Ein Approximationsverfahren zur rechnerischen Bestimmung des Hydroabrasionsverschleißes an überströmten Betonoberflächen

An approximation procedure for computing of the hydroabrasion on surfaces of flow stressed hydraulic structures. Computations of the abrasion on surfaces of hydraulic structures subjected to extreme flow velocities are not practiced yet. However it is a fact that different damages particularly caused by abrasion on hydraulic structures are frequently detected and described. The following specified procedure allows to approximate the value of the wear of new concrete on the basis of Bania's [1] established correlation between compressive strength, stress‐time factor and the impacting kinetic energy. The angle of incidence, the flow velocity and the resulting transport of solids play a relevant role.     

Ein Ansatz zur versuchstechnischen Simulation und Übertragbarkeit der Hydroabrasion strömungsbeanspruchter Betonoberflächen im Wasserbau

An approach to the experimental simulation and transferability of hydroabrasion on surfaces of flow stressed hydraulic structures. Different damages particularly caused by hydroabrasion on hydraulic structures are regularly monitored and described in the technical literature. The following derived method using abrasion barrels describes an approach to the experimental simulation and transferability of diverse practically occured regimes of abrasion. Thus flowing waters possess variable parameters concerning flow velocities, mixtures of sediment and resulting bed loads. This context has to be attended both in designing of hydraulic structures surface and in experimental replication.     

Möglichkeiten zur Erhöhung der Festigkeit abrasionsbeanspruchter Betonoberflächen bei wasserbaulichen Anlagen

Possibilities for increasing the abrasion resistance of concrete surfaces in hydraulic structures. The results of abrasion test for textile reinforced concrete layers show that the abrasion resistance of the samples is dependent on the fineness of the reinforcement material as well as the fibre volume. High fibre volume can be achieved by a combination of textile reinforcement and short fibre reinforcement. These samples show reduced abrasion values of about 50% compared to the purely textile reinforced samples and likewise lower abrasion values to the non‐reinforced samples. Significant improvements concerning the abrasion behaviour are possible by further adjustment and optimisation of the used fine grade concrete matrices and the reinforcement materials. Beside a higher surface resistance of thin concrete layers against erosion and abrasion loads the use of near surface textile reinforcements leads to additional structural strength against other loads.     

A new method for evaluating the surface roughness of concrete cut for repair or strengthening

Deterioration to concrete structures usually starts at the surface and progresses into the structure. The deteriorated concrete has to be removed and replaced by new repair material, which leads to a composite concrete/repair material structure. In order to ensure full structural interaction between the old and new material, it is necessary to have a good bond between them. The bond itself depends on having a clean and rough surface. The importance of surface preparation and the effect of roughness have been emphasised by many researchers. In order to study the effect of surface roughness on the bond between a repair material and the concrete substrate, the roughness of the surface needs to be measured. No standard method for measuring surface roughness of concrete has been adopted. A range of methods are available and are in use for measuring the surface texture of concrete pavements in the highway field, but no method is accepted as standard. A new method of quantifying surface roughness is proposed and compared with the only method reported in the literature. In this new method (referred to as the roughness gradient method) a new method of describing the surface roughness is proposed. The surface of the cut concrete is defined as a series of irregular waves. The roughness parameter is dependent on the peak-to-trough depth and the respective wavelength. The method adopted using the ‘roughness gradient’ (R.G.) gave a better indication of the treated surfaces used in testing concrete repairs. Visual observation of the treated surfaces seemed to be in agreement with the R.G. parameters, while the method reported in the literature failed to define the roughness of the surface of the whole substrate in an accurate and comprehensive way.     

