Ioanna-Kleoniki Fontara

Scalar Structure-Specific Ground Motion Intensity Measures for Assessing the Seismic Performance of Structures: A Review

ABSTRACT The assessment of the seismic performance depends on the choice of the earthquake Intensity Measure (IM). During the past years many IMs, which take into account not only earthquake characteristics but also structural information, have been proposed. However, no consensus on which IM is the best predictor of the seismic response exists. Along these lines, the objective of this paper is to present the various developed scalar structure-specific seismic IMs and the problems associated with their use in practice, so that the engineer may become familiar with them and their implications in the context of Performance-Based Earthquake Engineering.

Effects of Local Site Conditions on Inelastic Dynamic Response of R/C Bridges

The purpose of this work is to study the effects of site conditions on the inelastic dynamic analysis of a reinforced concrete (R/C) bridge by simultaneously considering an analysis of the surrounding soil profile via the Boundary Element Method (BEM). The first step is to model seismic waves propagating through complex geological profiles and accounting for canyon topography, layering and material gradient effect by the BEM. Site-dependent acceleration time histories are then recovered along the valley in which the bridge is situated. Next, we focus on the dynamic behaviour of a R/C, seismically isolated non-curved bridge, which is modelled and subsequently analysed by the Finite Element Method (FEM). A series of non-linear dynamic time-history analyses are conducted for site dependent ground motions by considering non-uniform support motion of the bridge piers. All numerical simulations reveal the sensitivity of the ground motions and the ensuing response of the bridge to the presence of local soil conditions. It cannot establish a priori that these site effects have either a beneficial or a detrimental influence on the seismic response of the R/C bridge.

Seismic Wave Field Generation in Heterogeneous Geological Media Containing Multiple Cavities

We develop a boundary integral equation (BIE) method for the numerical simulation of seismic motions in geological media containing multiple cavities under anti-plane strain conditions. We consider a half-plane of heterogeneous structure subjected to either time-harmonic incident shear waves or to body waves radiating from a seismic point source. Three different types of material heterogeneity are considered: (a) The density and shear modulus vary proportionally as quadratic functions of depth, but the wave speed remains constant; (b) the material is viscoelastic, with a shear modulus and density that vary with respect to the spatial coordinates in an arbitrary fashion, with a wave velocity is frequency and position–dependent; (c) the material has a depth-dependent shear modulus and constant density, yielding a linear wave velocity profile. This necessitates the development of three frequency-dependent integral equation schemes based on: (a) A Green’s function for a quadratically-graded elastic half-plane; (b) a fundamental solution for a viscoelastic full-plane with position–dependent wave speeds; and (c) a fundamental solution for an elastic full-plane with a linearly varying wave speed. Numerical examples are presented for inhomogeneous geological media containing any number of cavities of arbitrary geometry and position.

Seismic Response of Poroelastic Graded Geological Region with Underground Structures by BIEM

This work addresses horizontally polarized shear SH seismic wave radiated from an embedded seismic source in a continuously inhomogeneous poroelastic half-plane with cavities presenting underground structures as unlined tunnels and pipelines. The mechanical model and corresponding computational tool are: (1) viscoelastic approximation (isomorphism) to Biot’s equations of dynamic poroelasticity and (2) boundary integral equation method (BIEM) using frequency-dependent fundamental solution of the governing wave equation for continuously inhomogeneous media. The problem is formulated under anti-plane strain conditions and time-harmonic motions are assumed. Two different mechanical models for inhomogeneous in depth poroelastic half-plane are presented: (a) Model A: the density and shear modulus vary proportionally as quadratic functions of depth, but the wave velocity remains constant. In this case is used BIEM based on an analytically derived Green’s function for graded half-plane; (b) Model B: the material properties vary with respect to the spatial coordinates in a different manner, so that the wave velocity is both frequency and position-dependent. The formulation of the considered problem by boundary integral equations (BIE) is realized via fundamental solution of equation of motion for viscoelastic full-plane with position-dependent wave speed profiles. The parametric study reveals the dependence of the seismic signals along the free surface and inside the geological region on the following key factors: (a) type and properties of the material gradient; (b) characteristics of the applied load; (c) position and number of cavities; (d) dynamic cavities interaction; (e) cavity-free surface interaction; (f) poroelastic soil properties.

MULTIPLE SUPPORT EXCITATION OF A BRIDGE BASED ON BEM ANALYSIS OF THE SUBSOIL-STRUCTURE-INTERACTION PHENOMENON

Abstract. This study presents a numerical investigation of the influence of spatial variability of earthquake ground motion, site effects and Soil-Structure Interaction (SSI) phenomena on the inelastic dynamic analysis of bridge structures, considering a 2D analysis of the soil profile via Boundary Element Method (BEM). First, seismic waves propagating through complex geological profiles are modeled, so as to recover ground motion records that account for local site conditions. To that purpose, the BEM is employed for computing time-history records for four different geological profiles considering (a) canyon topography, (b) soil layering and (c) material gradient effect. Then bridge support-dependent ground motions and equivalent dynamic impedance matrices at the soil-foundation interface are generated for each support point of a bridge along the canyon. More specifically, a reinforced concrete, straight bridge with monolithic pier-deck connections is adopted as a case study. Next, a series of time history analyses considering local nonlinearities is conducted for the bridge using the Finite Element Method (FEM) taking into account subsoil-structure-interaction phenomena. To emphasize the relative importance of the topographic effects and the asynchronous motion, bridge response is determined under both synchronous and asynchronous earthquake input. In sum, the numerical results of this study show that the effect of spatially variable earthquake ground motion on the seismic response of the bridge studied depends on the interplay between the dynamic characteristics of the structure, the variability in space of soil and the properties of the incoming wavefield itself. It is also demonstrated that the detrimental or beneficial effect of spatially variable earthquake input is primarily dependent on the interplay of all the above mentioned key parameters.