冻融损伤对混凝土疲劳性能的影响

目的在于冻融损伤对混凝土疲劳性能产生的影响。通过分析研究冻融损伤对混凝土疲劳性能的影响,可以基于AC-13型、AC-16型、AC-20型3种不同级配的混凝土,通过模拟温差变化规律,进行冻融条件下的混凝土疲劳性能研究。结论证实,在实际混凝土施工中,随着混凝土冻融次数的增加,混凝土疲劳性能会逐渐下降,为避免冻融损伤对混凝土疲劳性能的影响,应该做好混凝土路面维护工作,避免冻融损伤,提高提高混凝土路面的使用年限与抗疲劳性。     

重载铁路用锻造高锰钢辙叉的结构设计和应用

高锰钢具有韧性好、承载硬化高、耐磨性好等优点,通过采用锻造的方法,在消除高锰钢铸造缺陷之后,高锰钢的性能将会大幅度提高。因此,为充分发挥高锰钢的性能优势,研制开发具有更高使用寿命的锻造高锰钢组合辙叉势在必行。中铁宝桥经过多年的技术攻关和工艺优化改进,成功开发了适合重载铁路锻造高锰钢组合辙叉产品,并在大秦、神朔等线路进行了上道试验,取得了良好的使用效果。     

既有铁路站场增建下穿框构小桥施工技术

主要介绍了既有铁路站场增建下穿框构小桥相关的顶进工作坑、D24型便梁加固既有铁路、框构小桥顶进、降水防水等施工技术,对既有铁路站场内增建下穿框构项目施工具有借鉴意义.     

某铁路车站地下组合结构疲劳适用性的研究

制定了某铁路车站地下通廊组合结构的疲劳荷载、动力系数、疲劳荷载循环次数等参数,并鉴于该结构处于初步设计阶段不具备具体构造细节的特殊情况,开发了一种非常规的疲劳评定方法对其疲劳适用性进行研究。研究结果表明,该车站地下通廊组合结构的疲劳性能能够满足铁路的运营要求,疲劳寿命能够达到100年以上。     

施工监测技术在下穿铁路工程中的应用

航新路位于东丽区中河村东侧,同时下穿既有津山铁路、在建津秦客运专线及京津城际延伸线。航新路下穿铁路北段U型槽及框构工程,包含12节U型(U17~U28)和一座联展东路框构20 m+14 m+20 m+19.97 m+32.06 m+16.42 m+7×20 m,基坑最大挖深7 m。文中详细介绍了施工监测技术在津山铁路、在建津秦客运专线及京津城际延伸线中的应用及监测效果,为同类型工程积累了丰富的施工监测经验。     

钩舌裂纹产生机理的分析与探讨

通过对机车车辆常用件13号车钩舌所产生裂纹的宏观和微观形貌进行了研究,并对其形成机理进行了探讨.结果表明钩舌裂纹既有典型的表面裂纹又有内部微观裂纹.其产生裂纹的主要原因是铸造过程中形成的组织缺陷以及钩舌在使用过程中的冲击和摩擦、磨损产生的应力集中.     

铸造十字形截面屈曲约束支撑的抗震性能试验研究

采用铸造工艺直接加工十字形截面核心的屈曲约束支撑(BRB,Buckling-Restrained Brace),避免在核心部件上直接施焊,可以消除焊接残余应力的影响。通过低周往复加载试验,研究了该类试件的滞回性能、骨架曲线、累积塑性变形、拉压不对称性、等效刚度等。试验结果表明,该类型的屈曲约束支撑可以避免焊接残余应力对试件抗震性能的影响,支撑试验滞回曲线饱满,具有稳定的受力特性,累积塑性变形基本达到200,且拉压不对称系数小于1.3,满足美国AISC钢结构规范的要求。由于铸造用钢有材料上的缺陷,导致试件没有获得较好的低周疲劳性能,但是对低周疲劳性能要求不高的承载型BRB仍具有一定的应用价值。     

大跨度框架桥顶进铁路既有线架空施工研究

结合孟平铁路增建二线梅园路框构顶进工程,对横抬梁与D型便梁相结合的方式进行了全面的探究,解决了铁路框构桥在顶进过程中线路不稳定、养护工作繁琐、人员配置多、顶进阶段久、安全风险大等缺陷。     

Q345-B H型钢的性能研究

在H300×300×10×15、H400×400×13×21、H500×200×10×16和H496×199×9×14等4个规格的Q345-BH型钢轧件的头、中、尾取样,进行腹板和翼缘力学性能、金相组织、晶粒度等检验,研究产品通条性能和腹板与翼缘性能的差异。     

铁路大跨度钢管混凝土拱桥拱肋管节点的疲劳性能研究

在研究大量资料文献的基础上,结合空间有限元分析,对比各种管节点疲劳检算方法的优缺点,研究了空心管节点疲劳检算方法在填心钢管-空心钢管节点疲劳性能分析中的适用性,对我国某在建大跨度铁路钢管混凝土拱桥(Y桥)拱肋管节点的疲劳性能作了可靠的分析评估,根据分析结果对该桥拱肋管节点的疲劳设计提出了合理建议.     

