Studies on the maximum vertical acceleration of flexible nonstructural components in earthquake-excited frame structures

The objective of this Master thesis is to investigate the maximum vertical accelerations of flexible nonstructural components (NTCs) in steel structures. The multi-story load-bearing structure is modelled as a frame and the acceleration-sensitive NTCs as a single-degree-of-freedom oscillator. In a first step, two mechanical models of an eight-story steel frame are created. In the first coupled model, the NTC and the frame structure are considered as one interacting system and the response of the NTC on this entire system subjected to earthquake excitation is determined. For the uncoupled model, the acceleration response of the load-bearing structure is computed without attached SDOF oscillator. Subsequently, the acceleration response of the connection node serves as the excitation of the SDOF oscillator. Moreover, the vertical accelerations of NTCs attached to one-, two-, four-, eight- and twelve-story steel frames subjected to the ground motions of a record set are computed and compared to the response of the decoupled modeling approach. The natural frequency of the NTCs is varied in the range from 0.1 to 30.5 Hz. In a comparative study on the eight-story steel frame, the mass ratio between the mass of the NTC and the floor mass of the frame is determined, where the coupled and decoupled modeling give practically the same result. The investigations of the response of the NTCs on the other frame structures are performed on a decoupled model to reduce the computation times. The vertical accelerations of the NTCs reach maximum values at the outer column lines and on the symmetry axis. The highest vertical accelerations of the NTCs are predicted at the roof floor. The results of this Master thesis show that the vertical acceleration at NTCs can be up to six times larger than the vertical acceleration at the frame node.

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