Behavior and modeling of high-strength concrete tied columns under axial compression

This article presents experimental and analytical results of 21 high-strength concrete tied columns under axial compression. Each 1500-mm-tall column had a 500 by 500 mm section reinforced with 12 D25 longitudinal bars enclosed by perimeter hoops only, or perimeter hoops plus typical crossties, or perimeter and intermediate hoops. The concrete strengths of cylinder tests ranged between 55 and 99 MPa. The column compression tests showed that the longitudinal bars could be laterally supported by hoop corners or 135-degree seismic hooks of crossties, but not restrained by 90-degree hooks, which lost effectiveness after spalling of cover concrete. The proposed analytical approach used the existing Mander model and the Euler equation to determine the confined concrete strength and the buckling strength of longitudinal bars, respectively. With rational assumptions of confinement effectiveness and unsupported lengths, the proposed analytical approach can well predict the complete load-deformation response of test columns.     

高温后C80高强混凝土的质量损失和抗压性能研究

对掺聚丙烯纤维的C80高强混凝土立方体试件模拟高温试验后,进行混凝土质量损失和抗压性能测试,研究分析了不同作用温度对聚丙烯纤维高强混凝土的质量损失和抗压强度的影响.结果表明,随着温度的升高,掺聚丙烯纤维高强混凝土的质量损失逐渐增加而抗压强度整体呈下降趋势,600℃高温后混凝土立方体抗压强度急剧下降,强度值仅为常温的25.05％;高温后聚丙烯纤维高强混凝土的相对质量损失和相对残余抗压强度的整体变化趋势基本相似.     

Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer

Carbon and glass fiber reinforced polymer (CFRP and GFRP) are two materials suitable for strengthening the reinforced concrete (RC) beams. Although many in situ RC beams are of continuous constructions, there has been very limited research on the behavior of such beams with externally applied FRP laminate. In addition, most design guidelines were developed for simply supported beams with external FRP laminates. This paper presents an experimental program conducted to study the flexural behavior and redistribution in moment of reinforced high strength concrete (RHSC) continuous beams strengthened with CFRP and GFRP sheets. Test results showed that with increasing the number of CFRP sheet layers, the ultimate strength increases, while the ductility, moment redistribution, and ultimate strain of CFRP sheet decrease. Also, by using the GFRP sheet in strengthening the continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase ultimate strength of beam. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. An analytical model for moment–curvature and load capacity are developed and used for the tested continuous beams in current and other similar studies. The stress–strain curves of concrete, steel and FRP were considered as integrity model. Stress–strain model of concrete is extended from Oztekin et al.’s model by modifying the ultimate strain. Also, new parameters of equivalent stress block are obtained for flexural calculation of RHSC beams. Good agreement between experiment and prediction values is achieved.     

Rail safety and rail privatisation in Britain

British Rail (BR), the former unified main line railway operator in Great Britain, was divided into about 100 separate organisations and privatised from April 1994. There was concern in the run-up to privatisation that the fragmentation of the system and the entry of new operators might compromise safety. This paper investigates what has happened to safety by analysing data on almost all fatal railway accidents, together with the most important non-fatal train accidents, from 1967 to 2003, with additional brief analyses back to 1946. BR had achieved downward trends in the mean numbers of accidents per train-kilometre for all the main classes of accident in the 27 years up to 1993, and the paper takes the extrapolation of these favourable trends as the yardstick by which to judge the safety performance of the privatised railway. The paper finds that the privatised railway had fewer accidents than this yardstick for all classes of accident. Only one indicator is adverse: the number of fatalities in train collisions and derailments is higher than expected, because of the severity of the accident at Ladbroke Grove in 1999. The principal conclusion is that there is no evidence that privatisation caused railway safety to deteriorate.     

数字技术在棒材成品飞剪电控系统的应用

为了解决棒材成品飞剪剪切倍尺精度不高,成材率和定尺率低,切损大,没有实现优化剪切等问题,在技术改造中采用了全数字电控系统,使飞剪剪切精度提高,由原来的剪切误差200 mm缩小到100 mm以内,有效提高了成材率和定尺率,对于现场备件储备和维护都比较方便,有效的提高了设备作业率.     

新型外包钢-高强混凝土组合梁的试验研究

针对普通混凝土组合梁在理论及工程应用上存的问题,首先提出了新型外包钢-高强混凝土组合梁,进行了8根足尺简支梁的试验研究,考虑的主要参数有截面几何特性、混凝土强度、跨高比等,分析了外包钢-高强混凝土组合梁试件荷载-位移曲线,荷载-应变关系和应变沿截面高度的分布,认为外包钢-高强混凝土组合梁具有较优越的力学性能和良好的工程应用前景.与一般的组合梁比较,其抗弯承载能力更高,延性好,施工方便,耐久性更高,整体经济效益优良,适用于跨度较大的结构.采用三维实体模型,对外包钢-高强混凝土组合梁进行非线性有限元分析,程序计算结果与试验结果比较吻合.     

高强度混凝土试验研究

高强度混凝土C80在建筑工程中的应用问题极为重要.为了使设计及施工单位正常设计及使用较高强度等级混凝土,扩大高强度等级混凝土C80在建筑工程中的应用,通过不同强度等级水泥、不同粉煤灰掺量、不同品种外加剂的混凝土进行试配试验,测定混凝土强度的变化过程,对水泥强度等级、粉煤灰掺量、外加剂掺量三者之间的相互关系进行了对比分析,得出了高强度等级混凝土C80在混凝土工程中应用的参考配合比.     

内燃机内甲烷水蒸气重整特性分析

为了较为系统地认识甲烷水蒸气重整反应对内燃机性能的影响。应用HSC 5.1软件对甲烷水蒸气重整反应在不同反应温度和水碳比的工况下进行分析,然后应用Chemkin-pro程序,计算了在相同供热量下甲烷水蒸气重整气在不同物质的量比下比CH_4的燃CH_4消耗降低率。结果表明,提高反应温度和水碳比可提高CH_4的转化率;当温度为700℃、水碳比为3时,发热量提高了13.58%,在供热相同情况下,燃CH_4消耗量可减少11.96%,CH_4的转化率越高,循环效率越高;重整气效率比纯天然气高,随着物质的量比降低,重整气优势降低。     

浅谈采用HSC新型灌浆材料进行隧洞阻水灌浆的方法

大伙房水库输水工程六河标段,围岩破碎、地下水丰富,开挖后仍然有大量渗、漏水,对二次混凝土衬砌施工产生了很大影响,为保证二次混凝土施工的质量,对严重渗、漏水部位采用HSC新型灌浆材料进行二次隧洞灌浆的方法,并成功抑制了大量渗、漏水的发生.