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Output only modal identification and structural damage detection using time frequency & wavelet techniques

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Earthquake Engineering and Engineering Vibration 2009年第4期8卷 583-605页

作者： S.Nagarajaiah B.Basu dept.of civil & Environmental Eng.and dept.of Mechanical Eng.& Material Sc. Rice University dept.of civil Structural& Environmental Eng.Trinity College Dublin

The primary objective of this paper is to develop output only modal identification and structural damage detection. Identification of multi-degree of freedom （MDOF） linear time invariant （LTI） and linear time variant （LTV--due to damage） systems based on Time-frequency （TF） techniques--such as short-time Fourier transform （STFT）, empirical mode decomposition （EMD）, and wavelets--is proposed. STFT, EMD, and wavelet methods developed to date are reviewed in detail. In addition a Hilbert transform （HT） approach to determine frequency and damping is also presented. In this paper, STFT, EMD, HT and wavelet techniques are developed for decomposition of free vibration response of MDOF systems into their modal components. Once the modal components are obtained, each one is processed using Hilbert transform to obtain the modal frequency and damping ratios. In addition, the ratio of modal components at different degrees of freedom facilitate determination of mode shape. In cases with output only modal identification using ambient/random response, the random decrement technique is used to obtain free vibration response. The advantage of TF techniques is that they arc signal based; hence, can be used for output only modal identification. A three degree of freedom 1：10 scale model test structure is used to validate the proposed output only modal identification techniques based on STFT, EMD, HT, wavelets. Both measured free vibration and forced vibration （white noise） response are considered. The secondary objective of this paper is to show the relative ease with which the TF techniques can be used for modal identification and their potential for real world applications where output only identification is essential. Recorded ambient vibration data processed using techniques such as the random decrement technique can be used to obtain the free vibration response, so that further processing using TF based modal identification can be performed.

关键词： Time-frequency methods short time Fourier transform Hilbert transform wavelets modal identification:output only structural health monitoring damage detection

The Structural Engineering Challenges Following the Wenchuan Earthquake

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四川大学学报（工程科学版） 2009年第3期41卷 223-230页

作者： GRUNDY Paul dept.of civil Eng. Monash Univ.

The "5·12" Wenchuan Earthquake presents two challenges-reconstruction of the devastated areas and building adequate seismic resistance into the rest of *** stages in recovery include structural condition assessment,identification of seismic weaknesses,appreciation of the variable seismicity of PR China,the development of a seismic performance index to aid the decision to relocate,rebuild or retrofit,development and application of the principles of retrofitting which recycles rubble and waste from Wenchuan "5·12",with an emphasis on integrating masonry construction into seismic *** recovery and resilience achieved through structural engineering must be integrated into a broader community involvement in disaster risk reduction.

关键词：建筑工程抗振结构建筑结构建筑物

Performance-based seismic design of nonstructural building components:The next frontier of earthquake engineering

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Earthquake Engineering and Engineering Vibration 2014年第S1期13卷 17-46页

作者： Andre Filiatrault Timothy Sullivan dept.of civil Structural and Environmental Engineering University at BuffaloState University of New York dept.of civil Engineering & Architecture University of Pavia Assistant Professor

With the development and implementation of performance-based earthquake engineering,harmonization of performance levels between structural and nonstructural components becomes vital. Even if the structural components of a building achieve a continuous or immediate occupancy performance level after a seismic event,failure of architectural,mechanical or electrical components can lower the performance level of the entire building system. This reduction in performance caused by the vulnerability of nonstructural components has been observed during recent earthquakes worldwide. Moreover,nonstructural damage has limited the functionality of critical facilities,such as hospitals,following major seismic events. The investment in nonstructural components and building contents is far greater than that of structural components and framing. Therefore,it is not surprising that in many past earthquakes,losses from damage to nonstructural components have exceeded losses from structural damage. Furthermore,the failure of nonstructural components can become a safety hazard or can hamper the safe movement of occupants evacuating buildings,or of rescue workers entering buildings. In comparison to structural components and systems,there is relatively limited information on the seismic design of nonstructural components. Basic research work in this area has been sparse,and the available codes and guidelines are usually,for the most part,based on past experiences,engineering judgment and intuition,rather than on objective experimental and analytical results. Often,design engineers are forced to start almost from square one after each earthquake event: to observe what went wrong and to try to prevent repetitions. This is a consequence of the empirical nature of current seismic regulations and guidelines for nonstructural components. This review paper summarizes current knowledge on the seismic design and analysis of nonstructural building components,identifying major knowledge gaps that w

