Time-dependent seismic fragility curves for aging jacket-type offshore platforms subjected to earthquake ground motions

This paper assesses the seismic vulnerability of a recently designed jacket-type offshore platform through development of fragility curves and presents the formulation of time-dependent seismic fragility curves to capture the effects of ageing and deterioration on the seismic vulnerability of the representative platform. Among the various ageing processes, the corrosion deterioration of the structure is taken into account by applying a time-dependent model of corrosion deterioration of the tubular elements in the splash zone. Incremental dynamic analysis is performed on the initial uncorroded and corroded platforms considering soil–pile–structure interaction. A full probabilistic analysis is then performed to develop time-dependent seismic fragility curves for the immediate occupancy and collapse prevention limit states. Finally, a time variant cubic model is proposed to develop fragility curves at any point in time during platform’s service life, without need to perform a complete time-consuming fragility analyses. Results show substantial increase in probability of failure of the platform throughout its lifetime due to corrosion deterioration. The results also indicate that the time-dependent fragility curves can be used in offshore platforms to assess the seismic vulnerability of the structure and demonstrate the influence of various factors affecting the seismic vulnerability of the platform during its lifetime.     

The influence of out‐of‐straightness imperfection in physical theory models of bracing members on seismic performance assessment of concentric braced structures

In physical theory models, the hysteretic response of concentric braces is simulated by modelling the bracings with two nonlinear fibre‐section beam–column elements connected together with an initial out‐of‐straightness imperfection (?₀). The width of such imperfection is the parameter governing the numerical prediction of the brace buckling. In this paper, the accuracy of different formulations of ?₀ is investigated and validated against monotonic and cyclic experimental results from literature carried out on different bracing configurations. Correlations and measures of scatter between the predicted response and experimental performance are evaluated. A statistical analysis on both X‐braced and inverted‐V‐braced frames based on Monte Carlo simulation is presented and discussed for the following reasons: (a) in order to account for the dispersion of the nonlinear dynamic‐evaluated seismic performance due to epistemic uncertainties associated with examined formulations for camber width and (b) to provide modelling correction factors of simulated interstorey drift demand. The analysis shows that the formulations used for ?₀ affect the drift demand, the collapse mechanism and have a noticeably impact on the seismic response parameters at collapse. In particular, inverted‐V‐braced frames are more influenced than X‐braced configurations, because the prediction of brace–beam interaction is very sensitive to ?₀. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic collapse assessment of reinforced concrete moment frames using endurance time analysis

In this paper, seismic collapse of reinforced concrete moment frames is assessed using endurance time (ET) analysis. A set of 30 frames that incorporate deterioration of concrete components is used for this assessment. Application of ET method for collapse assessment of structures is explained, and its accuracy for this purpose is evaluated by comparing its results with incremental dynamic analysis results. Input motions for ET analysis are generated based on ASCE7‐05 design spectrum, and also accelerograms used for incremental dynamic analysis are spectrally matched to the same spectrum. Distribution of different engineering demand parameters over frames height and their values at collapse occurrence are compared for two methods. Results show that spectral accelerations in which collapse occurs in both analyses are very similar for most of the frames, and ET method can appropriately predict the collapse mechanisms of the structures especially for taller frames. Accuracy of ET method in collapse assessment of reinforced concrete moment frames is satisfactory, and this method can be used as a good estimator for study of collapse mechanisms with much less computational effort. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic performance of MR frames protected by viscous or hysteretic dampers

This study concerns the behaviour of steel frames protected by different anti‐seismic devices (dampers). Typical hysteretic and viscous dampers are arranged in three steel moment‐resisting frames (MRFs) having different dynamical features but are designed to accomplish determined performance objectives. The proposed devices are selected following an iterative procedure based on the use of a suitable damage functional, which has been applied to control the behaviour of the protected structures under a specific seismic record. The outcomes obtained by implementing incremental dynamic analyses, carried out on the basis of seven historical records characterized by different features, allow to analyse the improvement of the structural performance due to the considered dampers and, therefore, to provide design information about their employment. The comparison of results is carried out taking into account the dampers capacity to protect the structures from damage, the inter‐storey drifts, the residual deformations and the possible amplification effects. In conclusion, the equivalent behaviour factors for each damper type are given, with the aim of providing useful design parameters for the implementation of simplified conventional linear analyses. Copyright © 2014 John Wiley & Sons, Ltd.     

