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The risk of a fatigue failure has to be evaluated at coupling joints of older post-tensioned, concrete bridges in Germany, because weaknesses were identified in the design of these bridges. Because of the nonlinear bearing behaviour of post-tensioned, concrete structures, the results of this analysis strongly depend on the distribution of the permanent internal forces, which are uncertain due to time-dependent losses and redistributions. In this paper, a method to determine the bearing behaviour and the actual bending moment of the examined coupling joint, which is based on non-destructive, long-term measurements under service conditions, is shown. Therefore, the crack at the coupling joint, the temperatures and the traffic loading are observed. The results are used to calibrate a finite element simulation of the cross section. With this, a more realistic fatigue evaluation could be done as of the approaches in codes for the design of new bridges are used (e.g. DIN EN 1992, 2011,Eurocode 2. Bemessung und Konstruktion von Stahlbeton- und Spannbetontragwerken, Berlin: Beuth). [ABSTRACT FROM AUTHOR]

Slabs are one of the main load-bearing elements in nearly every structure. Because of additional live loads or modifications of the building structure these slabs often have to be strengthened. Using externally bonded carbon-fiber reinforced polymer (CFRP) strips to strengthen existing concrete structures has become common practice. One of the main failure modes is the loss of the composite action between the concrete and the CFRP strip making the bond force transfer very important. This bond force transfer depends on many parameters including the concrete strength, the ratio between shear force, and bending moment. A new parameter recently discovered by the Technische Universität München (TUM) is the deflection of the structural elements themselves. Because of this deflection self-inducted contact pressure occurs. This contact pressure affects a higher bond transfer. The lower effective depth of slabs compared to beams causes higher deflections. In this article, first a few principles on the strengthening with adhesive-bonded CFRP strips and the characteristics of the bond are explained. Then, the basics of the bond force transfer, at the end anchorage and in the rest of the element, are summarized. Based on these essentials, as well as numerous experiments, the change in the bond force transfer at the structural element caused by the curvature is then derived. With these findings, a complete verification concept is presented, which is ideal for computerized calculations. This verification concept is finally compared to several full-scale test results presented in pertinent literature. [ABSTRACT FROM AUTHOR]

This paper presents the newly established ACI‐DAfStb database of shear tests on slender prestressed concrete beams without stirrups subjected to point loads. From the 574 collected tests 214 tests remain for the comparison with shear design approaches after the control and selection procedures were applied. The main features of these tests are described. Subsequently, these tests are used to perform evaluations of the shear design procedures of EC2, fib Model Code 2010, and ACI 318‐14. [ABSTRACT FROM AUTHOR]

Die Nachrechnungen bestehender älterer deutscher Spannbetonbrücken auf Grundlage der aktuell gültigen Normen zeigen im Allgemeinen erhebliche Defizite in Bezug auf die erforderliche Querkraftbewehrung in Längsrichtung. Es ist jedoch bisher kein Querkraftversagen eines bestehenden deutschen Brückenbauwerks bekannt. Bis heute gibt es nur sehr wenige Versuche an Spannbetonbalken als Durchlaufträger. Um das Tragverhalten durchlaufender Spannbetonbalken eingehender zu untersuchen, wurde im Rahmen eines von der BASt beauftragten Forschungsvorhabens an der TU Dortmund ein Großversuch an einem vorgespannten Zweifeldträger durchgeführt. Dabei sollte auch der zusätzliche Traganteil aus einer Druckbogenwirkung genauer betrachtet werden. Zur kontinuierlichen Erfassung der Beanspruchungen im gesamten Bauteil unter allen Laststufen wurde eine umfassende Messtechnik installiert. Im vorliegenden Beitrag werden der Großversuch und die daraus gewonnenen wesentlichen Erkenntnisse dargestellt. Zudem erfolgen eine Versuchsauswertung auf Basis geltender Normen und ein Vergleich mit dem Druckbogenmodell. Shear testing on a prestressed continuous concrete beam The structural assessment of existing older prestressed concrete bridges on the basis of current standards often uncovers substantial deficits in terms of the required shear reinforcement in the main girders of bridge superstructures. However, shear failures of existing German bridge structures have not been reported so far. Until now, only few tests on prestressed continuous concrete beams have been carried out. In order to investigate the load bearing capacity of such beams more precisely, a large scale experiment was executed at TU Dortmund in the course of a research project funded by the Federal Highway Research Institute (BASt). Within this project a particular focus was put on the investigation of the additional shear load bearing capacity caused by the compressive arch effect. Therefore an extensive range of measurement devices was used in the experiment to guarantee the continuous recording of structural behavior and internal forces. In this contribution the large scale experiment as well as the main findings are presented. An interpretation of the test results based on current standards and a comparison with the compressive arch model are carried out. [ABSTRACT FROM AUTHOR]

