全尾砂无耙深锥稳态浓密性能分析

结合沉降和压滤实验, 对脱水性能数据进行曲线拟合获得连续网状结构形成浓度、压缩屈服应力和干涉沉降系数, 引入Usher提出的稳态浓密性能预测算法, 建立了无耙深锥浓密模型, 分析了絮凝剂单耗、底流中固相的体积分数、泥层高度等对固体通量和固体处理能力的影响规律.研究结果表明: 絮凝剂添加量对沉降区域影响大于压密区域, 20 g·t-1时浓密性能较好, 底流中固相的体积分数越大固体通量越小; 在沉降区域, 固体通量仅与浓度有关, 不受泥层高度影响; 在压密区域, 固体通量为浓度与泥层高度的方程; 模型参数范围内, 当泥层高度 < 3.5 m时, 固体处理能力为浓度与泥层高度的方程, 当泥层高度>3.5 m时, 固体处理能力与固体通量随底流中固相的体积分数变化规律一致.      

深锥浓密机底流浓度模型及动态压密机理分析

泥层高度和底流浓度是深锥浓密机最为重要的两个参数,因此有必要研究底流浓度随泥层高度的变化规律.采用自制小型深锥浓密机,对尾矿非连续/连续动态压密过程进行了物理实验;借助于有效孔隙比与泥层压强间遵循的Power函数关系,结合对尾矿颗粒的受力分析,推导出了底流浓度与泥层高度的数学模型,揭示了浓密机底流浓度与泥层高度的内在关系,并从尾矿颗粒空间结构的角度解释了该模型的变化规律;结合矿山生产对于底流浓度的要求,应用该数学模型,为其推荐了泥层高度的合理范围,验证了底流浓度数学模型的可靠性.该模型为深锥浓密机的设计和运行提供了理论依据.      

高料层操作时烧结矿FeO含量的降低

最近正在Ｋｕｒｅ１号烧结机上进行厚料层作业。在厚料层作业开始之前，我们进行了不同料层高度下的烧结杯试验，来研究料层高度对烧结的影响。     

钛精矿流态化工艺条件选择试验

在不同的钛精矿粒径、流化床内料层高度和分布板开孔率下进行对比试验,探讨最小流化速度和流化质量的影响因子。结果表明,分布板开孔率和料层高度对最小流化速度影响不明显,最小流化速度随着粒径的增大而增大。在试验所选取的开孔率、料层高度、粒径大小下,均能达到较好的流化质量。     

球团竖炉料层情况对气流运动影响的试验研究

在冷态模型实验台上研究料层情况对炉内气流分布的影响规律 ,得出 :1)料层高度增加 ,上行冷却风趋势减小 ,下行焙烧风趋势增大 ;2 )料层倾角由 0°增加到 3 4°时 ,上行冷却风趋势增大 ,下行焙烧风趋势减小 ,气流均匀性得以改善 ;实验条件下 ,较佳的料层倾角为 2 9°～ 3 4° ,现有球团竖炉的料层倾角基本适合 ;3 )料层高度增加 ,风机出口流量减小 ,出口压力增加 ,在一定范围内料层高度与竖炉进风量接近线性关系 ;降低炉内粉尘量是提高进风量、降低风机出口压力的关键。生产实际中调整料层高度时 ,一定要兼顾其对炉内气流运动的影响 ,并有效地利用之 ;在生产可调范围内改变料层高度 ,进风量改变较小 ,一般通过风机自身能力的调节来保证进风量。     

基于DCS的氧化铝沉降泥层高度模糊控制的实现

氧化铝沉降槽泥层高度是生产中的关键控制参数,因影响因素众多,常规PID等控制无法实现自动控制。本文基于HOLLiAS-MACS DCS系统设计模糊控制器实现了对泥层高度的自动控制。     

