Querkraftversuche an Spannbetonträgern mit carbontextilbewehrter Spritzmörtelverstärkung unter zyklischer Beanspruchung

Shear tests on prestressed concrete beams strengthened with carbon textile reinforced spray mortar under cyclic loading Many highway bridges in Germany exhibit shear capacity deficits under static and cyclic loading. A lot of structures are expected to demand refurbishment and strengthening within the next years, especially due to the current condition of many older road bridges in Europe. Different strengthening methods with specific advantages and disadvantages have proven to be suitable for the shear strengthening of bridges. In order to investigate the effect of an additional spray mortar layer with carbon textile reinforcement on the webs on the shear capacity, two tests on prestressed concrete beams were carried out at the Institute of Structural Concrete at RWTH Aachen University. The results of the tests were compared with previous tests on two identical beams which were not strengthened. The tests have shown that the strengthening measure leads to a considerably higher shear resistance concerning cyclic loading as well as the remaining static shear capacity.     

Rechnerische Beurteilung der Schubtragfähigkeit einer Spannbetonbrücke mit geringem Querkraft bewehrungsgrad

Assessment of the shear strength of an existing post‐tensioned concrete bridge with a low amount of shear reinforcement – First application of the ”Flexural Shear Crack“ model in practice In recent years it was reported several times, that within a static assessment according to current standards the shear strength of post‐tensioned bridges, which were built in Austria before 1989, cannot be fulfilled any more. However, test results prove, that especially prestressed structures have additional load bearing capacities, which cannot be reproduced with current calculation models. In the framework of a pilot project a new developed shear model (Flexural Shear Crack Model) was used. In this paper the approach as well as the main results of a statical reevaluation of an existing post‐tensioned road bridge at the Tauern Autobahn A10 will be presented.     

Erhöhung der Verbundtragfähigkeit von aufgeklebten CFK‐ oder Stahl‐Lamellen auf Stahlbetonkonstruktionen durch Bügelumschließungen

Bei Bauteilverstärkungen mit CFK‐Lamellen ist nach geltender Zulassung das Lamellenende durch eine äußere Umschließung durch Stahlbügel oder CF‐Gelege gegen eine Lamellenentkopplung (LEK) zu sichern. Durch die Entkopplungsbehinderung der Umschließung wird bei beginnender LEK ein passiver (selbstinduzierter) Anpressdruck aufgebaut, der eine traglaststeigernde Wirkung hat. In einem durch die DFG geförderten Forschungsvorhaben wurde die Traglaststeigerung durch unterschiedliche Umschließungsmaterialien und ‐geometrien untersucht und beschrieben sowie für die Bemessung ein Ingenieurmodell entwickelt. Anders als bei einbetonierter Bewehrung tritt bei einer Lamellenentkopplung sowohl eine Längs‐ als auch eine Querverschiebung der Lamelle auf, verursacht durch die anhaftenden Zuschlagskörner in der Klebstofffuge. Wird die abhebende Verschiebung der Lamelle durch Umschließungsbügel behindert, baut sich der passive Anpressdruck auf, was zu einer Steigerung der Lamellenzugkraft infolge der erhöhten Reibung im Riss führt. Es konnte ein direkter Zusammenhang zwischen dem Anpressdruck F_AP und der Lamellenzugkraft F_l gefunden und abgebildet werden. Increase of the Bond Capacitiy of Externally Bonded CFRPor Steel‐plates on RC‐Structures as the Result of External Enclosures Strengthening of concrete structures with externally bonded CFRP‐ or steel‐plates has become a well established strengthening method in many countries. In Germany building authority approvals demand that the end of a plate has to be provided by a glued external enclosure. Glued enclosures are primarily needed in order to increase the shear force capacity of a RC member. It is known, that a transverse enclosure of longitudinal CFRP‐plates has a positive effect on the buckling load of the latter, which is yet completely unknown. The aim of this work is to assess the increase of the buckling load caused by the enclosure. In the paper the dependency between the so‐called self‐induced contact pressure of an external enclosure with steel frames or laminated carbon fiber sheets and the longitudinal force of the CFRP‐ or steel‐plate is shown. The self‐induced contact pressure is the result of the vertical lifting of the plate towards the external enclosure due to the beginning of plate's debonding process. The test results show, that the increase of the plate‐force depends on the type and size of the external enclosure. In some tests up to twice of the ultimate load was optained. An engineering model is presented to take into consideration the effect for dimensioning.