PSI - Issue 84

Pavlina Lakatosova et al. / Procedia Structural Integrity 84 (2026) 1278–1285

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hypothesis of plane sections remaining plane is no longer applicable. Typical examples include regions subjected to concentrated loads or abrupt changes in geometry, such as frame corners, short corbels, pier heads, cross-beams, or deviators in bridge structures. When designing such regions, engineers have several options for assessment and reinforcement design. One commonly used approach is the strut-and-tie method (STM), which is codified in EN 1992-1-1 and EN 1992-2. However, applying this method correctly requires considerable experience in idealizing the load-bearing mechanism and formulating an appropriate strut-and-tie model. For this reason, specialized software tools for solving two- and three-dimensional spatial problems are often advantageous, as they simplify the design process and improve understanding of structural behavior in discontinuity regions.

Fig. 1. Examples of discontinuity regions

One such application is IDEA StatiCa Detail, whose calculation core is based on the Compatible Stress Field Method (CSFM). The method was developed in cooperation with ETH Zurich for planar problems and subsequently extended to three dimensions to capture spatial structural behavior. A key advantage of this approach over general finite element analysis is the direct implementation of Eurocode assumptions and verification requirements, enabling direct code

compliant assessment of discontinuity regions. 2. Compatible Stress Field Method (CSFM) 2.1. General principle

As implied by its name, the Compatible Stress Field Method yields continuous stress fields within the analyzed structural segment. The principle of CSFM can be explained using a basic planar reinforced concrete element. In Fig. 2a, the stress state of the element is shown as obtained, for example, from a linear elastic finite element analysis. The element is subjected to horizontal compressive stress σₓ, vertical compressive stress σ z , and shear stress τ xz . From these stresses, the principal stresses and their inclination angle θ can be determined (Fig. 2b). In the principal stress system, shear stresses vanish; σ₁ represents the principal tensile stress and σ₂ the principal compressive stress.