Thermomechanical analysis of X-Braces in steel structures under fire conditions

Flavio Stochino

;Michele Cotza;Daniele Andriotto;Diego Cecchinato;Marco Zucca

2026-01-01

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Abstract

Bracing systems in steel structures are crucial for providing stability and resistance against lateral forces such as wind and earthquakes. However, when steel structures are exposed to fire, the bracing systems can also play an important role in maintaining the structural integrity of the building. Under fire conditions, steel members may lose strength due to heating, which can lead to collapse if not properly braced. In this article the effect of different X-braces cross-section in a steel warehouse under fire is analyzed and discussed using a non-linear thermomechanical model. Three fire scenarios have been considered: standard ISO834 fire, wood fire and plastic fire to investigate the influence of different temperature time history curves on the thermomechanical behavior of the structure. It has been found that an increase in the stiffness of the braces leads to a corresponding increase in the stiffness of the frame modifying its structural behavior; furthermore, since the compressed braces reach their buckling load in the initial minutes of a fire, the structure must redistribute its loads accordingly.