Improved design of tubular wind tower foundations using steel micropiles

The constant increase in the wind power production leads to the need of higher wind towers, which brings up some questions regarding the effectiveness of tubular towers and respective foundations. This work focuses on the comparative structural design, life cycle behaviour and costs of onshore concrete shallow foundations for tubular wind towers (WT) when steel micropiles are used to improve resistance of the soil–structure interface (hybrid foundation). Typical wind loading for Turbine Class II and moderate seismicity (.25 g peak ground acceleration) is used to design and analyse 18 WT foundation case studies. This allows the comparison between shallow and hybrid foundations designed for three different hub heights and respective turbine rated power (80 m/2 MW, 100 m/3.6 MW and 150 m/5 MW) and for three different tubular tower solutions (steel, concrete and hybrid steel–concrete). The possible benefits of the solution using steel grouted micropiles are discussed in terms of potential environmental and economic impacts using life cycle analysis. The use of micropiles reveals to be an interesting solution to improve common shallow WT foundations since it allows the reduction of the dimensions of the foundation leading to significant environmental and cost benefits.     

钢筋砼结构受硫酸盐腐蚀及其处理方法的几点探讨

为研究硫酸盐腐蚀下结构耐久性及其修复,本文主要针对钢筋混凝土结构,分析硫酸盐腐蚀的机理,论述了受蚀前提高钢筋混凝土结构耐久性的措施,探讨了修复和加固受蚀后钢筋混凝土结构的方法,并以一化工厂为例,在其受蚀后,采用添加一定比例外加剂的普通硅酸盐水泥进行修复,结果表明新老混凝土结合良好,工作状态正常。通过分析其腐蚀机理得到的修补措施行之有效。     

Stabilising the leaning tower of Pisa

 The 56-m high "leaning tower" of Pisa was constructed in three phases between 1173 and 1370 on the alluvial sediments of the River Arno, central west Italy. Although the tower deviated from the vertical at an early stage, the continuing tilt has led to concern about its safety. Having reviewed the construction of the tower and the underlying geology, the paper discusses the history of the tilting and describes the temporary remedial measures undertaken and permanent stabilization proposed. Received: 22 December 1997 · Accepted: 22 January 1998     

浅谈建筑塔机的使用安全

对塔机基础进行了介绍,并着重介绍了两种特殊情况下的基础处理,深入地探讨了塔机的安装与拆卸塔机的安全使用及群塔作业过程中应注意的问题,提出了群塔的运行原则,以保证塔机的使用安全。     

Bearing capacity of strip foundations in horizontal-vertical reinforced soils

The formula for calculating the ultimate bearing capacity of horizontal-vertical reinforced soil is investigated based on the failure mode and the mechanism of sand beds reinforced with horizontal-vertical reinforcement. Two components of soils and reinforcement are calculated separately. The ultimate bearing capacity of a shallow, concentrically loaded strip footing on homogeneous soil is commonly determined using the Terzaghi superposition method. The contribution of horizontal-vertical reinforcement is calculated based on the bearing resistance of the soil against the transverse members. A vertical inclusion is treated as a retaining wall, the confinement being calculated using Rankine's earth pressure theory. An analytical solution is presented including the traditional factors of soil, unit soil weight, footing width, number of horizontal-vertical reinforcement layers, and reinforcement geometry. The results were validated against experimental results and the mean error of the theoretical model was about 10%, with a maximum error of about 20%.     

Assessment of stainless steel reinforcement for concrete structures rehabilitation

The aim of this study was to revise the factors influencing the service life of galvanic coupling between carbon steel and stainless steel reinforcements in simulated concrete pore solution, simulating the condition of a damaged structure repaired with stainless steel reinforcing bars. Numerous investigations have reported that austenitic stainless steel rebar, compared to carbon steel, when embedded in concrete, offer superior corrosion resistance in aggressive environments, especially chloride contaminated concrete. In concrete, contact with other metals should be avoided because of the risk of galvanic corrosion. When passive, both carbon steel and stainless steel have comparable corrosion potentials and the coupling of the two materials is of little effect on the corrosion behavior of either material. Galvanic current values measured between carbon and stainless steel are negligible.     

谈输电塔螺栓连接设计

对输电塔连接螺栓的受力状态和可能出现的破坏形式进行了分析,通过研究孔壁挤压和螺栓剪切对节点螺栓个数的影响,提出采用临界厚度来判断螺栓连接控制因素的方法,总结了110 kV~500 kV输电线路角钢塔螺栓设计的注意事项和建议。     

浅谈混凝土结构工程修复加固技术

在过去的50多年间,我国的土木工程建设发展极为迅猛.建筑物和构筑物建造、使用中出现的质量、维护问题,及其老龄化问题,引起人们的高度关注和重视,各种修补加固方法也不断出现,笔者根据自身的施工经验,对钢筋混凝土结构的加固施工中所遇到的加固施工方案及施工方法进行简单的介绍,并对不同方案进行优化比较.     

Bearing capacity and failure mechanism of reinforced foundations based on rigid-plastic finite element formulation

A series of model loading tests on both unreinforced and reinforced foundations have been carried out, and in these tests the ground was modeled by aluminum rods. A rigid-plastic finite element analysis considering the effect of geometrical nonlinearity has been conducted to quantitatively investigate both the increase of calculated bearing capacity and the progress in deformation localization corresponding to the settlement of a loading plate. In the analysis, the reinforcing material and the surrounding soil were modeled as a composite material. Based on the comparative study between the test results and the numerical analysis, it is concluded that the proposed numerical method is capable of investigating quantitatively not only the bearing capacity but also the failure mechanism. In addition, the effectiveness of the proposed numerical analysis has been confirmed.     

