Weiße Wannen mit hochwertiger Nutzung – Chancen und Risiken im Hochbau

Ausgehend von den Grundprinzipien der Konstruktion von Untergeschossen in der Bauart Weißer Wannen werden zunächst die Nutzungen in ihrer Veränderung im Verlauf der letzten 20 Jahre aufgezeigt. Es wird dargestellt, dass die moderne Nutzung von Gewerbebauten in den Untergeschossen zu einem sehr großen Anteil als hochwertig eingeordnet werden kann zur Unterbringung von Technik, Lagern oder Einzelhandel. Für diese Nutzungskonzepte werden die technischen und entwurflichen Randbedingungen von WU‐Konstruktionen diskutiert. Neben der Trennung von wasserundurchlässigem Rohbau und raumbildendem Ausbau werden Risiken der Undichtheit für unterschiedliche Bauteile einer Analyse unterzogen. Abschließend werden aus vorliegenden Erfahrungen Empfehlungen für die Konstruktion, Qualitätssicherung und Wartung von Weißen Wannen mit hochwertiger Nutzung ausgesprochen. Watertight Concrete Construction in High Quality Use Chances and Risks of Structural Engineering Coming from the basic principles of the construction of basements as a watertight concrete construction there will first of all be a presentation of its use and change during the last 20 years. It is going to be illustrated that a modern use of commercial buildings in the basements – i.e. placing of technics, storage or retail – can most often be classified as high quality. For these utilisation concepts the technical and design related boundary conditions of watertight constructions will be discussed. Besides of the separation of a watertight carcass and space creating construction there will also be an analysis of the risks of leakage for different structural elements. Concluding there will be recommendations resulting from present experiences concerning construction, quality assurance and maintenance of watertight concrete constructions in high quality use.     

Beton‐Bodenplatten für Hallen‐ und Freiflächen: Konstruktion und Bemessung

Concrete Floor Slabs for Indoor and Outdoor Areas – Design and Construction Concrete floor slabs for industrial buildings are used as driveways, stock areas and foundations, e. g. for high rack warehouses. It is very exacting to serve the customer's demands as for slippery safety, evenness, wear and chemical resistance, durability and stability. Especially for concrete floor slabs it is particularly important to have an entire view on the construction and building requirements to fix an economic solution in cooperation with the client. The aim of this article is to summarize the substantial design and construction rules for concrete floor slabs in order to facilitate the finding of an ideal solution.     

Zum Tragverhalten von Slim‐Floor‐Konstruktionen

Load Bearing Behaviour of Slim Floor Constructions The shear capacity of hollow core slabs is considerably reduced due to transverse stresses when the slabs are bedded on flexible supports (e.g. slender beams). However, a standardised design model has not been established yet to determine the residual strength appropriately. This paper describes full scale tests concerning the load carrying behaviour of hollow core slabs supported on steel beams, so‐called slim floor constructions. Recommendations regarding the design and the construction on flexible supports are given.     

Holz‐Beton‐Verbunddecken (HBV) – Neue Deckensanierungssysteme mit Vollgewindeschrauben,Stahlfaserbeton und Online‐Bemessungstools

Composite timber‐concrete structures – new floor renovation systems with fully threaded shear connectors, steel fibre concrete and online design tools. Composite timber‐concrete structures – efficiently static, oscillation‐technical and sound‐technical improvement of old timber joist floor systems. New products, design codes, approvals and investigation results are ready for online using in planning and structural design calculation.     

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.     

Holzbrücken – Erkenntnisse zum Feuchteverhalten in den Tragquerschnitten aus Langzeitmessungen

Timber bridges – Long term monitoring results of moisture diffusion in the load carrying cross‐sections Timber road bridges have been built worldwide for centuries. The high performance of wood is approved through many constructions. However, there are still doubts about using wood by the planning engineer, which reduce the number of realized projects. The moisture induced stresses in cross‐sections according to the varied ambient climate are mainly investigated under laboratory conditions. The results show that the moisture content changes differently over the cross‐section and leads to moisture induced stresses. The discussion about methods for the assessment of the moisture induced stresses in timber bridge cross‐ections is continuing. Results observed in the long term monitoring of seven timber bridges provide first guidelines for practitioners. For all constructions, the moisture content was measured regarding the ambient micro climate. As result, the influences according to the ambient micro climate are not insignificant. Positive is that the directly measured moisture content is less compared to the equilibrium moisture content calculated from the data of a close by meteorological station. The analysis of the moisture gradient over the cross‐section allows the definition of an active or passive zone.     

