Seismic Performance of a Subway Station-Tunnel Junction Structure: A Shaking Table Investigation and Numerical Analysis

Qingjun Chen,Tianyu Zhang,Na Hong,Bin Huang 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.5

Damage cases show that during earthquakes, the sharp stiffness mutation of subway station-tunnel junction structures can lead to dislocations at the connections. To address this, shaking table tests were conducted followed by numerical simulations of a typical junction structure with rigid connections. The modeling method was verified based on the test results. Furthermore, numerical models of junction structures with rigid and flexible connections, single stations, and single tunnels were built, and deformation modes and stress distributions were comparatively analyzed. Combining the experimental and numerical results, it is found that there exists an intensive deformation inconsistency between the stations and the tunnels responsible for the junction structures’ dislocation failures. The station operates in both racking and distortion deformation modes when the tunnel undergoes ovaling deformation. The tunnel bends relative to the end wall at the connection. The junction structure with rigid connections is most at risk at the point located at the tunnel section connected to the end wall and near the bottom plate-sidewall joint. With flexible connections, the tunnels integrally translate relative to the end wall, and the stress response of the end wall openings can be larger than those with rigid connections.

An inerter-system chain and energy-based optimal control of adjacent single-degree-of-freedom structures

Qingjun Chen,Zhipeng Zhao,Ruifu Zhang 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.28 No.2

Because of the limited land resources and preference of centralized services, more structures are often built close to each other, correspondingly yielding a demand that mitigates the dynamic responses of adjacent structures. Utilizing the intrinsic potential of the inerter to improve structural energy performances, an inerter-system chain is proposed for the adjacent singledegree- of-freedom structures, which forms a novel configuration featuring the reduction in input energy transmitted to the adjacent structures. The inerter-system chain is realized by two end-placed inerter-dashpot dampers and inter-placed springinerter- dashpot elements arranged in parallel. Stochastic energy balance analysis is conducted to derive a closed-form energy equation that reveals the energy basis of the inerter-system chain. An energy-based and bi-objective optimization strategy is developed with simultaneous consideration of displacement and energy performances, particularly easy-to-use design formulae being derived. The findings of this study show that a complete inerter-system chain exhibits a significant multi-reduction in the structural displacement, shear force, and dissipation energy burden. Particularly, the effectiveness of reducing the input power and vibrational energy transmitted into the entire structures counts on the series inerter-chain, which differentiates the proposed chain from alternative layouts. The proposed energy-based design framework is capable of minimizing the energy dissipation cost, with target displacement control demand satisfied.

Experimental Investigation on Fatigue Strength of Joints between SRC Beams and Concrete-Filled RHS Columns

Qingjun Xian,Le-Wei Tong,Liying Zhou,Yiyi Chen 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5

Fatigue behavior, failure mechanism and fatigue strength of joints between steel reinforced concrete (SRC) beams and Concrete Filled Rectangular Hollow Section (CFRHS) columns is discussed in this paper. Three identical beam-to-column joint specimens were designed and tested under static loading and two stages of fatigue loading. In the first stage of fatigue loading, the specimens were subjected to design fatigue load for 2 million cycles, while during the second stage, they were loaded to failure under increased fatigue load in order to know failure mechanism and fatigue strength. It is found that the joints satisfied design requirements when subjected to static loading and design fatigue loading. Fatigue failure occurred after these joints were applied higher-level fatigue loading. The crack initiated at the weld toe of stud or stirrup hole in the upper flange of I-shaped steel in certain SRC beam, and then it propagated along flange width in winding trajectory until fatigue fracture occurred. Stress amplitude of tension flange in SRC beam can be regarded as the parameter representing fatigue strength of the joints. S-N curves in related codes are selected to evaluate fatigue strength of the joints. The design method is suggested to consider fatigue design of the joints.

