Displacement-based Analysis and Design of Rocking Structures
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Date
2021
Publication Type
Conference Paper
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yes
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Abstract
Rocking can be used as a seismic isolation strategy for bridges and buildings. Letting a structure uplift works as a mechanical fuse and limits the design forces of both the foundation and the superstructure. Interestingly, there is no correlation between the rocking oscillator and the elastic one. Therefore, there is not any “equivalent linear system” and the elastic spectra are useless when it comes to rocking. Thus, there is no simplified design procedure that a practicing engineer could use. In order to create design rocking spectra, the rocking oscillator should be described with the simplest possible way and the least necessary parameters. Since Housner’s seminal paper in 1963 the traditional DOF chosen to describe the motion of a rocking block has been its tilt angle. This description uncovers that out of two blocks with the same slenderness ratio, the larger one is more stable. This tilt-based description is mathematically correct, but not optimal.
This paper shows that the top displacement is a better descriptor of the rocking oscillator, because it uncovers a fundamental property useful for design: As long as the blocks are not close to overturning, the top displacements of a large and a small block of the same slenderness are going to be roughly equal. This property is proven for both analytical pulses and for recorded ground motions. In mathematical terms, the displacement demand on a rocking block is a unary function of its slenderness angle. In practical terms, this means that the displacement demand of any block can be computed by the displacement of a block of the same slenderness, yet very large size – likewise the displacement demand of a yielding oscillator can be computed based on the displacement of an equivalent linear system. Thus, the rocking-related seismic hazard can be computed by much simpler rocking spectra.
As an example, the proposed method is applied for the preliminary design of a rocking frame having the dimensions of a typical overpass bridge.
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published
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Book title
Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
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Pages / Article No.
Publisher
National Information Center of Earthquake Engineering
Event
17th World Conference on Earthquake Engineering (17WCEE 2020-21)
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Date created
Subject
rocking; uplifting structures; dimensional analysis; dimensionality reduction; displacement-based design
Organisational unit
09663 - Vassiliou, Michalis (ehemalig) / Vassiliou, Michalis (former)
Notes
Conference lecture held on September 28, 2021. Conference postponed due to Corona virus (COVID-19), and rescheduled from September 13-18, 2020 to September 27 - October 2, 2021
Funding
ETH-10 18-1 - Seismic analysis, design and experimental testing of precast controlled-rocking negative-stiffness systems (ETHZ)
Related publications and datasets
Is new version of: http://hdl.handle.net/20.500.11850/366268