Fundamentplatten aus Stahlbeton und Stahlfaserbeton. Experimentelle Untersuchungen zur Gebrauchstauglichkeit und Tragfähigkeit

Reinforced Concrete and Steel Fibre Reinforced Concrete Rafts Experimental tests on serviceability and ultimate loading performance Houses and residential buildings are increasingly built on rafts instead of strip foundations. The main advantages of rafts are more efficient excavation works and easy concreting of the rafts itself. The use of steel fibre reinforced concrete slabs offers economic advantages if there are no special requirements on service ability such as water tightness or crack limitations. At Aachen University of Applied Sciences a comparative experimental study on the load carrying behaviour of rafts made of concrete, reinforced concrete and steel fibre reinforced concrete was carried out. The tests have proven steel fibre concrete as suitable material for rafts in case of sufficient stiffness of the subbase. In case of special requirements on service ability, reinforced concrete or combined fibre and bar reinforced concrete should be used. In that case stresses should be calculated based on the elastic theory.     

Zeitabhängiges Verhalten von Makrokunststofffaserbeton und dessen Einfluss auf die Bemessung von Industriefußböden

Time Dependent Behaviour of Macro Synthetic Fibre. Reinforced Concrete and its Influence on the Design of Industrial Slabs on Ground Material tests and tests on structural elements with synthetic macro fibre reinforced concrete are presented. The experimental program included the investigation of the load carrying capacity and the deformation behaviour under short‐term as well as under long‐term loading conditions. Long‐term load tests were carried out on pre‐cracked fibrereinforced concrete beams to measure the load level above which creep failure can occur. At service load level creep coefficients for a time period of up to three years were determined. Centre point load tests were carried out on concrete slabson‐ground. Two slabs were reinforced with steel mesh and two with synthetic macro fibres only. The tests were performed under short‐term and long‐term loading conditions over a period of 18 month. The current main application of synthetic macro fibre reinforced concrete is slab‐on‐ground. Slabs‐on‐ground can be designed under the assumption of elastic subgrade reaction. The concrete slab itself can be calculated either by elastic theory for uncracked concrete or by yield line theory taking fibre reinforcement into account. Based on the test results of the experimental programme, design recommendations for permanently loaded slabs‐on‐ground are presented.     

Feuchtetransport in Bauteilen aus wasserundurchlässigem Beton

Moisture transport through water‐impermeable concrete elements Frequently during planning construction elements made of water‐impermeable concrete it is disregarded that they are a matter of design, not of material. The article comments on different ways of moisture transport in water‐impermeable concrete elements and explains the state of the knowledge. It goes into the German guideline “WU‐Richtlinie” published by the German Committee of Reinforced Concrete (DAfStb) and discusses the consideration of moisture transport for the specification of the guideline requirements. Additional possible measures to be taken in cases of high‐quality classification of design utilization in accordance with the guideline are described.     

Zur Tragfähigkeit unbewehrter Betonwände

Load Bearing Capacity of Non‐Reinforced Concrete Walls The simplified approach for the design of compression members made of non‐reinforced concrete according to DIN 1045‐1 leads to large cross sections for slender walls with eccentric loading. Based on the principles of DIN 1045‐1 a design method is deduced in this article. The use of this method allows a simple, standardised and economic design of non‐reinforced compression members. A further increase in load bearing capacity can be achieved by taking into account the concrete tensile strength.     

Tragverhalten von textilbewehrtem Beton

Load‐bearing Behaviour of Textile Reinforced Concrete. Bond Cracking Behaviour and Load‐bearing Behaviour The load‐bearing behaviour of Textile Reinforced Concrete (TRC) is similar to concrete reinforced by steel, however, it is more influenced by the bond of the technical textile in the fine concrete. Thus the cracking behaviour, loading capacity, the deformation behaviour and the durability are investigated besides the material properties. Based on the results of these investigations, design models have been developed and first applications have been realized. The article summarizes the recent results in the field of load‐bearing behaviour of TRC.     

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.     

