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,

Probabilistic limit state design methodof the axial resistance of post grouting pile

The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hyperbolic,modified hyperbolic,and polynomial models were employed to predict the ultimate bearing capacity of test piles that were not loaded to damage in field tests.The results were used for the calculation and calibration of the reliability index.The reliability of the probabilistic limit state design method was verified by an engineering case.The results show that the prediction results obtained from the modified hyperbolic model are closest to those obtained through the static load test.The proposed corresponding values of total,side,and end resistance partial coefficients are 1.84,1.66,and 2.73 when the dead and live load partial coefficients are taken as 1.1 and 1.4,respectively.Meanwhile,the corresponding partial coefficients of total,side,and end resistance are 1.70,1.56,and 2.34 when the dead and live load partial coefficients are taken as 1.2 and 1.4,respectively.

Evaluation of the Residual Capacity of a Submarine for Different Limit States with Various Initial Imperfection Models

The current design philosophy for submarine hulls,in the preliminary design stage,generally considers as governing limit states material yielding along with various buckling modes.It is common belief that,beyond the design pressure,material yielding of the shell plating should occur first,eventually followed by local buckling,while global buckling currently retains the highest safety factor.On the other hand,in the aeronautical field,in some cases structural components are designed in such a way that local instability may occur within the design loads,being the phenomena inside the material elastic range and not leading to a significant drop in term of stiffness.This paper is aimed at investigating the structural response beyond a set of selected limit states,using nonlinear FE method adopting different initial imperfection models,to provide the designers with new information useful for calibrating safety factors.It was found that both local and global buckling can be considered as ultimate limit states,with a significant sensitivity towards initial imperfection,while material yielding and tripping buckling of frames show a residual structural capacity.In conclusion,it was found that the occurrence of local buckling leads to similar sudden catastrophic consequences as global buckling,with the ultimate strength capacity highly affected by the initial imperfection shape and amplitude.

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.

Recent Industrial Developments of Marine Composites Limit States and Design Approaches on Strength

To further exploit the potential of marine composites applications in building ship hulls,offshore structures,and marine equipment and components,design approaches should be improved,facing the challenge of a more comprehensive and explicit assessment of appropriately defined limit states.The structure ultimate/limit conditions shall be verified in principle within the whole structural domain and throughout the ship service life.What above calls for extended and reliable materials characterization on the one hand and for accurate and wide-ranging procedures in structural analyses.This paper presents an overview of recent industrial developments of marine composites limit states assessments and design approaches,as available in open literature,focusing on pleasure crafts and yachts as well as navy ships and thus showing a starting point to fill the gap in this respect.After a general introduction about composites characterization techniques,current design practice and rule requirements are briefly summarized.Both inter-ply and intra-ply failure modes and corresponding limit states are then presented along with recently proposed assessment approaches.Three-dimensional aspects in failure modes and manufacturing methods have been identified as the main factors influencing marine composite robustness.Literature review highlighted also fire resistance and hybrid joining techniques as significant issues in the use of marine composites.

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.

Travel-Limiting Disabilities in the United States: Why Accessibility Matters?

This study evaluates the distribution of travel-limiting disabilities across genders and geographic locations in the United States. This study aims to describe and compare the socioeconomic and demographic variables of the people with and without travel-limiting disabilities across geographic locations and gender. The study further evaluates the trip purpose and impact of Covid-19 fourth wave pandemic on the use of public transit and travel to physical workplace for the people with and without travel-limiting disabilities across gender and geographic locations. The study uses the 2022 weighted National Household Travel Survey dataset and employs descriptive statistics. Results reaffirm the findings from previous literature that there are more people with travel-limiting disabilities in urban areas and among women. Over 50 percent of people aged 65 and above have a form of travel-limiting disabilities. The most trip for people with travel-limiting disabilities is made for shopping and medical purposes. Across all categories, rural areas, urban areas, male and female for the people without travel-limiting disabilities, COVID-19 fourth wave did not change the pattern of trips made to physical workplace as pre-COVID-19 era. This pattern is also observable for the people with travel-limiting disabilities in rural and urban areas. Females with travel-limiting disabilities reported making less trips to physical workplaces while male reported doing the same as before COVID-19 era. The study concludes that the quantification of travel-limiting disabilities across geographic location and gender is vital in disability study and could drive policy implementation for improved accessibility for the vulnerable population.

