Fatigue of profiled prestressed concrete beams with web reinforcement under shear load

• Applicant: Professor Dr.-Ing. Josef Hegger
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271387314

The shear strength of prestressed concrete beams with web reinforcement can be described by a concrete contribution and a truss contribution. Under cyclic loading their shear bearing behaviour is unresolved so far. This concerns especially the fatigue behaviour of members with medium and higher shear reinforcement ratios, since the ratio of concrete contribution and truss contribution changes with increasing amount of web reinforcement. Furthermore, a systematic investigation on the influence of cracking (flexural shear crack, diagonal tension crack) on the shear carrying components is missing. Since the deterioration and respective redistribution of forces between the different shear carrying components under cyclic loading are not quantified so far, the parameters of the common approaches for shear cannot be modified in order to obtain both safe and economic results. In addition, the common approaches do not consider the influence of the load level during cyclic loading observed in tests carried out by the applicant.The overall objective of the planned research project is to describe the load bearing behaviour of profiled prestressed concrete beams failing due fatigue fracture of the web reinforcement under cyclic loads. In this context, the distribution of shear forces between the different shear carrying components and their evolution with increasing number of load cycles are of special interest. In order to answer the open questions, experimental investigations on 24 prestressed concrete beams (I- and T-shaped) with medium and higher shear reinforcement ratios as well as numerical simulations are going to be carried out. The numerical simulations will be performed with the non-linear FE-programme Abaqus using the self-implemented microplane-model with anisotropic damage. They allow for the evaluation of the common approaches for static shear strength and the analysis of stresses under fatigue loads in the cracked state. Within the research programme, the influence of the type of shear cracking, shear reinforcement ratio, prestressing, maximum load and load amplitude should be investigated. Based on these results an approach for shear fatigue referring to the common models for static shear strength will be derived, accounting for the deterioration of the different shear carrying components.

• DFG Programme: Research Grants