On the applicability of veletsos' wave parameter (1/σ)

Xenia A. Karatzia, George E. Mylonakis

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations

Abstract

Wave parameter (typically denoted by 1/σ) is a dimensionless factor introduced by Veletsos and co-workers, to describe inertial Soil-Structure Interaction (SSI) effects on simple structures founded on soft ground. For a simple oscillator of height h and fixed-base natural period T resting on a rigid footing of radius r underlain by compliant soil having shear wave propagation velocity Vs and Poisson's ratio νs, the wave parameter is defined as (1/σ) = (h /T Vs). This factor was introduced in classical equations for period elongation and damping shift due to SSI, so that both could be expressed in terms of familiar parameters such as the fundamental structural period, soil shear wave propagation velocity and structural slenderness. Values of (1/σ) greater than 10-1 indicate significant SSI effects and vice versa. This article focuses on a certain weakness of the wave parameter leading to a previously unsuspected difficulty in carrying out parametric investigations with (1/σ) being an independent variable. Specifically, to employ (1/σ) one needs to introduce a mass ratio [usually γ= m/(π ρs r2 h)] to balance the effect of mass introduced via the natural period. It is shown that by introducing γ, it is difficult to alter (1/σ) in a parametric analysis without altering the values of the other governing variables, including γ and (h/r). In other words, (1/σ) is coupled with the other problem parameters and being such, it cannot be used as an independent variable in SSI investigations in (1/σ, h/r, γ, νs) space. A second difficulty associated with the use of (1/σ) lies on the apparent increase in period elongation due to SSI with structural height, a trait which is not supported by experimental and analytical evidence. Ways to overcome these difficulties by introducing alternative parameters are discussed.

Original languageBritish English
Title of host publicationCOMPDYN 2019 - 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings
EditorsManolis Papadrakakis, Michalis Fragiadakis
PublisherNational Technical University of Athens
Pages1924-1932
Number of pages9
ISBN (Electronic)9786188284463
DOIs
StatePublished - 2019
Event7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, COMPDYN 2019 - Crete, Greece
Duration: 24 Jun 201926 Jun 2019

Publication series

NameCOMPDYN Proceedings
Volume1
ISSN (Print)2623-3347

Conference

Conference7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, COMPDYN 2019
Country/TerritoryGreece
CityCrete
Period24/06/1926/06/19

Keywords

  • Dimensional Analysis
  • Period Elongation
  • Soil-Structure-Interaction
  • Wave Parameter

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