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.

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.

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.

Proper interpretation of sectional analysis results

Displacement control algorithms commonly used to evaluate axial force-bending moment(PM)diagrams may lead to incorrect interpretations of the strength envelopes for asymmetric sections.This paper aims to offer valuable insights by comparing existing displacement control algorithms with a newly proposed force control algorithm.The main focus is on the PM diagrams of three example sections that exhibit varying degrees of asymmetry.The comparative study indicates that conventional displacement control algorithms inevitably introduce non-zero out-of-plane bending moments.The reported PM diagram in such cases erroneously neglects the out-of-plane moment and fails to represent the strength envelope accurately.This oversight results in significant and unconservative errors when verifying the strength of asymmetric sections.

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。

吊杆断裂破坏安全极限状态下中、下承式拱桥悬吊桥面系简化计算方法

为简化吊杆断裂后中、下承式拱桥剩余结构动力响应的计算方法,提出悬吊桥面系强健性设计破坏安全极限状态,开展了大比例缩尺模型试验,采用ANSYS/LS-DYNA建立不考虑拱肋的悬吊桥面系结构有限元模型,提出弹性支撑悬吊桥面系简化计算模型,并采用五弯矩普通方程式,对弹性支撑悬吊桥面系计算长度进行简化,推导得到了悬吊桥面系简化计算方法;构建18种不同跨径标准拱桥的分析结果验证简化计算方法精度。研究结果表明:破坏安全极限状态恒载γG和活载γQ分项系数分别为1.2和0.9,1车道、2车道、3车道及以上的荷载横向分布系数分别取1.0、0.75和0.52,钢筋和钢结构强度分别取1.25倍和1.05屈服强度、其他材料强度取标准值;不考虑拱肋的悬吊桥面系结构有限元简化计算模型最大正误差仅为11.7%;建议短吊杆、次短吊杆以及长吊杆断裂工况下弹性支撑连续梁模型计算长度分别取D+2L、D+3L和4L,其偏差率分别为2.89%、2.40%、3.66%。吊杆断裂破坏安全极限状态下中、下承式拱桥悬吊桥面系简化计算方法的最大正误差分别为11.4%和10.1%,计算结果具有良好的精度且偏于安全。

基于可靠性方法的大口径天然气管段壁厚设计

我国陆上天然气管道规模庞大,管道路由地形、地貌和气候特征复杂多样。面对管道及管道所处环境的复杂性,提高油气管道的本质安全水平是行业和民众的共同需求,保证陆上天然气管道安全和可靠运行也越来越成为行业关注的焦点。为达到这个目标,可以采用从源头上对陆上天然气管道的设计方法进行改进的办法。目前天然气管道设计大多普遍利用传统的基于应力的设计方法,该方法由于采用单一的安全系数导致油气管道的安全裕度难以考量,针对此问题,基于可靠性的油气管道设计和评估方法(Reliability Based Design and Assessment,简称RBDA)正成为现代陆上天然气管道设计的趋向,该方法可量化管道全生命周期中的风险,避免采用不合理或过于保守的设计标准。故本研究综合CSAZ662《油气管道系统》标准规范的油气管道可靠性设计方法,并结合国内部分机构根据我国国情而修正的可靠性研究,利用RBDA方法流程,根据某段实际天然气管道确定该管道失效的主要原因(以腐蚀和第三方破坏为主),设计了管道在其生命周期内的极限状态,根据极限状态选择对应的极限状态方程类型,并利用多种数据统计分析方法和软件确定方程中所涉及各个随机变量参数的分布类型,之后利用蒙特卡洛法(Monte-Carlo法)计算设计壁厚条件下得到天然气管道失效概率,统筹考虑其他失效原因的权重,进而得到该管道的可靠度,将该可靠度数据与国内外标准规范确定的目标可靠度进行对比,检验是否满足可靠度目标。由此,对大口径天然气管段完成壁厚设计,实现了使用RBDA方法对1016 mm大口径天然气管道设计的整体流程。

