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Distributed strain measurements of prestressed concrete elements with fibre optic sensors The article presents the application of the technology of distributed strain measurements to prestressed concrete members. Distributed fibre optic sensing technology is based on light backscattering and enables strain measurements with high spatial resolution over the entire length of the optical fibre. Such an approach allows the replacement of thousands of conventional spot strain gauges, arranged in series, with a single optical fibre. The article presents composite fibre optic sensors and their application for strain measurements and crack development investigations. Three practical examples of prestressed concrete elements were described, namely truck scale platforms, prestressed concrete girders with a length of 24 meters, and one of the largest bridges in Poland. The structural members were analysed at different stages of construction, during fabrication and hardening, tendon activation, installation, proof loading, and also as a post‐installed measurement system. The aim of this article was to demonstrate the possibilities of measurements with composite distributed fibre optic sensors. [ABSTRACT FROM AUTHOR]

Influence of concrete shrinkage on crack widths in reinforced concrete members under direct loading Under long‐term loading, crack widths in reinforced concrete members increase due to the time‐dependent material behaviour of concrete. While many crack width approaches neglect shrinkage in crack width calculations, investigations in the literature indicate that shrinkage strains should be taken into account for crack width calculation. In order to classify the individual effects of shrinkage, bond creep and concrete creep on the crack pattern, they were analysed separately under direct loading. For this purpose, a parameter analysis was performed in the stabilized cracking stage with a rheological model validated by experimental tests to determine the proportion of concrete shrinkage on crack width increase. A comparison with the crack width approach of Model Code 2010 shows that the approach of Model Code 2010 is potentially well suited to describe time‐dependent effects realistically, but overestimates them. For this reason, the approach was modified without fundamentally changing the established crack width formula. With that modification, very good results were achieved in a further comparison. [ABSTRACT FROM AUTHOR]

Static analysis with linear elastic 3D building models – Effects of different modelling types on the vertical load distribution 3D building models are nowadays a widely used tool for structural analysis in practice. However, the determined load distribution using 3D building models sometimes differs significantly from the results of a conventional calculation with extracted 2D submodels. The background is that the results in a 3D calculation model are obtained with respect to the deformation compatibility in the entire structure, whereas the associated redistribution of stresses is neglected in a calculation with extracted 2D submodels. Using the example of a representative 15‐storey reinforced concrete high‐rise building with flat slabs and bracing core, different modelling approaches were therefore investigated in order to develop general recommendations for the practical application of holistic 3D building models. This article first shows to what extent the results of a linear‐elastic analysis with a 3D building model differ from those of a calculation with extracted 2D submodels. In addition, the influences from the construction progress, the soil‐structure interaction, the connection stiffnesses and the stiffness reduction of the slabs through bending crack formation are presented. Further influences on the load distribution in a holistic 3D building model as a result of the time‐dependent deformation behavior of concrete (viscoelastic consideration) are discussed in a further contribution of the authors. All in all, the various influences result in significant changes in the vertical load distribution, which are to be regarded in the practical application of 3D building models. [ABSTRACT FROM AUTHOR]

Concrete Hardening during traffic flow The elevated motorway Elbmarsch in Hamburg (K20) was completed in 1974. Featuring a total length of 3,8 km it is Germanys longest road bridge. In the course of upgrading the motorway A 7 the K20 will be broadened. For this purpose a composite girder is added to the superstructure consisting of precast girder elements. The deck slabs of the new and old superstructure are connected monolithically by filling a joint of 50 cm width between both of them with concrete. To test the conception and to get experience for the complete measure first a pilot of c. 100 m length was realized. The subsequent article refers about findings concerning hardening of the concrete in the joint under vibrations caused by traffic flow. The effects on the concrete strength, cracking and the bond of reinforcement were examined. [ABSTRACT FROM AUTHOR]

Experimental Investigations on crack formation in reinforced concrete due to restraint stress In the current Eurocode 2, a crack‐force‐based approach is used to determine the minimum reinforcement in restrained concrete members. Due to the tightening of the requirement by a change of the German national annex in Eurocode 2, an economic design is no longer possible. One of the reasons for the overdimensioning of the minimum reinforcement is that the design approach is based on incomplete empirical data and conservative assumptions. To investigate the influences on crack initiation and the effects of crack formation on restrained concrete members, precisely defined boundary conditions are necessary. These allow not only the comparability of the experimental investigations but also their reproducibility. The test setup used allows full restraint under constant climatic conditions of the test specimens. By systematic evaluation of selected tests, the crack formation of restrained plates is analyzed, allowing interpretations and the identification of basic phenomena. [ABSTRACT FROM AUTHOR]

Uniaxial tensile tests in textile reinforced concretes with inorganic impregnated carbon fibres The composite material textile reinforced concrete is being increasingly used in building construction. In particular carbon textiles are used with different impregnation materials, which are bound in mortar or concrete. Numerous research and practical projects have led to individual approvals for specific cases being granted and first directives for designing and using textile reinforced concrete being developed. The development and optimization of these materials still have huge improvement potential. Until now, most textiles have been impregnated with epoxy resin, styrene‐butadiene or acrylates. Beside the introduction of a polymer in the composite material, these polymers can cause load‐bearing capacity losses under temperature stresses above 80 °C. Mineral impregnation materials have hardly been researched, but are particularly interesting for use in drinking water structures in order to avoid polymer‐based materials. This publication shows that a very fine crack pattern can be achieved with inorganic impregnations of carbon rovings. Very small crack widths are particularly necessary in the repair sector, for example in the rehabilitation of drinking water reservoirs. In addition, mineral impregnations are less susceptible to temperature stresses. [ABSTRACT FROM AUTHOR]

