Seismic fragility analysis of highway bridges considering multi-dimensional performance limit state

Fragility analysis for highway bridges has become increasingly important in the risk assessment of highway transportation networks exposed to seismic hazards. This study introduces a methodology to calculate fragility that considers multi-dimensional performance limit state parameters and makes a first attempt to develop fragility curves for a multi-span continuous (MSC) concrete girder bridge considering two performance limit state parameters: column ductility and transverse deformation in the abutments. The main purpose of this paper is to show that the performance limit states, which are compared with the seismic response parameters in the calculation of fragility, should be properly modeled as randomly interdependent variables instead of deterministic quantities. The sensitivity of fragility curves is also investigated when the dependency between the limit states is different. The results indicate that the proposed method can be used to describe the vulnerable behavior of bridges which are sensitive to multiple response parameters and that the fragility information generated by this method will be more reliable and likely to be implemented into transportation network loss estimation.

Towards establishing practical multi-hazard bridge design limit states

In the U.S., the current Load and Resistance Factor Design （LRFD） Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of typical dead load and frequent vehicular loads. Various extreme load effects, such as earthquake and vessel collision, are on the same reliability-based platform. Since these extreme loads are time variables, combining them with not considered frequent. non- extreme loads is a significant challenge. The number of design limit state equations based on these failure probabilities can be unrealistically large and unnecessary from the view point of practical applications. Based on the opinion of AASHTO State Bridge Engineers, many load combinations are insignificant in their states. This paper describes the formulation of a criterion to include only the necessary load combinations to establish the design limit states. This criterion is established by examining the total failure probabilities for all possible time-invariant and time varying load combinations and breaking them down into partial terms. Then, important load combinations can be readily determined quantitatively,

THE AUTOMATIC GENERATION OF LIMIT STATE FUNCTION OF HINGED STRUCTURE

In this paper, the theorem of structure continual variation of truss structure in the analysis of structure reliability is derived, and it is used to generate limit state function automatically. We can avoid repeated assembly of global stiffness matrix and repeated inverse operations of the matrix caused by constant changes of structure topology. A new criterion of degenerate of the structure into mechanism is introduced. The calculation examples are satisfactory.

Target reliability index for serviceability limit state of single piles

The objective is to develop an approach for the determination of the target reliability index for serviceability limit state(SLS) of single piles. This contributes to conducting the SLS reliability-based design(RBD) of piles. Based on a two-parameter,hyperbolic curve-fitting equation describing the load-settlement relation of piles, the SLS model factor is defined. Then, taking into account the uncertainties of load-settlement model, load and bearing capacity of piles, the formula for computing the SLS reliability index(βsls) is obtained using the mean value first order second moment(MVFOSM) method. Meanwhile, the limit state function for conducting the SLS reliability analysis by the Monte Carlo simulation(MCS) method is established. These two methods are finally applied to determine the SLS target reliability index. Herein, the limiting tolerable settlement(slt) is treated as a random variable. For illustration, four load test databases from South Africa are compiled again to conduct reliability analysis and present the recommended target reliability indices. The results indicate that the MVFOSM method overestimates βsls compared to that computed by the MCS method. Besides, both factor of safety(FS) and slt are key factors influencing βsls, so the combination of FS and βsls is welcome to be used for the SLS reliability analysis of piles when slt is determined. For smaller slt, pile types and soils conditions have significant influence on the SLS target reliability indices; for larger slt, slt is the major factor having influence on the SLS target reliability indices. This proves that slt is the most key parameter for the determination of the SLS target reliability index.

New algorithm of mine slope reliability based on limiting state hyper-plane and its engineering application

Due to the influence of joint fissure, mining intensity, designed slope angle, underground water and rainfall, the failure process of mine slope project is extremely complicated. The current safety factor calculation method has certain limitations, and it would be difficult to obtain the reliability index when the performance function of reliability analysis is implicit or has high order terms. Therefore, with the help of the logistic equation of chaos theory, a new algorithm of mine slope reliability based on limiting state hyper-plane is proposed. It is shown that by using this new reliability algorithm the calculation of partial derivative of performance function is avoided, and it has the advantages of being simple and easy to program. The new algorithm is suitable for calculating the reliability index of complex performance function containing high order terms. Furthermore, the limiting state hyper-plane models of both simplified Bishop's and Janbu's method adaptive to slope project are obtained, and have achieved satisfactory effect in the study of mine slope stability in Dexing copper open pit.