A negative stiffness inerter system (NSIS) for earthquake protection purposes

Zhipeng Zhao,Qingjun Chen,Ruifu Zhang,Yiyao Jiang,Chao Pan 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.4

The negative stiffness spring and inerter are both characterized by the negative stiffness effect in the force-displacement relationship, potentially yielding an amplifying mechanism for dashpot deformation by being incorporated with a series tuning spring. However, resisting forces of the two mechanical elements are dominant in different frequency domains, thus leading to necessary complementarity in terms of vibration control and the amplifying benefit. Inspired by this, this study proposes a Negative Stiffness Inerter System (NSIS) as an earthquake protection system and developed analytical design formulae by fully utilizing its advantageous features. The NSIS is composed of a sub-configuration of a negative stiffness spring and an inerter in parallel, connected to a tuning spring in series. First, closed-form displacement responses are derived for the NSIS structure, and a stability analysis is conducted to limit the feasible domains of NSIS parameters. Then, the dual advantageous features of displacement reduction and the dashpot deformation amplification effect are revealed and clarified in a parametric analysis, stimulating the establishment of a displacement-based optimal design framework, correspondingly yielding the design formulae in analytical form. Finally, a series of examples are illustrated to validate the derived formulae. In this study, it is confirmed that the synergistic incorporation of the negative stiffness spring and the inerter has significant energy dissipation efficiency in a wide frequency band and an enhanced control effect in terms of the displacement and shear force responses. The developed displacement-based design strategy is suitable to utilize the dual benefits of the NSIS, which can be accurately implemented by the analytical design formulae to satisfy the target vibration control with increased energy dissipation efficiency.

Input energy spectra and energy characteristics of the hysteretic nonlinear structure with an inerter system

Yanchao Wang,Qingjun Chen,Zhipeng Zhao,Xiuyan Hu 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.6

The typical inerter system, the tuned viscous mass damper (TVMD), has been proven to be efficient. It is characterized by an energy-dissipation-enhancement effect, whereby the dashpot deformation of TVMD can be amplified for enhanced energy dissipation efficiency. However, existing studies related to TVMD have mainly been performed on elastic structures, so the working mechanism remains unclear for nonlinear structures. To deal with this, an energy-spectrum analysis framework is developed systematically for classic bilinear hysteretic structures with TVMD. Considering the soil effect, typical bedrock records are propagated through the soil deposit, for which the designed input energy spectra are proposed by considering the TVMD parameters and structural nonlinear properties. Furthermore, the energy-dissipation-enhancement effect of TVMD is quantitatively evaluated for bilinear hysteretic structures. The results show that the established designed input energy spectra can be employed to evaluate the total energy-dissipation burden for a nonlinear TVMD structure. Particularly, the stiffness of TVMD is the dominant factor in adjusting the total input energy. Compared with the case of elastic structures, the energy-dissipation-enhancement effect of TVMD for nonlinear structures is weakened so that the expected energy-dissipation effect of TVMD is replaced by the accumulated energy dissipation of the primary structure.

Seismic Performance and Failure Mechanism of a Subway Station Based on Nonlinear Finite Element Analysis

Wenting Li,Qingjun Chen 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.2

A nonlinear three-dimensional finite element model is employed to investigate the seismic performance and failure mechanism of a subway station. The interaction between subway station and surrounding soil is considered and the nonlinear behavior of the station structure is taken into account. Structural concrete and steel bars are simulated separately. The results demonstrated that the carrying capacities of structural middle columns and wall-to-roof slab connections are vital in underground structure’s seismic design. During an earthquake, the structure’s plastic damage first appears at beam-to-roof slab connections; but the damage at beam-to-roof slab connections does not develop significantly as seismic going. The heaviest damage parts is columns’ bottom, and then is columns’ top. The damage of wall-to-slab connections can, firstly, let the load transfer to columns and, secondly, reduce the restraint to the roof slab. The relative displacement between the roof slab and bottom slab leads to additional moment on structural middle columns. Besides, the damage at the connections of walls-to-diagonal bracings and slabs-to-diagonal bracings is remarkable. The structure is failure as an italic “M” shape. The results are consistent with the phenomena observed in the collapse of Daikai subway station during 1995 Great Hanshin Earthquake.

