Design and Preparation of High Elastic Modulus Self-compacting Concrete for Pre-stressed Mass Concrete Structures

Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.

A Statistical Analysis of the Modulus of Elasticity and Compressive Strength of Concrete C45/55 for Pre-stressed Precast Beams

Random behavior of concrete C45/55 XF2 used for prefabricated pre-stressed bridge beams is described on the basis of evaluating a vast set of measurements. A detailed statistical analysis is carried out on 133 test results of cylinders 150 ~ 300 mm in size. The tests have been running in laboratories of the Klokner Institute. A single worker took all specimens throughout the period, and the subsequent measurements of the static modulus of elasticity and the compressive strength of the concrete were performed. The measurements were made at the age of 28 days after specimens casting, and only one testing machine with the same capping method was used. Suitable theoretical models of division are determined on the basis of tests in good congruence, with the use of Z2 and the Bernstein criterion. A set of concrete compressive strength （carried out on 133 test results of cylinders 150 ~ 300 mm after test of static modulus of elasticity） shows relatively high skewness in this specific case. This cause that limited beta distribution is better than generally recommended theoretical distribution for strength the normal or lognormal. The modulus of elasticity is not significantly affected due to skewness because the design value is based on mean value.

Self-adjustment of Carrying Capacity of Concrete Embedded with CFRC

By heating up the embedded carbon fiber reinforced cement based material （CFRC）, the carrying capacity and deformation of concrete member could be adjusted. The relationship between temperature difference and expansion strain of CFRC was demonstrated, and the temperature-deformation-load effect of concrete embedded with CFRC was studied. Heating the CFRC up to different temperatures resulted in different degree of inner pre-stress in concrete. Thus, the load capacity of concrete could be regulated owing to counteracting the pre-stress.

Experimental study on seismic behavior of circular RC columns strengthened with pre-stressed FRP strips

Bonding fiber reinforced polymer （FRP） has been commonly used to improve the seismic behavior of circular reinforced concrete （RC） columns in engineering practice. However, FRP jackets have a significant stress hysteresis effect in this strengthening method, and pre-tensioning the FRP can overcome this problem. This paper presents test results of 25 circular RC columns strengthened with pre-stressed FRP strips under low cyclic loading. The pre-stressing of the FRP strips, types of FRP strips and longitudinal reinforcement, axial load ratio, pre-damage degree and surface treatments of the specimens are considered as the primary factors in the tests. According to the failure modes and hysteresis curves of the specimens, these factors are analyzed to investigate their effect on bearing capacity, ductility, hysteretic behavior, energy dissipation capacity and other important seismic behaviors. The results show that the initial lateral confined stress provided by pre-stressed FRP strips can effectively inhibit the emergence and development of diagonal shear cracks, and change the failure modes of specimens from brittle shear failure to bending or bending-shear failure with better ductility. As a result, the bearing capacity, ductility, energy dissipation capacity and deformation capacity of the strengthened specimens are all significantly improved.

Effect of concrete creep on pre-camber of continuous rigid-frame bridge

The effect of concrete creep on the pre-camber of a long-span pre-stressed concrete continuous rigid-frame bridge constructed by cantilever casting method was investigated.The difference of creep coefficients calculated with two Chinese codes was discussed.Based on the calculations,the pre-camber of a pre-stressed concrete continuous rigid-frame box bridge was computed for construction control purpose.The results show that the short-term creep coefficient and long-term creep coefficient calculated with the CC-1985 are larger than those calculated with the CC-2004,while the medium-term creep coefficient calculated with the CC-1985 is smaller than that calculated with the CC-2004.The difference of creep deformation calculated with these two codes is small,and the influences of concrete creep on the pre-camber for most of the segments are negligible.The deflections and stresses of the box girder measured during the construction stages agree very well with the predictions.

Stress Analysis of New Type Pre-Stressed Anchor Bearing Plate Combining Stamping with Welding Forming and Its Anchorage Zone

An anchor bearing plate transfers the anchoring force from anchor plate to the concrete and the pre-stress is formed in the concrete structure. Currently, the main type of anchor bearing plate is cast iron. It is brittle during transportation and tension process. This paper presents a new type of anchor bearing plate combined stamping with welding forming. The structure of the new type anchor bearing plate is introduced. The stress states of the anchor bearing plate and anchorage zone under work are studied. Various specifications of anchor bearing plate are studied by ANSYS finite element analysis software following the AASHTO specification. The analysis results are compared with the results of the same type of OVM round-shaped anchor plate. The study results show that the new pre-stressed anchor plates combined stamping with welding forming are feasible and more sturdy which can meet the engineering demand.

