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Influence of rib geometry on the bond strength of reinforcing steel from coils Reinforcing steel in coils has a modified rib geometry with wide ribs compared to conventional rebars, in order to ensure proper bending and straightening. The combination of small rib spacing and wide ribs result in reduced bond strength even though the rebars have a large relative rib area. To meet this concern, an experimental study with pull‐out tests was carried out to investigate the influence of rib geometry on the bond strength of reinforcing steel from coils. In pull‐out tests, significantly lower bond strength was obtained with reinforcing steel from coils compared with conventional straight reinforcing bars. By analyzing a test database with lap splice and anchorage tests from literature, a noticeable influence of the rib height and rib spacing on the bond strength was found. In addition, large rib widths resulted in lower bond strength. Contrary to previous findings, the bond strength was mostly independent of the value of relative rib area. The findings of the investigations reveal that other parameters and indicators would complement the value of relative rib area in order to describe the bond strength of reinforcing steel from coils in a more accurate manner. [ABSTRACT FROM AUTHOR]

Database for punching shear resistance of steel fibre reinforced concrete flat slabs without shear reinforcement – Verification of design approaches according to DAfStb guideline and Model Code 2010 The punching shear design of steel fibre‐reinforced flat slabs is currently carried out in Germany based on the DAfStb Guideline "Steel fibre reinforced concrete". The addition of steel fibres to the concrete allows an effective transfer of tensile forces across the crack and limits the progressive crack opening, which proves to be particularly favourable for the punching shear strength. Numerous investigations since the mid‐1970s have confirmed this and have enabled the derivation of empirical and partly mechanically based approaches for the calculation of the steel fibre contribution in the punching shear capacity of steel fibre reinforced flat slabs without punching shear reinforcement. For the evaluation and further development of these approaches, a critically reviewed database of punching shear tests on steel fibre reinforced flat slabs without punching shear reinforcement was created. Considering the practical construction requirements regarding the slab thickness, the degree of longitudinal reinforcement as well as the concrete compressive strength and the post‐cracking tensile strength, about 116 tests could be included in the punching shear database "Steel fibre reinforced concrete". This paper presents the database and discusses its evaluation about the prediction accuracy and the safety level of the design approaches according to the DAfStb guideline "Steel fibre reinforced concrete" as well as according to the Model Code 2010. [ABSTRACT FROM AUTHOR]

Copyright of Beton- Und Stahlbetonbau is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Investigations on the load bearing behavior of composite dowels in slender webs of ultra‐high performance concrete Ultra‐high performance fibre‐reinforced concrete (UHPFRC) is now being used more and more in the construction industry. Due to the current development of national and international guidelines and standards, it is to be expected that this trend will continue, and more and more constructions will be realised with this modern building material. This also applies to the field of composite construction. Composite girders with external reinforcement, in which the steel flange lies outside the concrete as a pure tension member, represent an interesting application possibility. The shear‐resistant connection between the external reinforcement and the UHPFRC‐web, which is as thin as possible, is then made using composite dowels. However, these then only have a very low lateral concrete cover, which is why the determination of the shear load‐bearing capacity of composite dowel bars is of particular importance in this case. This present paper describes the results and findings gained from experimental and numerical investigations on Push‐out specimens, which were used to investigate the load‐bearing and deformation behavior of composite dowels in thin UHPFRC webs. In a follow‐up article, proposals for appropriate design models are presented and both the experimental setup and the results of composite beam tests are explained and consequently discussed. [ABSTRACT FROM AUTHOR]

Copyright of Beton- Und Stahlbetonbau is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shear tests on profiled prestressed concrete beams made of UHPFRC Ultra High Performance Fibre‐Reinforced Concrete (UHPFRC) is a fibre composite characterised by very high density and strength. The material opens up completely new possibilities for weight‐reduced, slim and durable structures in precast concrete construction, especially for prestressed concrete girders. Special attention must be paid to the shear force bearing capacity of the mostly profiled, prestressed girders with thin webs. In this context, 14 shear tests were carried out on profiled prestressed girders varying the cross‐section height, the degree of prestressing, the fibre content and the shear reinforcement. For these tests, an innovative experimental setup was used which makes it possible to experimentally examine selected beam sections (in this case half beams using symmetry). The present article deals with the results of these tests, in particular with regard to the influences of the varied parameters. [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]

Germany's first application of UHPFRC in railway bridge construction – Part 1: Conception, realization and practical experiences with a promising material 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 over the creek Dürnbach on the railway network of the Tegernseebahn, the material could now be used for the first time in Germany for a railway bridge in a particularly practical and advantageous way. Thus, a slim structure with a very low construction height could be realized, which was lifted in as a comparatively light precast element in a short track possession. The desired increase of the flow cross‐section in case of flooding was therefore possible without any adjustment of the track position and the existing abutments could be retained due to the low dead weight of the new superstructure. The superstructure was designed as a trough‐shaped precast slab bridge in prestressed concrete construction. This contribution deals with the conception, realization and findings gained in the course of the project. [ABSTRACT FROM AUTHOR]

