Seismic fragility analysis of clay-pile-pier systems considering the optimization of ground motion intensity measures

The performance of clay-pile-pier system under earthquake shaking was comprehensively examined via three-dimensional finite element analyses,in which the complex stress-strain relationships of a clay and piled pier system were depicted by a hyperbolic-hysteretic and an equivalent elastoplastic model,respectively.One hundred twenty ground motions with varying peak accelerations were considered,along with the variations in bridge superstructure mass and pile flexural rigidity.Comprehensive comparison studies suggested that peak pile-cap acceleration and peak pile-cap velocity are the optimal ground motion intensity measures for seismic responses of the pier and the pile,respectively.Furthermore,based on two optimal ground motion intensity measures and using curvature ductility to quantify different damage states,seismic fragility analyses were performed.The pier generally had no evident damage except when the bridge girder mass was equal to 960 t,which seemed to be comparatively insensitive to the varying pile flexural rigidity.In comparison,the pile was found to be more vulnerable to seismic damage and its failure probabilities tended to clearly reduce with the increment of pile flexural rigidity,while the influence of the bridge girder mass was relatively minor.

基于矢量IMs的浅埋偏压黄土隧道地震易损性

为从概率角度对浅埋偏压黄土隧道的地震易损性进行定量评价,采用基于黏弹性边界的波动输入方法,并通过增量动力分析对土-结构相互作用有限元模型进行大量非线性动力时程计算,评估20个地震动强度参数(IMs),然后基于标量IM和矢量IMs分别对浅埋偏压黄土隧道展开地震易损性分析.结果表明:地表峰值速度(效益性指标ζ=0.15)是最适合的IM,其次是速度谱强度(ζ=0.20)和谱速度峰值(ζ=0.22);相比于标量IM,基于矢量IMs的拟合效果更好,可降低结构损伤预测的离散性;在建立地震易损性曲面时需考虑2个IMs之间相关性的影响以确定曲面的有效取值范围;采用标量IM会低估或高估隧道实际的损伤概率.基于矢量IMs可对隧道的地震易损性作出更准确的评估.

A global model of intensity autocorrelation to determine laser pulse duration

We present a new global model of collinear autocorrelation based on second harmonic generation nonlinearity.The model is rigorously derived from the nonlinear coupled wave equation specific to the autocorrelation measurement configuration,without requiring a specific form of the incident pulse function.A rigorous solution of the nonlinear coupled wave equation is obtained in the time domain and expressed in a general analytical form.The global model fully accounts for the nonlinear interaction and propagation effects within nonlinear crystals,which are not captured by the classical local model.To assess the performance of the global model compared to the classic local model,we investigate the autocorrelation signals obtained from both models for different incident pulse waveforms and different full-widthes at half-maximum(FWHMs).When the incident pulse waveform is Lorentzian with an FWHM of 200 fs,the global model predicts an autocorrelation signal FWHM of 399.9 fs,while the classic local model predicts an FWHM of 331.4 fs.The difference between the two models is 68.6 fs,corresponding to an error of 17.2%.Similarly,for a sech-type incident pulse with an FWHM of 200 fs,the global model predicts an autocorrelation signal FWHM of 343.9 fs,while the local model predicts an FWHM of 308.8 fs.The difference between the two models is 35.1 fs,with an error of 10.2%.We further examine the behavior of the models for Lorentzian pulses with FWHMs of 100 fs,200 fs and 500 fs.The differences between the global and local models are 17.1 fs,68.6 fs and 86.0 fs,respectively,with errors approximately around 17%.These comparative analyses clearly demonstrate the superior accuracy of the global model in intensity autocorrelation modeling.