超厚料层烧结过程固体燃料的分布规律

铁矿烧结以固体燃料作为主要热量来源,其热量高效利用对于烧结节能减排具有重要意义。本文聚焦超厚料层烧结条件下固体燃料在料层中的分布特性,系统解析其在泥辊宽度方向以及料层高度方向的分布规律。结果表明：沿泥辊宽度方向,整体混合料粒度中间偏细、两侧略粗,而含碳量则为中间偏高、两侧略低;布料之后,台车宽度方向混合料粒度组成和含碳量与泥辊对应位置处的混合料规律一致;在料层高度方向上,自上而下混合料粒度整体呈增大趋势,含碳量则逐渐减小,由于泥辊与九辊布料的偏析程度有限,在部分高度处粒度与含碳量会出现波动;利用台车高度方向混合料的粒度组成和泥辊下料处各粒级的含碳量计算出沿料层高度方向的燃料分布,与实际规律基本一致。研究结果可为超厚料层烧结过程固体燃料的优化分布提供指导。     

宣钢高线厂推行现场管理星级评价实践

介绍了宣钢高速线材厂通过推行现场管理星级评价标准,找到了各级工作层面中存在的问题,并依照现场管理星级评价标准进行改进,有效地加强了质量基础工作,形成了具有特色的现场管理模式,促进了产品质量的提升.     

超细全尾砂深锥动态絮凝浓密试验

为探明超细全尾砂的浓密特性,开展量筒沉降实验,小型和半工业深锥动态浓密试验。结果表明,分子量1200万的非离子型絮凝剂最利于尾砂沉降,随絮凝剂单耗增加,溢流浊度降低,底流浓度基本不变。随固体通量增加,溢流浊度增加,底流浓度降低。固体通量0.4 t·m?2·h?1,给料固体质量分数12%,絮凝剂单耗50 g·t?1的最佳参数条件下,小型和半工业动态浓密试验的底流平均固体质量分数分别为62.8%和74.4%,泥层高度对底流浓度影响显著。深锥浓密机底流固体质量分数随泥层高度增加呈DoseResp函数增长,分为缓慢增长（泥层1～4 m）、快速增长（泥层4～7 m）和基本稳定（泥层超过7～8 m）3个阶段,这跟尾砂絮团在不同泥层高度下的压缩性能有关。可根据底流浓度与泥层高度的函数关系,调节泥层高度来满足井下充填所需底流浓度。      

韶钢烧结料层孔隙率的实验研究

通过对韶钢烧结料层孔隙率的实验研究,给出了烧结混合料小球在不同料层高度、平均粒度、温度、含水量条件下的孔隙率变化规律的拟合公式,并对烧结矿孔隙率也进行了研究。实验结果表明,对于烧结小球,随着料层和温度的升高,孔隙率呈下降趋势,但孔隙率随小球平均直径增大而增大,含水量对于孔隙率有一个最佳值;对于烧结矿,料层高度对烧结矿的孔隙率影响很小,但随着料层温度升高,烧结矿孔隙率呈下降趋势。     

CFRP Prestressed High-Strength Concrete Prisms Subjected to Direct Tension

This paper describes the behavior of carbon fiber-reinforced polymer (CFRP) prestressed high-strength concrete prisms under direct tension. Seven prestressed concrete prisms with different levels of prestressing were cast and tested. Prisms were 50×50?mm in cross section and their lengths varied between 1,400 and 2,000?mm. Concrete compressive strength was as high as 147?MPa. Tension stiffening, crack width, and crack spacing in prisms were investigated. Concrete properties, such as the stress–strain relationship under direct tension and bond strength, were also determined. Test results revealed that tension stiffening in CFRP prestressed high-strength concrete is significant when higher concrete strength and higher prestressing level are applied. Tension stiffening factors are proposed based on the postcracking behavior of concrete. Experimental results also showed that increasing the prestressing level increases the amount of tension stiffening and reduces the number of cracks, which delays their appearance. However, cracks widened at a faster rate in the prisms with higher prestressing levels. Experimental results were compared with Comite Euro-International du Beton and American Concrete Institute proposed equations. Modifications were suggested for the above-mentioned equations to account for use of CFRP bars in prestressed sections.     