Magnetic Field Measurement with Heisenberg Limit Based on Solid Spin NOON State

The maximum entangled number state （NOON state） can improve the sensitivity of physical quantity measure- ment to the Heisenberg limit 1/N. In this work, the magnetic field measurement based on the individual solid spin NOON state is investigated. Based on the tunable effective coupling coefficient, we propose a generation scheme of the three-spin NOON state, i.e, the Creenberger-Horne-Zeilinger （CHZ） state, and discussed the mea- surement resolution reduction due to decoherence. It is unnecessary to entangle spins as many as possible when decoherence exists. In practice, defect spins in diamond and alp donors with long coherence time can be applied with current techniques in the nano-scaled high resolution magnetic measurement.

Estimation of drift limits for different seismic damage states of RC frame staging in elevated water tanks using Park and Ang damage index

Damage to elevated water tanks in past earthquakes can be attributed to the poor performance of their supporting frame staging. In order to ascertain the performance of these elevated water tanks, it is crucial to categorize the damage in quantifiable damage states. Among various parameters to quantify the damage states, the top drift of frame staging can be conveniently correlated to the different damage levels. In literature, drift limits corresponding to different damage states of the frame staging of the elevated water tank are not available. In the present study, drift limits for RC frame staging in elevated water tanks corresponding to different seismic damage states have been proposed. Various damage states of the elevated water tank have been determined using the Park and Ang damage index. The Park and Ang damage index utilizes results of both pushover analysis and incremental dynamic analysis. Twelve models of elevated water tanks have been developed considering variation in staging height and tank capacity. Incremental dynamic analysis has been performed using the suite of twelve actual earthquake ground motions. Based on the regression analysis between damage indexes and drift, limiting drift values for each damage state are proposed.

开挖前抽水条件下基坑围挡两侧非极限土压力计算模型

基坑开挖前的坑内抽水可引起围挡发生厘米级的侧移,但现行基坑设计理论仅提出了基于弹性支点法的土方开挖诱发围挡受力变形的计算方法,却并未提出如何计算基坑开挖前抽水引起的围挡侧移。若要沿用弹性支点法进行抽水侧移的计算,则如何确定抽水过程中围挡两侧土压力分布成为关键。为了提出基坑开挖前抽水条件下围挡两侧土压力的计算模型,首先提出了基坑开挖前抽水过程中围挡两侧土体受扰动区形态与范围;然后探明了扰动区内土体应变分布规律并提出土体应变分布模式;进一步地,建立了土体应变与围挡侧移的数学方程,并结合土体应力−应变方程最终构建了开挖前抽水条件下考虑基坑围挡侧移影响的土压力计算模型。所提出的土压力模型能够反映基坑开挖前抽水过程中围挡侧移对土压力的非线性影响,公式形式简单,参数取值方便,可为后续预测抽水引起的基坑围挡侧移提供重要基础。

应用于直流微电网的分级固态限流器研究

针对固态断路器面临故障等级超出断路器遮断容量,威胁断路器故障隔离的问题,研究了基于晶闸管的直流分级固态限流器以减少固态断路器对遮断容量的需求,其具备分级限流、故障隔离后电抗器自旁路的功能。基于600 V直流微电网的场景,通过公式推导、计算参数配置,对限流器的工作过程进行仿真验证并对不同参数下的故障隔离速度及限流幅值进行对比分析,仿真结果表明,该限流器投入后,故障电流下降了35.62%以上,有效减少对固态断路器遮断容量的需求。

桥梁承载能力多水准可靠度评定方法

为在中国桥梁评定规范中引入“保守设计,非保守评定”的思想,提出一种“新-旧桥”两水准可靠度评定方法.对比分析了中、美桥梁评定规范分析检算公式、评定可靠指标和分项系数的异同,并将美国规范通过折减活载分项系数调整评定可靠度的方法引入中国规范中.首先提出了将新桥设计可靠指标折减0.5作为旧桥评定可靠指标的方法,之后通过一次二阶矩方法对不同受力形式、不同荷载运营状况的评定活载分项系数进行校准,给出了“新桥1.4,旧桥1.2”的评定活载分项系数取值建议,最后通过一个RC简支T梁桥评定算例验证了方法的可行性.结果显示,所提出评定方法与规范方法相比最不利需求能力比降低了0.07,实现了在役旧桥的非保守评定.