Investigation on tension and bonding behaviour of basalt fibre reinforced polymers in concrete structures For retrofitting of RC structures, the concrete cover of the renewed reinforcement has to be sufficient to ensure the durability. Alternative reinforcement like rebars of basalt fibre reinforced polymers (BFRP) gives the possibility to minimize the concrete cover ensuring durable structures due to their resistance against carbonation and chlorides. In this paper investigations on load‐bearing behaviour of BFRP reinforced test specimens as an excerpt from a research project on basalt fibre reinforced concrete as repairing material with shotcrete and also basalt rebars as additional strengthening reinforcement for fair faced concrete facades are presented. The tested BFRP rebars show higher tension strength and lower Young's Modulus as comparable steel reinforcement bars. In centrical tension tests on the BFRP reinforced concrete specimen longitudinal cracking due to high tension in the contact zone and a higher number and also higher widths of crosswise cracking appear. The load bearing behaviour can be confirmed by numerical simulation. The results of the investigation with the incident light microscope on prepared specimen after tension tests show an enhanced number of microcracks in the contact zone between BFRP rebar and cement matrix. In pull out tests always the concrete failed, never the BFRP rebars. The results of this investigation confirm the possibility to ensure durable concrete structures using BFRP reinforcement. Further tests have been carried out on the flexural strength behaviour, the fatigue strength and durability. At the moment BFRP rebars of various designs are tested. [ABSTRACT FROM AUTHOR]

Germany's first application of UHPFRC in railway bridge construction Part 2: Accompanying scientific investigations and measurement supervision of manufacture and in operation Ultra‐high performance fibre‐reinforced concrete (UHPFRC) is characterized by an extremely dense microstructure and thus very high strengths as well as excellent durability properties. This enables a material‐saving and weight‐reduced, slim construction method that opens up completely new possibilities and areas of application in precast bridge construction. In the course of the superstructure renewal of an existing railway bridge the material could now be used for the first time in Germany for a railway bridge in a particularly practical and advantageous way. The superstructure was designed as a trough‐shaped precast slab bridge in prestressed concrete construction with a very low construction height. This part 2 of the article deals on the one hand with accompanying experimental investigations on crack formation and on the flexural behavior of a purely steel fibre reinforced mock‐up of the bridge superstructure. On the other hand, the technical paper deals with the measurement supervision of manufacture and in operation. In addition to determining losses of prestress and hydration heat development, structural measurements were also carried out to determine the real structural responses in the course of test loads with defined axle loads. [ABSTRACT FROM AUTHOR]

Abstract: Influence of Thermal Treatment on the Strength of Fine‐Grained Ultra‐High Performance Concrete (UHPC/RPC) By means of targeted specific thermal post‐treatment, the bending tensile strength and compressive strength of Ultra‐High Performance Concrete (UHPC) can significantly be increased. In most publications, a pre‐storage time of 1–2 days, a holding temperature of 60–90 °C and a dwell time of 24–48 hours are recommended [1, 2]. Own preliminary investigations on the thermal treatment of fine‐grained UHPC (RPC) at the Institute for Structural Concrete of the University Duisburg‐Essen showed that improved results could be achieved by other variations. Therefore, more detailed investigations were carried out on the pre‐storage time and the holding temperature of two different UHPC mixtures. Furthermore, the influence of protection of the samples against dehydration during the thermal treatment was investigated. The results of these studies are documented and evaluated in this publication. It was found that the treatment temperature has the greatest influence on the compressive strength. The protection of the samples was crucial for the flexural strength. It should also be noted that different thermal treatment regimes led to the best results for the various mixing compositions. [ABSTRACT FROM AUTHOR]

Abstract: Calculation of the deflection of reinforced concrete members – general procedures for slabs and beams This paper introduces the fundamental procedures to calculate the deflection in the cracked state taking into account creep and shrinkage. A range of different methods with various degrees of accuracy is presented for beams and one‐way slabs, based on the guidelines of EC2. For simple systems these methods can also be used for hand calculations, permitting a high degree of control over the procedure. Subsequently, the usually rather complex calculation of deflections caused by the shrinkage of the concrete is considered in more detail. For a selection of systems, diagrams containing coefficients for a more efficient estimation of shrinkage deflections can be derived. Furthermore, the cracked state deflection of concrete slabs is addressed more closely. It can be calculated with the help of suitable finite element programs or using simplified manual procedures. The basic principles can be transferred from the previously considered beam structures. However, other influence factors have to be addressed, such as the procedure to reduce the flexural stiffness and the redistribution of the internal forces caused by cracking. [ABSTRACT FROM AUTHOR]

Abstract: Sealing of joints in concrete with waterstops – the new German Standard DIN 18197 – Waterstops correctly designed, dimensioned and used The DIN 18197 “Sealing of joints in concrete with waterstops”, provides a set of rules for both, the planer and the contractor. In addition to relevant details for the design and the professional handling of waterstops on the construction site, selection diagrams are included which, in a simple way, allows the planner to select waterstops in dependence of the loads. This article addresses to the essential rules concerning the joint waterproofing with waterstop and explains by means of several examples and the DIN 18197 selection diagrams, how the planner can specify a waterstop complying with the loads. It is explained in detail what to consider when dealing with waterstops on the construction site. [ABSTRACT FROM AUTHOR]

