Strut-and-Tie Model for Development of Headed Bars in Exterior Beam-Column Joint

Abstract

Headed bars have been proposed as an alternative to hooked bars in anchoring longitudinal reinforcement terminated within exterior or corner beam-column joints. This paper proposes a strut-and-tie model (STM) for the development of headed bars in an exterior beam-column joint that investigates realistic force transfer by headed bars within the joint. The tensile force in a headed bar is considered to be developed by head bearing together with bond along a partial embedment length. The model consists of struts with nodal zones for head bearing and fan-shaped stress fields for bond resistance along the bonded length. The model shows how to decompose the tensile force developed in headed bars into direct strut action and fan action and their effects on joint shear strength. Tests on exterior beam-column joints without transverse reinforcement, and that neglect axial forces due to self-weight and live load, are intended to focus on the effect of anchorage capacity of headed bars on joint shear strength. Findings show that the STM explains two different load transfers from the headed bar to the exterior beam-column joint. The proposed model is also capable of considering not only the head size and material strengths, but also the structural configurations of the system under consideration. Finally, it is applicable to anchorage zones of headed bars with various geometries and boundary conditions.