岩石节理吻合系数及其对节理特性的影响

根据节理表面的接触特性提出了一个节理几何特性的新参数──节理吻合系数 ＪＭＣ。实验显示，节理吻合系数是描述节理孔隙、形变、刚度、剪切强度和水渗导等特性的 重要指标。因此，将节理吻合系数和原有的节理粗糙系数相结合，可以更全面地描述节理的 几何特性，进一步估测岩石节理的水力特性。     

Sand–concrete interface response: The role of surface texture and confinement conditions

Sand–concrete interface direct shear tests were used to investigate the effects of surface roughness, surface waviness, mean sand diameter and relative density on interface strength and behavior under different confinement conditions. Extreme concrete surface textures, including smooth, rough and rough–wavy textures, were reproduced. Surface plowing was assessed via image analysis, laser scanning and extended multifocal micrographs. The experimental results showed that smooth concrete surfaces exhibited high values of interfacial–to–internal friction angle ratios, ranging 88–90%, due to the angular shape of sand particles. The rough concrete surfaces generated higher interface strength than smooth concrete surfaces; however, the interface strength was still inferior to the surrounding sand strength. Surface plowing, which identified a mixed shear plane at the sand–concrete interface, was developed as particles were detached from the surface, thus inhibiting the interface friction angle from reaching the sand friction angle. Higher sand–concrete interface strength was achieved as surface waviness increased, and interface friction angles greater than the surrounding sand friction angle were reached. Under a constant normal stiffness condition, significantly high interface strength is achieved due to the increase of the current normal stress, which was directly influenced by the initial normal stress, stiffness, surface roughness, mean sand diameter and relative density; surface waviness did not have a marked effect on the normal stress variation. Based on these results, multiple regressions were proposed to estimate the sand–concrete interface strength by the interfacial–to–internal friction angle ratio and the effect of the constant normal stiffness condition.     

分形理论在新-老混凝土粘结强度研究中的应用

介绍了对混凝土断裂面进行分形研究的重要性、分形理论及混凝土断裂面分析中几种主要的分数维测量方法.利用自行研制的分维仪对试验后的老混凝土断裂面进行测试,并应用分形几何这一理论工具对测试结果进行分析,得到了老混凝土断裂面的分数维与新-老混凝土界面粘结强度的关系.结果发现:用分数维来表征老混凝土表面的粗糙度,其预测结果精度较高;在粗糙度较高(分数维D较大)的老混凝土表面上浇注较高强度的新混凝土,获得的新-老混凝土界面粘结强度较高.     

Untersuchungen zur technischen Optimierung von Stahlbetonvorsatzschalen an bestehenden Wasserbauten

Investigations for the technical optimization of reinforced concrete lining at hydraulic structures. The reconditioning of defective concrete surfaces to hydraulic structures takes place usually with set forward linings of reinforced concrete. In the linings frequently cracking occurs. These cracks are caused by restaint due to the heat of hydratation of concrete. Serviceability and durability require the control of the crack width. On the basis of numeric computations and measurements in situ recommendations regarding the reduction of the cracking are presented.     

Neues BAW‐Merkblatt zur Bewertung der Tragfähigkeit bestehender massiver Verkehrswasserbauten

New BAW Code of Practice for the assessment of the load bearing capacity of existing solid hydraulic structures Many of Germany's solid hydraulic structures, i. e. structures made from concrete, reinforced concrete or masonry, are of above‐average age. For example, about a third of all locks for which the Federal Waterways and Shipping Administration (WSV) is responsible is more than a hundred years old. In other words they have exceeded the design lifetime of 100 years that is nowadays the requirement for such structures. Not only existing locks, but also numerous weirs and canal bridges show static characteristics, such as construction methods or very large cross sections, that are no longer common practice today. If any alterations are made to these structures, or if they exhibit visible damage, it is essential to re‐assess the statics of the supporting structure and perform new calculations to verify its conformity with stability requirements. This re‐assessment can be done with a new BAW‐Code of Practice „TbW”. In contrast to bridges and buildings, no adapted regulations have been released until now for re‐assessing the statics of existing solid hydraulic structures.     