Fatigue life of the bolted yoke connection in single support beam (SSB) modular bridge expansion joints

The objective of this article is to demonstrate a comprehensive procedure for the estimation of the fatigue life of the component centre-beam-to-support-beam (CB/SB) bolted yoke connection. In this procedure, all the aspects are included such as fatigue vehicle loading, cycles per truck passage, lifetime average daily truck volume, fatigue classification of the detail and determination of fatigue infinite life. A typical single support beam (SSB) steel modular beam expansion joint (MBEJ) was modelled as 3D space frame. Moreover, three F.E. sub-models were created for the simulation of the (CB/SB) bolted yoke connection with preloaded bolts M16, M20 and M22 respectively. The Fatigue Load Model 2 (FLM2), recommended in EN 1991-2:4.6.4 for infinite fatigue life was chosen for the fatigue verification of the bolted yoke connection detail, assumed to be travelling at 90 km/h over the expansion joint. The 3D space frame was analysed by using Time-history dynamic analysis and thereafter, the calculated outputs were introduced in the F.E. sub-models. From the analysis of the sub-models the stress ranges were obtained and the fatigue evaluation of the yoke joint was performed. The investigation shown that poor detailing at the connection between the centre-beam-to-support-beam (CB/SB) bolted yoke connection is susceptible with reference to fatigue. Finally, important conclusions were extracted for both the behaviour of the entire modular joint and the fatigue life of the bolted yoke detail.

     

Use of foundry silica-dust in manufacturing economical self-consolidating concrete

This paper presents results of an experimental work conducted on the use of foundry silica-dust in self-consolidating concrete (SCC). A control SCC mixture was made, in which ASTM C 618 Class C fly ash constituted 40 mass% of the total cementitious materials. Three more SCC mixtures were made using silica-dust obtained from an iron foundry, collected by a high-efficiency baghouse. Silica-dust was used to replace 10%, 20%, and 30% of fly ash at a 1:2 (fly ash to foundry dust) ratio by mass. The extra amount of foundry dust was treated as very fine sand. Use of foundry dust in SCC resulted in high air content (7–10%), possibly due to reaction between foundry dust and the particular chemical admixtures used. With the increase in foundry dust content containing iron, the color of concrete changed to dark gray or black. At 30% replacement of fly ash with foundry silica-dust, the demand for high-range water-reducing admixture (HRWRA) increased. As the foundry dust content increased, the demand for viscosity-modifying admixture (VMA) decreased. It was concluded that foundry silica-dust material could be used in producing economical SCC.     

Functional and environmental performance of waste foundry sand applied in landfills

The use of waste foundry sand (WFS) up to 70% of soil mixtures in landfills has shown substantial promise, taking into account the great volume of this waste and the environmental parameters. The objective of this research was to investigate the utility and environmental benefits of a clay soil mixed with a waste foundry sand sample to cover landfills of solid waste. Environmental, physical, chemical and mechanical tests were performed on a sample of WFS and a mixture of soil plus 70% waste foundry sand.     

钢板-超薄UHPC-TPO组合桥面静力和疲劳试验研究

为探明钢-超薄UHPC （Ultra-high Performance Concrete）-TPO （Thin Polymer Overlay）组合桥面基本力学性能,设计5块钢-超薄UHPC-TPO组合板进行抗弯静力试验及疲劳试验。静力试验结果表明：在负弯矩作用下,UHPC层的开裂强度为22.1～24.3MPa;TPO先于UHPC进入非线性阶段。疲劳试验结果表明：若将此方案应用于虎门大桥悬索桥,则UHPC层在设计应力幅下疲劳开裂寿命可达925.7万次,TPO层将不会因疲劳而开裂;疲劳加载后,组合板剩余弯拉强度均值为26.9kN,整体抗弯刚度与静力试验结果相比仅下降13%。研究表明,钢桥面-超薄UHPC-TPO组合桥面具有优良的抗弯拉性能。     

Effect of used-foundry sand on the mechanical properties of concrete

Used-foundry sand is a by-product of ferrous and nonferrous metal casting industries. Foundries successfully recycle and reuse the sand many times in a foundry. When the sand can no longer be reused in the foundry, it is removed from the foundry and is termed used/spent foundry sand. In an effort to utilize used-foundry sand in large volumes, research is being carried out for its possible large-scale utilization in making concrete as partial replacement of fine aggregate.This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (regular sand) was partially replaced with used-foundry sand (UFS). Fine aggregate was replaced with three percentages (10%, 20%, and 30%) of UFS by weight. Tests were performed for the properties of fresh concrete. Compressive strength, splitting-tensile strength, flexural strength, and modulus of elasticity were determined at 28, 56, 91, and 365 days. Test results indicated a marginal increase in the strength properties of plain concrete by the inclusion of UFS as partial replacement of fine aggregate (sand) and that can be effectively used in making good quality concrete and construction materials.     