Estimation of Aleatory Randomness by S_(a)(T_(1))-Based Intensity Measures in Fragility Analysis of Reinforced Concrete Frame Structures

Based on the multiple stripes analysis method,an investigation of the estimation of aleatory randomness by S_(a)(T_(1))-based intensity measures(IMs)in the fragility analysis is carried out for two typical low-and mediumrise reinforced concrete(RC)frame structures with 4 and 8 stories,respectively.The sensitivity of the aleatory randomness estimated in fragility curves to various S_(a)(T_(1))-based IMs is analyzed at three damage limit states,i.e.,immediate occupancy,life safety,and collapse prevention.In addition,the effect of characterization methods of bidirectional ground motion intensity on the record-to-record variability is investigated.It is found that the damage limit state of the structure has an important influence on the applicability of the ground motion IM.The S_(a)(T_(1))-based IMs,considering the effect of softened period,can maintain lower record-to-record variability in the three limit states,and the S_(a)(T_(1))-based IMs,considering the effect of higher modes,do not show their advantage over S_(a)(T_(1)).Furthermore,the optimal multiplier C and exponentαin the dual-parameter ground motion IM are proposed to obtain a lower record-to-record variability in the fragility analysis of different damage limit state.Finally,the improved dual-parameter ground motion IM is applied in the risk assessment of the 8-story frame structure.

Optimal vector-valued intensity measure for seismic collapse assessment of structures

The present study is aimed to investigate the ability of different intensity measures （IMs）, including response spectral acceleration at the fundamental period of the structure, Sa（T1）, as a common scalar IM and twelve vector-valued IMs for seismic collapse assessment of structures. The vector-valued IMs consist of two components, with S（T1） as the first component and different parameters that are ratios of scalar IMs, as well as the spectral shape proxies εSa and N, as the second component. After investigating the properties of an optimal IM, a new vector-valued IM that includes the ratio of Sa（T1） to the displacement spectrum intensity （DSI） as the second component is proposed. The new IM is more efficient than other IMs for predicting the collapse capacity of structures. It is also sufficient with respect to magnitude, source-to-site distance, and scale factor for collapse capacity prediction of structures. To satisfy the predictability criterion, a ground motion prediction equation （GMPE） is determined for Sa（T1）/DSI by using the existing GMPEs. Furthermore, an empirical equation is proposed for obtaining the correlation between the components of the proposed IM. The results of this study show that using the new vector-valued IM leads to a more reliable seismic collapse assessment of structures.

The effect of different intensity measures and earthquake directions on the seismic assessment of skewed highway bridges

In this study the probable seismic behavior of skewed bridges with continuous decks under earthquake excitations from different directions is investigated. A 45° skewed bridge is studied. A suite of 20 records is used to perform an Incremental Dynamic Analysis （IDA） for fragility curves. Four different earthquake directions have been considered： -45°, 0°, 22.5, 45°. A sensitivity analysis on different spectral intensity measures is presented; efficiency and practicality of different intensity measures have been studied. The fragility curves obtained indicate that the critical direction for skewed bridges is the skew direction as well as the longitudinal direction. The study shows the importance of finding the most critical earthquake in understanding and predicting the behavior of skewed bridges.

Intensity measures for the seismic response evaluation of buried steel pipelines under near-field pulse-like ground motions

Ground-motion Intensity Measures (IMs) are used to quantify the strength of ground motions and evaluate the response of structures. IMs act as a link between seismic demand and seismic hazard analysis and therefore, have a key role in performance-based earthquake engineering. Many studies have been carried out on the determination of suitable IMs in terms of effi ciency, suffi ciency and scaling robustness. The majority of these investigations focused on ordinary structures such as buildings and bridges, and only a few were about buried pipelines. In the current study, the optimal IMs for predicting the seismic demand of continuous buried steel pipelines under near-fi eld pulse-like ground motion records is investigated. Incremental dynamic analysis is performed using twenty ground motion records. Using the results of the regression analysis, the optimality of 23 potential IMs are studied. It is concluded that specifi c energy density (SED) followed by VSI[ω1(PGD+RMSd )] are the optimal IMs based on effi ciency, suffi ciency and scaling robustness for seismic response evaluation of buried pipelines under near-fi eld ground motions.

THE ESTIMATE AND MEASUREMENT OF LONGITUDINAL WAVE INTENSITY

Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending waves. In a two-dimensional quasi-longitudinal wave held, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities and in the measurement, it is measured by a pair of two-transducer arrays. In a one-dimensional quasi-longitudinal wave field, the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves.

