry Management
Journal of Engineering Mechanics | Year: 2011

With the aid of the response surface methodology, which is a combination of mathematical and statistical techniques, this paper presents a method for updating a finite-element model based on the measured static responses of structures. Unlike in the traditional model updating procedure, original finite-element models are replaced with response surface models constructed using the uniform design. By this means the complexity of a structure can be easily expressed by explicit functions with low dimensions. A parameter scope shrinking technique is also proposed to construct response surface models. The proposed method is verified against a numerical beam and an experimental full-scale continuous box-girder bridge. It is demonstrated that the proposed response surface-based finite-element-model updating in structural statics has the advantages of easy implementation, high cost-efficiency, and adequate updating accuracy. Once the response surface model that is formulated explicitly is constructed, no finite-element calculation is required in each optimization iteration during updating. Therefore, such finite-element model updating can be easily implemented in practice with available commercial finite-element analysis packages. © 2011 American Society of Civil Engineers.

Liu Z.,Central South University | Liu Z.,National Engineering Laboratory for High Speed Railway Construction | Deng D.,Central South University | Deng D.,National Engineering Laboratory for High Speed Railway Construction | And 3 more authors.
Cement and Concrete Composites | Year: 2013

Normally, MgSO4 is considered to promote thaumasite sulfate attack (TSA) due to pH drop of solution caused by insoluble brucite formation. However, some test results indicate that thaumasite formation (TF) should occur in the solution with relatively high pH. In the current paper, cement, cement + fly ash, cement + limestone powder and high sulfate resisting (HSR) cement pastes were immersed in sealed bottles containing Na2SO 4:MgSO4 = 0:5, 1:5, 3:5 and 10:30 at 10 °C. The pH was measured and corrosion products were identified by means of XRD. The results indicated that the existence of relatively low content MgSO4 (even 5%) may not cause significant pH drop under non-exposed condition. The pH was still kept at the level of 13.0, while the increase of MgSO4 could promote TF. The pH fell below 10.0 in the solution containing saturated MgSO4, however, gypsum dominated the mechanism of paste deterioration. © 2012 Elsevier Ltd. All rights reserved.

Liu Z.,Central South University | Liu Z.,National Engineering Laboratory for High Speed Railway Construction | Deng D.,Central South University | Deng D.,National Engineering Laboratory for High Speed Railway Construction | And 3 more authors.
Construction and Building Materials | Year: 2012

When concrete elements are partially exposed to sulfate rich environment, the upper part of concrete in contact with air will be deteriorated more severely than the underground part. Fly ash additions seem to accelerate the collapse of concrete in such an environment. Although concrete technologists attribute concrete damage mainly to salt crystallization or physical sulfate attack, the influence of chemical sulfate attack cannot be neglected and should also be studied. The objective of this paper is twofold. First, pore solution expression test was conducted to squeeze pore solution of different parts of cement paste partially exposed to Na 2SO 4 solution. The sulfate concentration and pH value of pore solution were measured. Results showed that the sulfate concentration of the pore solution in the upper part of paste in contact with air was much higher than in the lower submerged part. Fly ash additions could draw more sulfates into the paste in a shorter time, forming a higher concentration sulfate pore solution than in normal concrete. The second test was designed to simulate the effect of severe exposure condition on reactive products of cement paste. Pure cement and cement + fly ash (25% dosage) pastes were immersed in 5%, 15% and 30% at 30 °C and 15% at 40 °C Na 2SO 4 solutions. Thermogravimetric analysis was used to analyze the reaction products of the paste. The results indicate that more ettringite and gypsum were formed in cement + fly ash paste than pure cement paste. © 2011 Elsevier Ltd. All rights reserved.

Wang X.-H.,Central South University | Wang X.-H.,National Engineering Laboratory for High Speed Railway Construction | Zhang M.,Central South University | Zhang M.,National Engineering Laboratory for High Speed Railway Construction
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2013

By virtue of the 3D axisymmetric three-phase elastodynamic theory and considering the effect of matric suction on the dynamic shear modulus, the harmonic dynamic response of end-bearing piles embedded in unsaturated poroelastic medium subjected to vertical loading is investigated. The resistance factor and vibration modes of the soil layer are obtained from the direct decoupling of the governing equations by employing the differential operator splitting and variable separation method. On the basis of the assumptions of perfect contact along the pile-soil and the rigid supported type at the pile tip, the wave equation for the pile treated as a bar and described by the conventional 1-D structure vibration theory is then solved. Ultimately, the functions of complex stiffness at the top of the pile together with the soil impedances in the frequency domain are derived, and the selected numerical solutions are presented to portray the influences of principal parameters on the dynamic behaviors of pile. The results show that as the saturation decreases, the dynamic stiffness factor and the equivalent damping both decrease, while the resonance frequencies of the pile-soil system are almost not affected. It is necessary to differentiate the various responses evoked by the moduli of soil and pile during the analysis of pile-soil modulus ratio. The proposed model reveals an entire evolutional process of dynamic response of soil from single-phase media to two phase saturated media, and provides a comprehensive theoretical framework to describe the dynamic behavior of pile under actual soil environment.