Abstract: Crack geometry in reinforced concrete construction – A modified view of the measurement and definition of crack width Cracks are part of everyday reality in reinforced concrete construction. Nevertheless, there is no standard for crack width measurements, but only for the determination of calculated values of the crack width. There is also no control of how the measured and calculated values have to be adjusted. A comparison between measured and calculated values is currently associated with larger scatters. The measuring methods used – optical measurement or displacement measurement – result in different measured values for the same crack. The displacement of the crack edge (distance measurement) is always slightly larger than the crack gap width (optically measured). This is due to plastic deformation of the crack ridge surfaces during crack formation with a strain of up to about 0.1 mm, which is detected during distance measurement but not during optical measurement. The two measured values are only compared with the crack width. A certain proportion of the scatter in the comparison between calculated and measured values is attributed to this difference. The formation of microcracks along the transfer length leads to deformations and a reduction of the crack width at the surface of the reinforcement steel. This leads to the proven changes in the crack width within the concrete covering, which have led to incorrect definitions of the calculated crack width. The differences in the measurement results have an effect on the calibration and prediction of the calculated values for small crack widths as well as the assumptions about the self‐healing probability. [ABSTRACT FROM AUTHOR]

Abstract: Influence of lateral constraint on the loadbearing and deformation characteristics of hollow core slabs in fire Prestressed hollow core slabs (HC slabs) are used particularly as ceiling systems in building construction for economic reasons. In 2007, a fire incident in a car park in Rotterdam caused partial detachment of the bottom concrete layer [1]. This resulted in a Europe‐wide discussion on the fire safety assessment of this type of construction. By now, many expert opinions, literature analyses and recent research on the fire resistance of constructions of prestressed hollow core slabs exist [2]. In the investigations, the bearing behaviour of HC slabs with rigid support, in particular with regard to the lateral force bearing capacity, was investigated among other things. Until now in the testing and evaluation of prestressed hollow core slabs in fire the obstruction of thermal induced lateral expansion is hardly considered. In practice, in case of fire an obstruction of the lateral expansion of the HC slabs may occur, if there is a very stiff boundary around the fire‐exposed ceiling area, e.g. by staircase cores or surrounding ceiling areas without any fire exposure. To investigate this question, appropriate experimental and numerical investigations were carried out at BAM on ceilings made of prestressed concrete hollow core slabs with different lateral restraint [3]. This article describes in detail the fire tests carried out in real scale and the results obtained from these tests. The investigations carried out at BAM have shown that with an increase in the lateral constraint, the horizontal cracking in the webs of the HC slab increases and the longitudinal cracking decreases. Despite the distinctive horizontal crack formation, the fire tests did not show a detachment of the bottom concrete layer. Likewise, there was no negative influence of the horizontal cracks on the load‐bearing and deformation behaviour of the fire‐stressed ceiling construction. The results from the fire tests will be available for the validation of numerical models in the future. [ABSTRACT FROM AUTHOR]

Abstract: Investigation of the crack developement in the historical piers of the bridge across the Elstertal close to the village of Pirk The construction works for the bridge over the Elstertal in Pirk started in the year of 1938 and were stopped 1940 because of World War II. Until then the bridge piers made of tamped concrete and granitic masonry and the arches between the piers were built so far. Because of its location in the border area of the GDR the bridge remained unused until it was refurbished and completed by the construction of the missing superstructure in 1993 after the German reunification. Since then vertical cracks developed in the granitic masonry of the pier heads. In order to determine the causes of the crack development first finite element analysis were performed to investigate the bearing behavior and the stresses in the piers and especially in the pier heads. Furthermore, nonlinear finite element analysis of the granitic masonry were conducted in order to evaluate the tensile stresses which can be carried until a crack occurs. [ABSTRACT FROM AUTHOR]

Abstract: Double wall systems in pressing groundwaterplanning – regulations – waterproofing – construction – typical errors The use of double wall systems in a pressing groundwater requires a special care during design, execution and supervision. This article highlights fundamental background information, explains typical faults and gives advice for the avoidance of them. [ABSTRACT FROM AUTHOR]

Abstract: Subsequent installation of ”white tank“ waterproof concrete basements in existing buildings Cases of damp damage, which are due to changed groundwater conditions in combination with construction that is not suitable for the exposure, have increased in recent years all over Germany. The affected basements often not only have to be waterproofed but also structurally strengthened. In the following article, various methods are described to waterproof and simultaneously structurally strengthen the affected buildings, depending on the relevant local conditions, by installing a waterproof concrete basement designed to resist water under pressure. [ABSTRACT FROM AUTHOR]

Abstract: Planning and execution of joints and joint sealing and waterproofing solutions for watertight concrete structures Watertight concrete structures, so called ”White Tanks“ or ”White Boxes“, generally have to prevent water penetration into the structure, or to its contents; alternatively they are designed and built to prevent water leakage from the structure, or to do both. In many cases joints in structures of waterproof concrete turn out to be a weak point. For this reason in watertight concrete construction works, the design engineers and the contractor must pay special attention to the waterproofing solutions for all of the joints. Construction joints, movement or expansion joints, controlled crack induced joints and penetrations are sealed and made watertight. Therefore the responsible engineer needs to have a good knowledge of the different joint sealing and waterproofing solutions that can be used. This article goes into the details of the different joint sealing and waterproofing systems and the basic rules for sealing. [ABSTRACT FROM AUTHOR]

