水灰比对混凝土强度影响的多元回归分析

论述了水灰比对混凝土强度的影响,回顾了多元回归分析的基本理论好方法后,建立了水灰比、含气量等与混凝土抗压强度的多元回归方程,并与试验结果进行了对比分析,结果表明,与实测数据有较好的拟合效果。     

谈拱形焊接球网壳的块体制作及质量控制

结合工程概况,从块体划分、杆件下料、块体制作胎模设置、块体拼装、块体焊接等方面介绍了网壳结构块体的制作过程,并对网壳结构块体质量控制进行了阐述,指出施工中严格控制小型网块的制作质量对整个网壳结构的质量具有十分重要的意义。     

应用激光扫描技术对天津西站站房大跨度网壳钢屋架提升对接过程形态监测与分析

针对天津西站站房钢屋架跨度大、结构复杂、高空对接点多等特点,采用三维激光扫描法对钢结构拼装后的上下接口偏差和形态、预提升时上下接口偏差和形态、卸载前后形态分3阶段进行变形监测。通过统计图表的方法,对钢屋架提升过程的变形进行了分析,从分析结果可知,利用三维激光扫描技术法对大跨度钢屋架提升过程中变形的监测是行之有效的。此技术既保证了施工质量,又为玻璃幕墙安装提供了形态依据。     

肋环四撑杆型大开口弦支网壳体育场罩篷结构形态分析及优化设计

为从结构体系层面改善大跨度屋盖结构受力性能和经济性,提出一种肋环四撑杆型大开口弦支网壳的结构形式,可应用于大跨度体育场环形罩篷结构。与常规的弦支网壳不同,该结构的下弦节点设置四根撑杆,提高了整体结构的稳定性;且上弦层网格可采用铰接节点,减少环索和斜索的用量,预应力张拉施工便捷。区别于多撑杆类索穹顶,该结构上弦不采用索系而采用杆系,使造价经济,且便于铺设刚性屋面。针对该大开口弦支网壳,根据节点平衡方程,推导出了预应力态索杆内力一般性计算公式,分析了弦支网壳预张力分布随几何参数的变化规律。以跨度200 m的大开口体育场罩篷为例,通过全局敏感性及相关性分析,揭示了该弦支网壳整体刚度的主要影响因素为几何参数,而预张力仅起到维持局部稳定和预起拱的作用。基于两种改进遗传算法对该弦支网壳结构进行了优化设计与权衡分析,结果表明在满足稳定性前提下适当提高结构矢高和厚度,有利于改善结构刚度和经济性。最后对张拉施工和静力加载至整体失稳的全过程进行了模拟分析,表明该弦支网壳可高效利用上弦杆拉、压两端的截面强度,而施工阶段仍有必要引入临时支撑。     

考虑初始几何缺陷的网壳结构整体稳定性可靠度分析

网壳结构的设计由重力荷载和初始几何缺陷共同作用下的整体稳定性控制,而结构的初始几何缺陷形状和最大值是未知的。采用联立自回归模型分别对球面网壳和柱面网壳结构的初始几何缺陷进行建模,研究空间相关初始几何缺陷对结构整体稳定极限承载力概率分布和可靠度的影响。评估杨氏模量对不同荷载工况作用下极限承载力概率分布和可靠度的影响。在永久荷载与雪荷载作用下,杨氏模量的影响可以忽略不计;如果各节点初始几何缺陷标准差的最大值等于1/2或1/3规范推荐的初始几何缺陷最大值,按规范中安全系数满足2的规定进行设计,结构的失效概率约小于6.5×10^-5;若安全系数取1.5,结构失效概率约小于5.1×10^-4。考虑永久荷载与活荷载的组合时,如果各节点初始几何缺陷标准差的最大值等于1/2或1/3规范推荐的初始几何缺陷最大值,安全系数取2时,网壳结构的失效概率均可忽略不计;若安全系数取1.5,球面网壳及柱面网壳的失效概率分别小于10^-7和10^-6。即若达到规范采用的可靠度,规范中的安全系数也许可降低至1.5且可针对不同地区确定不同安全...     

施工质量对钻孔灌注桩承载性状的影响

探讨了西安地区黄土地基中泥浆护壁钻孔灌注桩的施工质量 ,特别是钻成孔施工质量对桩的竖向承载力、变形、桩身轴力传递和侧阻力发挥性状的影响 ,以期引起对桩孔施工质量严格检测必要性的重视。     

双层柱面网壳整体模型的建立及分析

采用有限元法,借助SAP2000对双层柱面网壳模型进行整体建立和静力分析,研究了关于双层柱面网壳在静力荷载作用下各杆件内力与位移的分布规律,得出了各杆件受静力荷载影响程度,进而了解了双层柱面网壳的静力特性。     

球面组合网壳的有限元法分析及受力特性的研究

组合网壳是一种新型空间结构形式,本文首次采用板壳元、空间偏心梁单元的组合结构有限元法对这种结构的受力特性作了探讨分析,研制了组合网壳受力分析专用计算软件ＣＧＡＳ。文中给出了某一代表性球面组合网壳工程实例,通过分析,阐述了这种结构位移、内力分布规律,讨论了几种与组合网壳相似结构的受力比较,以及肋、钢杆的偏心对受力的影响,总结出的规律对组合网壳结构设计应用有一定参考意义。     

