Effect of ground motion duration on inelastic displacement ratio of SDOF systems

In this paper,the influence of ground motion duration on the inelastic displacement ratio,C_(1),of highly damped SDOF systems is studied.For this purpose,two sets of spectrally equivalent long and short duration ground motion records were used in an analysis to isolate the effects of ground motion duration on.The effect of duration was evaluated for observed values of C_(1) by considering six ductility levels,and different damping and post-yield stiffness ratios.A new predictive equation of C_(1) also was developed for long and short duration records.Results of non-linear regression analysis of the current study provide an expression with which to quantify the duration effect.Based on the average values of estimated C_(1) ratios for long duration records divided by C_(1) for a short duration set,it is concluded that the maximum difference between long and short duration records occurs when the damping ratio is 0.3 and the post-yield stiffness ratio is equal to zero.

Inelastic displacement ratio of low-to mid-rise BRBFs designed under variable levels of seismicity

Buckling-restrained braces(BRBs)have shown their capability to provide building structures with stiffness,strength,and ductility.Estimating the seismic drifts of buckling-restrained braced frames(BRBFs)is an important design step to control structural and non-structural damage.In current practice of seismic design,the estimation of seismic drifts of BRBFs is performed by using empirical calculations that are independent upon either the type of the structural system or the design level of seismicity.In these empirical calculations,the seismic drifts are estimated by amplifying the reduced elastic drifts obtained under design lateral loading with a displacement amplification factor(DAF).The value of DAF is considered equal to the product of the response modification factor R and the inelastic displacement ratioρ.The goal of the current research is to assess the value ofρfor low-to mid-rise BRBFs designed under low and high levels of seismicity.This goal has been achieved by conducting a series of elastic and inelastic time-history analyses pertaining to an ensemble of earthquake records on 3-,6-and 9-story BRBFs.The results indicate that theρ-ratio increases with an increase in design seismic intensity and an increase in experienced inelasticity.The range ofρfor low seismicity designs ranges from 0.63 to 0.9,while for high seismicity designs this range stretches from 0.83 to 1.29.It has been found that the consideration of a generalρ-ratio of 1.0 is a reasonable estimation for the design of the BRBFs considered in this study.

P-Δ effect on inelastic displacement ratio spectra for inelastic structures

For the evaluation of structures with known ductility demands,the constant-ductility displacement ratio spectra(CDDRS) are particularly useful for providing inelastic displacement ratios to estimate maximum lateral inelastic displacement demands from maximum elastic displacement demands.The CDDRS are computed for single-degree-of-freedom systems(SDOF) by considering or ignoring P-Δ effect for different ductility levels when subjected to 344 earthquake ground motions recorded in four site classes.The modified expressions of CDDRS for P-Δ effect are proposed.It is concluded that the P-Δ effect on CDDRS is significant,and the effect increases with the increase of ductility level.In the long-period region,the CDDRS ignoring P-Δ effect almost conforms to the equal-displacement rule.But in the case of higher ductility level,the CDDRS considering P-Δ effect are much higher than 1.0,which do not conform to the equal-displacement rule.

Study on inelastic displacement ratio spectra for near-fault pulse-type ground motions

In displacement-based seismic design, inelastic displacement ratio spectra （IDRS） are particularly useful for estimating the maximum lateral inelastic displacement demand of a nonlinear SDOF system from the maximum elastic displacement demand of its counterpart linear elastic SDOF system. In this study, the characteristics of IDRS for near-fault pulse-type ground motions are investigated based on a great number of earthquake ground motions. The influence of site conditions, ratio of peak ground velocity （PGV） to peak ground acceleration （PGA）, the PGV, and the maximum incremental velocity （MIV） on IDRS are also evaluated. The results indicate that the effect of near-fault ground motions on IDRS are significant only at periods between 0.2 s - 1.5 s, where the amplification can approach 20%. The PGV/PGA ratio has the most significant influence on IDRS among the parameters considered. It is also found that site conditions only slightly affect the IDRS.

Lateral displacement of silty clay under cement-fly ash-gravel pile-supported embankments: Analytical consideration and field evidence

Based on back analysis of lateral displacements measured in situ by using the analytical solution, a useful method for estimating stress concentration ratio of geosynthetic-reinforced and pile-supported(GRPS) embankments was proposed. In order to validate the proposed method, a full-scale high-speed railway embankment(HSRE) with four instrumented subsections over medium compressibility silty clay was constructed in three stages. The soil profile, construction procedure and monitoring of settlements and lateral displacements of the four test sections were described. The field deformation analysis results show that 1) the combined reinforcement of CFG piles and geosynthetic layer perform well in terms of reducing lateral displacements; 2) the development of lateral displacements lags behind the increase of fill load, which can be attributed to the vertical load transfer mechanism of the pile foundation; and 3) pile length has a dominant effect on the stress distribution proportion between piles and surrounding soils. The comparison between predicted and experimental results suggests that the proposed analytical solution and the back analysis-based method are capable of reasonably estimating the lateral deformation and the stress concentration ratio, respectively, if the appropriate soil elastic modulus is chosen.

