Shear fatigue in reinforced concrete members without shear reinforcement – Experimental characterization and analytical modeling

• Applicant: Professor Dr.-Ing. Martin Claßen
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541376417

Fatigue of reinforced concrete (RC) significantly shortens the lifespan of important civil engineering structures. Their replacement leads to high financial pressure on public budgets, massive raw material consumption, and increased CO2 emissions. A profound understanding of the degradation processes causing fatigue failures is therefore vital to ensure the durability of new and existing structures like bridges and wind power plants. Unfortunately, our current mechanistic understanding of fatigue in RC is not sufficiently advanced for this challenge and our design procedures based on phenomenological-empirical models are neither precise nor scalable. Thus, the main objective of this proposal is the development of a combined multiscale experimental and theoretical framework that can thoroughly explain the physical causalities of shear fatigue in RC structures. The central hypothesis suggests that the propagation of a critical shear crack into the compression zone – leading to the ultimate failure of shear fatigue-loaded RC members – results from cyclic degradation of various stress transfer mechanisms (STMs) along the crack. To validate this hypothesis and implement the proposal objective, a coordinated research program is proposed, consisting of four interconnected work packages (WP): In WP1, the continuously changing crack kinematics under shear fatigue loading will be meticulously studied in macroscale member tests using up-to-date measuring techniques like digital image correlation, and distributed fiber optic sensors. WP2 will apply the monitored pulsating crack deformations to mesoscale tests (using the new large-scale combined torsional and axial loading system TorAx), to analyze STM activation/degradation and identify the source of crack propagation. WP3 will quantify the yet unknown high-cyclic behavior of STMs within fatigue-induced cracks of RC structures and establish a set of constitutive fatigue degradation laws. Finally, in WP4, an analytical model for the structural fatigue response prediction of RC members will be developed. This model will consider crack propagation, integrate fatigue laws of all STMs, and provide the evolution of crack opening/sliding as well as steel/concrete strain over the entire fatigue loading process. Crucially, the primary intention of this research program is not to conduct an extensive empirical investigation of parameter combinations, but rather the fundamental exploration of innovative techniques such as deformation-controlled fatigue testing and analytical macro-modeling driven by crack propagation. These novel methods will provide deep insight into the intricate nature of structural degradation under shear fatigue loading and will help to establish a new approach in fatigue design, that is not limited to state-of-failure inspection but will consider the entire life-cycle of a structure and deliver the required input towards more sustainable, economical, and reliable RC-construction of the future.

• DFG Programme: Research Grants