边界条件对大跨复杂网壳的静力性能分析

文章应用MIDAS/Gen结构设计有限元分析软件,计算分析了不同边界条件对大跨复杂网壳结构内力、位移的影响。网壳结构的支座型式应符合边界计算假定,边界支承刚度应根据下部结构的刚度和支座本身的刚度定量计算,为大跨复杂网壳结构支座设计提供了理论依据。     

沉渣对钻孔灌注桩承载性状影响的数值分析

受诸多因素影响,钻孔灌注桩桩身易出现多种缺陷,沉渣缺陷是其中最常见的一种。本文运用PLAXIS有限元软件进行数值模拟,分析评价灌注桩桩底沉渣的厚度、弹性模量等参数变化对其竖向承载性状的影响。荷载一沉降曲线、沉渣参数变化对单桩竖向极限承载力的影响曲线、沉渣参数变化对桩顶沉降的影响曲线等相关曲线的分析结果表明：沉渣的存在会降低单桩极限承载力、增加桩顶沉降变形,这种影响随沉渣材料参数的变化呈现一定的变化规律。     

局部混凝土收缩对壳体圆仓影响的研究

由于施工条件和方法的限制，混凝土壳体圆仓的肋与板产生了不同收缩，破坏了原壳体结构自身的力的平衡。由于收缩受到钢筋的抑制，从而促进了壳体内部微裂缝的形成和发展，影响了结构的部分承载能力。本文根据温度和收缩对结构影响的相似性，建立了温度和收缩的转换模型，并进行了数值计算，结果表明该方法具有一定的精度。     

The strain approach to the development of thin cylindrical shell finite elements

The method of forming thin cylindrical shell finite element displacement functions by initially developing the strain function is presented. The Kirchhoff-Love assumptions are used together with deep thin shell finite elements to develop a number of 20 degrees-of-freedom rectangular and 15 degrees-of-freedom triangular cylindrical shell elements. The elements are tested on an extended range of barrel vault roof problems and results are presented. Only in the very specific case of N_φ for the free straight-edged barrel vault using the triangular elements are the results found to be inaccurate. In all cases where the displacements and stresses can be analytically checked, the strain approach gives accurate results.     

基于模态应变能和小波分析方法的网壳结构损伤识别研究

工程结构损伤的识别与定位研究以往主要针对梁、框架等结构形式.损伤表现为信号局部特征的改变,而小波分析在时域和频域上都具有表征信号局部特征的能力.为提高结构损伤识别方法的准确性和适用性,将小波分析引入到网壳结构损伤识别中.根据小波奇异性检测理论,提出将模态应变能和小波变换相结合的方法对网壳结构进行定位,即以结构损伤前后单元模态应变能差作为结构损伤指标,对其分别进行bior6.8连续和离散小波变换,利用小波系数极大值点判断网壳结构有无损伤和损伤位置.以跨度40m的Kiewitt网壳结构为例进行数值模拟,结果表明:基于模态应变能和小波变换相结合的方法,在测得一阶模态下,不但对单一损伤而且对多损伤均能有效地识别出结构的损伤位置,证明该方法对此类结构损伤定位具有有效性和实用性.     

Geochemical survey and metal bioaccumulation of three bivalve species (Crassostrea gigas, Cerastoderma edule and Ruditapes philippinarum) in the Nord Medoc salt marshes (Gironde estuary, France)

A 15-month experiment combining a geochemical survey of Cd, Cu, Zn and Hg with a bioaccumulation study for three filter-feeding bivalve species (oysters, Crassostrea gigas; cockles, Cerastoderma edule; and clams, Ruditapes philippinarum) was conducted in a breeding basin of the Nord Medoc salt marshes connected to the Gironde estuary, which is affected by historic polymetallic pollution. Regular manual surface measurements of temperature, salinity, pH and dissolved O(2) concentration and hourly multiprobe in situ measurements throughout several periods for 6-8 weeks were performed. The geochemical behavior of metals in water, suspended particulate matter and sediment and their ecotoxicological impact on the three bivalve species were evaluated by in situ exposure of juvenile oysters (water column) and adult cockles and clams (sediment surface). The physico-chemical parameters reflected seasonal variations and basin management. A distinct daily periodicity (except salinity) indicated intense photosynthesis and respiration. In summer, low dissolved O(2) saturations ( approximately 40-50%) occurred in the early morning at 30 cm above the sediment, whereas in depressions, the water column near the sediment surface was suboxic. Cadmium, Zn and Cu concentrations in suspended particulate matter exceeded typical estuarine values and were much higher than the homogeneously distributed concentrations in different depth ranges of the basin sediment. Particles collected in sediment traps showed intermediate metal concentrations close to sediment values. These results suggest trace metal recycling due to reductive dissolution under suboxic conditions at the sediment surface resulting in trace metal release to the water column and adsorption onto suspended particles. Dissolved Cd, Zn and Hg concentrations (e.g. 13-136 ng l(-1); 0.3-25.1 microg l(-1) and 0.5-2.0 ng l(-1), respectively) in the basin corresponded to the concentration range typically observed in the Gironde estuary, except for some maximum values attributed to metal recycling. In contrast, dissolved Cu concentrations (1.08-6.08 microg l(-1)) were mostly higher than typical estuarine values, probably due to recycled Cu complexation by dissolved organic matter. Growth, bioaccumulation rates and kinetics in the whole soft body of the bivalves were analyzed every 40 days. Although Cd bioaccumulation of oysters was lower in the basin than in the estuary during the same period (27,000 ng g(-1), dry weight and 40,000 ng g(-1), respectively) these values are largely above the new human consumption safety level (5000 ng g(-1), dw; European Community, 2002). For cockles and clams, Cd bioaccumulation was lower, reaching 1400 ng g(-1) and 950 ng g(-1), respectively. Similar results were obtained for Zn and Cu suggesting physiological differences between the species and/or differences in the exposure of the organisms due to physico-chemical conditions and metal distribution between dissolved and particulate phases. In contrast, Hg bioaccumulation was highest for cockles reaching bioconcentration factors of approximately 200,000, which even exceeded that of Cd in oysters (50,000) for the same exposition period. Nevertheless, Hg concentrations remained relatively low in the three bivalve species.     