3D Coordinating Relations between Steel Cables and Concrete of Prestressed Concrete Beam Bridges

Interaction between steel cables and concrete is complicated in prestressed concrete bridges, especially in curved prestressed concrete bridges. The most significant behavior of curved beam bridges under the loads is that, at the same time of vertical flexure, torsion occurs on the cross section, which complicates the mechanical analysis to curved beam bridges. Based on coordinating relations of steel cables and concrete (CRSC), the grillage structure finite-element method was adopted to analyze the spatial effect of curved beam bridges. This way, the effect of all prestressing procedures can be simulated properly, including the prestressing loss due to concrete shrinkage and creep, batch prestressing of the cables, etc. Furthermore, it is effective to analyze the integrated behavior of the combined steel cables space out and concrete. The efficiency and reliability of the CRSC method is demonstrated by our analysis system WXQ2.0 developed for curved-skew bridges.     

Development of FRP Reinforcement Guidelines for Prestressed Concrete Structures

Several national programs define the testing protocols and design guidelines for fiber reinforced polymer (FRP) reinforcement in concrete structures. This paper offers a review of these documents, comparing the materials testing and design philosophies for FRP reinforcement of different working groups. The work references Canadian, European, and Japanese efforts to codify these materials and assess the relative merits of each approach. The emphasis is on prestressing applications since the demands for sustained load capacity and full bond are more severe than for reinforced concrete.     

Concrete Beams Strengthened with Prestressed Near Surface Mounted CFRP

Retrofitting concrete structures with fiber reinforced polymer (FRP) has today grown to be a widely used method throughout most parts of the world. The main reason for this is that it is possible to obtain a good strengthening effect with a relatively small work effort. It is also possible to carry out strengthening work without changing the appearance or dimensions of the structure. Nevertheless, when strengthening a structure with external FRP, it is often not possible to make full use of the FRP. The reason for this depends mainly on the fact that a strain distribution exists over the section due to dead load or other loads that cannot be removed during strengthening. This implies that steel yielding in the reinforcement may already be occurring in the service limit state or that compressive failure in the concrete is occurring. By prestressing, a higher utilization of the FRP material is made possible. It is extremely important to ensure that, if external prestressing is used, the force is properly transferred to the structure. Most of the research conducted with prestressing carbon fiber reinforced polymer (CFRP) for strengthening has been on surface bonded laminates. However, this paper presents research on prestressed CFRP quadratic rods bonded in sawed grooves in the concrete cover. This method has proven to be an advantageous means of bonding CFRP to concrete, and in comparison to surface bonded laminates, the shear and normal stress between the CFRP and the concrete are more efficiently transferred to the structure. In the presented test, no mechanical device has been used to maintain the prestress during testing, which means that the adhesive must transfer all shear stresses to the concrete. Fifteen beams with a length of 4?m have been tested. The tests show that the prestressed beams exhibited a higher first-crack load as well as a higher steel-yielding load as compared to nonprestressed strengthened beams. The ultimate load at failure was also higher, as compared to nonprestressed beams, but in relation not as large as for the cracking and yielding. In addition, the beams strengthened with prestressed FRP had a smaller midpoint deflection. All strengthened beams failed due to fiber rupture of the FRP.     

刚架替代框架中框架梁的结构设计

在底层框架上部砖混的建筑结构中,以刚架替代框架中的框架梁,刚架降蔽在砖混墙体内。此结构设计既可以增大建筑空间,又可以满足层高和净空的要求。     

Deflection Control of Concrete Beams Pretensioned by CFRP Reinforcements

Use of carbon fiber reinforced polymers (CFRP) reinforcement for prestressing concrete structures introduces a promising solution for deterioration of concrete structures due to corrosion of steel reinforcements. Due to the low elastic modulus and limited strain at failure of CFRP reinforcement, partial prestressing could be the most appropriate approach to enhance deformability and reduce the cost in comparison to fully prestressed concrete structures. For members reinforced or prestressed with fiber reinforced polymers reinforcements, serviceability requirements may be the governing criteria for the design; therefore, deflection under service loading conditions should be well defined. This paper introduces simplified methods to calculate the deflection of beams prestressed by CFRP reinforcement under short-term and repeated loading. It also examines the applicability of current approaches available to calculate the deflection. Based on an experimental program undertaken at the University of Manitoba, bond factors are introduced to account for tension stiffening of concrete beams prestressed by CFRP. A procedure to determine the location of the centroidal axis of cracked prestressed sections is also proposed. The proposed methods for deflection calculation are calibrated using the results obtained from different experimental programs. Design guidelines are proposed to predict the deflection of beams partially prestressed by CFRP reinforcement.     

