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Item type:Publication, Access status: without files , Versuche zur Querkrafttragfähigkeit von gevouteten Stahlbetonbalken ohne QuerkraftbewehrungThe shear capacity of concrete members without transverse reinforcement is still under debate. Within this paper one aspect, the favourable contribution of inclined tension and compression chords (Vtd and Vccd) of members with variable depth, like haunched beams, will be discussed in detail. A series of 18 tests on 9 different specimens was performed to examine the real shear capacity of haunched beams without shear reinforcement. The evaluation of the test results revealed, that none of the available design methods can describe the shear behaviour of haunched beams. The vertical component of the inclined compression chord Vccd leads in some cases to unsafe values.Publicationtype: Journal Article66 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Shear design of concrete members without shear reinforcement - A solved problem?The design of concrete members for shear without stirrups has become a major issue worldwide especially for bridge decks as the shear capacity according to the 'new' regulations like the Eurocode often gives significant smaller values than the one predicted by former codes. Therefore nowadays stirrups are required in bridge decks. In addition the safety of existing structures mainly build without shear reinforcement has been brought into focus. The lack of the available design models will be demonstrated by comparing the results of various codes. The inaccuracy of the EC2 approach is checked by means of a shear database. Experimental as well as numerical studies revealed that the shear capacity of haunched beams is different from members with constant height. It is questionable whether this behavior is caused by the vertical component of the inclined compression chord Vcc.Publicationtype: Journal ArticleScopus© Citations 15 259 398 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Shear design of straight and haunched concrete beams without stirrupsIn spite of very long research activities with the first tests conducted by Mörsch in the 1920th, the design for shear of concrete members without transverse reinforcement is still not cleared. This may be demonstrated in the fact that most shear design procedures are not based on mechanical models but on empirical equations which show very big uncertainties. Thus very high safety factors have to be used. The problem of shear design exists primarily for slabs. In Germany numerous old concrete bridges show a lack of safety in transverse direction since the year 2001, when a new DIN-code was introduced. Furthermore the shear design principle of haunched concrete structures, as for example, cantilever slab of bridges, is hardly cleared, up to now. This research work aims to improve the understanding of the shear behaviour, to identify the significant shear resistance mechanisms and finally to develop new shear design models for practical use which is valid for straight and haunched concrete beams without stirrups. The essential, partially very different approaches known from the literature are analysed first and their accuracies are checked by a comparison with the test values from a shear database. Considerable differences appear between the arithmetic results and the test values. To study the behaviour of concrete members under high shear loads an extensive test program with 18 reinforced concrete beams without web reinforcement of different shear slenderness and inclination of compression chord was conducted. These experiments focused on haunched beams. It appears that the existing approaches describe the influence of an inclined compression chord on the shear capacity only in an insufficient manner. In some cases the design according to the DIN- or EC-Code results in unsafe values. To get a better understanding of the load-bearing mechanisms all tests are simulated by means of non-linear Finite Elements analysis with the programme ABAQUS. Very good agreement appears between the test results and those of FE-analysis including the load-deflection curves, the load bearing capacity and the crack patterns. Thus the developed numerical model can simulate the behaviour of reinforced concrete beams up to the ultimate limit state. The FE-analysis demonstrates that the shear forces are transferred in uncracked compression zone mainly. Therefore crack friction and dowel action plays no significant role on shear bearing capacity at the ultimate limit state. As a result of the FE-analysis and the test program, a shear resistance action of uncracked concrete part in the tension zone is firstly introduced to be one of the two main shear bearing actions of concrete structures without stirrups. Based on the theoretical and experimental investigations an easy analytic model is developed for the estimation of the shear capacity of straight and haunched reinforced concrete beams without stirrups. It shows more accurate results than the known approaches.Publicationtype: Doctoral Thesis3873 7406 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Querkrafttragfähigkeit von gevouteten Stahlbetonbalken ohne Querkraftbewehrung : Versuchsbericht Q01-2009(2009-12-21); This research report summarizes the experimental and numerical investigations which were conducted to clarify whether haunching of reinforced concrete beams without shear reinforcement significantly affects the ultimate shear capacity (V_ccd). The experimental results show that the approach of V_ccd in shear design is questionable.Publicationtype: Research Report54 556