Abstract: Waterproof concrete constructions – recommendations for the cooperation of client, planner, special planner and contractor For a successful implementation of waterproof concrete constructions, a particularly high planning and execution quality is essential and the monitoring of the execution is required. The present paper provides advice and assistance to builders, designers and contractors for the design and execution of waterproof concrete constructions. [ABSTRACT FROM AUTHOR]

Abstract: Essential changes in the new DAfStb‐Guideline on watertight concrete structures 2017 he DAfStb‐Guideline on watertight concrete structures (WU‐Guideline) of 2003 has been reviewed and is finished as new issue in 2017. In this process the gathered experiences and new knowledge has been considered. Essential changes and additions in the WU‐Guideline are the required design steps, an informative annex for coordination of the responsibilty for design parts, the introduction of rules for watertight concrete roofs, the using conditions of the design principles, increased requirements for design principle (b) with self‐healing of cracks and also for watertight element walls and the improvement of the readability and understandability as well as refined obligations of documentation. The use of the WU‐Guideline for high‐grade used basements requires a rethinking by using the design principles from calculating to construction with lower imposed deformations. [ABSTRACT FROM AUTHOR]

Abstract: Impermeable concrete constructions – Legal considerations Ensuring defect‐free sealing of a building is of utmost importance if it is to be fit for use. As a result, the requirements imposed by German case law on the planning and execution of impermeable buildings under case law are very high. To avoid damage and liability the parties involved in construction must take account of the requirements they are expected to fulfil. The principal may specify the attributes and the quality (Beschaffenheit) of the building to the contractor. These may go beyond the recognised rules of technology, in which case this will be a decisive factor in judging whether the construction is free of defects. The architect commissioned by the principal to design the impermeable construction must always choose the safest planning option, which he can be entirely sure will satisfy the specific requirements. [ABSTRACT FROM AUTHOR]

Zusammenfassung: Forschungsvorhaben wie die „Materials Genome Initiative“ haben zum Ziel, Werkstoffe skalenüberbrückend zu beschreiben. Die einzelnen Elemente ihrer Mikrostrukturen spielen dabei eine ähnliche Rolle wie das Genom einer Zelle in der Biologie. Das genaue Verständnis des Zusammenhangs zwischen der Mikrostruktur von Werkstoffen und ihren makroskopischen Eigenschaften soll es ermöglichen, diese zielgerichtet für bestimmte Anwendungen zu designen. Auf der Mikroskala können physikalische Ab‐initio‐Modelle ihren Vorteil einer hohen Vorhersagekraft ausspielen, zudem benötigen sie wenige freie Parameter. Da die Rechenkapazität von Computern beschränkt ist, erfordert die skalenüberbrückende Materialmodellierung ein geschicktes Kombinieren von mikro‐, meso‐ und makroskopischen Ansätzen. Die amerikanische „Materials Genome Initiative” hat zum Ziel, Werkstoffe skalenüberbrückend zu beschreiben. Auch die europäische Forschung will physikalische Ab‐inito‐Modelle für die atomare Skala erfolgreich mit meso‐ und makroskopischen Modellen der Material‐ und Werkstoffwissenschaften verknüpfen, um Werkstoffe gezielt designen zu können. [ABSTRACT FROM AUTHOR]

Impact of a concrete coating on the reinforcement corrosion in cracked concrete Cracks in reinforced concrete structures exposed to chlorides can significantly impair the durability. Cracks are a fast pathway for chlorides and corrosion initiation of the reinforcement is more likely. Relevant standards [1, 2] require additional measures to prevent chloride ingress into structures exposed to chlorides such as parking decks. Additional design principles to ensure the durability of parking decks are given by the German Society for Concrete and Construction Technology (DBV) [3]. One principle consists of the application of a crack bridging concrete coating to prevent further chloride and moisture supply once early cracking is completed even though chlorides are already present in the crack. This recommendation is in line with the repair principle W-Cl according to RL SIB [4] and the procedure 8.3 DIN EN 1504-9 [5] respectively with the objective to increase the concrete resistivity. In an extensive experimental study it can be shown that concrete coating prevents corrosion and can even stop macro cell corrosion successfully in bending cracks with short-term chloride exposure. The repassivation is based on the increase of the anodic polarization resistance due to oxide layer formation and/or limited supply of chlorides. The concrete resistivity increases as well because of ongoing drying of the concrete but its effect on the macro-cell activity is negligible. It remains to be determined which amount of chlorides can be left in the concrete to exclude on-going reinforcement corrosion reliably. [ABSTRACT FROM AUTHOR]

Design of industrial concrete floors The German Society for Concrete and Construction Technology (DBV) has completed a significant revision to the Guide to Good Practice 'Industrial Concrete Floors for covered and open areas' from the year 2004. The new Guide to Good Practice 'Industrial Concrete Floors' (version February 2017) deals with special requirements for the planning, design, detailing and construction of industrial concrete floors for covered and open spaces. It contains significant variations to the safety concept through the reduction of partial safety factors for non-load bearing and non-stiffening industrial floors on grade. In addition, design principles with varied approaches to cracking of the concrete are introduced. This Guide to Good Practice is intended to be an aid to all members of the construction team (owner, planer, contractor), with the aim to realize a project which satisfies the owner and end-user requirements, within the technical framework and project constraints. In the present article, innovations relating to the design and construction rules for non-load-bearing and non-stiffening industrial concrete floors are presented. [ABSTRACT FROM AUTHOR]

