风荷载对高耸电塔拆除爆破影响研究及实践

为安全拆除爆破某百米高混凝土电塔,在电塔倒塌方向偏转角理论推导分析的基础上,研究了风荷载对电塔倒塌方向的影响规律,并组织了拆除爆破施工。研究表明,当预设倒塌方向与风向一致时,对塔体倒塌方向影响最大;随着基本风速的增加,塔体倒塌偏转角逐渐增大,当基本风速在12 m/s以内时,倒塌偏转角可控制在3.2°以内;当基本风速为7.5～8.5 m/s时,应考虑横风向共振效应的影响。通过精心的设计、施工,实际电塔倒塌偏转角度控制在理论分析范围内。该成功案例对类似高耸建筑物爆破拆除具有一定借鉴作用。     

高耸烟囱爆破拆除数值模拟及分析

介绍在倒塌空间有限的条件下,180 m高钢筋混凝土烟囱采用距离地面25 m的高位爆破切口爆破拆除的基本设计情况,运用Ansys/Ls-Dyna软件模拟烟囱的倒塌过程,模拟结果与实际拆除结果吻合很好.结合摄影监测和数值模拟,分析了180 m烟囱高位切口爆破拆除的倒塌过程、烟囱倒塌时支撑部失稳破坏过程及其受力情况,研究表明烟囱在爆破切口形成后1.1 ～1.35 s时支撑部于初始闭合角处开始破坏并向后发展,1.85 ～2.0 s时支撑部沿水平方向破坏断裂,支撑部破坏过程中中性轴不断后移.     

冷却塔爆破拆除塔壁触地解体规律研究

针对爆破拆除冷却塔倒塌过程中的偏转形态与钢混材料破坏之间的关系,采用最大线应变理论方法建立关于母线L的函数表达式,利用LS-DYNA软件模拟倒塌过程中对材料设置多因素破坏条件,据此分析塔体在触地碰撞瞬间结构体的破碎位置及塑性铰转角极值[θ]。研究表明:除切口处塔壁发生破碎外,上部塔壁也发生破碎,且截面破碎位置在倒塌方向两侧;破碎截面随塑性铰转角极值增大而减小,上部塔壁截面破碎高度降低,当塑性铰转角极值达到3°时,塔壁仅在切口处发生破碎;增设剪应力失效阈值控制人字柱材料破坏条件,模拟倒塌效果与实际过程一致,证明采用最大线应变理论分析结构倒塌特征的准确性。     

横风向共振对高烟囱爆破倾倒方向的影响

在顺风向荷载的基础上建立横风向荷载作用下高烟囱爆破倾倒的力学模型,分析了横风荷载对高烟囱定向爆破倾倒方向的影响,得到爆破倾倒偏转角的计算公式,并以南昌电厂210 m高烟囱为例进行验证.计算表明,烟囱共振频带在4～6级风的风振频率区域,定向爆破倾倒偏转角和风向角(0°～30 °)呈近似线性关系,随着风向角的增大,偏转角也随之增大,此外,考虑横风共振后倾倒偏转角显著增大,建议在设计爆破参数时应对横风荷载予以考虑.     

爆破拆除烟囱倒塌过程中风效应影响研究

在烟囱爆破拆除倒塌过程中,不同形式的风可使烟囱产生顺风向效应及横风向效应。横风向效应又包括横风向旋涡脱落及共振效应、横风向空气动力失稳。烟囱在风的长期作用下会发生失稳倾斜。本文揭示了爆破拆除过程中烟囱由于风振影响而发生倾斜、失稳的机理,分析了不同风向的三类风效应对爆破拆除时烟囱倒塌方向发生偏移的影响。根据分析计算结果可得,纵向风振影响最为显著,静力风效应影响相对较小,横向风振产生影响随机性较强。同时作者得出了爆破拆除烟囱时考虑风效应影响需采取的相应技术手段和措施。     

80m高烟囱高位切口定向爆破拆除

介绍了在复杂环境下,采用控制爆破技术成功爆破拆除80 m高的钢筋混凝土烟囱的工程实例。由于倒塌方向仅有90 m长度,达不到烟囱高度1.2倍的要求,因此,采用高位切口定向倒塌爆破方案,将爆破缺口提高到距地面20 m处。同时,介绍了爆破拆除的设计与施工技术:通过开凿定向窗及将爆破缺口高度提高到2 m等措施保证倒塌方向准确;通过计算及试爆,确定每孔装药量为30 g,并采取有效防护措施控制爆破飞石的影响;开挖减振沟和堆砌防护土堤等措施减小倒塌触地引起的振动强度。经过精心设计与施工,烟囱向设计方向倒塌,达到了定向准确、安全的效果。     

高耸建筑物爆破实践与分析

被拆爆的跳伞塔为薄壁筒形变截面钢筋混凝土结构,总高度为60.2m,总重约为442t。塔体外三个不同方向装有跳伞大臂及两个环形跳台,外形结构特殊,周围环境较复杂。为确保跳伞塔顺利倒塌,在确定倒塌方向、制定爆破方案、设计爆破缺口、减小爆破震动等方面,都经过反复论证和科学验算后,才予以实施。经过精心组织和施工,跳伞塔爆破拆除取得圆满成功。     

高耸建筑物爆破实践与分析

被拆爆的跳伞塔为薄壁筒形变截面钢筋混凝土结构,总高度为60.2m,总重约为442t。塔体外三个不同方向装有跳伞大臂及两个环形跳台,外形结构特殊,周围环境较复杂。为确保跳伞塔顺利倒塌,在确定倒塌方向、制定爆破方案、设计爆破缺口、减小爆破震动等方面,都经过反复论证和科学验算后,才予以实施。经过精心组织和施工,跳伞塔爆破拆除取得圆满成功。     

薄壁型钢混结构烟囱控制爆破拆除

为消除石溪野水泥厂废弃薄壁钢混结构烟囱的安全隐患,在分析烟囱周边环境及拆除技术难点的基础上,采用与高压线平行的定向倒塌方案进行控制爆破拆除。设计爆破切口高度2.25 m,切口角度225°,三角形定向窗高度1 m,筒壁和烟道处炸药单耗分别取3.8 kg/m~3和2.3 kg/m~3;倒塌方向上设置两道高度1 m的土挡墙以减弱塌落振动,采用铁丝网和多层密目网防护措施以控制爆破飞石。通过精细的爆破设计和组织施工,成功实现了烟囱的定向爆破拆除,爆破振动和飞石控制在安全允许范围内。     

复杂环境下两座烟囱交叉定向爆破拆除

为了确保电厂生产区内高150 m和180 m两座钢筋混凝土烟囱在一次性爆破拆除中的安全倒塌,在周围环境复杂、设备正常运行的条件下,采用了高位切口控制爆破和延时起爆技术,交叉定向倾倒爆破拆除两座烟囱的爆破技术方案,切口位置分别位于距地面25.0 m和30.0 m处,两烟囱间起爆延期时间为5 s。实践表明,爆破参数、切口位置、倒塌方向和5 s延期时间的选择合理可行,爆破效果良好。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

卧式金属罐容量的测量结果不确定度

本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。     

盐酸浓度不确定度的评估

通过对盐酸浓度标定的过程分析，找出影响结果的各个分量，进行不确定度的评定，按照计量技术规范给出标准的表示法。     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.