Experimental and numerical investigation of I-beam to concrete-filled tube (CFT) column moment connections with pipe-stiffened internal diaphragm

Abstract

This paper presents an experimental and numerical investigation of two full-scale I-beam to concrete-filled tube (CFT) column internal-diaphragm moment connection specimens. In this type of connection, to allow the passage of concrete through the column tube wall, the internal diaphragms are perforated, which, as a result of drilling, creates stress concentration in these plates, reducing their strength and stiffness. In this study, first, to improve the diaphragms' performance, these plates were stiffened utilizing steel pipes, and the effect of this stiffening on the connection behavior under cyclic loading was investigated in the laboratory. In the second part, the specimens were analyzed by the finite element (FE) method in the Abaqus software. Results indicated that stiffening the internal diaphragm plates with the pipes increased the connection's flexural strength and cumulative energy dissipation by 20% and 22%, respectively. It also prevented the yielding of the diaphragm plates and increased the connection's stiffness by 8% to 22%. Furthermore, the stiffening of the internal diaphragms led to better stress distribution at the plastic hinge region in the beam and shifting of the maximum rupture index location from the outer edge of the beam flanges by about 40% of the beam flange width towards the beam's longitudinal axis. It was also concluded that the proposed connection with stiffened internal diaphragm meets the criteria for utilization in intermediate moment frames (IMFs) in seismic regions.