循环振动对饱和粉土初始动剪模量的影响

初始动剪模量是土体多种结构性因素的综合反映,除固结压力和孔隙比(密度)这两个主要因素外,还受循环振动影响。以往对该因素的研究偏重于干砂,且预振时施加的剪应变幅多低于10-3;对于饱和土体,尤其是对经受过较大振幅振动后土体初始动剪模量的研究十分有限。本文利用安装弯曲元的动三轴仪,在等向固结条件下对不同相对密度的饱和粉土进行不排水循环三轴试验,同时监测试样的剪切波速,获得循环动力加载过程中土的初始动剪模量。为保证试验结果的可靠性,同时进行了共振柱试验,比较确定弯曲元接收信号的到达点;评估了不同孔压发展程度下试验暂停时间对测试结果的影响。结果表明:在一定次数大振幅循环荷载作用下观察到初始动剪模量有别于相同应力下固结后得到的模量值,出现附加衰减或增长,正是循环荷载作用下土微观结构变化的外部宏观表现。这种附加变化由土颗粒接触行为决定,受到试样初始条件和振动幅值等多种因素的影响,表现出不同的变化模式。     

Effects of initial molecular weight on removal rate of dextran in biofilms

Degradation kinetics of different size dextrans in a biofilm reactor were evaluated. Degradation rates of dextran standards, measured as time series of oxygen utilisation rates, decreased with increasing initial molecular weight. Removal of bulk phase total organic carbon with time was highly correlated (R2>0.99) and could be modelled with variable half-order degradation rate expressions. A power correlation between initial molecular weight and the variable half-order degradation rate coefficient was found for polymers in the range 6-500 kDa. Degradation of dextran in the colloid size range (MW>1 Mda) did not follow the same kinetics. Reductions in the observed removal rate with polymer size can be explained by the effect of reduced diffusivities of the substrate, without assuming reaction rate effects.     

温度、应变率对碳纤维混凝土变形特性的影响

采用自主研制的高温SHPB试验系统,对高温条件下碳纤维混凝土(CFRC)的变形特性进行了试验研究.结果表明:高温下CFRC的动态峰值应变同时存在加载速率强化效应和温度弱化效应.动态极限应变存在加载速率强化效应;同一加载速率下随温度的升高先降低后增大的变化趋势,200℃以前,以温度弱化效应为主,200℃以后,以温度强化效应为主;800℃时的动态极限应变要高于常温时的情况.碳纤维可以有效提高混凝土在不同温度和加载速率下的动态变形能力,当碳纤维体掺量为0.3％时,增幅最大,其次是0.1％CFRC和0.2％CFRC.     

消防队伍平静水域应急救援实战化教学与训练研究

目前,湖泊、河流、水库等平静水域溺亡事故已成为我国居民意外死亡的主要原因之一,消防队伍作为一支专业的救援力量,在处置此类事故中面临着巨大的工作压力和挑战,也投入了很多精力与汗水,然而,救援人员的能力素质略显不足、安全意识淡薄、处置程序不够明确、救援理念不到位等问题越来越突出。文章针对这一问题,探索出一套平静水域事故处置教学与培训方案,希望为各类救援队伍更好地培育专业救援人才提供参考。     

消防队伍平静水域应急救援实战化教学与训练研究

目前,湖泊、河流、水库等平静水域溺亡事故已成为我国居民意外死亡的主要原因之一,消防队伍作为一支专业的救援力量,在处置此类事故中面临着巨大的工作压力和挑战,也投入了很多精力与汗水,然而,救援人员的能力素质略显不足、安全意识淡薄、处置程序不够明确、救援理念不到位等问题越来越突出。文章针对这一问题,探索出一套平静水域事故处置教学与培训方案,希望为各类救援队伍更好地培育专业救援人才提供参考。