During hardening of concrete temperature depending strains occur. In the same period the material properties young's modulus, compressive strength and tensile strength etc. develop. Because of the reason that resistances and stresses are developing dependent the ongoing hydration a time history calculation is one way to calculate the ability to crack in every single time step. In a research project about decreasing the cost of reinforced concrete protection measures against natural hazards in water engineering the influence of different cement types on the possibility to get cracks because of restraint is worked out. This paper gives a detailed description of the used ABAQUS Finite-Element-Model. Two aspects of the results of the calculations are pointed out: The influence of different cement types on the crack ability and the consequences of different age of the concrete when the formwork is removed. [ABSTRACT FROM AUTHOR]

Mechanical model with aggregate interlock for pry-out failure of composite dowels in cracked concrete The shear capacity of composite dowels with pry-out failure decreases in the presence of transverse concrete cracks. Concrete cracks induce a detachment of the pry-out cone. Here, the shear force transfer is limited to crack friction. The well-known design models for composite dowels do not account for concrete cracking. Therefore, they usually overestimate the shear capacity of composite dowels with pry-out failure in cracked concrete. To prevent an unsafe shear design, the present paper describes a novel physical approach for the pry-out failure in cracked concrete. The developed engineering model can be applied to cracked and uncracked concrete slabs and shows good agreement with experimental investigations. The engineering model is validated by a comprehensive test data base and converted into a safe design model. In the future, it can be assigned to other issues (for example to fasteners and studs in cracked concrete). All investigations are part of [1], where they are documented in detail. [ABSTRACT FROM AUTHOR]

Guideline for the assumption of the effective concrete tensile strength within the minimum reinforcement check due to early cracking according to Eurocode 2-2 (DIN EN 1992-2/NA) In December 2015, the A1-amendment [1] for the German National Annex [2] of DIN EN 1992-1-1 was published. The amendment affects among others the assumption of the effective concrete tensile strength within the minimum reinforcement check due to early cracking. The following contribution elucidates the background, why a respective A1-amendment for DIN EN 1992-2/NA has not been provided. Furthermore, the main differences between building- and bridge constructions are outlined in order to constitute the different approach. [ABSTRACT FROM AUTHOR]

Crack width control according to Eurocode 2 - Explanatory notes on factor k c Reinforced concrete members are designed now according to EC2 [1]. A significant aspect is the determining of the minimum reinforcement area specified in section 7.3.2. Due to the shortened illustrations of the equations (7.1) and (7.2), the mechanical background is difficult to be highlighted. This often results in inaccurate use of the model parameters, which might lead to an unsafe design, particularly for members predominantly reinforced only by the minimum reinforcement. Therefore the mechanical background of the equations (7.1) and (7.2) is focused on in this contribution. Proper discussions and explanations might help the structural engineer in the practical design. [ABSTRACT FROM AUTHOR]

Die experimentelle Bewertung eines Stahlbetonbauteils mit der Gefahr eines möglichen spröden Schubversagens ist aufgrund der geringen Duktilität und damit Vorankündigung des Versagens bisher nicht durch die Richtlinie für Belas‐tungsversuche des DAfStb abgedeckt. Dieser Beitrag fasst die theoretischen und experimentellen Untersuchungen aus [1] zusammen, die durchgeführt wurden, um eine sichere experimentelle Tragsicherheitsbewertung bei vorwiegender Schubbeanspruchung zu ermöglichen. Um die spröden Versagensprozesse während des Versuchs zeitlich und räumlich besser auflösen zu können, wurde eine Kombination modernster Messverfahren eingesetzt. Es werden die Ergebnisse der experimentellen Untersuchungen berichtet und Empfehlungen für die experimentelle Versuchsdurchführung abgeleitet. Experimental Evaluation of the shear bearing safety The experimental evaluation of a reinforced concrete member with the danger of a brittle shear failure is yet not covered by the Guideline of the DAfStb for load testing because of the low ductile failure process. This paper describes the theoretical and experimental investigations carried out in [1] to allow a safe evaluation of the shear bearing safety in‐situ. For a high resolution of the beginning failure processes a combination of modern measuring techniques was applied. The results of the experimental investigations are shown and discussed. Finally advises are given for the experimental evaluation of the shear bearing safety during load testing of reinforced concrete members. [ABSTRACT FROM AUTHOR]

Um das tatsächliche Verhalten von Stahlbetonbauteilen unter vorwiegender Zwangbeanspruchung experimentell zu untersuchen, wurde an der Technischen Universität Graz ein neuer Versuchsaufbau konzipiert. Im Vordergrund steht hierbei die zusammenhängende Betrachtung der Spannungsgeschichte und Rissbildung, beginnend mit der erhärtungsbedingten Zwangbeanspruchung (früher Zwang) und der anschließenden Überlagerung mit weiteren Zwangbeanspruchungen in der Nutzungsphase (später Zwang). Ziel der experimentellen Untersuchung war es, die verbleibenden Zwangspannungen nach Spannungsrelaxation und Rissbildung zu quantifizieren sowie die Rissbreitenentwicklung im Nutzungszeitraum zu beobachten. Für den frühen Zwang wurde hierbei besonderes Augenmerk auf den Einfluss der realistischen Behinderungssituation (in der Regel teilweiser Zwang) und der thermischen Randbedingungen (insbesondere Auswirkungen thermischer Nachbehandlungsmaßnahmen) gelegt. Im späten Zwang fällt vor allem der Berücksichtigung des Bauteilzustands (Einzelriss oder abgeschlossenes Rissbild) eine entscheidende Rolle zu. Mit den Versuchsergebnissen kann gezeigt werden, dass die Effektivität von thermischen Nachbehandlungsmaßnahmen zur Vermeidung von Trennrissen sehr begrenzt ist und eine getrennte Betrachtung von frühem und spätem Zwang nicht immer zu einer sicheren Bemessung führt. Restrained Concrete Members - New Findings from Systematic Investigations with Restraint Frames for Reinforced Concrete In order to investigate the real structural behaviour of reinforced concrete members mainly subjected to restraint a new experimental set-up was designed at the Graz University of Technology. In the focus of interest is the continuous investigation of the stress history and crack development starting with restraint due to hardening and the subsequent superposition with further deformation impacts during service life. The experimental investigation aims at quantifying the remaining restraint stresses after stress relaxation and crack formation as well as observing crack development during service life. In the hardening phase the influence of a realistic placement condition (normally partial restraint) and the thermal boundary conditions (especially thermal curing) was paid attention to. During service life the consideration of the member condition (single crack pattern or stabilized crack pattern) is highly significant. Based on the experimental results it can be concluded that thermal curing has only a limited influence on preventing through cracks and the separate consideration of early restraint and service life impacts does not always lead to design on the safe side. [ABSTRACT FROM AUTHOR]