Feuchtetransport in Bauteilen aus wasserundurchlässigem Beton: Grundlagen und Praxisbetrachtungen

Moisture Transport in Components made of Water‐Tight Concrete Basics and Practical Considerations In water‐tight constructions, the concrete takes charge of a sealing function beside a load bearing function. A skin‐sealing on the surface is not necessary. The property of water‐tightness can be seen herewith as additional serviceability‐property. A very often occurring question is, whether despite the in soil appearing ground‐humidity or the upcoming water and the in concrete existing building moisture, dry interior rooms are achievable. To give answer to the questions, examinations by the help of a building physical calculation programme were carried out. Essential input parameters were calibrated in laboratory tests. A comparison of the inherent material moisture to the removable humidity by ventilation and to the humidity caused by using is given.     

Kein kritischer Wasserdampfdurchtritt in WU‐Betonkonstruktionen

No Crucial Water Vapour Penetration through Constructions, made of Concrete of High Resistance against Water Penetration Concrete constructions in groundwater in accordance with the WU‐guideline are not allowed to show wetness on the inside. A high‐quality using of such underground‐concrete‐constructions requires additionally a limitation of the penetrated water vapour. The investigations of the authors had shown that it does not come to any agglomeration of humidity behind a coating on the inner surface of a concrete‐construction in groundwater under the following conditions: crack‐free concrete, water pressure up to 5 bar, w/z ≤0.6, h ≥20 cm and not too dry concrete. Thus there is no threat of osmosis damage. The presented humidity profiles in drill cores, taken of constructions, which are in touch with groundwater since decades, confirm this: There is neither with nor without an interior coating any humidity concentration in the internal half of the groundwater‐ affected base plates detectable. This on the condition that the concrete is of high resistance against water penetration. In the presented new laboratory tests the penetration of watervapour through concrete cylinders, obeying the aforementioned concrete quality conditions, is measured for water pressure on one side: With 5 bar water pressure only a small range of water vapour penetrates, under atmospheric pressure (foot bath) there is no water vapour penetration registrated.     

Biegetragfähigkeit von textilbetonverstärkten Stahlbetonplatten

Textilbeton (TRC) ist eine sehr effektive Methode zur Verstärkung von Stahlbetonkonstruktionen. An der TU Dresden wurden im Rahmen des SFB 528 umfangreiche Forschungen zum Einsatz von Textilbeton zur nachträglichen Biegeverstärkung bestehender Beton‐ und Stahlbetonbauteile durchgeführt. Die experimentellen Untersuchungen erfolgten im Regelfall an textilbetonverstärkten kleinformatigen Stahlbetonplatten mit Spannweiten von 1,60 m und Plattendicken von 0,10 m. Parallel zu diesen Versuchen erfolgte die Entwicklung von Berechnungsmodellen, mit denen unter anderem die maximale Biegetragfähigkeit der verstärkten Bauteile vorhergesagt werden kann. Der vorliegende Aufsatz beschreibt experimentelle und theoretische Untersuchungen zur Überprüfung der Übertragbarkeit der bisher gewonnenen Ergebnisse auf großformatige Stahlbetonplatten mit Spannweiten von 6,75 m und Plattendicken von 0,23 m. Durch die Verwendung textiler Hochleistungsbewehrungen aus Carbon auf Basis von so genannten Heavy‐Tow‐Garnen wurden sehr hohe Verstärkungsgrade realisiert. Die Ergebnisse zeigen signifikante Steigerungen der Tragfähigkeiten im Vergleich zu unverstärkten Referenzplatten. Dadurch konnte die sichere Anwendung von Biegeverstärkungen aus Textilbeton auch für Bauteile mit großen Spannweiten und großen Verstärkungsgraden gezeigt werden. Gleichzeitig wurde bei vergleichbarem Lastniveau mit zunehmendem Verstärkungsgrad eine deutliche Verringerung der Durchbiegungen nachgewiesen. Die experimentell ermittelten Tragfähigkeiten sind mit dem vorgestellten Berehnungsansatz zur überschläglichen Biegebemessung textilbetonverstärkter Stahlbetonplatten gut nachvollziehbar. Bending Capacity of Reinforced Concrete Slabs Strengthened with Textile Reinforced Concrete Textile Reinforced Concrete (TRC) is a very effective method to strengthen reinforced concrete constructions. The SFB 528 of the TU Dresden has been carrying out vast research concerning the use of TRC for a subsequent bending strengthening of existing concrete and reinforced concrete components. As a rule the experiments TRC strengthened small format reinforced concrete slabs with span widths of 1.60 m and thicknesses of 0.10 m were used. Parallel to these tests calculation models were developed enabling a prediction of the maximum bending load carrying capacity of the strengthened units among others. The paper describes the experimental and theoretical research for checking the transferability of the results gained until now onto large‐size reinforced concrete slabs with span widths of 6.75 m and thicknesses of 0.23 m. Through the use of high performance textile reinforcements based on carbon Heavy‐Tow‐Yarns very high reinforcement degrees were realized. The results show significant increases of the load carrying capacity compared to the unstrengthened reference slabs. Thus the safe use of bending strengthening out of TRC for components with large span widths and high reinforcement degrees could be proven. At the same time we were able to demonstrate considerably lower deflection with growing reinforcement degrees. The experimentally determined load bearing capacity can be well comprehended with the introduced calculation models of the bending measurement of TRC strengthened reinforced concrete slabs.     

