Special Truss Moment Frame Component Test 5 - 2C12x20.7

Special truss moment frame component test 5, made of double channels 2-C12x20.7, was tested under the same cyclic history loading as experiment 4. The test setup is still a representative of half of the chord in the special segment of the prototype special truss moment frame. In experiment 4, web bulging was heavily concentrated between the first two pairs of the web stiffeners which was the location of the plastic hinge. In this experiment, the first, second, and third pairs of stiffeners were placed at 9.25 in., 11.5 in., and 16.75 in. from the column face, respectively. This resulted in smaller spacing of 2.25 in. between the first and the second pairs of web stiffeners intending to push web bulging away from the plastic hinge region. The number of horizontal stitches was reduced to one pair placed at 1 in. away from the edge of the gusset plate. The other stitches were conventional. Weld crack started early in this experiment at 0.75% story drift. Crack propagation progressed faster than in previous specimen and the bottom flange and web of the west channel fractured at 1.5% story drift which was equivalent to 4.18% member drift. Premature fracture was believed to be a result of the restraint on the channel flanges by the stiffeners at plastic hinge region. The very short length of the flange between the two stiffeners translates into smaller elongation allowed and higher stress concentration.