Abstract: In‐situ tests at the bridge Hammelburg regarding the shear capacity of existing pre‐stressed bridges Part 2: Measuring concept, results of the in‐situ tests, comparison with different theoretical approaches Due to the relatively high average age of the existing bridges, a dramatic increase in traffic volume and axle loads and modified design standards, a realistic prediction of the shear capacity of existing pre‐stressed concrete bridges with little shear reinforcement has become an important topic in research. In 2017 the Chair of Concrete and Masonry Structures of the Technical University of Munich (TUM), supported by the Federal Ministry of Transport and Digital Infrastructure, was able to conduct unique field tests at the 1955 built Saalebrücke Hammelburg. According to systematic strength evaluations many concrete bridges, especially those which have been built prior to 1966, show severe (theoretical) deficits regarding the longitudinal shear capacity. Often the results of the strength evaluation cannot be verified at the real bridges though. The primary objective of the field test was therefore to determine the shear capacity of existing pre‐stressed bridges in order to contribute in closing the gap between calculations and experience for older concrete bridges. In the first part of this article the general assessment of the bridge and the original design concept as well as the conceptual approach, the execution of the in‐situ tests and the used measuring equipment were described. In the present paper the measuring concept and the results of the conducted tests are presented. Furthermore, the results of the in‐situ tests are discussed, and the measured maximum loads are compared to the results of different theoretical approaches and engineering models, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Beton- Und Stahlbetonbau is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Site-specific traffic load models for road bridges - an important tool for advanced evaluation strategies in bridge reassessment Definition and calibration of traffic load models is usually done on the level of structural demands (resulting from actual load impact). Consequently, such load models are affected by both the characteristics of traffic on site, and the structure itself. Starting from universal load models - as specified in codes and guidelines for general use in engineering practice and reasonable for application in design of new bridges - consequent consideration of site-specific characteristics regarding local traffic and structure allows for a more realistic representation of the actual traffic load demand and hence, possible reductions in the considered load level for application in reassessment for a specific structure. Site-specific load models are developed using a comprehensive procedure based on numerical traffic simulations (analysis of various possible traffic scenarios for robustness of load models) and ideally calibrated with real measurements on site. A stepwise approach for application in engineering practice is proposed, to allow for development of modified load models with a variable degree of considering site-specific characteristics, depending on desired cost and expected benefit. Results from primal analysis with an exemplary bridge structure already reveal the potential of this approach. [ABSTRACT FROM AUTHOR]

Consideration of in-plane tensile stresses in precast tunnel segments induced by thrust forces In-plane tensile stresses due to concentrated jacking loads induced by the tunnel boring machine (TBM) in precast concrete (PCC) tunnel segments is a subject that is rarely found in literature. This is mainly due to TBM advance being a temporary construction state leading to local tensile stresses with the segment reinforcement required typically does not exceed the predefined minimum reinforcement specified e.g. in design standards and guidelines. The relevance of the in-plane stress state is often misjudged although the related tensile stresses govern with respect to the majority of damages, i.e. cracks in segmental linings, according to our experience in tunnel projects over many years. A careful consideration of this load case is necessary, especially in cases where the minimum reinforcement may be decreased or an alternative type of reinforcement such as steel fibres is utilised. The present article provides some useful tables for analysing in-plane tensile stresses due to TBM-jacks (without further numerical calculations) considering the governing input parameters. The tables provide a quick method to optimise the various jack configurations and jack shoe sizes and may also be used as the basis for detailed design. In addition, the consideration of unavoidable tolerances in the structural system is discussed. For these cases guidance is provided regarding the structural models of the relevant load situations and the different design philosophies, in particular for calculation of the crack width. A brief discussion in the context of the divergent requirements (cost-efficient construction, robustness) and recognition of relevant influences follows. Finally, the authors propose an engineering design strategy for this particular load case. [ABSTRACT FROM AUTHOR]