Intensity measures for seismic liquefaction hazard evaluation of sloping site

This work investigates the correlation between a large number of widely used ground motion intensity measures(IMs) and the corresponding liquefaction potential of a soil deposit during earthquake loading. In order to accomplish this purpose the seismic responses of 32 sloping liquefiable site models consisting of layered cohesionless soil were subjected to 139 earthquake ground motions. Two sets of ground motions, consisting of 80 ordinary records and 59 pulse-like near-fault records are used in the dynamic analyses. The liquefaction potential of the site is expressed in terms of the the mean pore pressure ratio, the maximum ground settlement, the maximum ground horizontal displacement and the maximum ground horizontal acceleration. For each individual accelerogram, the values of the aforementioned liquefaction potential measures are determined. Then, the correlation between the liquefaction potential measures and the IMs is evaluated. The results reveal that the velocity spectrum intensity(VSI) shows the strongest correlation with the liquefaction potential of sloping site. VSI is also proven to be a sufficient intensity measure with respect to earthquake magnitude and source-to-site distance, and has a good predictability, thus making it a prime candidate for the seismic liquefaction hazard evaluation.

THE ESTIMATE AND MEASUREMENT OF TRANSVERSE WAVE INTENSITY

Transverse waves are a type of structural waves and should be considered in the analysis of high frequency vibration because the energy carried by transverse waves increases with the increase of frequency and becomes important at high frequencies. This paper studies the estimate theory and measuring technique of the transverse wave intensity in two-dimensional homogeneous structures. In general, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Each axial intensity component is proportional to two imaginary parts of cross spectral densities and its estimate is complicated. For the special case where transverse waves propagate in one direction, the intensity variation is zero and the estimate of the intensity is simplified. The intensity technique is formed based on the finite difference principle. Transverse wave intensity can be measured using a pair of two-transducer arrays lying in the orthogonal direction for the general case or a two-transducer array lying in the propagating direction for the special case. In order to assess the measurement accuracy of transverse wave intensify, the coupling loss factors from bending to transverse waves in building structures were measured using the intensity technique and compared with the results predicted and measured using the conventional method. It is shown that the agreement between the results measured using the intensity technique and that by the conventional method is good.

Digital Image Correlation Using Specific Shape Function for Stress Intensity Factor Measurement

The stress intensity factor (SIF) is a critical parameter associated with the fracture behaviour of materials. In this paper, we select the displacement function around a crack tip as the shape function of the digital image correlation (DIC), which makes it possible to directly calculate the SIF by the correlation scheme. Moreover, we use a non-rectangular subset, which can reduce the influence of plastic deformation and crack width on the DIC measurement accuracy. We measured the SIF of a mode I crack in a super-hard aluminium alloy specimen to verify the performance of the proposed method. Our experimental results show that a DIC with a specific shape function can be used to accurately and efficiently calculate the SIF. Furthermore, we also present a practical application of our proposed method for determining the SIF, crack propagation angle and crack tip displacement. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

压缩感知在斜轴式马达声强成像中的应用研究

斜轴式轴向柱塞马达内部噪声源距离较近,如马达配流盘进、出油口间的距离为38 mm,且马达噪声源存在同频及倍频现象。斜轴式马达内部密集复杂的噪声源,导致频谱分析方法难以准确识别同频及倍频信号,传统声强测量的最高分辨率为50 mm,无法满足马达内部噪声源的辨识精度要求。针对传统方法难以准确辨识马达噪声源的问题,文中提出了一种基于压缩感知的声强测量方法,将压缩感知理论运用于声强云图高精度重构中,获取马达高分辨率的声强重构图像。首先,通过对斜轴式马达进行噪声辐射仿真分析,获取其外表面声场特性;然后,以马达外表面声强云图为先验信息,设计应用于马达声场的压缩感知框架,获取高精度重构马达声强云图;最后,通过马达传统声强测量与压缩感知声强测量的对比实验验证压缩感知理论对于提高马达噪声源辨识精度的可行性。结果表明,基于压缩感知的声强测量方法将马达噪声源辨识尺度从原来的70 mm提升至30 mm,提高了马达噪声源的辨识精度,实现了马达噪声源的高精度定位。

