预应力钢筋混凝土梁破坏过程的声发射特性实验研究

利用全波形声发射技术记录了预应力钢筋混凝土梁在3点弯曲荷载下整个破坏过程的声发射信号,并在研究了声发射累计能量随时间变化关系曲线的基础上,采用谱分析对声发射全波形数据进行了分析和处理。以全波形声发射信号的能量分布特性为依据,通过对时域和频域内信号的振幅、频率特征和构件破坏过程的比较,初步得出了预应力钢筋混凝土梁破坏过程的声发射信号的参数特性,发现全波形声发射信号能够实时反映预应力混凝土梁破坏过程中的特征信息。     

Instream sensor results suggest soil–plant processes produce three distinct seasonal patterns of nitrate concentrations in the Ohio River Basin

The Ohio River Basin (ORB) is responsible for 35% of total nitrate loading to the Gulf of Mexico yet controls on nitrate timing require investigation. We used a set of submersible ultraviolet nitrate analyzers located at 13 stations across the ORB to examine nitrate loading and seasonality. Observed nitrate concentrations ranged from 0.3 to 2.8 mg L⁻¹ N in the Ohio River's mainstem. The Ohio River experiences a greater than fivefold increase in annual nitrate load from the upper basin to the river's junction with the Mississippi River (74–415 Gg year⁻¹). The nitrate load increase corresponds with the greater drainage area, a 50% increase in average annual nitrate concentration, and a shift in land cover across the drainage area from 5% cropland in the upper basin to 19% cropland at the Ohio River's junction with the Mississippi River. Time-series decomposition of nitrate concentration and nitrate load showed peaks centered in January and June for 85% of subbasin-year combinations and nitrate lows in summer and fall. Seasonal patterns of the terrestrial system, including winter dormancy, spring planting, and summer and fall growing-harvest seasons, are suggested to control nitrate timing in the Ohio River as opposed to controls by river discharge and internal cycling. The dormant season from December to March carries 51% of the ORB's nitrate load, and nitrate delivery is high across all subbasins analyzed, regardless of land cover. This season is characterized by soil nitrate leaching likely from mineralization of soil organic matter and release of legacy nitrogen. Nitrate experiences fast transit to the river owing to the ORB's mature karst geology in the south and tile drainage in the northwest. The planting season from April to June carries 26% of the ORB's nitrate and is a period of fertilizer delivery from upland corn and soybean agriculture to streams. The harvest season from July to November carries 22% of the ORB's nitrate and is a time of nitrate retention on the landscape. We discuss nutrient management in the ORB including fertilizer efficiency, cover crops, and nitrate retention using constructed measures.     

不同pH值下含铁矿物对硫酸侵蚀混凝土的影响研究

硫酸侵蚀为混凝土耐久性损伤的一个重要方面.在硫酸盐侵蚀过程中,含铁矿物等侵蚀产物不断形成,导致混凝土材料形成不同程度的腐蚀.为研究不同pH值环境下含铁矿物对混凝土结构腐蚀的影响,在实验室配置了pH值为2.0、3.0和4.0的稀硫酸溶液,结合不同洗刷作用方式来模拟酸雨环境,采用室内长期浸泡试验方法对混凝土试件进行不同程度...     

填充粘弹性材料的开缝钢筋混凝土剪力墙性能试验研究

建立了填充粘弹性材料的开缝钢筋混凝土剪力墙的力学模型,基于通用有限元软件ABAQUS,对具有不同形式的钢筋混凝土剪力墙进行了数值模拟,通过对其在相同加载速率下的弹塑性分析,探讨了开缝填充粘弹性材料的剪力墙和整体墙、开缝墙的性能,以及粘弹性材料缝的尺寸等因素对剪力墙性能的影响.试验结果表明,开缝后填充粘弹性材料,在剪力墙...     

ABAQUS混凝土损伤塑性模型的动力性能分析

地震作用在混凝土结构上会在其材料中产生较高的应变率,混凝土材料具有一定的率敏感性,准确模拟混凝土结构在地震作用下的反应需采用混凝土动态本构模型.为评估ABAQUS有限元软件中的混凝土损伤塑性模型模拟混凝土动力性能的能力,采用该模型对混凝土材料和构件在不同加载速度下的动态反应进行了有限元数值分析.结果表明,随着加载速度的...     