Experimental and parametrical investigation of pre-stressed ultrahigh-performance fiberreinforced concrete railway sleepers

In this study,ultrahigh-performance fiber-reinforced concrete(UHPFRC)used in a type B70 concrete sleeper is investigated experimentally and parametrically.The main parameters investigated are the steel fiber volume fractions(0%,0.5%,1%,and 1.5%).Under European standards,35 UHPFRC sleepers are subjected to static bending tests at the center and rail seat sections,and the screw on the fastening system is pulled out.The first cracking load,failure load,failure mode,crack propagation,load–deflection curve,load–crack width,and failure load from these tests are measured and compared with those of a control sleeper manufactured using normal concrete C50.The accuracy of the parametric study is verified experimentally.Subsequently,the results of the study are applied to UHPFRC sleepers with different concrete volumes to investigate the effects of the properties of UHPFRC on their performance.Experimental and parametric study results show that the behavior of UHPFRC sleepers improves significantly when the amount of steel fiber in the mix is increased.Sleepers manufactured using UHPFRC with a steel fiber volume fraction of 1%and a concrete volume less than 25%that of standard sleeper B70 can be used under the same loads and requirements,which contributes positively to the cost and surrounding environment.

离心成型超高性能混凝土电杆简介

介绍了影响卧式离心成型超高性能混凝土(UHPC)电杆质量的关键因素,主要包括原材料选择(胶凝材料、骨料、外加剂、纤维等)、UHPC制备(投料顺序、拌和时间等)、离心成型制度(模具转速、离心时间等)及蒸汽养护控制(养护时间、养护温度等),可为卧式离心成型UHPC电杆的应用提供参考。

预应力加固框架梁对节点抗震性能分析

为研究预应力加固混凝土框架梁后框架节点的抗震性能变化,文中以框架节点为研究对象,应用位移法分析斜腹杆体外预应力技术加固混凝土框架梁后框架节点的受力情况,通过ABAQUS建立有限元模型以及组织一个三层两跨的试验框架模型,对数值模拟的结果进行验证。研究表明ABAQUS建立的有限元模型可以用于斜腹杆体外预应力加固框架梁节点的抗震性能分析,相比于未加固框架,在竖向荷载作用下,节点区域钢筋应力相对减小,节点极限抗剪能力提高;在水平荷载作用下,加固框架比未加固框架混凝土受压损伤严重,尤其梁端比未加固框架延伸更多,对框架节点抗震不利,故应采用相应技术对节点进行加固,为斜腹杆体外预应力整体加固提供理论依据。

Comparison Voltage across Insulator Strings of 69 kV and 24 kV Lines due to Lightning Strokes to Top Pole and Mid Span

This paper analyzes the effects of the voltage across insulator of 69 kV and 24 kV lines installed on the same pole. The case studies illustrated the lightning strike to direct top pole and mid span of ground wire using the ATP-EMTP （Alternative Transient Program-Electromagnetic Transient Program）. The results found that when lightning strike the voltage across the 69 kV line insulator at mid span is 1.55 times and 1.34 times higher than at top pole when the front time is 0.25/100μs and 10/350 μs, respectively. When lightning strike the voltage across the 24 kV line at mid span is 1.04 times and 0.64 times higher than at top pole when the front time is 0.25/100μs and 10/350μs, respectively. So the effect of lightning strike is more severe at mid span than at the direct top pole, especially for the 69 kV insulator.

基于双目视觉的混凝土电杆立杆参数测量方法

为准确掌握混凝土电杆立杆参数,及时对抗倾覆能力不足的混凝土电杆进行加固以预防电杆倾倒事故,提出一种基于双目视觉的混凝土电杆埋深与倾斜率方法。首先通过修改主干特征提取网络、优化特征融合并引入改进CBAM注意力机制的Deeplab V3+语义分割模型,并基于采集的混凝土电杆图片数据集进行训练,确定混凝土电杆在全景图像中的区域;然后,采用基于局部区域效应的亚像素边缘检测算法提取分割区域内的混凝土电杆边缘点,并根据混凝土电杆的几何特性使用最小二乘法拟合边缘获取所需特征点,最后利用双目视觉的坐标变换计算混凝土电杆埋深与倾斜率。结果表明:该方法的埋深测量误差值小于10 cm,误差率小于5%,倾斜率测量误差值小于0.3°,程序运行耗时小于4 s,该方法在混凝土电杆立杆参数测量问题上具有可行性,测量精度与测量速度满足实际应用需要。

错层悬挑结构立杆斜撑支模施工技术

随着人们对建筑外观造型及功能要求的不断提高,建筑高空悬挑混凝土构件大量涌现,针对本工程图书综合楼逐层外突悬挑结构的特点,相较于传统高支模的支撑形式,本工程采用下部立杆斜撑的支模形式,并通过midas Gen进行结构与架体模型建立,错层区域结构及支撑架体进行有限元分析。提高了模板支撑体系的安全系数,缩短施工工期的同时,还降低施工难度和成本。以期为类似工程提供借鉴参考。

通信架空杆路荷载分析

针对通信架空杆路安装架空吊线数量及每条架空吊线附挂光缆数量增多能否满足杆路荷载的问题,本文结合某地区的气象条件和某通信运营商杆路资源现状,对既有通信预应力混凝土电杆和架空吊线荷载进行系统理论分析,给出该地区在满足安全条件下的新建或利旧既有杆路安装吊线数量及每条镀锌钢绞线上附挂光缆数量的建议。

