Effect of the haunch angle and stiffener types on column-beam connection behaviour under static loading

Column-beam connection zones play an active role in the structural behavior of steel structures. According to the strong column-weak beam principle, which is one of the earthquake resistant building design principles, it is required that the joints are typically designed to induce plastic hinges within the beam span by moving them away from the face of the columns. Adding a haunch at the bottom of the beam flange gives the possibility of designing a joint with sufficient overstrength against the beam and ensuring the position of the plastic hinge. In this study, the behavior of column-beam connections that are reinforced with haunches were investigated, numerically. Throughout the study, models were created based on three different haunch angels: 15,30 and 45 degrees. In addition to strengthening the column web, each model was reinforced with six different types of straight and diagonal stiffeners. A total of twentyone numerical steel haunched beams to column connections with different haunch angels, and different types of stiffeners models were developed and analyzed under 100mm displacement loading by means of finite element method using Abaqus software. Material and geometrical non-linearities, contact between adjacent surfaces and the pretension force in the bolts are taken into account in the modelling. The analysis of the finite element modeling involved two loading steps. Firstly, fixed supports were applied at the end of the column and the pretension forces were applied to the bolts. After solving the first loading step, the second loading step involved a downward displacement load being applied at the loading point identified on the beam. In the analysis performed, joint evaluation indices such as Von Mises stress, plastic deformations, load-displacement curves and plastic hinge formation were examined comparatively in order to evaluate the effects of haunch angle and stiffeners reinforcements on the behavior of column-beam connections. As a result of the study, for the 30 and 45 degree haunch angles, while both met the requirements of codes, the 30 degree haunch angle was defined as the most fitting angle between the 15, 30 and 45 degree haunch angles examined throughout the study. Although, the joint's bearing capacity increased more than the 45-degree haunch angle. To sum up, among the six different types of stiffeners investigated in order to strengthen the column web and prevent buckling in the haunched connections, three parallel and K-stiffened joint types were determined as the most suitable types of reinforcement. Keywords: Column-beam connections, haunch, haunch angel, stiffeners, Finite element method, Abaqus