Advancement of standards is generally assumed to be one of two things. Either the introduction of more efficiency into the prediction, or the eradication of previously unknown and unwanted effects. Both are strived for and welcomed by the community, as it allows for the reduction of material and cost, while ensuring the required degree of safety. This, however, can not be said for the development of the shear verification method of reinforced and/or prestressed concrete slender beams. The latest chapter of this development being written by the Eurocode 2, where the partaking of the concrete compression zone, amongst other influences, in the shear-bearing capacity of said specimens is neglected, leading to far higher conservatism in design. Since neither damages or failures nor new research results exist, pointing towards an unsafe design prior to it, this increased safety is not warranted. Therefore the following work aims to showcase the impact, strength and weaknesses and reasoning of the current design standards as well as provide a design approach, incorporating multiple shear-bearing mechanisms, that mimics reality more closely. Facing the challenge of having biased test databases, leaning strongly on single span test setups under concentrated loads, basically eliminating interactions of normal and shear stresses, as well as small cross-sections, a numerical modelling approach is developed. It is validated against tests reported in literature and allows for a more precise investigation as well as acknowledgement of certain parameters, when being compared to physical testing. Further on it is used to create a set of tests in accordance to the Design of Experiments, allowing assertions about the dependence of the test results on individual variables. The modelled test setup aims to represent bridge girders at intermediate supports, as research shows large discrepancies between the calculable critical load for the old and new standards at these points. Spotlighted variables consist of the span length, the slenderness and the transverse reinforcement ratio. Especially the allocable independence of the predicted critical load from the transverse reinforcement ratio in case of compression stresses, resulting from bending or prestressing, coinciding with the large shear stresses shows the inability of the currents design standard to correctly predict the physical behaviour of the reinforced and/or prestressed concrete slender beams. Furthermore the interaction of the overlapping point of large normal stresses and large shear stresses partaking in this effect needs to be stated. Based on these findings an engineering model approach is developed, accounting for the partaking of the uncracked concrete compression zone in the shear-bearing mechanisms, in form of the compression arch with tension chord. Interaction of bending moment and transverse forces is ensured by the model via the shape of the compression arch and the coupling of the individual systems via the deformation. This ensures a stiffness dependency of the model, which is used to allocated the load onto the individual systems. Partaking of the transverse reinforcement is covered by a smeared truss system, similar to the one in Eurocode 2. The applicability of the approach is determined on basis of compatibility of deformation. For evaluation of the engineering model approach, the deformation of the smeared truss at its individual load-bearing capacity is taken and applied to the compression arch with tension chord, resulting in an additional load, that the combined system is able to bear, before reaching the failure load of the smeared truss subsystem. In coupling these subsystems in this way, the physical behaviour of the beam is mimicked. In this the engineering model approach differentiates itself from many existing shear models, which more often than not add individual load-bearing mechanisms, that are mostly assumed to be indifferent to each other as well as the actual physical behaviour of the specimen they attempt to predict. Due to its stress dependency, aka the acknowledgement of stress interactions, the ratio of the load-bearing capacities of the two subsystems are dependent on the structural system as well as the loading. This is the major difference to the current design standards, which does not account for this effect due to it being grounded on a biased test database.    «

Advancement of standards is generally assumed to be one of two things. Either the introduction of more efficiency into the prediction, or the eradication of previously unknown and unwanted effects. Both are strived for and welcomed by the community, as it allows for the reduction of material and cost, while ensuring the required degree of safety. This, however, can not be said for the development of the shear verification method of reinforced and/or prestressed concrete slender beams. The latest...    »