Testing for SSI and wave propagation

Fault rupture box at NTUA

This joint research activity focuses on the development of new capabilities and techniques for experimental studies of wave propagation and soil structure interaction (SSI) phenomena, for surface and embedded structures. The work involves the use of reaction wall, shaking table, centrifuges and field testing in developing the appropriate techniques for SSI assessment and strong ground motion estimation intended for SSI studies.

Field testing for assessment of wave propagation and ground motion requires an instrumentation scheme that allows to study radiation damping, complex impedance functions, modification of the incident wave due to the structure etc. For this purpose, a 3D testing array of accelerometers, strain gauges, pressure and displacement transducers should be further developed and tested. This monitoring system will be calibrated through tests performed in the Euroseistest experimental facility. A validation of the system will be achieved through comparison with experimental and theoretical results and particularly with data from free field experiments performed in USA and Japan.

SSI test techniques for centrifuge tests of shallow foundations on dry sand layers and on layered soils will be assessed in terms of the quality of input acceleration, the response of the foundation and the superstructure and the instrumentation used. Additionally, the data from these tests will be used for quantifying the boundary effects due to the limited size of the model container and for proposing ways in which these effects can be accounted for in numerical models. The last phase of this task will integrate the response of shallow foundations obtained from centrifuge tests as input motion into shaking table and PsD tests of superstructures, paving the way to geographically distributed testing.

The results of tests on models including the soil will be used to develop a non-linear SSI macroelement for shallow foundations, capable of reproducing the observed foundation settlements and tilts and covering both cohesive and frictional soils. This macroelement will be extended to dynamic loading conditions and it will be validated against centrifuge, shaking table and field tests. Finally, the validated macroelement model will be used for proposing recommendations for a test protocol for PsD testing including SSI.

The aim of implementing the Fast Hybrid Testing (FHT) technique is to enable full-size SSI shaking table tests. More specifically, the following tasks will be implemented:

  • use of laminar boxes in strong motion testing;
  • investigation of the effect of boundary reflections;
  • application of FHT with the foundation and the soil simulated as a numerical substructure and the superstructure as physical model on the shaking table;
  • application of FHT with the foundation and the soil modelled using a laminar shear-box on a shaking table and a numerical model for the superstructure;
  • comparison of the results obtained by the two FHT alternatives;
  • investigation of fault rupture propagation using the fault rupture box and development of a simplified methodology to compute the faulting-induced stressing on foundations and structures.

Field testing techniques to assess SSI will be studied to propose the most efficient techniques and to identify the critical SSI parameters. A monitoring system will be used to investigate in real-scale the effects of SSI and of shock excitation on the response of the structures at the Euroseistest facility. The results will be compared with results from centrifuge and shaking table experiments as well as from numerical simulation. Finally, numerical simulations will be compared with field evidence in order to investigate scaling effects.

The synthesis of the previous tasks will lead to the integration of different techniques for testing and assessing SSI for structural and geotechnical systems. The capabilities and limitations of the various approaches will be examined and recommendations will be proposed on how to incorporate SSI into current testing approaches. Synergies between the various available testing procedures will be sought and emphasized.

Released Deliverables:

WP14 Report on Pseudo-dynamic test techniques with SSI (.pdf, 5.1Mb)
Motivated by the need to facilitate and standardize pseudo-dynamic testing with account of soil-structure interaction, the report focuses on development, implementation and validation of a nonlinear dynamic macro-element for shallow foundations. The macroelement is a numerical tool to be used both for design, in the context of nonlinear time history structural analyses, and for testing, in particular for reaction wall pseudo-dynamic testing and shaking table hybrid testing.
WP14 Report on field testing for assessing input motions and SSI (.pdf, 59.4Mb)
The most recent developments on field testing techniques for the assessment of soil-foundation-structure interaction (SFSI) are presented. The Euroseistest site in Greece is used to assess site response and field ground motion, wave propagation and damping due to structural oscillation. Moreover, SFSI experiments are performed in full-scale in a newly constructed structure (EuroProteas). Numerical 3D simulations of the experiments confirm the effects of the soil-foundation system compliance on the foundation motion.
WP14 Report on centrifuge test techniques with SSI (.pdf, 2.17Mb)
In this report details are given on the general theory of centrifuge modelling. This is followed by the experimental facilities, centrifuge model containers, instrumentation and data acquisition used at the UCAM and IFSTTAR facilities. Details of the design of different model structures and model preparation techniques including the air-pluviation devices are presented. The technique of PIV analysis using digital images from a fast digital camera is introduced.
WP14 Report on shaking table test techniques and fault rupture box testing with SSI - Revision 1 (.pdf, 14.94Mb)
This deliverable was produced under Task JRA3.4 aiming on the implementation of the Fast Hybrid Testing (FHT) technique to full-size Soil-Structure Interaction (SSI) tests that are performed on the shaking table. This technology was never been implemented for shaking table-based SSI applications. The task focused on extending the FHT technique so it can be implemented at existing shaking tables in Europe. The test beds at UNIVBRIS and NTUA shaking tables were used for this purpose.  
WP14 Summary report for testing and assessing SSI from different experimental techniques (.pdf, 6.29Mb)
The scope of this deliverable is to provide a synthetic presentation of the main results and conclusions obtained within the 48-month period of research activities related to JRA3. Joint Research Activity 3 (JRA3) has focused on the investigation of testing techniques for Soil-Structure-Interaction (SSI) and wave propagation.

 

Highlights

What's next

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  Joint with US-NEES "Earthquake Engineering Research Infrastructures

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