Properties of concrete using metallurgical industrial by-products as aggregates

The use of industrial by-products and waste materials in concrete opens a whole new range of possibilities in the reuse of materials in the building industry. In this research study, concretes were made with chemical foundry sand (QFS) and green foundry sand (GFS) as substitution for raw sand. Also Electric arc furnace slag (EAFS) and blast furnace slag (BSF) were used as substitution for coarse raw aggregates in 25%, 50% and 100% of concrete production. Two concrete production stages were carried out. In stages 1 and 2, slump test and compressive and tensile splitting strengths and modulus of elasticity were determined. Due to adequate properties of all concretes found in stage 2, length change (during 56 weeks), sorptivity and high temperature exposure evaluation were also determined. The tests results obtained from concretes produced in stages 1 and 2 were compared with those of conventional concrete (CC) and the adequate use of the by-products for concrete production was verified.     

大型模锻压机基础及深基础设计及施工

由于生产工艺的需要,大型模锻压机的地下泵站以及模锻压机基础的埋置深度都很大.某重机集团地下泵站的底标高是-13m,该部位承台底标高已达-15m,且地下泵站的尺寸是38.15m×66.6m,对厂房基础设计的影响较大.大型模锻压机厂房的上层行车的轨顶标高是36m,2台300t行车；如果承台底标高为-15m时,对厂房的基础设计与施工都是一个新的课题,本项目的目标就是研究在上述不利条件下,使厂房的基础设计与施工能满足我国规范的要求,满足吨位大、轨项高、精度高的厂房安全、经济、合理的设计理念.     

铁路工程用闪光对焊连接高强钢筋疲劳性能试验研究

针对铁路工程应用的HRB400、HRBF400、HRB500、HRBF500共4种规格的闪光对焊连接高强钢筋开展疲劳试验研究,其中每种规格的钢筋按直径可分为16mm、20mm、25mm和32mm四种类型。疲劳试验以高频疲劳试验为主,低频疲劳试验为辅,疲劳试验的应力比为0.2和0.4,试验共计完成285根试件,其中有效试件数253根,试件破坏数212根,试件未破坏数41根。得到各种规格高强钢筋的S-N曲线,共计19根,其中高频试验曲线16根,低频试验曲线3根,进而得出闪光对焊连接高强钢筋的200万次、500万次和1000万次疲劳寿命对应的疲劳应力幅,在统计分析的基础上,提出了考虑钢筋直径效应、疲劳应力比和钢材牌号影响的闪光对焊连接高强钢筋疲劳应力幅设计建议值计算式,为铁路设计规范的完善提供依据。     

冻融循环对轻质填料抗压强度的影响

通过对不同配合比的13组试样在不同冻融循环次数下的无侧限抗压强度试验,研究了冻融循环对轻质填料抗压强度与变形特性的影响.结果表明,轻质填料经历冻融循环后仍具有良好的力学性能,各组分对轻质填料抗冻融特性的影响程度不同,掺加水泥可有效抵抗冻胀力,EPS颗粒和粉煤灰在掺量适中的情况下,可显著提高轻质填料的抗冻融性能,水分是造成轻质填料冻融破坏的主要因素,在满足水泥水化所需水分的前提下,寒区工程中应用轻质填料需适当降低含水率.另外,在分析不同控制强度下轻质填料冻融破坏特点的基础上,分析了该轻质填料抗冻融破坏机理.     

Alpha and beta radioactivity in groundwater of the hickory,mid‐cambrian and ellenburger‐san saba aquifers,central texas,USA

Gross alpha and beta activity in sandstone and limestone aquifers of central Texas locally exceed drinking water standards. The Hickory (sandstone), Mid‐Cambrian (sandstone) and Ellenburger‐San Saba (ESS) (limestone) Aquifers registered median alpha levels of 13, 17 and 4 pCi/l, and median beta levels of 18, 17 and 4.5 pCi/l, respectively. Several observations, 46% (Hickory), 67% (Mid‐Cambrian) and 16% (ESS), exceeded the 15 pCi/l maximum contaminant level (MCL) for alpha activity. Fewer observations, 18% (Hickory), 0% (Mid‐Cambrian) and 10% (ESS), exceeded the 50 pCi/l level of concern for beta activity. There were significant positive correlations between alpha and beta activity in each aquifer, alpha activity and well depth in the ESS Aquifer, and beta activity and well depth in the Hickory and ESS Aquifers. Constituents of sandstone aquifers derived from underlying granite and groundwater moving through weathered zones in granite and overlying shale likely contribute to the radioactivity trends outlined above.