基于离散元模拟的不同挡土墙位移模式下非极限主动土压力

针对刚性挡土墙主动位移过程中砂土非极限主动土压力问题,利用PFC 2D分别对挡土墙绕墙顶转动(RB)模式、绕墙顶转动(RT)模式和平动(T)模式下砂土主动破坏过程进行模拟分析。分析结果表明,不同位移模式下土体内摩擦角及墙土摩擦角调动规律存在差异。挡土墙主动位移过程中,RB模式下土体破坏从墙顶开始,向墙脚发展,土楔体内部只有靠近墙背侧区域出现主应力偏转现象,并且土楔体中内摩擦角调动值均能达到极限值。RT模式下,土体破坏沿着墙背和滑裂面从墙脚开始,向土体表面发展,墙后土楔体中上部区域主应力偏转角度较大,形成了大主应力拱,与此对应的是该区域内摩擦角调动值相对初始内摩擦角减小。T模式下,土体破坏分别沿着墙背从墙顶向墙脚发展以及沿着滑裂面从墙脚向土体表面发展,墙后土楔体内部会出现小主应力拱,且内摩擦角调动值从初始内摩擦角增加,但达不到极限值。

无筋钢纤维混凝土管片正截面结构设计方法

为完善无筋钢纤维混凝土管片的设计方法,加速其在城市轨道交通中的应用,提出一种新的无筋钢纤维混凝土管片正截面结构设计方法。根据已有对钢纤维混凝土本构关系的研究成果,依据地铁管片的受力特点,分析了影响地铁管片正截面承载力的主要因素。依据无筋钢纤维混凝土管片极限拉应变与钢筋混凝土的极限拉应变不在一个数量级上的差异,结合现行混凝土规范,采用平面假设,把应力和应变作为无筋钢纤维混凝土管片设计的特征值;用钢纤维混凝土应变的取值范围对应不同的设计工况,将不同工况下的无筋钢纤维混凝土管片的设计验算结果归结到同一张应力应变图中。论述了采用轴力-弯矩包络图进行正截面设计验算的主要流程,并通过一个工程实例展示不同工况下无筋钢纤维混凝土轴力-弯矩包络图的相互关系。计算结果表明:在正常使用极限状态下,强度是影响承载能力的主要因素;而承载能力极限状态下,特别是偶然荷载作用下,无筋钢纤维混凝土的韧性是影响承载能力的主要因素。

基于改进合成少数类过采样技术的非概率可靠性指标解

当结构的功能函数呈现高度非线性、极限状态曲面为多区域的情形时,现有算法无法有效求解非概率可靠性指标,为解决此类问题,将合成少数类过采样技术(SMOTE)进行改进,提出了基于改进SMOTE算法的非概率可靠性指标解法。首先基于非概率可靠性指标的几何意义,将样本分类策略、超球限制策略与标准SMOTE算法相结合,提出了改进SMOTE算法来进一步提升算法在极限状态曲面附近的采样效率;然后结合改进SMOTE算法在标准化空间中高精度的拟合局部极限状态曲面,进而搜索得到非概率可靠性指标;最后给出了基于改进SMOTE算法的非概率可靠性指标解的主要流程。数值算例表明,当极限状态曲面呈现局部闭合、多区域的特点时,改进后的SMOTE算法可以高效地获取位于极限状态曲面附近的样本点,进而高精度地拟合极限状态曲面。将本文方法的计算结果与解析解对比,相对误差远远小于工程中的最大误差限值5%,说明改进SMOTE算法能够较好地处理高度非线性功能函数,验证了所提算法的有效性和实用性。

基于雷达测距的飞行器交会对接误差补偿控制技术

为解决由视线倾角、视线偏角过大造成的飞行器对接存在误差的问题,实现飞行器交会轨迹的精准对接,提出基于雷达测距的飞行器交会对接误差补偿控制技术;建立空间参考坐标系,根据轨道根数计算结果,推导动力学状态方程,实现对飞行器交会对接过程中的动力学作用分析;按照雷达测距原理,计算飞行器的理论飞行时长及雷达装置作用距离,再联合相关参数指标,确定精度极限的取值范围,实现基于雷达测距的对接误差控制;在三坐标测量机结构模型中,定义飞行位姿拟合条件,再根据位姿误差求解结果,实现对误差参数的补偿修正处理,完成基于雷达测距的飞行器交会对接误差补偿控制方法的设计;对比实验结果表明,应用所提方法可以同时将视线倾角、视线偏角的取值控制在0~45.0°的范围之内,能够较好地解决飞行器错误对接的问题,符合精准对接飞行器交会轨迹的实际应用需求。