Bei der statischen Berechnung von Tragsystemen des Massivbaus werden zur Schnittgrößenermittlung und zur Verformungsprognose zunehmend numerische Gesamtmodelle verwendet. Bei solchen Modellen kommt vor allem bei komplexeren Strukturen aufgrund der statisch oft hochgradigen Unbestimmtheit einer möglichst wirklichkeitsnahen Abbildung der Steifigkeitsverhältnisse besondere Bedeutung zu. Das gilt aufgrund des großen Steifigkeitsabfalls beim Übergang in den Zustand II insbesondere auch dann, wenn sich torsionsbeanspruchte Stahlbetonbalken maßgeblich am Lastabtrag beteiligen oder/und deren Steifigkeit einen entsprechenden Einfluss auf die Schnittgrößenverteilung im System besitzt. Die zu erwartende reduzierte Torsionssteifigkeit kann dabei gemäß DAfStb Heft 240 für die Schnittgrößenermittlung mit etwa 30 % abgeschätzt werden, während Heft 239 [1] im gerissenen Zustand II einen Wert von 10 % der Steifigkeit der ungerissenen Querschnitte (Zustand I) vorschlägt [2]. Um diese Ansätze kritisch zu hinterfragen und praxistaugliche Empfehlungen für die numerische Berechnung zu geben, werden im vorliegenden Beitrag zunächst an Einzelbalken dokumentierte Versuche der Literatur ausgewertet und bis zur jeweiligen Versagenslast mithilfe des Finite‐Elemente‐Programms ABAQUS systematisch nachgerechnet. Darüber hinaus werden mittels nichtlinearer Berechnungen unterschiedliche Lagerungsbedingungen in Balkenlängsrichtung untersucht, um den Einfluss einer behinderten Längsdehnung und den damit verbundenen anteiligen Lastabtrag über Wölbkrafttorsion genauer zu beurteilen. Abschließend werden zur Verifizierung der nichtlinearen numerischen Analysen eigene Torsionsversuche durchgeführt und diskutiert. Load‐bearing behaviour and deformation characteristics of RC beams subjected to torsion Structural analyses of reinforced concrete structures, including the evaluation of internal reactions and deformations, are increasingly characterized by the utilisation of overall numerical models. In doing so, a realistic approximation of stiffness properties becomes more and more important especially in case of complex and highly hyperstatic structural systems being investigated. Due to a dramatic decrease in torsional rigidity upon reaching the so‐called cracked state II, this particularly applies where the overall load‐bearing behaviour and internal stress distribution is decisively influenced by RC beams subjected to torsion. According to DAfStb report no. 240 [1] internal reactions may be calculated taking into account a reduced torsional stiffness of some 30 % whereas report no. 239 [2] recommends upon completion of the crack formation (state II) to only consider 10 % of the uncracked rigidity (state I). In order to critically discuss these proposals and to derive reasonable recommendations for numerical analyses, the present paper firstly evaluates existing experimental results of individual RC members under torsion which are then numerically analysed along the entire loading path (until failure) using the finite‐element‐programme Abaqus. In addition, by performing non‐linear simulations individual members with different longitudinal bearing conditions are investigated, in order to assess the influence of longitudinal restraints and the related load portion being carried by warping torsion. Finally, corresponding torsion tests are carried out to verify the non‐linear analyses. [ABSTRACT FROM AUTHOR]

Die Entwicklung und Erforschung des Ultrahochleistungsbetons hat dazu geführt, dass es heute vorteilhaft ist, viele klassische Betonbauteile aus diesem innovativen Werkstoff herzustellen. Für Wandscheiben bedeutet dies, dass sich die Dicke aufgrund der hohen Druckfestigkeit reduzieren lässt, während sich die Dauerhaftigkeit infolge der geringen Porosität erhöht. Da Wandscheiben aus Ultrahochleistungsbeton im Vergleich zu Wänden aus Normalbeton bei gleicher Querschnittstragfähigkeit deutlich größere Schlankheiten aufweisen können, gewinnt das Stabilitätsverhalten entsprechend an Bedeutung. Der vorliegende Beitrag beschreibt Untersuchungen zum Stabilitätsverhalten von Wandscheiben, die am Lehrstuhl für Massivbau der Technischen Universität München (TUM) durchgeführt wurden. Der Forschungsschwerpunkt lag dabei auf zweiseitig gehaltenen Scheiben aus unbewehrtem Normalbeton sowie faserbewehrtem Ultrahochleistungsbeton. An diesen wurden experimentelle und numerische Untersuchungen zum Trag‐ und Verformungsverhalten durchgeführt. Nachfolgend werden die Ergebnisse dieser Untersuchungen sowie ein Ingenieurmodell zur Berechnung der maßgebenden Stabilitätslasten von schlanken, zweiseitig gehaltenen Scheiben vorgestellt. Load bearing behavior and stability of slender wall panels made of normal strength and ultra‐high performance concrete. Following more than one decade of theoretical and experimental research on ultra‐high performance concrete (UHPC) today there is a series of possible applications to efficiently utilize this new and innovative material in load‐bearing structures. One example are walls and wall panels respectively, the thickness of which may be decisively reduced thanks to the high compressive strength, leading to increasingly slender structures being more sensitive in terms of stability. The present paper describes theoretical and experimental investigations on the load‐bearing and buckling behavior of normal strength and UHPC wall panels being currently performed at the chair of concrete and masonry structures of TUM. In doing so, exemplary results of these investigations are presented and discussed and an engineering model determining critical loads of slender walls is derived. [ABSTRACT FROM AUTHOR]

Copyright of Beton- Und Stahlbetonbau is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Beton- Und Stahlbetonbau is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)