Derzeit werden auf europäischer und nationaler Ebene in Deutschland verschiedene neue Regelwerke und Arbeitshilfen zur Nachrechnung bestehender Massivbauwerke vorbereitet, die sich speziell mit der Festlegung mechanischer Kennwerte historischer Baustoffe befassen. In diesem Zusammenhang wurde der neue DAfStb‐Sachstandbericht “Mechanische Kennwerte historischer Betone, Betonstähle und Spannstähle für die Nachrechnung von bestehenden Bauwerken” [1] erstellt, der die Umrechnung von aus der Herstellzeit in Deutschland dokumentierten mechanischen Materialkennwerten auf Größen, wie sie zur Anwendung der aktuell bauaufsichtlich eingeführten Eurocodes benötigt werden, beinhaltet. Der Sachstandbericht ist das Ergebnis eines von der TU Kaiserslautern und Zilch + Müller Ingenieure GmbH, München gemeinsam bearbeiteten und vom Deutschen Ausschuss für Stahlbeton DAfStb finanzierten Verbundprojektes. Der Sachstandbericht [1] wurde im DIN‐Unterausschuss NA 005‐07‐01 UA “Bewertung von Bestandsbauwerken”bearbeitet und erweitert. Zusätzlich wird zurzeit ein weiterer DAfStb‐Sachstandbericht zur Bestimmung charakteristischer Betondruckfestigkeiten im Bestand mittels Bestandsanalyse ausgearbeitet [2]. Parallel dazu wird das DBV‐Merkblatt “Bauen im Bestand – Beton und Betonstahl” [4] überarbeitet und ein neues DBV‐Merkblatt “Bewertung der In‐situ‐Druckfestigkeit von Beton” [1] herausgegeben. Mechanical properties for the reanalysis of existing reinforced concrete structures – Preparation of new tools Currently, in Germany new technical regulations for the structural reanalysis of existing reinforced concrete structures are being prepared. The new DAfStb‐Report “Mechanical properties of historical concretes, reinforcing steel and prestressing steel for the structural analysis of existing structures” [1] contains the conversion of historical mechanical properties into values, used in Eurocodes. For this purpose, the annex of the new DAfStb‐Report also contains background information on the mathematical conversion. The Report is the result of a study conducted by the TU Kaiserslautern and Zilch + Müller Ingenieure GmbH, München that was financed by the DAfStb. The DIN subgroup NA 005‐07‐01 UA “Bewertung von Bestandsbauwerken” has reviewed it. Furthermore a second report on the determination of characteristic material properties is currently being prepared by DAfStb [2]. At the present time the DBV‐Guide‐to‐good‐practice “Existing Structures – Concrete and Reinforcing Steel” [3] has been updated and a new DBV‐Guide‐to‐good‐practice “Assessment of in‐situ Compressive Strength of Concrete” [4] will be published. [ABSTRACT FROM AUTHOR]

Die Verstärkung von Betonbauteilen mit geklebter Bewehrung wurde in Deutschland bisher alleinig durch allgemeine bauaufsichtliche Zulassungen und Zustimmungen im Einzelfall geregelt. Da sich das Verstärken von Betonbauteilen mit geklebter Bewehrung immer mehr zur Regelbauweise entwickelt und die europäische Harmonisierung auf diesem Gebiet voranschreitet, wurde ein neues Regelwerk für die Verstärkung von Betonbauteilen mit geklebter Bewehrung geschaffen. Dazu haben sich alle von der Themenstellung betroffenen Parteien in einem Unterausschuss des Deutschen Ausschusses für Stahlbeton zusammengefunden und sich in die Formulierung der DAfStb-Richtlinie 'Verstärken von Betonbauteilen mit geklebter Bewehrung' eingebracht. Nach Abschluss des Einspruchsverfahrens und anschließender Notifizierung erscheint die Richtlinie voraussichtlich im September oder Oktober 2012. The new DAfStb-Guideline 'Strengthening of concrete structures with adhesive bonded reinforcement' The strengthening of concrete structures with adhesive bonded reinforcement has in Germany only been governed so far through national technical approvals and approvals in individual cases. Since the strengthening of reinforced concrete structures with adhesive bonded reinforcement has become a standard construction method and due to the starting of a harmonisation process in European standardisation committees a new guideline in this area of interest was created. For that purpose all groups, which are concerned about this topic were assembled in a committee under the responsibility of the German Committee for Structural Concrete and created the DAfStb-guideline 'strengthening of concrete structures with adhesive bonded reinforcement'. The guideline will be published in September or October 2012. [ABSTRACT FROM AUTHOR]

This paper documents the results of a joint research project dealing with the loading of formwork systems used with highly flowable concretes. First calculation approaches concerning the pressure of fresh concrete on vertical formwork were developed on the basis of the investigations conducted on the material behaviour of highly flowable concretes. In doing so, construction management questions regarding, for instance, process design and quality assurance in the application of highly flowable concretes were also investigated. Different scientists from German research institutes collaborated in a research group to pool their knowledge in the field of the pressure of fresh concrete. Because of the extent and complexity of the tasks to be tackled, the joint research project was divided into five subprojects (A to E), which were performed by the research institutes according to their individual respective capacities. [ABSTRACT FROM AUTHOR]