Hochleistungsbeton im Behälterbau

High Performance Concrete for tanks. By using High Performance Concrete durable water‐ and sewagewatertanks could be produced. To achieve an economic solution it is important to optimize the mixdesign of the concrete concerning its thermal characteristics and its applicability under site conditions. Regarding to that a mixdesign based on blast‐furnance cement could be developed by tests. To define the minimum restraint‐reinforcement in an expedient way, it is very important to determine and to consider the effects of actions during the construction phase realistically.     

Schädigung einer schlaff bewehrten Betonbrücke durch Verkehrsbelastung

Evaluation of Damage Due to Traffic on a Reinforced Concrete Bridge An investigation of the damage caused by road traffic on a reinforced concrete bridge was performed. Focus was given to damage induced by extra‐heavy vehicles. A damage model based on fatigue of reinforcement bars was employed. The stress cycles in the reinforcement bars were determined using measurements of the crack widths under traffic loading which were analysed using the rainflow method and Miner's rule. A monitoring system was mounted and used for seven weeks continuously to collect input data for the damage model. Computer software was developed to process the monitoring data in the sense of the damage model. The results indicate that a singular passage of an extraheavy vehicle over the investigated bridge causes damage equivalent to the damage caused by one day of average weekly traffic. The described method was developed and used for the first time in the described project.     

Stahlbetonträger mit Öffnungen. Ein vereinfachtes Bemessungskonzept

Reinforced Concrete Beams With Openings – A Simplified Design Concept – A comprehensive design concept for reinforced concrete beams with large openings was presented in Beton‐ und Stahlbetonbau 97, booklet 3, 2002. In recent years six laboratory tests were carried out to verify the design concept. Additionally extensive Finite Element computations with physically nonlinear material models were conducted to analyse the structural behaviour of reinforced concrete beams with opening groups. In this paper a simplified design concept for reinforced concrete beams with large openings and opening groups is presented which is based on the results of the test series and the FE‐computations.     

Querschnittsberechnung von Stahlbetonstäben – Stand der Forschung

Cross‐Sectional Analysis of Reinforced Concrete Beams – State of the Art Many common structures consist of one‐dimensional members. For such structures beam theory is applicable. Within beam theory, the material behaviour can be captured on cross‐sectional level. Regarding reinforced‐concrete structures, material nonlinearity has generally to be considered. The present article provides an overview of the state of the art in cross‐sectional analysis of one‐dimensional reinforced‐concrete elements. A crosssectional analysis describes the relationship between the internal forces and the generalized strains. There is a large number of different models, for which a classification is suggested here. Existing models can be classified into resultant models, truss models, uniaxial models, wall models, and finite element models. For each class, the characteristics are outlined and the most important models are presented.     

杜拉纤维水泥混凝土性能试验研究

通过室内试验,研究了杜拉纤维水泥混凝土的工作性、抗压强度、抗劈拉强度、收缩性能,并与普通水泥混凝土进行了对比分析.研究发现,在混凝土中掺加杜拉纤维对混凝土的劈拉强度有很大的提高,提高了约14.6%,对混凝土的早期抗收缩性能也有显著的提高.研究结果表明,杜拉纤维增强水泥混凝土具有许多优于普通水泥混凝土的优良特性.     

