Shaking Table Test of Two-Story Steel Moment Frame With Seismic Floor System

Abstract eng:
Seismic floor system, which can decrease seismic responses (e.g., story drift, absolute acceleration on the floor, and stress of members) by means of inserting visco-elastic materials (VEMs) between concrete floor slab and beams, has been developed to enhance not only seismic performance but also workability of dismantlement of buildings. The effects of the floor system on the seismic responses have been studied by both dynamic analysis and shaking table tests of single-story simplistic structure model, however the detail of setup of VEMs was not considered. Therefore, this paper describes a shaking table test of two-story steel moment frames with seismic floor system in consideration with real details, and discusses seismic responses of real frames to which the seismic floor system is adopted. Test specimen is one-third scale of bi-directional steel moment resisting frame, and the long span is 3 meters, the short span is 2 meters, and the height of the story is 1 meters. The frame consists of H-shaped beams and square tube columns. The bending strength of the columns are enough to remain elastic under bi-directional input ground motion. There are two kinds of specification of beam-floor connection, one is full-composite beams which are connected to the concrete floor slab rigidly by headed studs, and another is non-composite beams which are separated from the concrete floor slab. In case of non-composite beam specimen, the tests were conducted when relative displacement of the floor against the beam, that is shear deformation of VEM on beam flange, was unfree (without damping) or free (with damping) respectively. 3D shaking table, whose capacity of the maximum ground acceleration is 1G, was used for the test. The input wave was BCJ L2, which is the art-wave of almost flat pseudo velocity spectrum at over 1 second. The intensity of the input wave increased gradually from 0.25 to 1.5 times of the original level, and the input direction was adopted as 0, 45 and 90 degrees against long span direction. Before each input of BCJ L2, preliminary vibration was conducted by white noise wave of quite small intensity to check the vibration characteristics of specimen. As a result, it is confirmed that in case of the composite beam specimen without damping the story drift is smaller but the absolute acceleration on the floor is larger than those of the non-composite beam specimen without damping, because the horizontal strength of the composite beam specimen is the largest of all specimens. On the other hand, in case of the noncomposite beam specimen with damping, both the story drift and the absolute acceleration on the floor are the smallest of all specimens because of energy dissipation of VEMs. Consequently, it is clarified that utilization of the seismic floor system for real steel structures is valid.

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