环形混凝土电杆基于无损检测的健康状态评估研究

我国目前存在着大量的环形混凝土电杆老旧输电线路,其结构健康状况日益下降,影响了电网安全稳定运行。为了在不影响线路运行的前提下开展环形混凝土电杆的健康状态评估,本文基于超声回弹法,选取山东临沂的三条在运220kV线路进行了电杆现场无损检测。经现场实测可知,超声回弹法则是一种准确有效、方便快捷的电杆无损检测方法,推荐在实际检测中采用。环形混凝土电杆强度检测应考虑工艺及环境因素的影响进行声速修正及碳化修正。基于现场无损检测数据,判断三条线路的电杆健康状态均为正常状态,可继续运行。

电杆在荷载作用下的仿真模拟研究

随着科技的发展和社会的进步,生产生活中对电力的需求越来越大,对供电质量的要求也越来越高。为验证地聚物混凝土在电杆中应用的可行性,采用ABAQUS有限元模拟对地聚物混凝土锥形电杆在极限承载状态和正常运行情况下进行一定荷载下的受力状态分析,确保电杆的强度、刚度、稳定性。结果表明:地聚物混凝土电杆的极限承载力是传统混凝土电杆的1.23倍;根径与土体接触的受压位置应力最大,电杆稍径处位移最大,主要横向变形为23.48 mm,垂直位移为6.75 mm,远小于挠度限值,从理论与计算的角度验证了地聚物混凝土电杆的可行性。

防腐蚀混凝土电杆的设计以及性能研究

沿海地区和盐碱地区的混凝土电杆易受高盐环境腐蚀,导致混凝土结构碳化、钢筋腐蚀,影响电杆的耐久性。为了提高电杆的防腐性能,电杆材料采用高强度混凝土以及抗硫酸盐防腐剂,并对电杆基础和杆身进行防腐涂层覆盖以及PE板/膜锚固,该防腐工艺结合了化学防腐和物理隔绝法的优点,创造性地将混凝土电杆从地基处理至顶部防腐作为一个整体进行设计,将化学防腐方法和物理防腐方法有机结合起来,提高了电杆的防腐性能,减轻了混凝土电杆重量,增强了混凝土电杆的稳固性。

离心成型预应力钢纤维混凝土电杆设计试验研究

对研制的呼称高27m离心成型预应力钢纤维混凝土电杆进行了受力性能试验研究。结果表明，在断线工况荷载作用下，电杆的受力表现出良好的整体性，各项性能均满足设计要求：杆身采用预应力和钢纤维双重增强作用，使电杆的抗裂能力提高，变形减小：一旦发生超载运行出现裂缝，裂缝细短且非贯通，卸载后变形回复能力强，残余变形很小：在极限承载时，整杆变形明显，具有良好的延性破坏预兆。同时，预应力钢纤维混凝土电杆在预应力筋放张和杆段对焊组装过程中，避免了普通预应力混凝土电杆在预应力筋挂板和杆段连接钢圈附近混凝土起皮爆裂现象。根据试验结果对比分析，建立了预应力钢纤维混凝土电杆抗裂度、裂缝宽度、挠度和正截面承载力设计计算方法。研究成果为河南省漯河～淮阳220kv线路工程建设提供了重要科研依据，为钢纤维混凝土在预应力电杆中的应用提供了重要参考。

环形钢筋混凝土电杆裂缝深度的超声波检测

研究采用超声波检测环形钢筋混凝土试件和环形钢筋混凝土电杆中裂缝深度的方法,导出纵向裂缝和环向裂缝深度计算公式。对环形钢筋混凝土试件和环形钢筋混凝土电杆裂缝深度的检测结果表明:用本文提出的检测和计算方法对于环形钢筋混凝土构件裂缝深度的检测具有较高的准确度;对于环向裂缝,用两换能器的连线斜跨环向裂缝的布置方法可以基本消除钢筋的影响。

碳纤维水泥石电阻测试方法研究

准确测量碳纤维水泥石的电阻率是碳纤维水泥石的压敏和温敏性能得以应用的关键问题之一。已有研究表明 ,电阻率测量结果准确性受电极的制作形式及电阻的测试方法影响较大。本文在试验的基础上 ,分析了几种适用于碳纤维水泥石的电极布置形式的特点及两极法和四极法对电阻测试结果的影响。研究表明 ,碳纤维水泥石电阻宜采用插入式四极法测量。

锥形钢筋混凝土电杆的力学性能检测与有限元分析

为探求通过非破损检测方法有效评价锥形钢筋混凝土电杆的力学行为的方法,用回弹法检测推定了锥形钢筋混凝土电杆中混凝土强度,并用自行设计的试验装置测定电杆的实际力学性能;结合钢筋配筋情况,应用ANSYS有限元分析程序,计算了电杆的荷载-挠度关系和弯矩-应变关系,并与实测结果进行了分析对比.结果表明,应用无损检测结果,利用ANSYS有限元分析软件进行拟合,钢筋混凝土电杆中混凝土采用非线性弹性模型,钢筋采用弹塑性模型,采用以拉应力控制的破坏准则和位移收敛模式进行计算,可以得到与试验结果吻合度较高的稍端荷载-挠度、控制区弯矩-应变曲线及裂缝分布状态,从而可以较好地反映锥形混凝土电杆的力学行为.