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Analytical and experimental study on mild steel dampers with non-uniform vertical slits

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Earthquake Engineering and Engineering Vibration 2015年第1期14卷 111-123页

作者： Zheng Jie li aiqun Guo Tong School of Civil Engineering Southeast University Key Laboratory of Concrete and Prestressed Concrete Structure of China Ministry of Education Southeast University

This study proposes a novel mild steel damper with non-uniform vertical slits. The influence of different shapes of vertical slits of the core energy plate on the energy dissipation and buckling resistance capacities is analyzed. Based on the theoretical analysis, formulas of key parameters of the dampers, including the elastic lateral stiffness, shear bearing capacity and yield displacement, are derived. The effectiveness of the proposed damper is demonstrated through pseudo static tests on four 0.25-scale specimens. Performance of these dampers, i.e. cyclic deformation, stress distribution, energy dissipation capacity, etc., are presented and discussed. Using the numerical models of dampers calibrated through test data, earthquake time-history analyses were conducted, and it is observed that the dampers significantly reduce the seismic responses of the prototype frame and have a desirable energy dissipation capacity.

关键词： mild steel damper vertical slit pseudo static test energy dissipation

Model updating of a bridge structure using vibration test data based on GMPSO and BPNN:case study

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Earthquake Engineering and Engineering Vibration 2021年第1期20卷 213-221页

作者： Xia Zhiyuan li aiqun Shi Huiyuan li Jianhui Jiangsu Province Key Laboratory of Structure Engineering Suzhou University of Science and TechnologySuzhou 215011China School of Civil Engineering Southeast UniversityNanjing 210096China Beijing Advanced Innovation Center for Future Urban Design Beijing University of Civil Engineering and ArchitectureBeijing 100044China College of Civil Engineering Nanjing Forestry UniversityNanjing 210037China

Model updating issues with high-dimensional and strong-nonlinear optimization processes are still unsolved by most optimization *** this study,a hybrid methodology that combines the Gaussian-white-noise-mutation particle swarm optimization(GMPSO),back-propagation neural network(BPNN)and Latin hypercube sampling(LHS)technique is *** this approach,as a meta-heuristic algorithm with the least modification to the standard PSO,GMPSO simultaneously offers convenient programming and good performance in *** BPNN with LHS establishes the meta-models for FEM to accelerate efficiency during the updating process.A case study of the model updating of an actual bridge with no distribution but bounded parameters was carried out using this methodology with two different objective *** considers only the frequencies of the main girder and the other considers both the frequencies and vertical displacements of typical *** updating results show that the methodology is a sound approach to solve an actual complex bridge structure and offers good agreement in the frequencies and mode shapes of the updated model and test *** on the shape comparison of the main girder at the finished state with different objective functions,it is emphasized that both the dynamic and static responses should be taken into consideration during the model updating process.

关键词： model updating hybrid methodology advanced particle swarm optimization neural network case study

Environmental variability study on the measured responses of Runyang Cablestayed Bridge using wavelet packet analysis

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Science China(Technological Sciences) 2008年第5期51卷 517-528页

作者： DING Youliang li aiqun liU Tao College of Civil Engineering Southeast UniversityNanjing 210096China

The structural damage alarming method based on wavelet packet energy spectrum (WPES) for long-span cable-stayed bridges is presented through combination of ambient vibration test and wavelet packet analysis. The environmental variability in the measured WPES and damage alarming indices ERVD of the Runyang Cable-stayed Bridge are discussed in detail using the wavelet packet analysis of the measured acceleration responses of the bridge under daily environmental conditions. The analysis results reveal that the actual environmental conditions including traffic loadings, environmental temperature and typhoon loadings have remarkable correlations with the measured WPES. The changes of environmental temperature have a long-term trend influence on the WPES, while the influences of traffic and typhoon loadings on the measured WPES of the bridge present instantaneous changes because of the nonstationary properties of the loadings. The analysis results of the measured responses further reveal that the damage alarming indices ERVD can sensitively reflect the influences of environmental temperature and typhoon loadings on the dynamic properties of Runyang Cable-stayed Bridge. Therefore, the proposed structural damage alarming indices ERVD under ambient vibrations are suitable for real-time damage alarming for long-span cable-stayed bridges.

