Design and Evaluation of a Prototype Low-Damage Beam-Column Connection for Mass Timber Moment Frames

A moment-resisting, beam-column connection for mass timber moment frames was developed, designed and tested. The design was intended to limit damage to the timber members by creation of a ductile failure mechanism in steel U-shaped flexural plates (UFPs). Using design equations developed by previous research on UFPs by Baird, et al. (2014) as well as accepted design practices from the NDS and AISC, the components were sized to eliminate failure in the timber. The connection was tested using a quasi-static lateral displacement method following the procedure outlined in section K2.4b of AISC 341-16. A vertical load was placed on the system to replicate lower level behavior of mid-rise construction. During testing, visible and audible cracking of the timber column was observed, indicating the UFPs were not properly engaged to limit failure of the timber members. Further analysis of the measured load displacement result indicated that much of the energy dissipation seen in the system was likely due to failure of timber column. Analysis also indicated that the system was not as stiff as expected due to slip of the connection relative to the timber. The failure of the system to meet expectations indicates that further efforts are required to better understand the performance of UFPs. The results of this project also indicate the challenge of developing a low-damage moment resisting connection which streamlines installation without sacrificing functionality.