Development of a new design approach of reinforced concrete structures based on strength reduction method

The design of complex reinforced concrete structures or elements of structures can be a challenging task for practitioner structural engineers in some specific non-conventional projects. For these specific cases, the use of well-established and standard design methods such as sectional methods or strut-and-tie methods can result into complex and sometimes inappropriate designs. On the other hand, the use of sophisticated numerical methods such as nonlinear finite element methods is not common in these situations because of their complexity and the lack of consensus on their validity within the engineering community. This work presents an innovative new design approach for complex reinforced concrete structures. The approach is inspired from the strength reduction numerical method, well-established in the field of slope stability in geotechnical engineering. It can be considered as an intermediate approach between the conservative and universally well accepted strut-and-tie method, and the powerful nonlinear finite element method. A new simple constitutive law for concrete has been developed for that purpose as a user subroutine under the software ABAQUS-Explicit. It allows for the degradation of concrete by gradually reducing its tensile strength during the analysis. This law is presented within an overall new framework for the design of reinforced concrete structure based on two steps. The structure is loaded in a first linear elastic step and then degradation of the tensile post-pic occurs in a second nonlinear step. At the end of this second step, a re-organisation of the internal stresses occurs within the structure. A resisting pattern and failure modes similar to those in the strut and tie models occur as well. Two application examples are presented at the end of the study and demonstrate the potential and the feasibility of the new approach.