Beschichtungen auf direkt befahrenen Tiefgaragenbodenflächen von Weißen Wannen. Physikalische Beanspruchungen – Planungsgrundlagen – alternative Beschichtungsvarianten

Coatings on directly vehicle‐carrying floor slabs of watertight concrete constructions in underground carparks physical stresses – design codes – alternative coating systems According to DIN 1045‐1 directly vehicle‐carrying park decks have to be realized with additional measures (crack‐bridging coating systems). At least surface protection system 11 (SPS 11) according to the Guidelines for the Protection and Repair of Concrete Components of the German Committee on Reinforced Concrete (DAfStb) are among others a possibility to meet this requirement. On the market available crack‐bridging coating systems with a general technical approval are not usefull on concrete surfaces with high water contents (water saturation values of 90 %) as they may occur in floor slabs of watertight concrete constructions. Experiences with practical damage cases show, that with approved SPS 11‐systems osmotic induced bubbles may occur preferably on backside saturated floor slabs of watertight concrete constructions. In consequence the physical stresses of a coating (osmotic processes, capillarity reactions, hydraulic pressures as well as gas pressures) will be quantitatively estimated and compared with the capability of market systems. Alternative coating systems are presented and practical recommendations in order to avoid damages are given.     

Improving the abrasion resistance of hydraulic-concrete containing surface crack by adding silica fume

Abrasion damage generally results from constant friction and impact of waterborne silt, sand, gravel, rocks, ice, and other debris on concrete surfaces during the operation of a hydraulic structure. In this study, a waterborne abrasion over a large area of the test slab was developed to investigate the influence of surface cracks on the abrasion–erosion resistance of concretes, with variable surface crack type and silica fume content. The test results concluded that: (1) the abrasion rate is higher for water flow impinging directly on the crack than that above the crack; (2) increased crack width reduces the abrasion resistance of the tested concrete; (3) the abrasion rate increased with the angle of the crack to the water flow; and (4) the abrasion resistance increased with the addition of silica fume for concrete having a surface crack. These findings and may be of interest to engineers designing concrete hydraulic structures.     

超高性能混凝土-普通混凝土界面抗剪性能试验研究

力学性能和耐久性优异的超高性能混凝土(UHPC)非常适用于损伤普通混凝土(NC)结构的修复加固,其中UHPC-NC界面的抗剪性能对确保良好的加固效果至关重要。论文通过7组抗剪推出试验,评估NC表面光滑、凿毛、露筋、刻槽、钻孔和植筋等UHPC-NC界面的抗剪性能和破坏模式;并利用斜剪试验,探讨UHPC龄期、NC基体湿润度、NC表面粗糙度和UHPC养护条件对界面抗剪强度的影响。试验结果表明,UHPC-NC界面抗剪黏结性能优异,界面破坏方式基本为NC剪切破坏或界面+NC破坏两种模式,未出现完全的界面剥离破坏。NC表面粗糙度是影响界面抗剪强度的主要因素,凿毛或刻槽的UHPC-NC界面获得了最佳的抗剪承载力,植筋和刻槽界面在抗剪破坏时表现出较好的延性。此外,NC越湿润,UHPC-NC界面的抗剪强度越高,在UHPC早期龄期(3～7d)时界面可获得绝大部分抗剪强度(88.5%～95.0%),在常温养护条件下UHPC-NC界面的抗剪性能优于高温养护界面。     

混凝土表面太阳辐射吸收系数测试研究

混凝土表面太阳辐射吸收系数是求解混凝土结构温度问题的重要参数之一.本文从热平衡的基本方程出发,提出了混凝土表面太阳辐射吸收系数的测试方法.并通过对不同表面性状混凝土试件的测试,研究了混凝土模板种类、混凝土表面色泽等因素对太阳辐射吸收系数的影响.文中给出了混凝土表面太阳辐射吸收系数的建议值,并讨论了减小结构日照温度效应的相关措施.     

Isogonal moulding surfaces: A family of shapes for high node congruence in free-form structures

The design of free-form structures is governed by structural and geometric considerations, the latter ones being closely linked to the costs of fabrication. If some construction constraints have been studied extensively, the question of the repeatability of nodes in free-form structures has rarely been addressed yet. In this paper, a family of surfaces that can be optimized regarding typical geometrical constraints and that exhibit high node congruence is proposed. They correspond to particular meshes of moulding surfaces and are called isogonal moulding surfaces by the authors. The geometrical properties of these surfaces are discussed. In particular, it is shown how to derive edge offset mesh from them. It is also demonstrated that they represent all the possible meshes parallel to surfaces of revolution. Finally, the reader is introduced to some computational strategies linked to isogonal moulding surfaces.     

