Numerical modeling of SFRC tunnel segments: influence of material constituents and segmental joints

• Grant number: 25/06405-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2025
• End date: June 30, 2026
• Field of knowledge: Engineering - Civil Engineering - Structural Engineering
• Principal Investigator: Luís Antônio Guimarães Bitencourt Júnior
• Grantee: Pedro Geovani de Oliveira Sperandio
• Host Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 22/03179-0 - Multiscale modeling of plain and steel fiber reinforced concrete and its application to predicting the behavior of structural members, AP.PNGP.PI

Abstract

Discontinuous steel fibers have been added to the concrete as primary reinforcement to avoid abrupt tensile failure. The main role played by the fibers becomes more evident after the cracking of the cementitious matrix, at which point the fibers resist crack propagation by transferring stresses across crack faces, thus maintaining some load-carrying capacity and preventing sudden composite failure. The high potential of this composite, known as steel fiber-reinforced concrete (SFRC), has led to its application as a structural material, improving the performance of structural elements at both the Serviceability Limit State (SLS), by reducing crack width and spacing, and the Ultimate Limit State (ULS), by enhancing material toughness and enabling the partial or even total replacement of conventional reinforcement. In the coming years, the use of SFRC in national infrastructure projects is expected to grow, especially following the recent publication of the Brazilian standard NBR 16935 - Design of fiber-reinforced concrete structures (2020). In this context, precast concrete segments reinforced with steel fibers have gained prominence in tunnel construction due to the improved mechanical performance provided by this type of reinforcement. However, despite the potential of SFRC as a structural material, market skepticism still exists, mainly due to the variability observed in experimental tests conducted on structural elements and material characterization tests. Moreover, the behavior of the composite can be influenced by several parameters, such as the structure of the concrete matrix, fiber material, shape and geometry, fiber content, fiber distribution, and the fiber/matrix interface structure. Therefore, developing research that considers all factors and their combinations affecting the composite's mechanical response, focusing solely on experimental investigations, is a time-consuming and costly process. This research project aims to contribute through a numerical study to predict the behavior of SFRC segments, considering the influence of material constituents as well as the interaction between segments (joints) in segmented tunnel rings. A numerical tool developed by the research group associated with this project will be used and adapted to explicitly represent all material constituents that affect, at the mesoscale level, the composite behavior. In addition, coupling finite elements and appropriate damage constitutive models will be used to represent the contact between segments.