Jiang L.,Central South University | Jiang L.,National Engineering Laboratory for High Speed Railway Construction | Shao G.,Central South University | Jiang J.,Central South University | Wang H.,Central South University
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2013

Solid piers with round ended cross-section are widely used in China high-speed railway. Bridge piers of this type have relatively high aspect ratio and low longitudinal reinforcement ratio. Existing experiments are not systematic and sufficient, so the seismic performance of this type of pier is still not understood enough. Derived from the prototype of round-ended piers in high-speed railway, nine large scale model piers were designed according to the model similitude theory. The orthogonal experiment method was used to consider the different design variables which can affect the seismic behaviors. The failure characteristics, hysteresis curves and skeleton curves were obtained based on cyclic loading tests considering axial load, and then the influence of each variable on the displacement ductility, energy dissipation, strength and stiffness degradation of the piers were analyzed. The main factors affecting ductility, including the axial compression ratio, the longitudinal reinforcement ratio and the volume-stirrup ratio were discussed. It is found that the hysteresis curves have significant pinch in the models with low reinforcement ratio. The displacement ductility decreases with the axial load ratio and longitudinal reinforcement ratio, while the volume-stirrup ratio and shear span ratio have little effect on the ductility. The energy dissipation ability is poor when the longitudinal reinforcement ratio of the piers is relatively low, while the energy dissipation performace can be significantly improved by increasing the longitudinal reinforcement ratios.

Peng J.,Central South University | Peng J.,National Engineering Laboratory for High Speed Railway Construction | Deng D.,Central South University | Deng D.,National Engineering Laboratory for High Speed Railway Construction | And 6 more authors.
Construction and Building Materials | Year: 2014

Cement emulsified asphalt (CA) paste is a suspension with organic and inorganic components, whose rheological behavior is more complicated than that of plain cement paste. The placement quality of CA mortar cushion layer of ballastless track is strongly influenced by its rheological behavior. In this paper, the shear conditions of construction of CA mortar in practical engineering were characterized, and effect of important parameters on its rheological behavior (specially focus on shear rate in practical engineering) was investigated, including solid volume fraction (Vs), mass ratio of asphalt to cement (A/C), and superplasticizer (SP) type and dosage. Pastes were proportioned with A/C of 0.3, 0.5, 0.7 and 0.9, various Vs of 30%, 40%, 50% and 60%, and SPs of polycarboxylate (PCA) and polynaphthalenesulfonate (PNS). Rheological curves were measured at 25 °C, using a rotating coaxial cylinder viscometer. Results indicate that most of the CA pastes are shear thinning flow in the shear rate range of practical engineering. The shear thinning behavior is slacked down with the decreasing of Vs, increasing of A/C and concentration of SPs. Severe shear thinning behavior maybe not good for the placement quality of CA mortar cushion layer. © 2014 Elsevier Ltd. All rights reserved.

Ren W.-X.,Central South University | Chen H.-B.,National Engineering Laboratory for High Speed Railway Construction
Engineering Structures | Year: 2010

Fast-running response surface models that approximate multivariate input/output relationships of time-consuming physical-based computer models enable effective finite element (FE) model updating analyses. In this paper, a response surface-based FE model updating procedure for civil engineering structures in structural dynamics is presented. The key issues to implement such a model updating are discussed such as sampling with design of experiments, selecting the significant updating parameters and constructing a quadratic polynomial response surface. The objective function is formed by the residuals between analytical and measured natural frequencies. Single-objective optimization with equal weights of natural frequency residual of each mode is used for optimization computation. The proposed procedure is illustrated by a simulated simply supported beam and a full-size precast continuous box girder bridge tested under operational vibration conditions. The results have been compared with those obtained from the traditional sensitivity-based FE model updating method. The real application to a full-size bridge has demonstrated that the FE model updating process is efficient and converges fast with the response surface to replace the original FE model. With the response surface at hand, an optimization problem is formulated explicitly. Hence, no FE calculation is required in each optimization iteration. The response surface-based FE model updating can be easily implemented in practice with available commercial FE analysis packages. © 2010 Elsevier Ltd.

Dai G.,Central South University | Dai G.,National Engineering Laboratory for High Speed Railway Construction | Su M.,Central South University
Archives of Civil and Mechanical Engineering | Year: 2016

This paper presents the experimental observations and results of six full-scale field ballastless track structure specimens, and tested under longitudinal and transverse shear load. The tests aimed to examine the interfacial shear capacity of the continuous slab track structure and investigate the interfacial bond-slip behaviour. The results show that bond strength of the two interfaces which were on the top and bottom of mortar layer, respectively, have a large difference. Until the top interface of the mortar layer fractured, no slip displacement was observed in the bottom interface. In addition to the experimental study, a finite element model using nonlinear interface elements was employed to simulate the tests. The numerical calculated capacity agreed well with the experimental results, showing that the proposed bond-slip law is reliable. Finally, the track slab's evenness with the bond-slip effect under the dynamic load was studied. © 2016 Politechnika Wrocławska.

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