Use of laser interferometry for measuring concrete substrate roughness in patch repairs

The overall success and long-term durability of a patch repair is significantly influenced by the bond developed at the interface between the concrete substrate and the repair material. In turn, the bond strength is influenced by the topography (roughness) of the substrate surface after removal of the defective concrete. However, different removal methods of defective concrete produce substrate surfaces with different topographies. Hence, the ability to measure and characterise the topography of substrate surfaces is of great importance for evaluating the effectiveness of different removal methods. In this paper, the effect of two removal methods: electric chipping hammers and Remote Robotic Hydro-erosion (RRH) on the surface roughness is investigated through the use of a prototype non-contact (optical) laser interferometry measuring device. Laboratory results show that the above equipment can be used to characterise substrate roughness and confirm the ability of RRH to create rougher surfaces as opposed to chipping hammers.     

Entwurf von Flüssigkeitsbehältern

Design of Liquid Retaining Structures – Remarks on the Rules of the Guideline “Watertight Concrete” The use of watertight concrete structures is regulated by the guideline “Watertight Concrete” of the German Committee of Reinforced Concrete, especially requirements on the serviceability limit states. The scope of the guideline is valid for liquid retaining structures too. The essential characteristic of those structures is their defined tightness. Design concepts in order to fullfill requirements on durability of concrete tanks are discussed. Moreover, recommendations due to the design of moderate prestressed reinforced concrete tanks are given, containing the durable filling of planned cracks. Design aspects of the European Standard EC 2 Part 3 are discussed too.     

现场无损检测法控制混凝土-混凝土界面的质量

在混凝土结构规范中,混凝土-混凝土界面抗剪强度的设计以"剪-摩理论"为基础。因此,抗剪强度很大程度上取决于混凝土表面的粗糙度。最新的研究聚焦在混凝土表面的纹理特征以及现场检测方法上,然而,这些方法只能在混凝土覆盖前进行表面的纹理评估。提出一种无损试验法对覆盖后混凝土基体的表面粗糙度进行评估。选择超声法、边界有限元法、有限差分法模拟不同材料和界面结构的双层板,对试验结果与数值计算结果进行了验证。研究表明:超声方法能够用于刻画同质两层板的界面结构,但是对于非均质材料,如混凝土,则需要进一步研究。     

Stabwerke auf Freiformflächen

Reticulated Structures on Free‐Form Surfaces. Promoted by buildings like the DG‐Bank in Berlin (Architect: Frank Gehry), the Arts Center in Singapore (Architect: Vikas Gore), the British Museum in London (Architect: Norman Foster) and recently the New Fair in Milan (Architect: Massimiliano Fuksas) with its roofs above the Central Axis and the Service Center, free‐form envelopes have become more and more popular in recent years. The paper is a brief review of the geometrical and the corresponding structural problems related to the design of those structures. In particular, a number of node connector types are described, which are essential for the realization of reticulated structures on free‐form surfaces.     

Application of distributed optical fiber sensors for the health monitoring of two real structures in Barcelona

The versatility and ease of installation of Distributed Optical Fibre Sensors (DOFS) compared with traditional monitoring systems are important characteristics to consider when facing the Structural Health Monitoring (SHM) of real world structures. The DOFS used in this study provide continuous (in space) strain data along the optical fibre with high spatial resolution. The main issues and results of two different existing structures monitored with DOFS, are described in this paper. The main SHM results of the rehabilitation of an historical building used as hospital and the enlargement of a pre-stressed concrete bridge are presented. The results are obtained using a novel DOFS based on an Optical Backscattered Reflectometry (OBR) technique. The application of the optical fibre monitoring system to two different materials (masonry and concrete) provides also important insights on the great possibilities of this technique when monitoring existing structures. In fact, the influence of strain transfer between the DOFS and the bonding surface is one of the principal effects that should be considered in the application of the OBR technique to real structures. Moreover, and because structural surfaces generally present considerable roughness, the procedure to attach the optical fibre to the two monitored structures is described.