关键词： cable-stayed bridge wavelet packet analysis wavelet packet energy spectrum ambient vibration structural damage alarming

Calculation of stress intensity factor in two-dimensional cracks by strain energy density factor procedure

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Science China(Technological Sciences) 2018年第4期61卷 542-550页

作者： FANG Zhao li aiqun BAO HaiYing WANG Hao School of Civil Engineering Southeast UniversityNanjing 210096China Beijing Advanced Inovation Centerfor Future Urban Design Beijing University of Civil Engineering and ArchitectureBeijing 100044China

In order to calculate the stress intensity factor(SIF) of crack tips in two-dimensional cracks from the viewpoint of strain energy density, a procedure to use the strain energy density factor to calculate the SIF is proposed. In this paper, the procedure is presented to calculate the SIF of crack tips in mode I cracks, mode II cracks and I+II mixed mode cracks. Meanwhile, the results are compared to those calculated by traditional approaches or other approaches based on strain energy density and verified by theoretical solutions. Furthermore, the effect of mesh density near the crack tip is discussed, and the proper location where the strain energy density factor is calculated is also studied. The results show that the SIF calculated by this procedure is close to not only those calculated by other approaches but also the theoretical solutions, thus it is capable of achieving accurate ***, the mesh density around the crack tip should meet such requirements that, in the circular area created, the first layer of singular elements should have a radius about 0.05 mm and each element has a circumferential directional meshing angle to be15°–20°. Furthermore, for a single element around the crack tip, the strain energy density factor is suggested to be calculated in the location where half of the sector element's radius from the crack tip.

关键词： stress intensity factor two-dimensional crack strain energy density factor averaged strain energy density

Infl uence of structural parameters on dynamic characteristics and wind-induced buffeting responses of a super-long-span cable-stayed bridge

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Earthquake Engineering and Engineering Vibration 2014年第3期13卷 389-399页

作者： Wang Hao Chen Chunchao Xing Chenxi li aiqun Key Laboratory of Concrete & Prestressed Concrete Structures of Ministry of Education Southeast University Dept. of Civil and Environmental Engineering Virginia Tech Blacksburg VA 24061 USA PhD Candidate

A 3D finite element （FE） model for the Sutong cable-stayed bridge （SCB） is established based on ANSYS. The dynamic characteristics of the bridge are analyzed using a subspace iteration method. Based on recorded wind data, the measured spectra expression is presented using the nonlinear least-squares regression method. Turbulent winds at the bridge site are simulated based on the spectral representation method and the FFT technique. The influence of some key structural parameters and measures on the dynamic characteristics of the bridge are investigated. These parameters include dead load intensity, as well as vertical, lateral and torsional stiffness of the steel box girder. In addition, the influence of elastic stiffness of the connection device employed between the towers and the girder on the vibration mode of the steel box girder is investigated. The analysis shows that all of the vertical, lateral and torsional buffeting displacement responses reduce gradually as the dead load intensity increases. The dynamic characteristics and the structural buffeting displacement response of the SCB are only slightly affected by the vertical and torsional stiffness of the steel box girder, and the lateral and torsional buffeting displacement responses reduce gradually as the lateral stiffness increases. These results provide a reference for dynamic analysis and design of super-long-span cable-stayed bridges.

关键词： cable-stayed bridge dynamic characteristics finite element (FE) method wind field simulation buffetingresponse parameter effects elastic connection device

A new isolation device using shape memory alloy and its application for long-span structures

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Earthquake Engineering and Engineering Vibration 2011年第2期10卷 239-252页

作者： Ding Youliang Chen Xin li aiqun Zuo Xiaobao Key Laboratory of Concrete and Prestressed Concrete Structure of Ministry of Education Southeast University Nanjing 210096 China Department of Civil Engineering Nanjing University of Science ＆ Technology Nanjing 210094 China

The key points to consider in determining the effectiveness of using structural isolation with shape memory alloys （SMA） are the constitutive model, the SMA isolation device and the analysis method. In this paper, a simplified constitutive model based on the classic theory of plasticity is proposed to simulate the behavior of the superelasticity of the SMA, in which the martensite volume fraction is considered as one of the state variables. Comparisons between simulation results and experimental results are made and indicate that the proposed constitutive model yields stress-strain curves that are in good agreement with the experimental ones. Thus, the proposed model can correctly simulate the yield mechanism and energy dissipation capacity of the SMA. Next, in order to make full use of the superelasticity of SMA, a new SMA isolator composed of pre-tensioned SMA bars is presented. Then, a finite element analytical model is established to simulate the behavior of the SMA isolator according to its configuration and simplified constitutive model. Finally, a simplified design method for long-span structures installed with SMA isolators is proposed, which is further used to investigate the isolation effects of a space grid structure. Results show that the SMA isolator can reduce the seismic responses of the structure effectively, which indicates the effectiveness of the proposed SMA isolation method.

