Bond and anchorage of pre-tensioning tendons

Pre-tensioning is a type of prestressed concrete and is commonly used in precast construction. In pre-tensioning, the bond anchorage between the prestressing tendons and the concrete is of great significance. The bond mechanisms of the anchorage are complex and depend on various influencing factors. To consider the mechanisms in the design process, a sophisticated design model is required. The current codes contain design models for pre-tensioniong anchorage; however, they have some deficiencies. For this reason, theoretical and experimental investigations on different aspects of pre-tensioning anchorage were conducted. Finally, the results were used to derive an enhanced design model for pre-tensioning anchorage. The first part of this work summarizes the state of the art on pre-tensioning anchorage. The bond mechanisms of pre-tensioning anchorage and the relevant design models are presented. In addition, an overview of testing setups for the investigation of pre-tensioning anchorage is given, and derivation approaches for constitutive laws for the description of bond are shown. The second part covers experimental investigations on the bond behavior of indented wires and on the influence of cyclic loading on pre-tensioning anchorage. To investigate the bond behavior of indented wires with low indentation depth, numerous pull-out tests and small-scale tests were performed. The evaluation shows that an adaptation of the transmission length values is not necessary in Eurocode 2 and Model Code 2010. Furthermore, adjustments for the minimum concrete cover of indented wires to ensure a crack-free transfer of the prestressing force are proposed. In further experimental investigations, the bond behavior of pre-tensioning anchorage with cyclic loading was investigated in sixteen four-point bending tests. Based on the results of the tests and on a systematic numerical analysis, a modification of the Eurocode 2-formula for the anchorage length of pre-tensioned tendons is proposed. The modified formula for the anchorage length enables a simple and reliable design of pre-tensioned components with cyclic loading. Finally, a new design model for pre-tensioning anchorage was developed. Initially, a database analysis with more than 1200 tests was accomplished. The evaluation of the database shows that the design concept of the current Eurocode 2 is best suited as a starting base for the new model. The enhanced model considers the knowledge gained in the work. In doing so, it also considers the influences of time-dependent concrete strength development and cracking on pre-tensioning anchorage, which are included in theoretical investigations. Altogether, the proposed design model enables a simple and safe design of the pre-tensioning anchorage. The model also makes it possible to consider numerous influencing parameters in the design. The proposed model was developed within the framework of the development of the next Eurocode generation