新生儿重症监护病房肺炎克雷伯菌医院感染暴发事件的调查与防控

目的调查一起在新生儿重症监护病房(NICU)发生的肺炎克雷伯菌(KP)医院感染暴发事件,评价控制措施实施效果,为医院感染防控提供依据。方法采用流行病学调查和环境卫生学监测方法对2020年6-8月在NICU检出KP的患者进行原因分析并采取控制措施。结果14例检出KP的患者中,9例医院感染,KP引发的医院感染例次率高于3-5月(P<0.05)。84份环境卫生学标本,2份标本检出KP。采取综合性与针对性控制措施后,复查未检出KP,9-11月医院感染例次率显著下降(P<0.05)。结论本次事件推测为外源性的KP定植于电热烧水器托盘,经由医务人员手或水杯等物品直接或间接接触传播。通过查找感染源,采取集束化、针对性干预策略,有效控制医院感染的蔓延。

荧光测温方法的测量误差与测量不确定度分析综述

介绍了荧光测温方法的基本原理及典型系统的组成,分析了荧光测温方法中的系统误差和随机误差的主要来源,并探讨了基于数学模型的测量不确定度评估方法,指出了在荧光测温装置的研究与应用中测量误差分析和测量不确定度评估的重要性。在测量误差分析方面,需要充分考虑装置内部参数及测量环境对荧光测温参数(如荧光寿命或荧光强度比)的影响,通过优化激发光源、荧光材料、检测器、数据采集和数据处理方案,并进行环境因素分析与校准,最大程度地降低系统误差,提高测温结果的准确性。此外,研究荧光材料发光特征随温度以外其他因素变化的物理机制,可以为开发更具适应性的荧光测温材料提供理论基础。在测量不确定度评估方面,基于荧光寿命和荧光强度比的温度测量不确定度可以通过数学模型进行描述,以温度测量不确定度为依据可指导高精度荧光测温系统的优化设计和应用。

基于地下结构整体损伤表征的复合地震动参数构造及其性能验证

在地下结构抗震设计中,不同的输入地震动引起的地下结构响应有显著差异,因此,合理通过地震动参数选择输入地震动是正确开展地下结构抗震设计的重要前提。针对单一地震动参数难以表征地下结构地震动潜在破坏势问题,文章构造了能更好表征地下结构损伤破坏的复合地震动参数。具体开展了以下工作:提出基于变形与滞回耗能的地下结构整体损伤指标作为结构需求参数,以定量化评估地下结构的整体破坏状态。选取64条真实地震动记录作为输入地震动,开展四层三跨地铁车站地震弹塑性动力时程分析。基于分析结果提供的数据样本,采用偏最小二乘法从统计角度构造复合地震动参数。最后,选用100条真实地震动记录开展两层三跨地铁车站弹塑性动力时程分析,对文章所构造的复合地震动参数进行验证。对比分析复合地震动参数、12个常用地震动参数与地下结构整体损伤指数的回归统计特征。结果表明:复合地震动参数与结构需求数之间具有更好拟合优度值,其Pearson相关性、有效性也优于单一地震动参数。

Ca_(2)MgTeO_(6)∶Bi^(3+),Mn^(4+)材料的发光性能和温度探测

通过高温固相法成功制备了一系列Ca_(2)MgTeO_(6)∶Bi^(3+),Mn^(4+)荧光粉,对其微观结构、形貌、发光特性和温敏特性进行了表征。Ca_(2)MgTeO_(6)∶Bi^(3+),Mn^(4+)荧光粉具有不同温度敏感性的双发射中心,分别来自于Bi^(3+)离子^(3)P_(1)→^(1)S_(0)跃迁和Mn^(4+)离子的^(2)E_(g)→^(4)A_(2g)跃迁。由于Bi^(3+)、Mn^(4+)离子的发光强度随温度变化的规律不同,利用该特性进行测温研究,在200~500 K范围内,该荧光粉的最大绝对灵敏度和相对灵敏度分别达到0.027 K^(-1)和1.83%·K^(-1),并且观察到荧光粉的发光颜色由橙黄色逐渐变为紫红色。实验结果表明,Ca_(2)MgTeO_(6)∶Bi^(3+),Mn^(4+)荧光粉作为光学测温材料在温度探测方面有一定的潜力。