Scaling of residual displacements in terms of elastic and inelastic spectral displacements for existing SDOF systems

Structures undergoing inelastic displacements during earthquake ground motions are known to sustain some amount of residual displacements, which may make them unusable or unsafe. In this study an attempt is made to estimate residual displacements for elastic-perfectly-plastic single-degree-of-freedom oscillators with a given lateral strength ratio. It is observed in the case of a class of ground motions that there are no trends in the dependence of residual displacement on the temporal features of the ground motion, and thus any estimation of residual displacements should be carried out only in the statistical sense. Statistical estimation of residual displacement spectrum via normalization with respect to inelastic or elastic spectral displacements is considered, and it is found that normalization with respect to inelastic spectral displacements is preferable. Expressions for residual displacement spectra are proposed for both types of normalizations and for the givenlateral-strength-ratio type oscillators.

Displacement damage in optocouplers induced by high energy neutrons at back-n in China Spallation Neutron Source

Neutron radiation experiments of optocouplers at back-streaming white neutrons(back-n)in China Spallation Neutron Source(CSNS)are presented.The displacement damages induced by neutron radiation are analyzed.The performance degradations of two types of optocouplers are compared.The degradations of current transfer ratio(CTR)are analyzed,and the mechanisms induced by radiation are also demonstrated.With the increase of the accumulated fluence,the CTR is degrading linearly with neutron fluence.The radiation hardening of optocouplers can be improved when the forward current is increased.Other parameters related to CTR degradation of optocouplers are also analyzed.

Maximum Relative Displacement of Adjacent Buildings During Ground Motions

In order to give the reasonable width of seismic gaps to prevent the structural pounding during ground motions,the maximum relative displacement of adjacent structures is studied in this paper.The factors that may have effects on the maximum relative displacement are discussed.As for multi-degree-of-freedom(MDOF) systems,they can be equivalent to single-degree-of-freedom(SDOF) systems with the influences of high modes neglected.The results show that the period ratio,height ratio and peak ground acceleration are the main factors that have great effects on the maximum relative displacement of adjacent structures.The maximum relative displacement of MDOF systems can be obtained from calculating the maximum relative displacement of the equivalent SDOF systems.

高地层倾角油藏高低部位油井液量配比研究

在高倾角断块油藏中,受重力作用影响,高、低部位油井开发效果差异大。运用物理模拟实验分析了地层倾角对高、低部位油井开发效果的影响,推导了考虑均衡驱替的水驱断块倾角油藏高、低部位油井产液量配比计算方法,并通过与数值模拟结果对比,验证了油井产液量配比计算方法的准确性。研究发现:随着储层倾角的增加,高部位流线变少、水驱波及区域变小、采出程度变低。随着储层倾角增加,达到均衡动用所需的油井产液量配比(高部位油井产液量与低部位油井产液量比)增加。在相同储层倾角的情况下,随着原油密度和注水强度增加,倾角对达到均衡驱替所需的油井产液量配比的影响变弱,油井产液量配比降低。该研究对高倾角断块油藏均衡开发具有指导意义。

纳米材料在油田开发领域的研究及应用

可利用石油资源逐渐减少、开采难度在增大。纳米材料具有卓越的粒子尺寸和性能,通过表面改性还可在同一纳米材料上集成多种驱油功能,其被认为是解决传统提高采收率(EOR)技术所面临众多问题的潜在方案。本文主要介绍了纳米材料的制备与改性、种类,综述其在油田开发各阶段的应用与研究进展,特别是EOR方面。结合油田开发需求与纳米技术的优势,指出了纳米颗粒在EOR过程中应用的挑战和未来研究的机遇。

利用声强比衰减原理探究角位移法声源定位系统

设计了一种利用声强衰减规律进行三维声源定位的实验方法,声源定位主要通过测量声源相对探源中心的距离、方向和高度实现。利用声强比呈对数衰减的原理,推导了声波强度在空气中的衰减规律与声源距离的关系式;设计了一种角位移法测量声源方向,并给出了角位移大小与声强比到达峰值时的时间之间的关系式;通过电控升降平台,测定了声源到参考平台水平面的高度。并制作了在1立方米范围内的三维声源定位实验装置,实验结果表明,本实验装置在二维平面内,声源距离测量的最大相对误差为2.3%,方位角测量的最大误差为1.6°;在三维空间内,声源距离测量的最大相对误差为2.9%,高度测量的最大相对误差为4.9%,方位角测量的最大误差为0.8°,通过实验证明了本实验系统定位效果较好。

