Stiffness modeling of bolted thick built-up T-stub connections including secondary prying effect

• Stiffness-based model predicts the force-deformation of T-stub/column flange.
• The model takes into account the effect of secondary prying.
• Strength model for K-zone plastification followed by interior tension bolt fracture.
• New failure limit states are highlighted.
• Simple tool in predicting strength, stiffness, ductility, and energy dissipation.

The results of experimental tests and finite element (FE) simulations are used to develop a stiffness model that predicts the behavior of bolted thick built-up T-stub connections including column flange deformation, and accounting for primary and secondary prying effect. The model incorporates the overall T-stub and column flange deformations of key component elements, and includes nonlinear material behavior of bolts and base material, and accounts for pretension of fasteners and contact interactions. The stiffness model consists of linear and nonlinear springs which model deformations from tension bolt elongation, slip-bearing, bending of T-stub flange, elongation of the T-stem, column flange deformation, and accounts for primary and secondary prying forces. The behavioral characteristics of the T-stub/column flange system are examined including strength, stiffness, deformation, and energy dissipation. A proposed strength model that predicts the capacity of the column flange for the failure mode of full plastification at the flange-to-web connection of the column (K-zone) followed by interior tension bolt fracture is developed. Furthermore, closed form expressions that are based on stiffness modeling techniques are developed to predict the energy dissipation capacity of the T-stub/column flange system with and without continuity plates. Comparison of the models predictions with experimental and FE data shows that the proposed models accurately predict the connection and the column flange load-deformation response. This study provides guidelines for engineers to account for the additional forces induced in the tension bolts and for the maximum rotational capacity demand in the connection which are required for seismic analysis and design.