The risk of hydrogen embrittlement in high-strength prestressing steels under cathodic protection

High strength prestressing steels in prestressed concrete structures are protected against corrosion due to passivation resulting from the high alkalinity of the concrete. If depassivation of the prestressing steel occurs due to the ingress of chlorides the corrosion risk can be minimized by application of cathodic protection with impressed current. The risk of hydrogen embrittlement of the prestressing steel is especially pronounced if overprotection is applied due to hydrogen evolution in the cathodic reaction. The present work considers this risk by hydrogen activity measurements under practical conditions and application of different levels of cathodic protection potentials. Information on threshold potentials in prestressed concrete structures is provided, too.     

Behavior of Prestressed Concrete Strengthened with Various CFRP Systems Subjected to Fatigue Loading

Many prestressed concrete bridges are in need of upgrades to increase their posted capacities. The use of carbon fiber-reinforced polymer (CFRP) materials is gaining credibility as a strengthening option for reinforced concrete, yet few studies have been undertaken to determine their effectiveness for strengthening prestressed concrete. The effect of the CFRP strengthening on the induced fatigue stress ratio in the prestressing strand during service loading conditions is not well defined. This paper explores the fatigue behavior of prestressed concrete bridge girders strengthened with CFRP through examining the behavior of seven decommissioned 9.14?m (30?ft) girders strengthened with various CFRP systems including near-surface-mounted bars and strips, and externally bonded strips and sheets. Various levels of strengthening, prestressing configurations, and fatigue loading range are examined. The experimental results are used to provide recommendations on the effectiveness of each strengthening configuration. Test results show that CFRP strengthening can reduce crack widths, crack spacing, and the induced stress ratio in the prestressing strands under service loading conditions. It is recommended to keep the prestressing strand stress ratio under the increased service loading below the value of 5% for straight prestressing strands, and 3% for harped prestressing strands. A design example is presented to illustrate the proposed design guidelines in determining the level of CFRP strengthening. The design considers the behavior of the strengthened girder at various service and ultimate limit states.     

高层建筑框架梁柱节点的强度验算和施工处理

随着我国高层建筑混凝土结构高度的不断增加,在高层建筑底部区域,柱混凝土强度等级高于梁板混凝土强度等级的情况经常存在,本文根据(高层建筑混凝土结构技术规程》(JGJ3—2002)的规定,经实例定量验算,提出一种节点区较简易处理方法,保证高层建筑框架梁柱节点区混凝土满足承载力要求。     

Long-Term Behavior of Prestressed Old-New Concrete Composite Beams

This paper presents both theoretical and experimental studies of the long-term behavior of prestressed old-new concrete composite beams under sustained loads. General differential equations governing the relationship between the incremental deflection and incremental internal forces of the composite beams were deduced in the theoretical study. Closed-form solutions for simply supported composite beams were obtained and validated using test results reported in previous literature on steel-concrete composite beams. The experimental investigation consisted of static long-term load tests carried out on four prestressed old-new concrete composite beams. The behavior of the old-to-new concrete interface, time-dependent deflections, concrete strains, and prestress losses was carefully observed over 260?days. The long-term test program showed that the midspan deflections and concrete strains increased with time because of creep and shrinkage of the new prestressed concrete. The slip strains at the old-to-new concrete interface were found to be relatively small, indicating that the interface bond was sound enough to prevent slip and that the prestressing loads were effectively transferred to the old concrete. The proposed theoretical models predicted the long-term behavior of the prestressed old-new concrete composite beams with an acceptable degree of accuracy.