In der Praxis wird für die Ermittlung der Mindestbewehrung zur Begrenzung der Rissbreite oftmals der zentrische Zwang im frühen Betonalter zugrunde gelegt. Aus mechanischer Sicht kann diese Vorgehensweise nur als eine pragmatische Lösung angesehen werden, da hierbei die maßgebenden Faktoren, wie die zeitliche Entwicklung der Materialeigenschaften und die damit einhergehenden bauteiltypischen Verformungseinwirkungen sowie deren Behinderungssituation, nicht berücksichtigt werden. Darüber hinaus kann gezeigt werden, dass die Mindestbewehrung für den zentrischen Zwang im frühen Betonalter nicht immer auf der sicheren Seite liegt. Schäden, insbesondere in der Form von wasserführenden Rissen bei WU-Konstruktionen, sind deshalb keine Seltenheit. Die Schwächen des empirisch modifizierten Nachweises auf Grundlage der Rissschnittgröße wurden detailliert in [] aufgezeigt und in [] wurde bereits ein Konzept für die Festlegung der Mindestbewehrung auf Grundlage der Verformungskompatibilität vorgestellt. In einem dem vorliegenden Beitrag vorangegangenen ersten Teil [] wurde bereits ein allgemeines Modell zur verformungsbasierten Ermittlung der Mindestbewehrung und dessen Anwendung für Bodenplatten präsentiert. Im vorliegenden zweiten Teil wird die Anwendung für den klassischen Fall 'Wand auf Fundament' gezeigt und die Leistungsfähigkeit des vorgeschlagenen Modells durch einen direkten Vergleich mit Ergebnissen einer risskraftbasierten Bemessung gemäß heutiger Bemessungsstandards demonstriert. Insgesamt lässt sich die Empirie bei der Bestimmung der Mindestbewehrung mit der verformungsbasierten Methode deutlich abschwächen, da hierbei stets Verträglichkeit entlang des gesamten Bauteils nachgewiesen wird. Im Gegensatz dazu wird bei der risskraftbasierten Bemessung gemäß EC2 [] nur das Kräftegleichgewicht im Querschnitt betrachtet. Minimum reinforcement for crack width control considering the real member behaviour It is standard practice to determine the minimum reinforcement for crack width control on base of centric restraint due to concrete hardening. Although this concept gives straightforward results, it can only be seen as a pragmatic solution which is generally not on the safe side. In detail, this simplification neglects the deformation compatibility and considers therefore not the real member behaviour. As a result of this, structural damage - especially in form of leakage in watertight constructions - often occurs. A detailed presentation of the weakness of this empirically modified cracking force approach can be found in []. However, the mechanically consistent determination of the minimum reinforcement for crack width control can be achieved by considering the deformation compatibility of the restrained member, see []. The previous first part of this contribution [] presented the general application of the deformation-based design concept and its particular application in case of 'ground slabs'. The following second part presents the particular application in case of 'walls on foundations' as well as a direct comparison with results from a cracking force-based minimum reinforcement design according to current design standards. Altogether, the introduced approach reduces the empiricism of minimum reinforcement design significantly. The main reason is the verification of deformation compatibility along the member length. In contrast, however, the cracking force-based minimum reinforcement design according to EC2 [] solely verifies the equilibrium in a cross section. [ABSTRACT FROM AUTHOR]

Im vorliegenden Aufsatz werden die rechnerischen Rissbreiten bei frühem und bei spätem Zwang verglichen. Insbesondere wird der Fall betrachtet, dass nach einer frühen Rissbildung infolge Abfließens der Hydratationswärme im fortgeschrittenen Betonalter Zwängungen durch Schwinden und/oder Temperatureinflüsse entstehen. Es wird gezeigt, dass die im jungen Betonalter entstandenen Risse zunächst breiter werden, bevor neue Risse infolge späten Zwangs entstehen können, und dass die resultierende Rissbreite dann größer ist, als wenn die Risse ausschließlich durch späten Zwang entstehen. Für die rechnerische Behandlung dieser Problematik wird ein einfaches Rechenverfahren aufgezeigt. Des Weiteren wird auf die Konzentration von zwangsbedingten Rissen in Schwachstellen, z. B. bei Bodenplatten und Decken mit großen Aussparungen, eingegangen und es wird dargestellt, wie für solche Bauteilgeometrien die rechnerische Begrenzung der Rissbreite erfolgen kann. Considerations of the Crack Width Resulting from Early and from Late Restraints and in Constrained Concrete Members with Locally Reduced Cross Sections This paper compares the theoretical crack widths resulting from restraints of concrete members occurring early and restraints occurring later. In particular the special case of early restraint cracking due to cooling after hydration followed by later restraints due to shrinkage or ambient temperature changes is considered. It is shown that the cracks that have formed early must widen before new cracks can form at a later stage when the concrete tensile strength has increased to a higher value. The cracks thus become wider than those forming only at the later stage. A simple model is presented for the calculation of crack widths in such situations. Further, the paper discusses the concentration of restraint cracks in portions of concrete members that possess a reduced cross sectional area as in slabs with large openings. It is shown how the crack width control can be effectively achieved in such situations. [ABSTRACT FROM AUTHOR]