地下连续墙受力变形光纤监测与数值模拟研究

地下连续墙是一种常见的深基坑支护方式,具有刚度大、防渗性能好、适应范围广等优点,但其受力变形规律较为复杂。基于超弱光纤光栅感测技术,对某地铁车站基坑地下连续墙水平位移进行实时监测。将监测数据与数值模拟结果进行对比,验证了数值分析模型选取的合理性,并基于该数值分析模型研究了不同厚度软土层中,地下连续墙水平位移的变化规律,通过墙体位移梯度(D_(w))和软土位移梯度(D_(r))进行临界厚度比计算。研究结果显示:水平位移随软土厚度的变化呈“凸肚”状,沿深度方向划分为相对稳定区、线性增长区、最大变形区和线性下降区。利用D_(w)和D_(r)标定出临界厚度比为0.24;土压力变化在基坑前四步开挖过程中较为稳定,而在第五步开挖与施工后40 d变化显著。上述研究结果为类似工程的设计、施工和监测方案的制定提供了重要参考。

竖向荷载对高承台群桩基础侧向位移影响规律的振动台试验

基于大型振动台模型试验,以高承台群桩为研究对象,模拟了地震作用下高桩承台基础的振动响应,通过超静孔压比(简称孔压比)、加速度和地基土位移研究饱和砂土液化场地竖向荷载对桩基侧向位移的影响规律。结果表明:近桩区域受桩基竖向荷载影响最为显著,孔压比与竖向荷载呈负相关关系,桩基两侧孔压比差值与地基土浅层加速度是造成桩基侧向位移的主要原因;地基土对台面输出加速度主要起放大作用,且随着竖向荷载的增加,加速度放大系数显著减小;在振动输入与竖向荷载相同的条件下,地基土在地震动作用下引起的侧向流动及显著变形极大影响了桩基的侧向位移;竖向荷载为9%桩基极限承载力条件下,桩基倾斜角为4.80°,侧向位移较小,结合地基土抗液化能力,桩基抗倾覆能力最优。

考虑永久位移的锚索框架减震锚头弹簧组件合理刚度研究

强震作用下预应力框架锚索可能出现内锚段松脱、锚索拉断等震害,在锚头处设置弹簧是一种新型抗震措施,而弹簧刚度的合理选取对改善锚索受力至关重要。建立在锚头处设置弹簧预应力锚索框架的加固基岩-覆盖层边坡三维数值模型,研究边坡在不同峰值加速度、不同持时地震波作用下响应规律,调整锚索-弹簧串联体系等效刚度大小,分析坡体永久位移和锚索轴力减载比随弹簧刚度的非线性变化特征;以控制边坡位移及锚索减载效果为目标,提出弹簧组件的合理刚度确定方法。研究表明:随弹簧刚度降低,缓冲减震作用逐渐显著;坡顶水平加速度受刚度变化影响较小,但当弹簧刚度低于临界值后边坡位移及弹簧变形量急剧增加;以边坡永久位移实际调查经验限值为首要控制条件,结合位移、弹簧峰值行程随刚度变化拟合“直-曲分界点”曲线,以共同确定弹簧刚度下限;同理,依据减载比拟合曲线轴力削减明显区段得出刚度上限,以保证一定工程经济性。针对算例模型取永久位移10 cm、拟合曲线曲率k小于0.002 k max作为直曲分界判断依据,得0.4 g~0.6g强震下弹簧刚度区间为(2.5,3.8)kN/mm,研究方法可为边坡预应力锚固工程抗震设计提供参考。

低渗油田N_(2)驱气窜特征及泡沫防窜实验研究

针对B油田氮气驱气窜问题,通过室内物理模拟实验分析了长岩心N_(2)驱替过程的生产特征和气窜规律,由于B油田具有高温高盐低渗的特点,采用瓦林搅拌法筛选出合适的泡沫防窜体系,并通过物理模拟实验研究了体系的防窜效果和注入时机。实验结果表明,以采出程度和累积气油比作为指标可将气驱过程划分为三个阶段:无气采油阶段、油气同产阶段、气窜阶段。适合目标油田的泡沫防窜体系是:0.6%ZHDQ-5起泡剂+0.1%WP-1稳泡剂溶液。该体系封堵率可达到90%,推荐在累积气油比达到20 cm^(3)/cm^(3)注入泡沫防窜体系,可在前期气驱的基础上提高采收率17%。

