Structural mechanics of reinforced concrete hinges: experiments, modeling, and design recommendations

Abstract

This dissertation refers to engineering-mechanics research on reinforced concrete hinges. The latter are used as supports of integral bridges. In that case, the reinforcement consists of steel rebars crossing at the centerline of the neck. Concrete hinges are also used as interfaces between neighboring tubbings of segmental lining rings in mechanized tunneling. In that case, the reinforcement consists of eccentrically positioned steel bolts. The present dissertation bridges the gap between the two seemingly disconnected fields. Experiments and nonlinear Finite Element simulations are combined in order to develop an engineering-mechanics model for elastic and ultimate limit states of reinforced concrete hinges. The experiments were carried out at the material scale of concrete and the structural scale of reinforced concrete hinges. Normal strength concrete and high-strength concrete were included. A sensitivity analysis regarding the maximum aggregate size was performed. The time-dependent material and structural behavior was tested at load levels representative for regular service. The bearing capacity was determined using two different test protocols: one for eccentric compression and the other one for prescribing a specific normal force and imposing variable relative rotations. The following main conclusions were drawn: concrete hinges are very creep-active structural elements. Creep and bending-induced tensile cracking are coupled. Reinforced concrete hinges fail in a very ductile fashion, at large imposed loads. Nonlinear Finite Element simulations of a reinforced concrete hinge, subjected to eccentric compression up to the bearing capacity, was carried out with Atena Science.1 The following main conclusions were drawn: significant triaxial compressive stress states are activated in the region of the neck of concrete hinges. The confinement-induced strengthening of concrete can be quantified according to Eurocode-regulations for partially loaded areas. The ductile structural failure of reinforced concrete hinges is a consequence of the ductile material failure of concrete which is located at the surface of the compressed lateral notch. Engineering-mechanics modeling of reinforced concrete hinges was based on the Bernoulli- Euler hypothesis in combination with linear-elastic and ideally-plastic material behavior of concrete in compression and steel in tension. The developed model describes the relationship between the normal force and the bending moment transmitted across the hinge as well as its shortening and relative rotation. As for the application of the engineering-mechanics model in integral bridge construction, Eurocode-compatible recommendations for verification of serviceability and ultimate limit states of reinforced concrete hinges were elaborated. Serviceability limits were related to configurations where the elastic limit strain is reached by concrete in compression and/or by steel in tension. Ultimate limits were related to ultimate limit strains. Analytical formulae were derived as the basis for dimensionless design diagrams, illustrating limits of tolerable relative rotations as a function of the degree of utilization of the normal force. The usefulness of these diagrams was demonstrated by comparing model-predicted serviceability and ultimate limits with experimental data from bearing capacity tests of reinforced concrete hinges. Finally, a concept for verification of serviceability and ultimate limit states was developed and applied to an existing integral bridge. As for the application in mechanized tunneling,2 its satisfactory performance was shown by comparing model predictions with results from testing of a segment-to-segment interface. The validated model was used to describe elastic and ultimate limit states of segmental tunnel rings subjected to anisotropic ground pressure.