Limits of the method

The solution for the stress field presented previously, with constant stresses in the compressed struts, is just one of the possible solutions in accordance with the lower bound theorem of plasticity theory.

The figure below shows another solution in accordance with the lower bound theorem, with compressed struts at a shallower inclination. This solution is less representative of reality, as the cracking of the concrete due to bending does not allow for the formation of stress fields with such a shallow inclination. Furthermore, this solution requires a greater amount of reinforcement to balance the more inclined strut.

Solution in accordance with the lower bound theorem, but less favourable

We can conclude that a choice of stress field model that is not close to the actual behaviour of the structure may lead us to overestimate or underestimate its dimensions.