Konzepte des Verbundbaus für hohe Stanzlasten – Grundlagen und Anwendung

Concepts of Composite Constructions for High Punching Loads – Basic Principles and Application The bearing capacity of flat slabs is largely limited by deformation due to bending and punching resistance. By means of the use of punching shear cruciform head systems on the basis of building authority approval or engineering models of composite constructions, the punching loads can be increased considerably. The article at hand describes the beneficial use of punching shear cruciform head systems of composite constructions for highest punching loads in a flat slab of a transferring level taking the example of the new building of the Ernst‐August gallery in Hannover.     

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.     

Zur Ermittlung der rißbreitenbeschränkenden Bewehrung bei Zwang in erhärtenden Betonbauteilen: Die Problematik einer “ausreichenden” Mindestbewehrung

Determination of Crack Width limiting Reinforcement due to Constraint in Hardening Concrete If restraint‐induced tensile stresses can occur, for the guarantee of the serviceability and durability the appearing crack width has to be limited due to the purpose and the environmental conditions of the building up to now in accordance to DIN 1045 (Edition 7.88), section 17.6, and furthermore to DIN 1045‐1 (2001‐07), section 11.2. The control of a defaulted crack width has a key position within the standard for durability and serviceability of the structures. The parallel selection of constructive or concrete‐technological measures for the decrease of the restraint stresses is always reasonable, because the defaulted crack widths can be hold and in consideration of the minimum reinforcement und crack injection the building costs can be optimized. Although in the following only the limitation of crack width of early restraint stresses will be considered in the planning of bearing structure the development of further tension situation have to be included. For example, in external building members under winter conditions restraint strain can occur which lead to a crack force in connection with higher tensile strength, for which the minimum reinforcement is not sufficient.     

Übergreifungsstöße von Betonstahl in selbstverdichtendem Beton

Load Carrying Capacity of Lap Splices in Self Consolidating Concrete This paper presents the results of experimental investigations on the load carrying capacity of lap splices under compression and tensile forces in self consolidating concrete (SCC). The test program consisted of four full scale beam tests and three column tests. It was concentrated on two common types of SCC, a powdertype concrete with limestone powder and a combination‐type concrete with fly ash. Depending on the specific lap length l_s/d_s the transmission mechanisms as well as the distribution of the bond‐, steel‐ and concrete stresses within the joint area were examined. The research project was sponsored by the German Association of Structural Concrete (DAfStb – V429).     

Unterspannte Holzbalkendecke (UHB‐Decke) – Ein neuartiges Decken‐Sanierungsverfahren mit gekreuzten Vollgewindeschrauben

Screw trussed timber joist floor – a new floor renovation system with crosswise ordered fully threaded screws. The UHB renovation system makes possible static, oscillation‐technical and sound‐technical improvement of old timber joist floor systems without opening the bays. Crosswise ordered fully threaded screws take over the axial tensile and compression stresses. Besides a big translation module appears. He the compliantly connected bracing system very positively affects.     

