Performance of viscous damping in inelastic seismic analysis of moment‐frame buildings

Rocking motion is sensitive to the boundary and initial conditions of a rocking structure, making experiments nonrepeatable. Thus, the claims that numerical rocking motion models are not only inaccurate but that all rocking structures behave unpredictably. Hence, rocking is not used as a seismic design approach. This paper revisits the issue of rocking motion unpredictability. Seismic behavior of structures is inherently stochastic, because the loading is stochastic. Therefore, the question of interest is not whether models can predict the seismic response to a single ground motion, but if the statistical characteristics of the ensemble of responses to a set of ground motions that define the seismic hazard can be predicted. For this purpose, a rocking podium, which is a three‐dimensional structure comprising an aluminum slab supported by four tubular steel columns, was tested on a shake table excited by two sets of 100 consistently generated ground motions. It was found that the cumulative distribution function (CDF) of the experimentally obtained displacements is statistically stable. Next, a blind prediction contest was organized. The contestants were invited to predict the CDFs of the slab lateral displacement. They were able to predict the slab displacement CDF relatively well. Both finite element and discrete element modeling approaches were used, but no clear pattern emerged as it was found that the performance of either approach depends on the input parameters used and the assumptions made. It was also observed that the contestants who did not use Rayleigh damping in their models produced better predictions.

Section: Wobbling Seismic Response Blind Prediction Contestmentioning

confidence: 99%

Section: Role Of Energy Dissipation In Modeling Of Wobbling Responsementioning

confidence: 99%

Shake table testing of a rocking podium: Results of a blind prediction contest

Vassiliou

Broccardo

Cengiz

et al. 2020

“…Thus, the estimated median spectral acceleration causing collapse may be overestimated to some extent, because the mass proportional damping probably overestimates the effect of damping in a nonlinear range, even if the damping is modelled only proportional to masses concentrated at the storey levels. However, the damping in the nonlinear range is not yet fully understood . Peak‐oriented hysteretic rules were adopted for nonlinear plastic hinges (ie, the uniaxial material »Hysteretic«, in OpenSees).…”

Section: Example: Estimation Of a Risk‐targeted Seismic Action Forcementioning

confidence: 99%

“…However, the damping in the nonlinear range is not yet fully understood. 69 Peak-oriented hysteretic rules were adopted for nonlinear plastic hinges (ie, the uniaxial material »Hysteretic«, in OpenSees 68 ). Parameter β that controls the unloading stiffness was assumed equal to 0.8, as this value was calibrated in the previous study 67 based on the results of pseudo-dynamic tests.…”

Section: Risk Assessment Of the Structure Using Nonlinear Dynamic Amentioning

confidence: 99%

Formulation of risk‐targeted seismic action for the force‐based seismic design of structures

Žižmond

Dolšek

2019

Summary A risk‐targeted design spectral acceleration and the corresponding seismic design action for the force‐based design of structures is introduced by means of two formulations. The first one called direct formulation utilizes the seismic hazard function at the site of the structure. Because the seismic action defined in the codes is often associated with a designated return period, an indirect formulation is also introduced. It incorporates a risk‐targeted safety factor that can be used to define a risk‐targeted reduction factor. It is shown that the proposed formulations give analogical results and provide an insight into the concept of the reduction of seismic forces for the force‐based seismic design of structures if the objective is defined by a target collapse risk. The introduced closed‐form solution for the risk‐targeted reduction factor can be used to investigate how the target collapse risk, the seismic hazard parameters, the randomness of the seismic action, and the conventional parameters (ie, the overstrength factor and the deformation and energy dissipation capacity) affect the seismic design forces in the case of force‐based design. However, collaborative research is needed in order to develop appropriate models of these parameters. In the second part of the paper, the proposed formulations are demonstrated by estimating the risk‐targeted seismic design action for a six‐storey reinforced concrete building. By verifying the collapse risk of the designed structure, it is demonstrated that the risk‐targeted seismic action, in conjunction with a conventional force‐based design, provided structure with acceptable performance when measured in terms of collapse risk.

“…Luco and Lanzi 13 recently proposed an elastic velocity damping model for nonlinear systems in which the damping force is proportional to the elastic component of the total velocity to address the issues of spurious damping forces. A study by Hall 14 presented a comparison of Rayleigh, modal, capped damping, 8 and elastic velocity damping model 13 for moment frame buildings.…”

Section: Introductionmentioning

confidence: 99%

Damping implementation issues for in‐structure response estimation of seismically isolated nuclear structures

Kumar

2021

Seismic (base) isolation of a nuclear power plant (NPP) is a viable strategy to reduce seismic demands in structural elements and nonstructural systems and components. Accurate estimation of in‐structure response of base‐isolated NPPs is critical to the analysis and design of safety‐related structural components. Damping models and their implementation in contemporary analysis platforms play a significant role in the numerical response estimation of a nonlinear system. Most of the recent damping studies cater to moment frame buildings for which nonlinearities are modeled using massless rotational springs. There are unique challenges associated with the implementation of damping to numerical models of the base‐isolated NPPs due to the broad frequency range of interest and the markedly different damping characteristics of the isolators and the superstructure. In‐structure response spectra of a base‐isolated NPP are sensitive to the chosen numerical and modeling techniques, both of which are investigated in this paper. Three representations of base‐isolated NPP are considered: (1) a two‐node macro model, (2) a lumped‐mass stick model, and (3) a detailed finite element model. Rayleigh damping, modal damping, uniform frequency damping, and several combinations thereof were used with the three NPP models to obtain the median response of the base‐isolated NPP subject to 30 sets of three‐dimensional ground excitations. The results allow informed decisions regarding the selection of a numerical model and damping implementation to different analysis platforms needed to obtain a reliable in‐structure response of base‐isolated NPPs subject to earthquake shaking.