Beton verhält sich unter dynamischer Belastung anders als unter statischer Belastung. Als wesentliche stoffliche Ursache hierfür werden üblicherweise innere Transporteffekte bei niedrigen Dehnraten bis ca. ϵ = 1/s angenommen. Bei höheren Dehnraten bis ca. ϵ = 300/s werden vermutlich Trägheitseffekte bei der Bildung von Rissen maßgebend. Die messtechnische Erfassung dieser Effekte und die klare Trennung von stofflichen und strukturellen Phänomenen sind Gegenstand aktueller Forschung. Eine Möglichkeit, das Verhalten von Beton bei höheren Belastungsgeschwindigkeiten zu untersuchen, bietet der Split‐Hopkinson‐Pressure‐Bar‐Versuch (SHPB‐Versuch). Nachfolgend werden Versuche für einen Normalbeton C35/45 mit Belastungen im quasi‐statischen Bereich bis hin zu Lasten, die Dehnraten von bis zu ϵ = 211/s erzeugen, vorgestellt, ausgewertet und durch Simulationen abgebildet. In der Simulation wird ein Materialmodell verwendet, das auf einem um eine nicht‐lokale Formulierung der Plastizität erweiterten Modell der Mikroebenen basiert. Zusätzlich wird die Massenträgheit der Struktur berücksichtigt. Es wird aufgezeigt, dass die experimentell ermittelte höhere Beanspruchbarkeit des Betons bei gesteigerten Dehnraten numerisch abgebildet werden kann. Dynamic properties of concrete in experiment and simulation Concrete subjected to dynamic loads behaves differently compared to static loading. As an explanation at low strain rates up to ϵ = /s, internal transport effects are assumed to be originated in the material. At higher strain rates up to ϵ = 300/s, inertial effects during the formation of cracks are postulated. The experimental identification of these phenomena and the definite separation of their substantial and structural sources are subject to current research. The split Hopkinson pressure bar experiment enables the investigation of the behaviour of concrete subjected to dynamic loading. In the following, experiments in the range of quasi‐static loading up to loads that induce strain rates until ϵ = 211/s on a standard concrete C35/45 grade are presented, evaluated and simulated. In the simulation, a material model is applied that bases on the micro‐plane model extended by a non‐local formulation of plasticity. Furthermore, structural inertia effects are taken into account. It is shown that the experimentally found increase in strength of the concrete at higher strain rates can be modelled by the simulation. [ABSTRACT FROM AUTHOR]

Im Dezember 2015 ist eine A1‐Änderung [1] zum deutschen Nationalen Anhang [2] des Teils 1‐1 von Eurocode 2 [3] veröffentlicht worden. Die Änderung betrifft die zwei Themen Dauerhaftigkeit von tausalzbeanspruchten Verkehrsflächen (insbesondere Parkdecks) und Ansatz der wirksamen Betonzugfestigkeit bei der Ermittlung der Mindestbewehrung zur Begrenzung der Rissbreite bei früher Rissbildung. Beiden Sachverhalten ist eine mehrjährige Diskussion in Fachkreisen vorausgegangen. Der Beitrag soll die Hintergründe der Änderungen und deren Folgen für die Praxis erläutern. Explanations of amendment of the German National Annex to Eurocode 2 An A1‐Amendment [1] of the German National Annex [2] of Eurocode 2, Part 1‐1 [3] has been published in December 2015. The amendment affects the two topics durability of traffic areas under chloride exposure (especially parking levels) and assumption of the effective concrete tensile strength at calculation of the minimum reinforcement for crack control due to early cracking. According these two topics a multiannual discussion in expert forums was foregone. This paper should explain the background of the changes and the consequences for the practice. [ABSTRACT FROM AUTHOR]

Innerhalb der beim DAfStb eingerichteten Ad‐hoc‐Gruppe “Dauerhaftigkeit von befahrenen Parkdecks” wurde vereinbart, eine Gesamtsystematik zu den Regelungen für die Dauerhaftigkeit von befahrenen Verkehrsflächen zu entwickeln, die aus einer Normenvorlage und aus Erläuterungen für das Heft 600 sowie Ausführungen für das DBV‐Merkblatt “Parkhäuser und Tiefgaragen” bestehen. Der Beitrag fasst die Ergebnisse der insgesamt vier Sitzungen der Ad‐hoc‐Gruppe zusammen, die im Laufe des Jahres 2015 veröffentlicht werden sollen. [ABSTRACT FROM AUTHOR]

