Damage mechanisms in cementitious coatings on steel members in bending

Cementitious coatings are widely used as fire protection for steel structures but they are vulnerable to damage from structural deformations. In this paper, damage mechanisms in cementitious coatings on steel members in bending are investigated. A series of monotonically loaded beam tests are conducted to observe the occurrence of cracks and their propagation leading to final failure. The experiments are then simulated using a cohesive zone finite-element scheme, capable of modelling interfacial damage between the coating and steel substrate as well as internal coating damage. The results of the experimental and numerical studies clearly reveal the distinct damage mechanisms of cementitious coatings on both tension and compression sides of structural steel members in bending. Findings from this study provide the foundation for developing practical methods to determine the condition of cementitious coatings on steel structures after a short-duration extreme loading event (earthquake, blast, windstorms), where there is minimal external damage to the building fabric or longduration cumulative damage from moderate levels of repeated non-monotonic loading. It is very unlikely in either of these cases that the integrity of cementitious fire protective coatings has been investigated in current practice.