水泥混凝土路面破损分析

对水泥混凝土路面断板进行了分类,分析了水泥混凝土路面早期开裂断板和使用期开裂断板的原因,提出了一些行之有效的预防与治理措施,从而减少路面断板数量,延长水泥混凝土路面的使用寿命。     

TCM870装载机变速操纵系统分析与修理

ＴＣＭ８７０装载机传动系统，采用三元件液力变矩器和定轴式常啮合动力换挡变速器，本分析了该机变速操纵液压系统的工作原理及特点，故障检测与诊断，并介绍了修理实例。     

水泥混凝土路面破损原因分析

主要讲述了混凝土路面破损的影响因素,并对破损类型进行了细致的分类,同时对路面破损原因进行了详细分析,从而解决了对破损道路进行维修、改造设计缺乏依据的问题.     

Study of the corrosion of reinforcement in concrete elements used for the repair of monuments

The conservation of cultural heritage is a demanding and imperative task. Of particular interest is the prevention of damage in monuments in load bearing elements made of reinforced concrete. In this case, the remediative intervention should be done with special caution, especially in places of the structure where earthquakes pose immediate threat for the integrity of historical monuments. The present work focuses on the problems associated with corrosion of steel in reinforced concrete, considered as a composite material consisting of steel and inorganic constituents. The study is concerned with S500s Tempcore^® steel and the associated corrosion phenomena, responsible for the degradation of the mechanical properties of the reinforced concrete. Corrosion of steel bars in reinforced concrete is attenuated due to either of the incomplete coverages of the metal with concrete, leaving it exposed to the aggressive marine environment or from galvanic corrosion. The latter is due to the presence of different types of metallic elements introduced by the welding process employed often in pre-earthquake and post-earthquake repairs in order to strengthen load bearing elements. In a microscopic scale the development of special conditions may lead to major damages of the structures. In the present work, we report on the results of mechanical stress measurements done on S500s Tempcore^® steel bar specimens. Prior to the stress measurements, the specimens were subjected to accelerated corrosion by exposure in salt spray chamber for time periods up to 90 days. Specimens in which welding side-by-side was applied were also exposed at the same conditions and the respective mechanical stresses were measured. The effect of increasing corrosion damage on the strength properties of the steel S500s Tempcore^® was moderate. The effect of salt spray exposure on the tensile ductility however was appreciable. All measurements have shown that corrosion had an adverse effect on the materials strength, while the ductility of the specimens was drastically reduced. The embrittlement of reinforcing steel due to corrosion was confirmed both by the gradual decrease of the specimens’ ductility and the examination of the morphology of the cross-section of the respective specimens by scanning electron microscopy.     

斜拉大桥塔梁混凝土应力监测与控制

结合工程实例，介绍了斜拉大桥塔梁混凝土应力监测与控制的过程．保证了斜拉桥在施工过程中的受力和变形状态始终处于设计所要求的安全范围。     

钢筋混凝土和钢纤维混凝土杂散电流腐蚀实验研究

依据地铁杂散电流对地下金属物质发生阳极氧化的电化学腐蚀机理,模拟了钢筋混凝土和钢纤维混凝土试件的杂散电流腐蚀实验。通过两种不同材料在相同的杂散电流环境中进行模拟腐蚀比较,分析了钢筋混凝土和钢纤维混凝土在抵制杂散电流腐蚀的耐久性和破坏形式方面的异同。结果表明,两种材料的耐久性能差异较大,破坏形式也不同,相同条件下,钢纤维混凝土的耐久性能显著降低。     

Stability of concrete retaining structures and their interface with rock foundations

Three failure mechanisms of concrete retaining structures situated on rock foundations: sliding, overturning and limit turning, are discussed. Investigations have shown that sliding is possible only in specific cases when weakened subhorizontal surfaces with low shear parameters are present near the interface between the structure and foundation. If these conditions are not present, then failure due to sliding does not occur. The classical overturning mode, which involves turning of the structure relative to the downstream toe, is not possible, as it requires unrealistic conditions of infinitely strong rock or concrete. The limit turning mode, which seems to be the most likely of the three, involves partial turning of the structure and is accompanied by downstream crushing and upstream rupture of the foundation. Finally, a practical method to analyze a structure's resistance to limit turning is presented, and preparation of the interface between a concrete retaining structure and its rock foundations, taking into account the specific characteristics of limit turning failure is discussed.     

清水混凝土在首都机场新塔台工程中的应用

首都机场新塔台参照国内外同行业相关经验制定了清水混凝土的质量标准,针对施工中可能出现的质量缺陷,精心进行了混凝土的配合比设计及试验工作,从施工中的源头混凝土自身的性能抓起,采取有效措施,确保清水混凝土表面达到平整光洁,色泽鲜明一致,线条清晰顺直的效果。     

重型塔吊基础沉降原因分析及加固纠倾技术

根据地层信息与基础沉降原因,制定合理的加固方案,采用格栅式旋喷桩加固某重型塔式起重机的基础,并在加固过程中持续进行沉降、垂直度等监测,同时制定符合该型塔机特征的纠倾方案,纠倾效果显著。     

Reliability-based management of inspection,maintenance and repair of offshore structures

Development of reliability-based management of inspection, monitoring, maintenance and repair (IMMR) of various types of offshore structures is described, with a focus on management of hull damage due to crack growth and corrosion. Operational experiences with respect to degradation of various types of offshore structures are summarized. The interrelation between design criteria and IMMR is emphasized. Explicit design for robustness in terms of an accidental collapse limit state and monitoring by the use of the leak before break principle to identify damage are highlighted. It is shown how design for robustness, choice of inspection method and scheduling as well as repair strategy, need to be implemented to obtain an acceptable risk for various types of offshore structures. Finally, the particular features of reliability based structural reassessment for extension of the service life, are briefly outlined and exemplified.