Üblicherweise wird bei der Erdbebenbemessung von durch Stahlbetonwände ausgesteiften Gebäuden entweder die ungerissene Biegesteifigkeit oder ein von dieser durch einen Abminderungsfaktor abgeleiteter Wert zur Berücksichtigung des Zustands II verwendet. Tatsächlich ist die Biegesteifigkeit von Stahlbetonquerschnitten jedoch vom Bewehrungsgrad und von der Normalkraft abhängig. Die Fließverschiebung, bei der sich am Fuß einer Stahlbetonwand ein plastisches Gelenk bildet, ist hingegen fast ausschließlich von ihrer Länge im Grundriss abhängig. Torsionswirkungen infolge Exzentrizität zwischen Massen‐ und Steifigkeitsmittelpunkt werden üblicherweise durch Vergrößerung der Bemessungskräfte der einzelnen Wände berücksichtigt. Den durch die Torsionswirkung vergrößerten Verschiebungen einzelner Wände wird dabei keine Beachtung geschenkt. Da die durch die Verhaltensbeiwerte der Normen implizit vorausgesetzte ertragbare Verformung des Tragsystems zusätzliche Verschiebungen infolge Torsion nicht explizit berücksichtigt, kann es so unter Umständen wegen Überschreitung der maximal möglichen Verformung einzelner Wände zu einem vorzeitigen Versagen kommen. Im vorliegenden Aufsatz wird ein quasi‐händisches Nachweisverfahren vorgestellt, mit dem die explizite Berücksichtigung von torsionsbedingten Verschiebungen möglich ist und bei dem realistische Biegesteifigkeiten für die Wände verwendet werden. Alternative seismic design methodology for reinforced concrete wall buildings incorporating the prediction of wall displacements Typically the seismic design of reinforced concrete wall buildings uses either the uncracked flexural stiffness, or a value derived from it by multiplication with a reduction factor in order to allow for the influence of cracking. In fact however, the cracked stiffness of RC sections depends on the reinforcing ratio and on the axial load level. The yield deflection at which a plastic hinge will form at the base of a RC wall on the other hand, depends almost exclusively on the length of the wall in plan. Torsional effects due to eccentricity between the centres of mass and rigidity are typically allowed for by increasing the design lateral loads for individual walls. The increase of the deflection of individual walls due to torsional effects is not taken into consideration. Because the structural deformations implied by code force reduction factors do not explicitly allow for the increase of wall deflections due to torsional effects there is a possibility of a premature failure due to the exceedence of the deformation capacity of the critical wall. The paper presents a design methodology using realistic cracked member stiffness and explicitly allowing for additional wall deformations related to torsion. [ABSTRACT FROM AUTHOR]

Hochduktiler Beton ist ein mit kurzen Kunststofffasern bewehrter Hochleistungsverbundwerkstoff auf Zementbasis, der unter Zugbelastung eine hohe nichtelastische Verformbarkeit und ein verfestigendes Materialverhalten aufweist. Der alleinige Einsatz von Fasern als Bewehrung ist im konstruktiven Ingenieurbau jedoch auf wenige Anwendungsgebiete beschränkt, sodass in tragenden Bauteilen eine Kombination von hochduktilem Beton und konventioneller Stahlbewehrung erforderlich wird. Das Zusammenwirken beider Bewehrungsarten soll ein günstiges Trag‐ und Verformungsverhalten von zugbeanspruchten Bauteilen herbeiführen. Die rissüberbrückende Wirkung der Fasern führt dabei zu einer deutlichen Steigerung der Tragfähigkeit und hat durch die geringen Verformungen im Zustand II einen günstigen Einfluss auf die Gebrauchstauglichkeit. Des Weiteren werden durch das Zusammenwirken von Fasern und Stahlbewehrung die Rissbreiten deutlich reduziert und dadurch eine wesentliche Verbesserung der Dauerhaftigkeit erzielt. Um diese Zusammenhänge im bauwerkrelevanten Maßstab nachzuweisen und zu analysieren, wurden einaxiale Bauteilzugversuche durchgeführt, auf deren Basis das globale und lokale Zugtragverhalten der großformatigen Verbundkörper beschrieben werden kann. In diesem Beitrag werden die Ergebnisse der experimentellen Untersuchungen dargestellt und Schlussfolgerungen in Bezug auf die Bemessung und Konstruktion von zugbeanspruchten Stahlbetonbauteilen aus hochduktilem Beton gezogen. Structural behaviour of steel‐bar‐reinforced SHCC elements subjected to tensile loading Strain‐hardening cement‐based composite (SHCC) is a high‐performance cementitious material which exhibits high, non‐linear deformation capabilities and strain‐hardening behaviour under tensile loading. This behaviour is achieved by utilizing micro‐mechanical effects which induce multiple cracking by bridging cracks with polymer fibres. The goal of the research work at hand is to acquire a deeper understanding of the interaction between steel reinforcement and SHCC under tensile loads. The mechanical interrelation between these two materials is governed by the tensile‐deformation behaviour of both steel and SHCC and the bond between them as well. The material properties and their combined influence on the global and local deformation behaviour of structural members under tensile load were analysed in order to enable the sustainable, efficient design of structures made of steel‐reinforced SHCC (R/SHCC). A series of large‐scale uniaxial tension tests was carried out to investigate the influence of the reinforcement ratio on the deformation and cracking behaviour of R/SHCC elements. The results showed that the load bearing‐deformation characteristics of the elements under tensile load is governed by the multiple‐cracking behaviour of the SHCC after initial cracking. It could be concluded that the multiple cracking of SHCC enhances the load‐bearing capacity of the slab in comparison to slabs made of ordinary RC and prevents the development of large cracks, even at low reinforcement ratios. [ABSTRACT FROM AUTHOR]