A method born more than
a century ago
The stress field theory, developed since 1899 and refined at EPFL, lies at the heart of ConcrIT. A look back at the history of a world-reference method for reinforced concrete design.
History of the method
Grounded in the theory of plasticity, the stress field method offers a physically consistent description of the strength of reinforced concrete structures. Its development spans more than 120 years — from Ritter’s trusses to the elastic-plastic stress fields of EPFL.
Wilhelm Ritter — 45° truss model
The Swiss engineer Wilhelm Ritter proposes the first mechanical model for the shear strength of a reinforced concrete beam after cracking. He models the compressed concrete as struts inclined at 45° and the reinforcement as tension ties — the first formalization of a “stress field” in concrete.
Emil Mörsch — Continuous diagonal compression field
Mörsch extends Ritter’s work by replacing the discrete struts with a continuous diagonal compression field in the shear zone. This distributed view of the stress flow is the direct ancestor of today’s method and remains the basis for designing transverse reinforcement in most codes.
Leonhardt & Walther — Elastic stress fields
Fritz Leonhardt and his collaborators extend truss models to the resultants of elastic stress fields, determined by elastic analyses or photoelasticity. This step paves the way for modern strut-and-tie methods for discontinuity regions.
Schlaich, Schäfer & Jennewein — Generalized strut-and-tie
Jörg Schlaich and his collaborators formalize the strut-and-tie method (strut-and-tie model) within a universal framework applicable to the whole structure, including discontinuity regions (D-regions). This seminal publication is incorporated into many international codes, including Eurocode 2.
Collins & Mitchell — Modified Compression Field Theory
Michael P. Collins (University of Toronto) develops the Modified Compression Field Theory (MCFT), able to predict the shear behaviour of cracked reinforced concrete members while accounting for crack rotation. The MCFT is the basis of the shear design rules of North American codes (ACI, AASHTO, CSA).
Aurelio Muttoni — PhD thesis, ETH Zurich
At ETH Zurich, Aurelio Muttoni defends his doctoral thesis on the application of the theory of plasticity to the design of reinforced concrete structures. In it he lays the foundations of a rigorous approach based on elastic-plastic stress fields, which would become the Swiss reference method and the scientific foundation of ConcrIT.
Muttoni, Schwartz & Thürlimann — A world-reference book
Publication by Birkhäuser of Design of Concrete Structures with Stress Fields. This book synthesizes the rigid-plastic and elastic-plastic stress field method and disseminates it internationally. It becomes the academic and professional reference on the subject.
Aurelio Muttoni — Professor at EPFL & founding of IBETON
Appointed full professor at EPFL, Muttoni leads the Structural Concrete Laboratory (IBETON). Under his direction, the laboratory becomes one of the world’s leading centres for stress field research, validating the method on hundreds of experimental tests.
SIA 262 standard — Official integration of the method
The Swiss standard SIA 262 (Concrete Construction) incorporates stress fields as a recognized design method for structures with transverse reinforcement. This normative choice validates the approach for professional practice in Switzerland. ConcrIT relies directly on this standard, alongside Eurocode 2.
i-concrete & JCONC — First public software (EPFL)
IBETON launches the i-concrete platform, a public portal giving access to JCONC, the first solver implementing elastic-plastic stress fields (EPSF). Developed by Miguel Fernández Ruiz, with the support of Aurelio Muttoni, JCONC lets engineers and researchers worldwide check reinforced concrete structures using this method. It is the direct precursor of ConcrIT’s solver.
EPSF — Massive experimental validation at IBETON
A series of doctoral theses at IBETON extends and validates the EPSF method for increasingly complex cases: beams and slabs subjected to combined actions, shell elements, existing structures. Filip Niketic’s thesis (2017) compiles a database of 315 experimental tests, confirming the reliability of the method (mean ratio = 1.03).
End of an era — closure of IBETON
On 29 February 2024, Prof. Aurelio Muttoni retires after 24 years at the head of IBETON, which closes its doors. The i-concrete.epfl.ch platform, in service since 2005, is gradually decommissioned and redirects to a new site, i-concrete.ch. Nearly 20 years of research on elastic-plastic stress fields and the JCONC solver have trained a whole generation of engineers and researchers — a legacy that ConcrIT intends to keep alive.
ConcrIT — Professional commercial suite
ConcrIT takes up the scientific foundations of JCONC and i-concrete and integrates them into a modern, fully online professional environment. The platform implements the stress field method in accordance with the SIA 262 and Eurocode 2 standards, with automatic generation of code-compliant calculation reports.
ConcrIT relies on the stress field theory as defined in the Swiss standard SIA 262 and the Eurocodes. The method provides lower-bound solutions of the theory of plasticity, ensuring a safe and economical design. It is recognized as one of the most rigorous and consistent approaches available for the design of reinforced and prestressed concrete.