关键词： nonstructural building components performance-based earthquake engineering seismic design and analysis

Analytical investigations of seismic responses for reinforced concrete bridge columns subjected to strong near-fault ground motion

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Earthquake Engineering and Engineering Vibration 2007年第3期6卷 237-244页

作者：苏进国宋裕祺张顺益黄昭勋 dept.of civil Engineering Taipei University of TechnologyChinese Taipei

Strong near-fault ground motion, usually caused by the fault-rupture and characterized by a pulse-like velocity- wave form, often causes dramatic instantaneous seismic energy （Jadhav and Jangid 2006）. Some reinforced concrete （RC） bridge columns, even those built according to ductile design principles, were damaged in the 1999 Chi-Chi earthquake. Thus, it is very important to evaluate the seismic response of a RC bridge column to improve its seismic design and prevent future damage. Nonlinear time history analysis using step-by-step integration is capable of tracing the dynamic response of a structure during the entire vibration period and is able to accommodate the pulsing wave form. However, the accuracy of the numerical results is very sensitive to the modeling of the nonlinear load-deformation relationship of the structural member. FEMA 273 and ATC-40 provide the modeling parameters for structural nonlinear analyses of RC beams and RC columns. They use three parameters to define the plastic rotation angles and a residual strength ratio to describe the nonlinear load- deformation relationship of an RC member. Structural nonlinear analyses are performed based on these parameters. This method provides a convenient way to obtain the nonlinear seismic responses of RC structures. However, the accuracy of the numerical solutions might be further improved. For this purpose, results from a previous study on modeling of the static pushover analyses for RC bridge columns （Sung et al. 2005） is adopted for the nonlinear time history analysis presented herein to evaluate the structural responses excited by a near-fault ground motion. To ensure the reliability of this approach, the numerical results were compared to experimental results. The results confirm that the proposed approach is valid.

关键词： bridge columns near-fault ground motion seismic modeling

Experimental study of vibration mitigation of mast arm signal structures with particle-thrust damping based tuned mass damper

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Earthquake Engineering and Engineering Vibration 2019年第1期18卷 219-231页

作者： Zhang Yunfeng Liu Heng dept.of civil & Environmental Engineering University of Maryland College Park

Large amplitude vibration of mast arm structures due to wind loads are the primary contributing factor to the reduced fatigue life of signal support structures. To alleviate this problem of wind-induced in-plane vibration of mast arm signal structures, a particle-thrust damping based turned mass damper(PTD-TMD) device is adopted and its damping effect is characterized experimentally. The particle-thrust damping is a passive damping device that does not require electric power and is temperature independent. Based on the calibration test, an equivalent dynamic model of the PTD-TMD device is developed and used for numerical simulation study. The damping effects of this PTD-TMD device on signal support structures was investigated through both numerical analysis and laboratory testing of a 50-ft(15.24 m) mast arm structure including both free vibration and forced vibration tests. The experimental test and numerical study results show that vibration response behavior of mast arm signal support structures can be significantly reduced by installing the PTD-TMD that can increase the critical damping ratio of the mast arm signal structures to 4%. The stress range at the welded connection between the mast arm and traffic pole is also reduced.

关键词： fatigue mast arm signal support structures tuned mass damper vibration

Modeling and cyclic behavior of segmental bridge column connected with shape memory alloy bars

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Earthquake Engineering and Engineering Vibration 2012年第3期11卷 375-389页

作者： Hwasung Roh Andrei M.Reinhorn Jong Seh Lee dept.of civil and Environmental Engineering Hanyang University dept.of civil Structural and Environmental EngineeringUniversity at Buffalo The State University of New York

This paper examines the quasi-static cyclic behavior, lateral strength and equivalent damping capacities of a system of post-tensioned segmental bridge columns tied with large diameter martensitic Shape Memory Alloy （SMA） link-bars. Moment-curvature constitutive relationships are formulated and analysis tools are developed for the PT column, including a modified four-spring model prepared for the SMA bars. The suggested system is exemplified using a column with an aspect ratio of 7.5 and twelve 36.5 mm diameter NiTi martensitic SMA bars. A post-tensioning force of 40% to 60% of the tendon yield strength is applied in order to obtain a self re-centering system, considering the residual stress of the martensitie SMA bars. The cyclic response results show that the lateral strength remains consistently around 10% of the total vertical load and the equivalent viscous damping ratios reach 10%-12% of critical. When large diameter NiTi superelastic SMA bars are incorporated into the column system, the cyclic response varies substantially. The creep behavior of the superelastic SMA bar is accounted for since it affects the re-centering capability of the column. Two examples are presented to emphasize the modeling sensitivities for these special bars and quantify their cyclic behavior effects within the column assembly.