Betonplatten unter Stoßbelastung – Fallturmversuche

In dieser Arbeit werden Fallturmexperimente an Stahlbetonplatten vorgestellt, die an der Technischen Universität Dresden durchgeführt wurden. Es wurden dabei Fallhöhen von bis zu 9 m realisiert. Eine Motivation für diese Experimente war es, das Wissen über nachträgliche Verstärkung von Stahlbetonplatten gegen Steinschlag oder harten Fahrzeuganprall zu erweitern und Möglichkeiten einer nachträglichen Struktursicherung näher zu untersuchen. Die experimentelle Zielstellung war daher, den Einfluss von Stoßgeschwindigkeit, unterschiedlichen Verstärkungsarten und Betonfestigkeiten auf das lokale Materialverhalten und globale Tragverhalten von Platten zu untersuchen. Für zwei der insgesamt 15 Platten wurden zusätzlich zur Standardbewehrung Bügel eingebaut, um die Durchstanzfestigkeit der Platten zu erhöhen. Für einen Teil der Versuchsplatten wurden Stahl‐ bzw. Carbontextilien als nachträgliche Verstärkung verwendet. Dabei konnte festgestellt werden, dass eine derartige nachträgliche textile Verstärkung das komplette Durchschlagen des Impaktors verhindert und daher eine wirksame Schutzmaßnahme, beispielsweise für Steinschlaggalerien, darstellt. Concrete Slabs under Impact Load – Drop Tower Experiments Impact experiments on reinforced concrete slabs are presented in this work. In order to analyse the behaviour of concrete under high strain rates, an impact mass was dropped from the maximum height of 9 m onto quadratic concrete slabs with a side length of 1 m. The aim of this work was to enlarge knowledge about subsequent structure protection against rock fall or vehicle impact. With this intention, experimental studies on impact velocity, reinforcement techniques were done to determine the influence to local material behaviour and global structure behaviour. Supplemental steel stirrup reinforcement was added to two of the 15 concrete slabs to increase punching resistance. Subsequent textile reinforcement was applied on six concrete slabs using steel fabric reinforcement as well as carbon fabric reinforcement. As a main result of this study it is shown, that a subsequent textile reinforcement prevents the perforation of the slab. For this reason, textile reinforcement can, for example, be used for protection component in rock fall galleries.     

Ermüdungsbeanspruchungen von Betonbrücken unter zunehmendem Schwerverkehr

Fatigue Life of Concrete Bridges under Consideration of Increasing Traffic Loads Increasing traffic loads lead to higher fatigue stresses on bridge structures. The effects on the stresses of the main load‐bearing structure depend on the load models representing weight and the ratio of the load model length to the bearing distance of the superstructure. Within a research project carried out on behalf of the Federal Ministry of Transport, Building and Urban Affairs several different bridge constructions (box girder bridge, skew slab construction, girder bridge with T‐beam elements) were analysed with respect to their fatigue strength. Hence, the stresses in concrete and steel components are examined on extensive numerical models in longitudinal and transversal direction. The fatigue investigations of these existing bridges are performed by specified load combinations according to the German Standard for the design of concrete bridges. Furthermore the future development of heavy traffic loads is included by calculating the effects of a 60to‐heavy traffic vehicle.     

Zemente mit mehreren Hauptbestandteilen im Betonbau

Cements with Several Main Constituents in Concrete Construction – Sustainable Solutions for Building with Concrete In view of the reduction of climate‐related CO₂ emissions in the cement industry the manufacture of cements with several main constituents is of particular significance. One reason is the production process, which is more energy‐efficient and more ecological compared to “traditional” CEM I‐cements (Portland cements). But also the durability and performance in their use in concrete constructions are reasons why Portland‐composite cements (CEM II) and blastfurnace cements (CEM III) have meanwhile reached a market share of about 65% in Germany. For a few years now, approximately only 30% Portland cements have been used throughout Europe – with a continuous downward trend. The application‐specific properties, the possible areas of use as well as the ecologic advantages of the cements with several main constituents used in Germany so far are described in the following and illustrated by two practical examples. An outlook into possible further developments is given by examples of the performance of new cements in concrete.     

Korrosionsmonitoring und Bruchortung in Spannbetonbauwerken – Möglichkeiten und Grenzen

Corrosion Monitoring and Fracture Detection in Prestressed Concrete Structures – Possibilities and Limits Corrosive influences may affect the long‐term functionality of prestressed elements of prestressed concrete constructions and may lead to catastrophic failure of the member. Hence, the objective of the condition assessment of prestressed components has to be detecting existing defects and damages of the prestressed elements, e.g. grouting faults, corrosion and steel fractures in time. For an objectively early diagnosis of corrosion damages on prestressing elements, the Structural Health Monitoring (SHM) based on non‐destructive testing and monitoring methods is predestined. In this contribution causes of tendon corrosion in prestressed concrete (PC) bridges will first be specified, furthermore advantages and the strategy of corrosion monitoring are presented. Afterwards the state of the research and art of non‐destructive techniques and evaluation (NDT/NDE) of the corrosion state and of fracture detection of the prestressed elements in bridges with its possibilities and limits will be discussed. In this context also innovative sensors and measuring methods developed by the authors at the iBMB within the collaborative research center (CRC) 477 “Structural Health Monitoring” will be introduced.     

