Modeling long-period ground motions, and assessment of their effects on large-scale infrastructures – MODULATE

A strong ground motion database will first be compiled to systematically and quantitatively study the key characteristics of basin-induced surface waves, generated at different basins around the world. A key element in this endeavor is our ability to effectively identify and extract surface waves from a strong motion record using a recently developed technique, referred to as ‘Normalized Inner Product’ procedure or ‘NIP’, for short. State-of-the-art techniques of computational seismology will be applied to study the physics of surface wave propagation on basins with realistic 3D geometries and geological models.

A stochastic description of strong motion in terms of its Power Spectral Density (PSD) function will be developed to facilitate the evaluation of the stochastic response of structures. The fact that surface waves are dispersive renders the use of an Evolutionary Power Spectrum Density (EPSD) unavoidable. Using our ground motion database we will estimate the EPSD function of the surface waves extracted from recorded strong motion time histories.

Passing to structural analysis, besides rigorous 3D FE models, we will develop simplified numerical models for the nonlinear seismic response of long-period structures, able to predict damage modes, accounting for fluid- and soil-structure interaction, multi-support excitation, as well as to accommodate the different characteristics of the ground motions (long-period, long duration, rotational motions, dispersion or non-stationarity). It will be then possible to assess the probabilities that the structural systems exceed critical levels when subjected to seismic ground motions of specified characteristics. The capability of generating ground motions with and without surface waves will allow the assessment of the effects of surface waves on structural vulnerability.

Results expected during the execution of the project:

A database of 3-component time histories of the separated (body and surface wave) phases, and the metadata to the associated basin structure and seismic settings.

Development of a stochastic model for surface waves in terms of EPSD.

Generation of 3-component synthetic time histories of ground motion containing surface waves along with the parameters and configurations selected for their generation.

Development of surrogate models of typical long-period structures to efficiently estimate seismic demands and capacity.

Identification of key parameters from system and input motion that control structural response of the studied structures.

Development of detailed 3D soil-structure models for simulating the effects of surface waves on the response of long-period structures.

Development of novel methodologies for the construction of fragility curves that take into account the dispersive characteristics of surface waves.

Evaluation and comparison of current seismic normative methods for reliability and vulnerability analysis of large-scale structures.

Development of recommendations for modifications to current design methodologies for buildings, tanks and bridges to include the effects of surface waves.

The theoretical contribution of this study lies in demonstrating that with an evolutionary stochastic model we can provide a complete and expedient, yet realistic, description of strong ground motion on sedimentary basins. Furthermore, the stochastic description of ground motion (in the form of evolutionary power spectra) provides the means for realistic practical assessment of the reliability of critical large infrastructures.

The results of the project will contribute to the safety of large-scale infrastructures, and thus, to the prevention of large financial losses for local communities and countries. Recent earthquakes showed remarkably (e.g., the 2017 Mw 7.1 Puebla earthquake in Mexico, the Mw 6.2 2016 Amatrice earthquake in Italy) that the construction of infrastructure with adequate seismic performance is the main factor in minimizing economic loses and long-term consequences to the communities.

The stochastic model of ground motion developed during this project can be implemented in studies of local and regional seismic hazard assessment. Furthermore, surrogate structural models can facilitate the rapid vulnerability assessment of large building stocks. Public authorities are expected to have great interest in the project results when planning measures for large-scale structures. Moreover, the project findings are expected to influence, or be adopted by international code development committees, while practicing engineers will take advantage of useful tools for seismic design.

Expected scientific production:

A compiled and parametrized database of recorded and simulated long-period ground motions.

A guide describing the methodology for seismic vulnerability and risk assessment of large-scale infrastructures.

Publication of articles in first class scientific journals (such as the Bulletin of the Seismological Society of America, and Earthquake Engineering and Structural Dynamics).

Conference papers in renowned international (World and European) conferences on Earthquake Engineering.

Special sessions on seismic performance of large-scale infrastructures for the National AFPS Conference in France.

This project is concerned with the analysis and modeling of long period motions and their effects on large-scale infrastructures such as high-rise buildings, liquid-storage tanks and long-span bridges. Intense long-period ground motions are usually generated at large distances from the source and consist primarily of surface waves that arise when seismic waves encounter sedimentary deposits. The project aims at developing a methodology based on the physics of surface waves, to describe the evolution of the spectral content of the ground motion at a site located in a sedimentary basin. 3D numerical soil-structure models that capture the particular dynamic characteristics of real large-scale structures will be developed for assessments of their performance when subjected to the ground motion model. The results of the project will allow the development of tools and guidelines to be used by the earthquake engineering community for more resilient designs of large-scale infrastructures.