关键词： segmental rocking columns shape memory alloy bars cyclic response energy dissipation damping recentering

Slope Stability Analyses of Outang Landslide Based on the Peak and Residual Shear Strength Behavior

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工程科学与技术 2019年第4期51卷 55-68页

作者： YANG Xiuhan VANAPALLI Sai dept.of civil Eng. Univ.of Ottawa

Most of the natural and compacted fine-grained soil slopes that are in saturated or unsaturated condition undergo a large deformation prior to reaching failure *** slopes should be designed taking account of their strain-softening behavior using the residual shear strength (RSS) *** this paper,the slope stability of a recently reactivated Outang landslide near the Three Gorges Dam in China is analyzed based on the RSS parameters of unsaturated *** addition,comparisons are provided in the FOS values of slope using both the peak shear strength (PSS) and RSS ***,a series of site investigations of the hydrologic and geologic conditions,ground surface displacements and cracks were *** PSS and RSS behaviors of the sliding soils derived from a series of direct shear test results performed on saturated and unsaturated soil specimens are ***,a series of slope stability analysis were conducted considering the precipitation and Yangtze River water level variation within a representative period of 7 months,based on the PSS and the RSS *** this study,three different scenarios were considered,which include: i) considering only the precipitation with a constant water level;ii) considering only the decrease in water level without rainfall;iii) considering the combination of precipitation and decrease in water *** each scenario,four steps were included to calculate the values of factor of safety (FOS) at different times.1) A steady-state seepage analysis was conducted with a constant total head at 525 m on the left boundary and 175 m on the slope surface below the Yangtze River water *** initial pore water pressures were simulated in the slope under no precipitation and variation of water level.2) A specific boundary condition was applied on the slope surface to model the precipitation and Yangtze River water level variation.A transient seepage analysis was conducted to calculate pore water pres

关键词： unsaturated soil landslide reactivation residual shear strength slope stability analysis

Probabilistic characterization of cyclic shear modulus reduction for normally to moderately over-consolidated clays

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Earthquake Engineering and Engineering Vibration 2016年第3期15卷 495-508页

作者： Iok-Tong Ng Ka-Veng Yuen Ngai-Kuan Lao dept.of civil and Environmental Engineering Faculty of Science and Technology University of Macao

Evaluation of the cyclic shear modulus of soils is a crucial but challenging task for many geotechnical earthquake engineering and soil dynamic issues. Improper determination of this property unnecessarily drives up design and maintenance costs or even leads to the construction of unsafe structures. Due to the complexities involved in the direct measurement, empirical curves for estimating the cyclic shear modulus have been commonly adopted in practice for simplicity and economical considerations. However, a systematic and robust approach for formulating a reliable model and empirical curve for cyclic shear modulus prediction for clayey soils is still lacking. In this study, the Bayesian model class selection approach is utilized to identify the most significant soil parameters affecting the normalized cyclic shear modulus and a reliable predictive model for normally to moderately over-consolidated clays is proposed. Results show that the predictability and reliability of the proposed model out performs the well-known empirical models. Finally, a new design chart is established for practical usage.

关键词： Bayesian analysis cyclic shear modulus empirical model geotechnical earthquake engineering normally tomoderately over-consolidated clays

CONSTRUCTION OF RECTANGULAR DISPLACEMENT-BASED ELEMENT FOR THICK/THIN PLATES

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Acta Mechanica Sinica 1993年第2期9卷 163-170页

作者：卜小明龙驭球 dept.of Mechanics Tianjin UniversityTianjin 300072China dept.of civil Engineering Tsinghua UniversitvBeijing 100084China

In this paper,a method of constructing displacement-based elment for thick/thin plates is devel- oped by using the technique of generalized compatibility,and a rectangular displacement-based element with 12 degrees of freedom for thick/thin plates is *** method enjoys a good accuracy with simple formulation and is free of shear- locking as the thickness of the plate approaches zero.

关键词： thick plate thin plate generalized compatibility finite element