MR Image Segmentation Using Graph Cuts Based Geodesic Active Contours

Dongsheng Ji,Yukao Yao,Qingjun Yang,Xiaoyun Chen 보안공학연구지원센터 2016 International Journal of Hybrid Information Techno Vol.9 No.1

In this paper, present a graph cuts based geodesic active contours (GAC) approach to object segmentation problems. Our method is a combination of geodesic active contours and the optimization tool of graph cuts and differs fundamentally from traditional active contours in that it uses graph cuts to iteratively deform the contour. Consequently, it has the following advantages. 1. It has the ability to jump over local minima and provide a more global result. 2. Graph cuts guarantee continuity and lead to smooth contours free of self-crossing and uneven spacing problems. Therefore, the internal force which is commonly used in traditional energy functions to control the smoothness is no longer needed, and hence the number of parameters is greatly reduced. 3 Our approach easily extends to the segmentation of three and higher dimensional objects. In addition, the algorithm is suitable for interactive correction and is shown to always converge. Experimental results and analyses are provided.

An Effective SVM Ensemble Algorithm Based on Different Thresholds of PCA

Yukai Yao,Bo Wang,Qingjun Yang,Dongsheng Ji,Tao Ma,Xiaoyun Chen 보안공학연구지원센터 2016 International Journal of Database Theory and Appli Vol.9 No.2

This paper proposes an effective ensemble classifier, named PCAenSVM, which consists of ten weak Support Vector Machine classifiers based on different Principal Component Analysis thresholds. Those ten base Support Vector Machine classifiers are made up to fulfill classification tasks using Majority Voting strategy. Experiments are made on four UCI data sets and a data set from the Uppsala University to evaluate the performances of PCAenSVM. The results of PCAenSVM are compared with that of LibSVM and EnsembleSVM. Experimental results show that PCAenSVM has better classification accuracy than other two algorithms. Moreover, PCAenSVM has the same confidence level with the LibSVM, and its confidences of accuracy and sensitivity on those five data sets outperform that of the EnsembleSVM.

Evaluation and Analysis on Quality of Different Radish Cultivars

Shaohui Wang,Rui Yang,Qingjun Chen,Jinfang Zhao 한국원예학회 2006 한국원예학회 기타간행물 Vol.- No.-

Experimental Investigation on Fatigue Behavior of Steel Reinforced Concrete Composite Beam-to-Girder Joints

Le-Wei Tong,Qingjun Xian,Liying Zhou,Yiyi Chen,Yunfeng Zhang 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.4

Fatigue behavior and failure mechanism of steel reinforced concrete (SRC) beam-to-girder joints is discussed in this paper,which is intended for use in high-speed railway station structures due to their high stiffness and load capacity. Three identical SRC beam-to-girder joint specimens were designed and tested under static loading and two stages of fatigue loading. In the first stage of fatigue loading, the specimens were subjected to design fatigue load for 2 million cycles, while during the second stage, the specimens were loaded to failure under increased fatigue loading amplitude in order to know its fatigue strength and failure mechanism. The constructional details of SRC beam-to-girder joint specimen and the method of loading and testing are presented. The comparison in structural behavior of the joint is made between under static and fatigue loading. Fatigue failure characteristics of the joint are described in detail. It is found that the SRC beam-to-girder joints remained in their elastic range and the concrete surface crack did not exceed 0.1 mm when subjected to design static loading and 2 million cycles of design fatigue loading. There was no significant difference in structural behavior of each component of SRC composite beam between static and fatigue loading. Fatigue failure occurred after these joints were applied higher-level fatigue loading for another 0.70to 0.91 million cycles. Fatigue crack was initiated at the tension flange of I-shape steel of beam connected by welding to the flange of I-shape steel of girder or at the hole in tension flange of I-shape steel of beam, and then the crack propagated along flange width and web height of the I-shape steel in beam until the I-shape steel lost loading capacity due to lack of enough cross section. The fatigue behavior of constructional detail of the I-shape steel played a key role in the fatigue strength of the SRC beam-to-girder joints. Discussions on improving the fatigue strength of SRC beam-to-girder joints and future research aspects are presented finally.