Stress-based Dimensioning of Reinforced Concrete Structures

• Applicants: Professor Dr.-Ing. Manfred Bischoff; Professor Dr.-Ing. Manfred Curbach
• Subject Area: Structural Engineering, Building Informatics and Construction Operation ; Applied Mechanics, Statics and Dynamics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559315176

Spatial or planar load bearing structures with compact geometries cannot be designed on the basis of internal forces from beam, slab or shell theories using material nonlinearity in the cross-section. An alternative design based on elastically determined stresses using finite elements is possible, but uneconomical. The design with strut-and-tie models is limited, especially for spatial structures and constrained load cases, as well as with respect to automation. The aim of the project is therefore to develop a stress-based, materially nonlinear design concept to close this methodological gap. The working hypothesis is that the consideration of nonlinear behavior leads to more economical designs than elastic stress-based concepts. The methodological idea is to generate the required reinforcement in an iterative sequence of nonlinear computations considering the material nonlinear behavior of the concrete and steel as well as their interaction in a kind of growth process. In this process, the bending stiffness of the reinforcement is also considered within the framework of the rebar concept, particularly to be able to represent the dowel effect, which is important for shear reinforcement. The purpose of the mechanical model is explicitly not the recalculation of tests or the detailed modeling of complex damage processes in reinforced concrete, but only the representation of design-relevant phenomena. As a result, the interaction between concrete and steel in the cracked state must be modeled as simply as possible, considering the bending stiffness of the reinforcement, but with sufficient accuracy for the requirements of a design task. For the derivation and specific formulation of statements about the required reinforcement (reinforcement growth), determining criteria as well as required quantities derived from structural-mechanical simulations will be investigated. In the algorithmic realization, the focus is on convergence, efficiency, and robustness. The scientific work program includes experiments that provide insights into the modeling of the bedding of the reinforcement transverse to the member axis in the region of cracks that are not orthogonal to the reinforcement. In the first application phase a structural mechanics and numerical model for the calculation of reinforced concrete structures with discrete consideration of the reinforcement, which represents design-relevant phenomena, is being developed, implemented in an in-house software, and validated for slabs and wall-like beams. The essence of the work pro-gram is the development of an algorithm for generating reinforcement based on such calculations. The concept will be systematically validated in particular with regard to the working hypothesis that the consideration of nonlinear behavior leads to more economical design results than elastic stress-based concepts.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Malte Von Scheven