Concrete hinges are hinges produced out of concrete, with no or almost no steel in the hinge neck, which allows a rotation without a relevant bending moment.[1] This high rotations[2][3] are resulting from controlled tensile cracks as well as creep.[4][3][1] Concrete hinges are mostly used in bridge engineering[1] as monolithic, simple, economic alternative to steel hinges, which would need regular maintenance. Concrete hinges are also used in tunnel engineering.[1][3] A concrete hinge consist of the hinge neck, which has a reduced cross section and of the hinge heads, which have a strong reinforcement.[3][1][5]
Freyssinet[6][7] invented the concrete hinges.[1][3] Leonhardt introduced guidelines in the 1960s which are still used till the 2010s.[1][3] Janßen introduced the application of concrete hinges in tunnel engineering.[8][3] Gladwell developed another guideline for narrowing cross sections, which predicts a stiffer behaviour than the Leonhardt/Janßen-model[3] Marx and Schacht translated Leonhardts guidelines for the first time in the nowadays used semipropablistic safteyconcept. Schlappal,[3] Kalliauer[1] and coworkers introduced for the first time both limit caces (service-limit-states (SLS) and ultimate-limite-states (ULS)). Kaufmann, Markić und Bimschas did further studies on concrete hinges.[9]
Due to triaxial compression, strength in the neck region is much higher than for uniaxial compression,[4] because lateral expansion is restricted.[1] Eurocode 2 suggests for typical dimensions a compressive strength equal to about twice of the unixalial compressive strength.[1] Also the concrete hinge neck has no, or almost no reinforcement,[1] but the concrete hinge heads need a dense reinforcement cache, because of the tensile splitting.[10][9]