考虑多阻尼状态与限幅环节的新能源电力系统一次调频备用整定

一次调频是电力系统抑制扰动后频率变化的重要手段,该文针对新能源电力系统一次调频备用整定问题开展研究。首先,分析新能源电源渗透率上升对系统频率响应模型阻尼比的影响,建立适用于多阻尼状态的系统频率响应模型。随后,考虑新能源电源调频动态响应的快速性与同步电源调速器限幅值的差异性,提出计及多机调速器限幅环节的系统频率响应改进模型。接着,将构建的系统频率响应改进模型等价转化到时域,建立各类电源一次调频备用与系统扰动后频率最低点的时域解析关系,并进一步提出其线性化表征方法。最后,面向扰动后频率稳定要求,在新能源电力系统经济调度问题中添加一次调频备用约束,建立新能源电力系统一次调频备用整定模型。IEEE 39节点算例仿真结果表明该文提出模型的正确性与有效性。

工程结构椭球凸集模型可靠度的二次型计算方法研究

工程结构概率可靠度在理论上已经建立了完整的计算体系,但在实际工程应用中却停留在近似或半经验阶段。对于既有工程结构的可靠度评估,由于测试数据有限,采用椭球凸集模型可靠度进行评估有很高的工程价值和广泛的应用前景。椭球凸集模型可靠度有很多种不同的定义,但无论何种定义,如果完全脱离概率可靠度与失效概率的基本假定,则很难与现在基于概率可靠度评估方法的主流实现有效的衔接。从多维正态联合概率密度出发,推导了斜椭球方程及其标准化方法,同时结合极限状态方程,给出了椭球凸集模型可靠度与概率可靠度之间的数学关系。算例表明,得出的特殊简化情况下的椭球凸集模型可靠度计算方法和几何解释,可进一步推动该类可靠度在工程中的应用。

洁净室洁净度分级标准探究

鉴于科技的进步和实验经验,ISO/TC 209出台ISO14644-1:2015《按粒子浓度划出空气洁净度等级》Classification of air cleanliness by particle concentration比ISO14644-1:1999《空气洁净度等级》Classification of air cleanliness技术概念更清晰,使用更方便;实事求是,更赋灵活性:分级表中,所有浓度值都是累积,包括所有大于等于关注粒径(Considered particle size)的粒子的最大允许浓度值(Maximun allowable concentration siae),浓度限值。区域粒子浓度太高,浓度限值不适用;或者由于低浓度时采样和统计方法的局限性区域分级不适用。按统计学技术概念,决定检测洁净度最少采样点数N_(L);N_(L)值与洁净度无直接关联。作为标准应用的补充,超净环境检测需关注超高过滤器滤材最易穿透粒径MPPS,Most penetrating particle size。

基于ELM方法的锂电池充电SOC和SOH状态评估分析

通过集成极限学习机(ELM)模型与集成算法来提升学习效率,设计了电池健康特征模型来实现各充电状态的迭代计算。研究结果表明:SOC和SOH达到最大相关度,可以有效防止电池发生过充或过放的问题。充电终止电压由电动汽车用户使用需求决定,根据恒流恒压充电分界来估算截止电压,完成联合估算SOC与SOH的效果。该研究有助于提高电动汽车锂电池的使用效率。

Limits to foundation displacement of an extra high voltage transmission tower in a mining subsidence area

Given the background of a transmission tower erected on a particular mining subsidence area,we used finite element modeling to analyze the anti-deformation performance of transmission towers under a number of different load conditions,including horizontal foundation displacement,uneven vertical downward displacement,wind loads and icing conditions.The results show that the failure in stability of a single steel angle iron represents the limit of the tower given ground deformation.We calculated the corresponding limits of foundation displacements.The results indicate that compression displacement of the foundation is more dangerous than tension displacement.Under complex foundation displacement conditions,horizontal foundation displacement is a key factor leading to failure in the stability of towers.Under conditions of compression or tension displacement of the foundation,wind load becomes the key factor.Towers do not fail when foundation displacements are smaller than 1% (under tension) or 0.5% (under horizontal compression or single foundation subsidence) of the distance between two supports.

论正当防卫的辅助性:理论基础与规则适用

正当防卫的辅助性所探讨的问题是,警察在场时,公民能否实施正当防卫。关于此,文献中基于罪刑法定原则、二元论法理基础、防卫权和警察权之分野等完全否定正当防卫辅助性之见解是难以成立的。此问题的关键在于明确正当防卫这一私人暴力和警察的危险防御这一国家暴力之间的关系。根据国家暴力垄断原则,正当防卫作为私人暴力,旨在填补国家保护的不足。由此,相较于警察的危险防御,私人的正当防卫处于辅助地位,两者间存在严格的顺位关系。正当防卫辅助性的适用规则为:当警察身处现场即“狭义在场”时,若其能有效地制止不法侵害,公民无正当防卫权;当警察虽不在现场但可及时赶到即“广义在场”时,公民无通知、等待警察到来的义务,可径直实施正当防卫权。