Special Truss Moment Frame Component Test 14 - 2C12x20.7 (RBS)

Specimen 14 was made of double channels C12x20.7 that the width of the flanges was cut off in order to reduce the moment capacity by 20%. This specimen employed the same idea of reduced beam section (RBS) used in wide flange sections, hence; 2C12x20.7 with reduced beam section (RBS). It was tested under cyclic loading with the test setup representing the chord members in the special segment of a prototype STMF. This prototype STMF specimen will utilize buckling restrained braces (BRBs) to enhance its behavior. In order to avoid heavy reinforcement of the members outside special segment which have to remain elastic, RBS will be used to reduce the special segment chord members’ capacity.
The specimen exhibited a stable and ductile behavior under cyclic loading. Its strength peaked at 1.5% story drift then gradually dropped starting at 2% story drift. The combination of crack propagation, bulging, and flange and web local buckling contributed to the gradual loss of strength. During the last cycles of the test, at 9.46% member drift, the stitches hit the gusset plate and initiated cracks in the stitches. In the end, the specimen failed when the stitch fractured completelyใ The reason behind this was probably because the bulging was so severe that it greatly pulled the stitch on the compressive flange toward the gusset plate. This incident was not believed to happen in the full scale STMF because the columns and other framing members could provide restraints to the chord members in the special segment. In the end, the specimen failed when the stitch fractured completely and the test was terminated.