基于模糊可拓层次分析法的在役混凝土桥梁耐久性评估

对在役混凝土桥梁的耐久性研究是目前学术界的热点问题。使用科学的方法对其耐久性进行合理的评估,是解决该问题的关键。考虑到在役混凝土桥梁耐久性评估中的不确定性,利用改进的三标度层次分析法及模糊可拓理论,建立了基于模糊可拓层次分析法的在役混凝土桥梁耐久性评估模型。首先,根据桥梁的结构及所处环境的特点,建立了在役混凝土桥梁耐久性评估指标体系。其次,运用改进的三标度层次分析法确定指标权重。然后,使用模糊可拓理论确定耐久性等级。最后,通过具体的实例分析,证明了该评估方法的科学性和有效性。     

Sustainable monitoring of concrete structures: strength and durability performance of polymer-modified self-sensing concrete

Concrete structures all over the world are reaching the end of their service life sooner than expected. This is due to the fact that ordinary Portland cement-based concrete deteriorates under environmental actions and also that structural inspections and conservation actions are expensive. Besides, as they consume energy and non-renewable resources, they have negative environmental impacts. Self-sensing concrete provides an alternative way of monitoring concrete-reinforced structures at a much lesser cost and with lesser environmental impact. Although the short-term mechanical properties of these materials are usually well documented, the long-term durability issues about carbon fibre concrete still deserve further investigations. This paper reports some investigation of the strength and durability characteristics of several concrete mixtures modified with different percentages of polymer and carbon fibre addition. The results show that the addition of carbon fibre decreases the strength and increases water penetration under pressure and also increases chloride diffusion, whereas polymer addition is responsible for a denser microstructure and higher concrete durability.     

透水混凝土路面对径流水量削减试验

透水混凝土路面作为低影响开发技术之一,对雨洪的管理与控制具有重要作用。对透水混凝土路面对径流的控制作用进行试验,结果表明:基于设计路面和北京降雨参数,降雨历时分别为30,60,120 min时,透水混凝土路面对径流总量的削减率分别达到60%、55%和40%以上,对洪峰流量的削减率分别达到65%、63%和40%以上;降雨重现期从1年增到100年,产流延迟时间从13 min降至5 min。试验表明,透水混凝土路面的雨量径流系数在0.18~0.54,远小于普通混凝土路面的雨量径流系数0.91。结果表明,透水混凝土路面对延迟产流时间、削减径流水量、削减洪峰流量以及降低径流系数具有很好的作用,可以为该低影响开发技术在国内的应用设计提供参考。     

电解金属锰渣制备泡沫混凝土实验研究

电解金属锰渣是锰矿石采用电解法生成电解金属锰时产生的浸出渣,其理化性质证实了其资源化利用的潜力。建立了电解金属锰渣-水泥-飞灰-细砂胶凝体系,经蒸压制备成超轻泡沫混凝土。主要探讨了水泥、石灰、石膏的添加对泡沫混凝土抗压强度的影响。结果显示,当凝结体系的配方为电解金属锰渣35.6%、水泥14.1%、细砂34.3%、石灰16.0%、石膏0.05%,在1.2MPa的蒸汽压下保养6h时的抗压强度最佳。中试实验生产出来的泡沫混凝土满足国家标准DBJ 50-055—2006中B07等级,可为电解金属锰渣资源化利用提供了一种创新的技术途径。     

高应力大变形软岩巷道“三壳”围岩控制机理及应用

为解决土城煤矿14运输上山软岩巷道变形量大、锚杆索失效严重等技术难题,通过现场调研、室内试验、理论分析、数值模拟及工业性试验等方法,揭示了围岩变形特征以及巷道失稳破坏机理,提出了“三壳”围岩控制理论。基于以上研究,设计了“锚杆锚索+灌浆+钢管混凝土支架”的复合支护方案,建立了基于“三壳”围岩控制理论的“三壳”支护结构体力学模型,计算出设计方案的极限承载能力为2.54 MPa,随后采用 FLAC3D数值模拟软件对设计方案进行模拟分析,验证了方案合理性。最后,该复合支护得到成功运用,现场监测结果表明:巷道顶底板以及两帮变形量均低于100 mm,巷道未发生明显变形,支护效果良好。