Rotation capacity and overstrength of steel beams: evaluation of prediction models

The ductility is the structure’s ability to sustain large deformations in plastic range without considerable loss of strength. The design concept based on the ductility properties of structures is the principle method to assure for an appropriate structural behavior against strong ground motions. The capacity to predict required and available ductility under severe loads is a key-point in earthquake design. The actual progress in this problem is given by the possibility to prove the ductility of the structure at the same level as for rigidity and strength. Unfortunately, in present design specifications, there are only vague provisions relating to the evaluation of the structure ductility, mainly based on cross-section classes. However, the actual ductility is affected by the properties of full member [1]. In this regard, the knowledge of the rotation capacity and flexural ultimate resistance of the steel member is of prime importance for an appropriate application of hierarchy criteria in seismic design of structures [2]. In this paper, a critical review of the existing prediction models for the rotation capacity and flexural overstrength factor for the steel members with a wide range of cross-section typologies is presented. Moreover, the description of rotation capacity and overstrength factor in current design codes is discussed comparatively.