STMF 2 - Cyclic Loading Test of Special Truss Moment Frame with Double-Channel Chord Members and Buckling Restrained Braces in Special Segment

The chord members of STMF 2 were double channels (2C12x20.7) whose flanges were cut within the special segment so that its moment capacity was reduced to 80%. The overall length (center-to-center of the columns) was 31'-9". The special segment length was 9'-11" long and the depth of the truss was 4'-0". The clear spacing of stitch was 22.5 in. which was greater than AISC 341-10 requirements. The connection detailing of the chord members in the plastic hinge regions, which were located at the ends of the chord members in special segment, was done according to the proposed new configuration.

The specimen was cyclically loaded according to a loading protocol similar to the AISC 341-10 loading sequence for beam-to-column moment connection. STMF 2 exhibited high stiffness and strength up to 1% due to the presence of BRBs. At 2% story drift, its strength dropped slightly due to failure of the BRB core members and yielding of the chord members and vertical members near special segment. While reaching 3% story drift, the stiffness of STMF 2 greatly dropped then it picked up strength again. This is believed to be resulted from the fact that BRBs would not buckle so distortion and movement occurred at the BRBs’ end plates and pins and the middle gusset plate. At 4% strory drift, the BRBs’ end plates and the chord members severely damaged which resulted in higher strength degradation.