关键词： shape memory alloy super-elasticity constitutive model seismic response structural isolation space gridstructure

Accurate stress analysis on rigid central buckle of long-span suspension bridges based on submodel method

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Science China(Technological Sciences) 2009年第4期52卷 1019-1026页

作者： WANG Hao li aiqun GUO Tong MA Shuang College of Civil Engineering Southeast UniversityNanjing 210096China

Runyang Suspension Bridge (RSB) with the main span of 1490 m is the longest bridge in China and the third longest one in the world. In this bridge the rigid central buckle is employed for the first time in the mid-span of the suspension bridge in China. For such a super-long-span bridge, the traditional finite element (FE) modeling technique and stress analysis methods obviously cannot satisfy the needs of conducting accurate stress analysis on the central buckle. In this paper, the submodel method is in- troduced and for the first time used in analyzing the stresses of the central buckle. After an accurate FE submodel of the central buckle was specially established according to the analysis results from the whole FE model, the connection technique between the two-scale FE models was realized and the ac- curate stresses of the central buckle under various vehicle load cases were then conducted based on the submodel method. The calculation results were testified to be accurate and reliable by the field measurements, which show the efficiency and reliability of the submodel method on analyzing the mechanical condition of the central buckle of long-span suspension bridges. Finally, the working be- havior and mechanical characteristics of the central buckle of the RSB under vehicle loads were ana- lyzed based on the calculation and measurement results. The results obtained in this paper can provide theoretic references for analyzing and designing the rigid central buckle in long-span suspension bridges in future.

关键词： suspension bridge central buckle accurate stress submodel method field measurements

Modal identification of long-span Runyang Bridge using ambient responses recorded by SHMS

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Science China(Technological Sciences) 2009年第12期52卷 3632-3639页

作者： QingGuo Fei aiqun li Xiaolin Han ChangQing Miao School of Civil Engineering Southeast University Nanjing 210096 China Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education Southeast University Nanjing 210096 China

Runyang Bridge is a newly built cable-supported bridge that crosses the Yangtze River in *** bridge is composed of one suspension bridge and one cable-stayed *** the construction of the bridge,a structural health monitoring system(SHMS)was installed,which was designed by the Southeast *** the bridge was open to traffic,quantities of structural ambient responses have been recorded by the ***,it’s really important to extract structrural information from these records for health *** paper presents the study on modal identification of the *** dynamic properites including modal frequencies,mode shapes and damping ratios are extracted from the ambient *** identification methods are employed including the enhanced frequency domain decomposition and the stochastic subspace *** identified modal parameters from the two methods are *** show that modal frequencies and mode shapes from the two methods are almost the same while the damping ratios are different.

关键词： cable-supported bridge Runyang Bridge structural health monitoring modal identification ambient response analysis

Fatigue reliability assessment for bridge welded details using long-term monitoring data

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Science China(Technological Sciences) 2011年第12期54卷 3371-3381页

作者： DENG Yang DING Youliang li aiqun ZHOU GuangDong Key Laboratory of Concrete and Prestressed Concrete Structure of Ministry of Education Southeast University Nanjing 210096 China

A reliability assessment method of fatigue life based on the long-term monitoring data is developed for welded details in steel box girder,and the application research is presented with examples of welded rib-to-deck details in Runyang Bridges. Firstly the fatigue damage limit-state function is established based on S-N curves and Miner's rule,and the probability distribution characteristics of the coefficients in the function are discussed in detail. The uncertainties in fatigue loading effects are mainly studied based on long-term monitoring data. In the traditional studies,only the uncertainty of equivalent stress range is considered in fatigue reliability assessment. However,stress cycle number is also treated as a random variable in this paper because we know traffic flow every day differs in a thousand ways. Then the optimization method is employed to calculate the fatigue reliability. After studying the changing law of the reliability indices with time and the effect of the randomness of stress cycle number on reliability,the effect of the traffic growth on the reliability is studied. This study shows that the uncertainty in the fatigue life of the welded details can be well studied based on structural health monitoring,so it is necessary to carry out long-term strain monitoring of the welded details for accurate fatigue reliability assessment during the whole service period.

关键词： steel box girder fatigue loading effects equivalent stress range stress cycle number fatigue reliability traffic growth