基于Kriging模型与FORM的钢板组合梁桥结构优化设计

考虑材料参数的不确定性以及设计变量多重约束条件的影响,提出了基于可靠性分析的钢板组合梁桥结构优化设计方法。首先,利用拉丁超立方试验设计(Latin hypercube design,LHD)构建试验组合方案,并通过有限元分析获取试验设计组合下的最大挠度响应值。基于获取的训练样本,构建能够表征结构最大挠度值与随机输入之间映射关系的Kriging代理模型。基于建立的代理模型,以钢结构截面积最小化为目标函数,建立符合规范要求与可靠度约束的优化数学模型,并采用一阶可靠性方法(first order reliability method,FORM),实现设计变量优化。通过比较具有相同设计变量上限,但下限分别为初始值的80%和70%两种优化设计方案,评估了两者在相同阈值以及不同阈值下设计变量的优化结果。最后对方案二在阈值为17 mm下的优化结果进行极限状态验算。结果表明:两个优化设计方案在阈值为17 mm下的优化结果更具合理性,并且方案二在同一阈值下具有更高的优化程度。随着阈值增加,优化程度增加,且腹板高度在较大阈值下对结果影响更大,而翼缘宽度在较小阈值下影响更大。

通信速率约束下一体化角度协同制导控制方法

针对多飞行器协同拦截过程中的角度协同问题,设计了一种基于量化编码器的分布式一体化协同制导控制律。首先建立多飞行器协同制导与控制数学模型,并基于扩张状态观测器理论,对单个飞行器各状态进行观测。在此基础上考虑各飞行器间单次传输数据的字长、两次传输数据间隔的通信速率约束,采用量化器-编码器-解码器实现限制通信速率情况下的协同一体化制导控制设计。之后,通过严格的理论分析证明了满足强连通图有向通信网络下,多飞行器系统能够达成一致性且收敛到期望的相对视线角,并给出了满足收敛条件的参数选择范围。最后,通过数学仿真校验,验证了所提出的方法在较低的通信速率下能够完成协同。

不同基础条件下预制板式无砟轨道结构设计与检算

基于城市轨道交通工程建设需求,在非预应力轨道板结构设计基础上,采用有限元软件建立了不同基础条件下的无砟轨道结构耦合模型,结合极限状态法,研究开展了综合考虑列车荷载、温度梯度和基础变形作用下预制板的弯矩及配筋计算。结果表明:合理的非预应力板式无砟轨道结构设计,能够满足工程建设需求,路基段承载能力极限状态配筋设计受偶然组合作用控制,不同基础类型的轨道板纵横向配筋均受正常使用极限状态标准组合控制。

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。

射电天文台址周边干扰电磁兼容分析

为研究射电天文台址周边固定、移动干扰源对射电天文观测的影响,细化射电天文业务与其他业务间的电磁兼容(electromagnetic compatibility,EMC)分析,提出一种基于干扰源状态和辐射量级的EMC分析方法。首先,判断干扰源状态,依据其类型采集电磁干扰评估区域,划分区域得到各点/网格至望远镜的相对地形;然后,计算射电天文天线指向干扰源的增益并根据地形特征选用适宜电波传播模型预测电波传输损耗,进而预估干扰到达望远镜的功率大小;最后结合干扰电平限值、望远镜的指向,确定该干扰源对望远镜的干扰影响。本文对移动状态干扰源和固定状态干扰源的EMC分析与评估结果,可为台址周边电磁干扰协调及干扰兼容性分析提供技术支撑。