Efficiency of alternative intensity measures for the seismic assessment of monolithic free-standing columns

102

Summary This paper characterizes the ability of natural ground motions to induce rocking demands on rigid structures. In particular, focusing on rocking blocks of different size and slenderness subjected to a large number of historic earthquake records, the study unveils the predominant importance of the strong‐motion duration to rocking amplification (ie, peak rocking response without overturning). It proposes original dimensionless intensity measures (IMs), which capture the total duration (or total impulse accordingly) of the time intervals during which the ground motion is capable of triggering rocking motion. The results show that the proposed duration‐based IMs outperform all other examined (intensity, frequency, duration, and/or energy‐based) scalar IMs in terms of both “efficiency” and “sufficiency.” Further, the pertinent probabilistic seismic demand models offer a prediction of the peak rocking demand, which is adequately “universal” and of satisfactory accuracy. Lastly, the analysis shows that an IM that “efficiently” captures rocking amplification is not necessarily an “efficient” IM for predicting rocking overturning, which is dominated by the velocity characteristics (eg, peak velocity) of the ground motion.

Section: Introductionsupporting

confidence: 61%

Rocking amplification and strong‐motion duration

Giouvanidis

Dimitrakopoulos

2018

102

“…They concluded that the blocks with imperfections are less stable than the theoretically perfect ones. Pappas et al [60] numerically explored the behavior of an ancient cylindrical column with a height of 6 m and a diameter of 0.66 m with the intension of defining proper ground motion intensity measures to characterize the rocking response of such structures.…”

Section: Introductionmentioning

confidence: 99%

The three‐dimensional behavior of inverted pendulum cylindrical structures during earthquakes

Vassiliou

Burger

Egger

et al. 2017

102

Summary In order to use rocking as a seismic response modification strategy along both directions of seismic excitation, a three‐dimensional (3D) rocking model should be developed. Since stepping or rolling rocking structural members out of their initial position is not a desirable performance, a rocking design should not involve these modes of motion. To this end, a model that takes the aforementioned constraint into account needs to be developed. This paper examines the 3D motion of a bounded rigid cylinder that is allowed to uplift and sustain rocking and wobbling (unsteady rolling) motion without sliding or rolling out of its initial position (i.e., a 3D inverted pendulum). Thus, the cylinder is constrained to zero residual displacement at the end of its 3D motion. This 3D dynamic model of the rocking rigid cylinder has two DOFs (three when damping is included), making it the simplest 3D extension of Housner's classical two‐dimensional (2D) rocking model. The development of models with and without damping is presented first. They are simple enough to perform extensive parametric analyses. Modes of motion of the cylinder are identified and presented. Then, 3D rocking and wobbling earthquake response spectra are constructed and compared with the classical 2D rocking earthquake response spectra. The 3D bounded rocking earthquake response spectra for the ground motions considered seem to have a very simple linear form. Finally, it is shown that the use of a 2D rocking model may lead to unacceptably unconservative estimates of the 3D rocking and wobbling seismic response. Copyright © 2017 John Wiley & Sons, Ltd.

“…Based on the above, a design method that uses a size‐independent rocking spectrum is suggested. This should be taken into account when intensity measures for rocking structures designed not to get close to overturning are explored.…”

Section: Discussionmentioning

confidence: 99%

Displacement‐based analysis and design of rocking structures

Manzo

Vassiliou

2019

Summary The response of a rigid rocking block is traditionally described by its tilt angle. This is a correct description, but this paper suggests that describing rocking via displacements is more meaningful, because it uncovers that two geometrically similar blocks of different size will experience the same top displacement, provided that they are not close to overturn. The above is illustrated for both analytical pulse excitations and for recorded ground motions. Thus, the displacement demand of a ground motion on a rocking block is only a function of its slenderness, not of its size. This reduces the dimensionality of the problem and allows for the construction of size‐independent rocking demand spectra.