腰臀比对腰椎退行性疾病术后疗效的影响

目的:探讨腰臀比对腰椎退行性疾病术后疗效的影响。方法:回顾性分析1220例腰椎退行性疾病患者的病例资料,其中低腰臀比组102例(男性腰臀比<0.85,女性腰臀比<0.75)、正常腰臀比组705例(男性腰臀比为0.85~0.9,女性腰臀比为0.75~0.8)、高腰臀比组413例(男性腰臀比>0.9,女性腰臀比>0.8)。比较3组患者的手术时间、术中出血量、术后1年Oswestry功能障碍指数(Oswestry disability index,ODI)及腰背部、臀部、腿部、足部疼痛数字评分。结果:(1)一般结果。3组患者的手术时间、术中出血量比较,组间差异均有统计学意义[(118.8±25.6)min,(125.5±18.8)min,(139.3±26.6)min,F=11.238,P=0.001;(125.4±20.6)mL,(140.9±28.6)mL,(188.2±31.6)mL,F=14.262,P=0.035]。高腰臀比组患者手术时间长于正常腰臀比组和低腰臀比组(P=0.001,P=0.001),术中出血量多于正常腰臀比组和低腰臀比组(P=0.001,P=0.001);正常腰臀比组患者的手术时间、术中出血量和低腰臀比组比较,组间差异均无统计学意义(P=0.136,P=0.117)。(2)术后1年疼痛数字评分。3组患者术后1年腰背部、臀部、腿部疼痛数字评分比较,组间差异均有统计学意义[(2.60±0.96)分,(2.17±0.84)分,(3.27±1.10)分,F=17.901,P=0.036;(1.45±0.52)分,(1.49±0.50)分,(2.78±0.85)分,F=54.421,P=0.001;(2.09±0.70)分,(2.13±0.98)分,(2.80±1.16)分,F=6.239,P=0.003];足部疼痛数字评分比较,差异无统计学意义[(1.55±0.52)分,(1.39±0.49)分,(1.29±0.46)分,F=1.731,P=0.182]。高腰臀比组患者术后1年腰背部、臀部、腿部疼痛数字评分均高于低腰臀比组和正常腰臀比组(P=0.045,P=0.001;P=0.047,P=0.003;P=0.029,P=0.001),正常腰臀比组患者术后1年腰背部、臀部、腿部疼痛数字评分和低腰臀比组比较,组间差异均无统计学意义(P=0.176,P=0.291,P=0.716)。(3)术后1年ODI。3组患者术后1年ODI比较,差异有统计学意义[(19.40±6.52)%,(12.59±6.81)%,(24.28±9.83)%,F=30.502,P=0.001]。高腰臀比组患者术后1年ODI高于正常腰臀比组和低腰臀比组(P=0.001,P=0.042),低腰臀比组患者术后1年ODI高于正常腰臀比组(P=0.019)。结论:高腰臀比会增加腰椎退行性疾病患者的手术时间和术中出血量,影响患者术后疼痛缓解和腰椎功能恢复。

基于遗传算法的剪力墙结构设计优化方法

剪力墙结构体系的高层结构容易出现剪力墙偏心布置的问题,同时引起其在水平作用下抗扭性能不足的问题。通过分析遗传算法的优点及适用性,确定采用遗传算法以实现对剪力墙抗扭性能优化问题。具体讨论了基于遗传算法的优化方法条件的设定,并阐述了基于遗传算法对剪力墙优化的具体步骤。以某工程项目建筑结构作为模型算例,对其简化模型进行基于遗传算法的400代迭代优化,并对优化后的原建筑模型进行验证。结果表明基于遗传算法对剪力墙结构的优化效果良好,优化后的剪力墙结构在水平荷载作用与扭转作用下楼层位移比能得到有效的降低,证明了基于遗传算法对高层剪力墙结构优化的可行性。

界限估计方法在高压配电系统地震易损性分析中的应用研究

配电系统中某一单体设备的抗震性能评估结果难以表征配电系统整体的抗震能力,高压配电系统的抗震安全性评估研究亟需开展。目前,用于结构系统可靠性评估的界限估计方法在土木工程结构领域得到应用和推广,此方法在电力系统抗震性能概率性评估中的应用较少。基于此,文中以某实际工程高压配电系统为例,采用一阶界限估计方法和二阶界限估计方法对配电系统的易损性进行研究。研究结果表明:该配电系统的超限概率大于系统中任一单体设备的超限概率;基于一阶界限估计方法求解的配电系统易损性曲线界限区间较宽,不利于工程的实际应用;基于二阶界限估计方法求解的易损性曲线界限区间窄,但下界对系统中单体设备的超限排列顺序较为敏感,在应用此方法时应特别注意。

蒸汽安全阀仿真分析与结构优化

采用ANSYS CFX流场仿真技术对优化后的锅炉管道用蒸汽安全阀流场排量和升力系数进行研究。结果表明:结构优化后的蒸汽安全阀开高设计合理,具有较好的排放性能,临界压力比在0.400~0.497之间,流阻损失小。阀瓣结构优化后,升力曲线得到改善,能够迅速达到设计开高要求,及时排放压力,减少颤振等问题的发生。

南海东部特低渗油田压裂改造实践与效果评价

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