Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

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Existing design guidelines for concrete hinges are focusing on serviceability limit states. Lack of knowledge about ultimate limit states was the motivation for this work. Experimental data are taken from a testing series on reinforced concrete hinges subjected to eccentric compression up to their bearing capacity. These tests are simulated using the finite element (FE) software Atena science and a material model for concrete implemented therein. The first simulation is based on default input derived from measured values of Young's modulus and of the cube compressive strength of the concrete. The numerical results overestimate the initial stiffness and the bearing capacity of the tested concrete hinges. Therefore, it is concluded that concrete was damaged already before the tests. A multiscale model for tensile failure of concrete is used to correlate the preexisting damage to corresponding values of Young's modulus, the tensile strength, and the fracture energy of concrete. This allows for identifying the preexisting damage in the context of correlated structural sensitivity analyses, such that the simulated initial stiffness agrees well with experimental data. In order to simulate the bearing capacity adequately, the triaxial compressive strength of concrete is reduced to a level that is consistent with regulations according to Eurocode 2. Corresponding FE simulations suggest that the ductile structural failure of concrete hinges results from the ductile material failure of concrete at the surface of the compressed lateral notch. Finally, Eurocode-inspired interaction envelopes for concrete hinges subjected to compression and bending are derived. They agree well with the experimental data.

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Reinforced concrete hinges, subjected to eccentric compression, are failing in a ductile fashion (Schlappal et al. 2017). Three-dimensional Finite Element simulations are prime candidates for a more detailed analysis of this interesting structural behavior. Such nonlinear simulations, however, typically require pocedures for updating of the underlying models. They involve fitting of input parameters such that the output of the simulations agree with experimental measurements (Kalliauer et al. 2017). In the present contribution, it is investigated to which extent fitting procedures, involving time-consuming nonlinear three-dimensional Finite Element simulations, can be avoided. Therefore, input parameters are identified by combining (i) results from destructive and nondestructive compression tests on plain concrete specimens, (ii) results from centric and eccentric compression tests on concrete hinges subjected to serviceability loads, (iii) a multiscale model for tensile failure of concrete, and (iv) linear-elastic twodimensional Finite Element simulations. Parameter identification aims of (i) quantifying the influence of damage of concrete (resulting from restrained shrinkage prior to structural testing) on the elastic stiffness, the tensile strength, and the fracture energy, and of (ii) determination of the characteristic triaxiality of the compressive stress states, prevailing in the neck region, in order to ensure modeling of the triaxial compressive strength of concrete in accordance with regulations of Eurocode 2. After parameter identification, a nonlinear three-dimensional Finite Element simulation of the bearing capacity tests by Schlappal et al. ( 2017) is carried out. The obtained numerical results agree well with experimental observations. This underlines the usefulness of the presented parameter identification strategy.