Seismic-Resistant Performance of Double Built-Up T Moment Connections

The double-T moment connection is considered in the AISC Seismic Provisions for use in steel structures subjected to seismic forces. Nowadays, the use of double-T connections requires the use of hot-rolled T-sections, which limits the optimal design. Hence, if there is a need to increase the flange or web thickness, this can only be achieved by increasing the entire T-section size, providing oversized and costly sections. In this research, this issue is addressed by studying the use of double built-up T (DBT) moment connections. Two full-scale specimens, as a complement to the five specimens previously tested by the authors, one considering a web panel zone failure mechanism and the other with the failure mechanism controlled simultaneously by the web panel zone and beam plastic hinging (balanced failure), were subjected to cyclic loading using the protocol established in AISC Seismic Provisions. Then, seven numerical models in ANSYS were developed, to reproduce the conditions of the seven specimens tested. The results showed an acceptable behavior of the specimens when the plastic hinge in the beam is the failure mechanism criterion controlling the seismic design. The specimens with a weak connection reached a lower resistance in comparison to the specimens with a weak panel zone and balanced failure. However, all specimens were able to achieve a story drift ratio of 4% with significant strength. The numerical models were calibrated from experimental data. No failures in the welds were observed in the specimens tested, which included full-penetration and fillet-welded specimens; therefore, the use of built-up T-stubs is reliable if their design is performed using a capacity design.