When horizontally acting loads from 🌬️ wind or 🌍 earthquakes act on a stiffening unreinforced concrete wall, the result is far more than just uniaxial compressive stress.
In the wall plane, vertical and horizontal normal forces overlap with shear forces—a plane stress state that requires a biaxial analysis of concrete behavior.
The basis for the load-bearing capacity assessment is, for example, the failure curve according to 📚 Kupfer et al. (1969) as well as the entire body of literature built upon it.
This describes concrete failure in three regions:Compression–compression:
- Compression–tension: The strength increases relative to the uniaxial value (~+16%).
- Compression–tension: As compressive stress increases, the shear strength decreases.
- Tension–tension: Failure occurs as soon as the principal tensile stress reaches the concrete tensile strength.
Using the example of an unreinforced concrete wall
(C25/30, thickness 20 cm, length 430 cm, height 280 cm), the principal normal stresses σ₁ and σ₂ are determined and plotted in pairs in the σ₁ σ₂ plane.📊
Since all points lie within the failure curve, the ✅ verification of the combined axial force and shear force capacity can be provided for this wall.