结构抗倒塌能力简化评估方法及其应用

针对增量动力分析(IDA)计算实际结构倒塌时常会遇到的工作量大、数值收敛困难等问题,提出结构抗倒塌能力的简化评估方法.该方法根据Pushover曲线与IDA曲线在定义结构倒塌极限状态上的相关性,通过单向和往复的Pushover分析确定结构的骨架参数和滞回特性,构建倒塌分析的等效单自由度模型,快速计算结构的倒塌强度.对一榀三跨六层钢框架和一榀三跨六层混凝土框架进行分析,结果显示简化方法得到的响应曲线和倒塌易损性曲线与IDA的结果接近,可以近似评估以第1振型为主的结构的抗倒塌能力.     

凿井绞车PLC集中监控系统设计与应用

结合工程实际,对4台凿井绞车悬吊吊盘和大模板提升过程进行控制系统设计。设计中加入的增量编码器、倾角传感器、压力传感器、显示报警等装置,可实现对多台凿井绞车的同步安全控制。该集中监控系统应用于马脊梁煤矿副立井工程,起到了应有的作用,实现了多台凿井绞车同步提升控制,并且就位准确,运行安全,加快了井筒施工速度,取得了最高月进尺达138m的好成绩。     

基于增量反步的复合翼无人机全包线姿态控制

针对某型复合翼无人机强非线性、不确定性和多模态的问题,从不确定性补偿非线性控制方法、跟踪微分器加速度测量和直接切换方法等角度开展全包线飞行控制研究。针对气动参数不确定问题,基于角加速度补偿方法,提出一种基于新型微分跟踪器的增量反步方法(incrementalbacksteppingcontrol,IBKS);为解决多模态特性问题,设计基于策略的直接切换方法,利用控制器参数切换实现复合翼无人机全包线姿态控制;通过不同模态下的仿真选取不同模式下的控制器参数,并联合选取的参数对起飞过程进行仿真。结果表明：所提姿态控制方法在样例复合翼无人机参数摄动30%的情况下,相较于反步法提高了66.8%的俯仰角控制精度,能消除攻角抖振,提升飞行品质。     

电子分析天平模糊自适应PID平衡调节方法研究

为实现电子分析天平的快速准确称量,提出基于增量式模糊调节和PID调节有机融合的电子天平模糊自适应PID平衡调节方法。在建立电磁力平衡传感器系统传递函数基础上,确定基于FOLPD模型及Z-N整定法的初始PID调节参数,结合电磁力平衡传感器的动态响应特性,设定电子分析天平的模糊调节规则,并通过阈值判断,在系统偏差较大时采用增量式模糊调节,偏差较小时采用PID调节,实现两种调节方法的优势互补,缩短系统调节时间,提高系统的鲁棒性。仿真及测试结果表明,量程220 g、感量0.1 mg的电子分析天平应用模糊自适应PID调节方法,各载荷点示值误差≤±0.3 mg,稳定时间≤3 s,优于国家标准《JJG1036—2008电子天平检定规程》规定的I级天平示值误差指标。     

AZ31B镁合金轴对称件单点无模温渐进成形新工艺规律

研究并掌握镁合金板材在不同工艺参数条件下的渐进成形规律对完善镁合金单点温渐进成形工艺有着重要的理论和实际应用价值。以变锥角圆台件为研究对象,以有限元软件ANSYS/LS-DYNA为工具,以成形件的等效应力、减薄率和板厚变化为研究指标,研究了不同工艺参数:成形温度、摩擦条件和工具头直径对AZ31B镁合金板材单点温渐进成形的影响。结果表明:在成形温度为250℃,静摩擦系数为0.2、动摩擦系数为0.1,工具头直径在10~12 mm范围内,AZ31B镁合金板材具有良好的单点渐进成形性能。     

虚拟成形速度对渐进成形数值模拟精度的影响

针对渐进成形数值模拟过程中精度不足的问题,以成形中板料动能和内能的比值小于5%、数值模拟零件和实验零件壁厚误差小于3%为判断准则,采用数值模拟与实验研究相结合的方法,并以圆锥件为例,研究了渐进成形数值模拟中工具头虚拟成形速度对模拟精度的影响。结果表明:虚拟成形速度对数值模拟精度影响较大,过大的虚拟成形速度会降低模拟精度;过小的虚拟成形速度虽然能提高模拟精度,但会降低模拟效率。当虚拟成形速度为800 mm·s-1时,既能保证模拟精度,也能提高模拟效率。