Ganzfertigteile bei der Verbundfahrbahnplatte der Bahretalbrücke – Eine Revision nach Ausführung und baubegleitender messtechnischer Überwachung

Fertigteilbauweisen für die Herstellung der Fahrbahnplatten von Verbundbrücken konnten sich bei kleineren Brücken bereits durchsetzen. Verschiedene Bautypen wurden entwickelt: die VFT‐Bauweise, die Halbfertigteilbauweise, die Ganzfertigteilbauweise. Im Großbrückenbau ist die Anwendung, zumindest in Deutschland, bisher auf einzelne Fälle beschränkt geblieben und eine abgeschlossene Stufe der Entwicklung noch nicht erreicht. Die Ganzfertigteilbauweise, wie sie bei der Bahretalbrücke eingesetzt wurde, stellt eine Möglichkeit dar, die Vorteile der deutlich schnelleren Herstellung der Fahrbahnplatte im Großbrückenverbundbau effektiv zu realisieren. Besonderes Augenmerk ist bei der Bemessung und Konstruktion auf die Rissproblematik zu legen. Die hier aufgetretenen Rissbildungen begründen sich durch die unterschiedlichen Materialeigenschaften und Herstellungszeitpunkte der Fertigteile und der Ortbetonergänzungen. Mit Hilfe des baubegleitenden Messprogramms für die Bahretalbrücke konnten die Rissbildungen sowie insbesondere die Spannungen in den Anschlussbewehrungen der Fertigteile gut nachvollzogen werden. Letztere liegen aufgrund des “Sammelrisseffektes” deutlich über den Spannungen der Ortbetonbewehrung und können nicht einfach am Zustand II‐Querschnitt berechnet werden. Zusammenfassend kann für die Bahretalbrücke eine gute Beurteilung der Bauweise gegeben werden. Prefabricated elements for the floor system of Bahretalbridge. The construction of floor systems of composite bridges, using prefabricated elements in concrete, could already achieve acceptance for smaller bridges. Different types were developed: VFT‐types, semi‐precast construction, precast construction. So far there are only a few cases of prefabricated elements in concrete for bigger bridges in Germany. Using the precast construction presents a possibility to produce floor systems faster and more effective, as done with the Bahretalbridge. Special attention is to be turned to the calculation and construction of the crack formations. The crack formations seen in this particular construction happened because of the different material property and the production time of the prefabricated elements as well as the addition of floor systems. During the construction progress several measurements helped to understand the appearance of the crack formations. The stresses of the reinforcement between prefabricated elements and the in‐situ concrete are much higher due to the effect of accumulated cracks. Summarizing the construction of the Bahretalbridge was done in a decent way and deserves a positive evaluation.     

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.     

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.     

Die neue DAfStb‐Richtlinie “Vorbeugende Maßnahmen gegen schädigende Alkalireaktion im Beton”

The new DAfStb‐Guideline “Preventive Measures against detrimental Alkali‐Reaction in Concrete (Alkali‐Guideline)” In 2002 the German Committee for Structural Concrete decided to revise the Alkali‐Guideline. The motivation for the revision may be summarised as follows: – further developments in the german concrete technology – damage cases in concrete pavements – development of new rapid test methods – further specification of alkali reactive aggregates The contribution gives a detailed overview of the main amendments in the new Guideline and illustrates the background behind the key regulations.     

Stahlbeton‐Verbundkonstruktionen – Ein Bemessungskonzept für schubbeanspruchte Fugen. Teil 1: Korrelation zwischen Simulation und Bemessung

R/C Composite Constructions – A Design Concept for Shear Loaded Joints – Part 1: Correlation between Simulation and Design. In the modern engineering practice composite constructions are often used. This constructions consisting of prefabricated R/C components and in situ concrete are marked by the interaction of concrete interfaces with different age and different strength. With various examinations will be show, that the present designing practice and the distribution of reinforcement is not effective and leads to high reinforcement concentrations in uncritical joint sections and also to an unbalanced reinforcement along the joint. This paper is divided into 2 parts: Part 1 summarizes the state‐of‐the‐art, a special structural model and important results. A design concept, continued in part 2, will be presented for the practical use according to European standard EC 2, which enables the differentiation between narrow and broad bond surfaces for the first time. Additional, the new concept considers the non‐rigid bond and also decisive parameter in a subtly differentiated, nearly realistic and bearing structure referred way.