Zum nachträglichen Kürzen und Verankern von glatten Spanngliedern im Verbund

Investigations on the Cutting and Anchoring of Existing Prestressed Concrete Beams Post Tensioned with Smooth Bars SSB has planned to provide a new lift arrangement for an underground tram station in its existing structural system. For implementing this proposal, it is required to cut existing prestressed concrete beams which presently carry a 3‐lane road. The challenge is that tendons without ribs have to be anchored by bond strength of concrete. Therefore, first of all the bond behavior had to be studied and alternatively a new anchorage device was developed. Besides laboratory tests on bond behavior, one of the prestressing cables in the existing structure was cut at midspan, on which a number of strain gages were pasted in the anchorage zone near the cutting point in advance. Hence, a long‐term monitoring of strain release was carried out under service traffic load as well as under a special static load (48t crane). It was also possible to show, that, under non static loading the anchorage of the prestressing force could be ensured only by bond. Using the results obtained from the push‐in tests for the bond behavior, the results of the field test could be predicted very well. Furthermore, laboratory tests for the new anchorage device under static and cyclic loading were performed. The results show the feasibility of the proposed procedure. The test programme was rounded off by numerical investigations on the stresses in the anchorage zone.     

Transport von drückendem Wasser in Betonbauteilen

Effect of Water Pressure on Moisture Transport in Concrete Structural Components The effect of water pressure on moisture transport in concrete has been investigated. The uptake of water under pressure at an end surface of concrete cylinders and the release of moisture at the opposite dry surface were measured over a period of 500 days. In addition, ¹H NMR was used to observe directly the penetration of water into mortar prisms. The results show that penetration depth and amount of absorbed water are both limited by the self‐sealing effect in concrete. It is concluded that moisture transport through water‐tight concrete thicker than 200 mm is negligible for water pressures up to 5 bar. Self‐sealing also reduces liquid penetration when concrete is exposed to NaCl solutions under pressure. The penetration of salt solutions is slower than water, less liquid being taken up.     

Textilbewehrter Beton zur Verstärkung eines Hyparschalentragwerks in Schweinfurt

Textile Reinforced Concrete for Strengthening of a Hypar Shell Structure in Schweinfurt For the first time the innovative strengthening method was applied at rehabilitation and retrofitting of the shell structure of FH Schweinfurt. The reinforced‐concrete structure was strengthened by textile reinforced concrete and made safer for future. Since textile‐reinforced concrete is still no standardized construction material single case technical approval was given by the authorities for the application of textile reinforced concrete. This first practical application of TRC for strengthening was carried out in October/November 2006. The textile reinforced concrete strengthening was applied layer by layer on the sandblasted rough concrete surface. The strengthening layer is only 15 mm thin and consists of fine grained concrete and three layers textile fabric made of 800 tex carbon rovings.     

AKR‐Prüfverfahren: Auf dem Weg zur Performance‐Prüfung

ASR Test Methods: On the Way to Performance Testing To avoid a deleterious alkali silica reaction in concrete structures (ASR) the alkali‐reactivity potential of aggregates must be known. Then appropriate preventive measures can be applied when reactive aggregates are used. In the past the alkali reactivity of dense aggregates was tested with the concrete prism test with the 40 °C fog chamber method. Comparative investigations with storage in an outdoor exposure site confirm, that reactive aggregates, that have to be tested according to Part 3 of the Alkali Guidelines of the German Committee for Reinforced Concrete (DAfStb), can be identified in the laboratory test. For a quick assessment the 60 °C concrete prism test can be used as an alternative. Its suitability was confirmed by a comparison to the 40 °C fog chamber method. The assessment of the suitability of specific concrete compositions in performance tests is necessary to avoid excluding aggregates or cements unnecessarily from application as well as to simulate an external supply of alkalis if necessary. These tests give information about the possible appearance of a deleterious ASR with a specific concrete composition depending on the exposure or humidity class of the concrete. To develop such a performance test, the Research Institute of the Cement Industry examined, amongst others, cores from affected and unaffected concrete pavements in concrete prism tests with the 40 °C fog chamber method and 60 °C concrete prism test with and without an external supply of alkalis.     

Verstärken mit textilbewehrtem Beton

Strengthening with Textile Reinforced Concrete The strengthening by textile reinforced concrete noticeably increases both the ultimate load bearing behaviour as well as the serviceability. This will be shown in the paper using experimental results and numerical simulations of strengthened concrete members.