基于信息度量的地震动参数优化选择方法

地震动参数(intensity measures, IM)的选择是地震易损性分析的重要环节。合适的IMs应具有良好充分性和效率性,以更好地反映地震动的破坏能力,获得更为可靠的易损性分析结果。为此,该文提出了一种基于信息度量的地震动参数优化选择方法。该方法利用互信息和相对熵度量作为IM选择的通用指标,结合前向选择算法在一到多维空间中高效地定位最优的IM。为了验证所提方法的有效性,在一组简支梁桥上进行了分析和讨论,并与传统的充分性和效率性分析方法进行了对比。结果表明,基于所提出方法所选择的IMs能同时满足充分性和效率性要求;较传统方法而言,所提出的方法不依赖概率地震需求模型的选择且不需要进行繁琐的条件独立性比较,具有高效普适的优势,有着良好的应用前景。

软土地区典型民防工程结构地震易损性分析

为揭示软土地区典型民防工程结构地震易损性变化规律,以某单建式民防工程为例,首先,基于ABAQUS有限元平台建立土体-民防工程结构系统非线性动力分析模型;其次,进一步考虑土体非线性特性和输入地震动的不确定性,通过数值模拟揭示民防工程结构易损性分析的合适地震动强度指标(IM);最终,建立软土地区典型民防工程结构地震易损性曲线。研究结果表明:1)峰值地面加速度(PGA)相较于其他地震动强度指标,其有效性和实用性较高,适合用于民防工程结构地震易损性分析;2)土层条件对民防工程结构的地震易损性有明显影响,土层越软,结构的易损性越高;3)软土地区民防工程结构在地震作用下有可能遭受严重破坏,随着地震动强度的增加,每种破坏状态的超越概率逐渐增加并接近100%。

近断层地震动作用下浅埋综合管廊地震易损性研究

为准确评估近断层地震动作用下浅埋综合管廊的地震损伤,利用ABAQUS建立土-结构整体有限元模型,以综合管廊层间位移角最大值为损伤指标,基于IDA方法进行结构地震易损性分析,重点考察近断层地震动强度指标和场地土特性对综合管廊抗震性能的影响。结果表明:近断层地震动加速度型指标的离散性最小,建议选取加速度型指标PGA、Sa作为地震动强度指标;以有限元计算数据为样本,采用BP神经网络可高效预测综合管廊结构的地震损伤,PGA、Sa及土体剪切模量对综合管廊地震易损性分析的影响较大,随着土体剪切模量的增大,超越概率逐渐减小,同时,LS、CP状态的超越概率变化范围要明显大于OP、IO状态;考虑PGA和Sa双参数更能准确反映不同地震动参数对结构损伤的影响,而仅考虑PGA或Sa单参数有可能高估结构的损伤程度。因此,对综合管廊等浅埋地下结构进行地震易损性分析时,建议综合考虑PGA和Sa的影响。

基于IDA的输电塔地震动强度指标与结构损伤指标研究

以输电塔为研究对象,利用20条典型地震动时程,分别采用10个地震动强度指标(intensity measure,IM)和4个结构损伤指标(damage measure,DM)对输电塔进行增量动力分析(incremental dynamic analysis,IDA)。通过双对数线性回归建立了地震动强度指标与输电塔损伤指标的无量纲化关联模型,并对不同强度指标和损伤指标组合下关联模型的有效性、实用性和效益性进行了综合评价。结果表明:针对输电塔结构,选取有效峰值加速度(effective peak acceleration,EPA)作为IM和节间位移角(inter-story drift ration,ISDR)作为DM进行组合时,具有较好的稳定性和较高的相关性;基于输电塔结构第一阶、第二阶反应谱的Sa_(avg)^(*)在指标关联性评价中的优势与EPA、Sa(T_(1))类似,而Sv*avg指标与有效峰值速度(effective peak velocity,EPV)、第一周期谱速度(Sv(T_(1)))指标相比,增强了与DM之间的关联性;构造的E(ad)作为结构总持时内的地震动能量输入指标与所有IM指标组合时,并不受输电塔对加速度型IM更敏感从而导致加速度型IM与DM组合时关联性更强的影响。研究结果可以为进一步提高输电塔结构抗震性能评价精度提供参考和借鉴。