Summary of discussions and recommendations

Presentations

1. Current Methods of Practice of SSI in U.S. and Japan
   1. Geotechnical Point of View
   2. Structural Point of View
2. Code Provisions and Limitations.
3. Observed Data.
4. Observational Arrays and Testing Facilities - Current, Future and Needs.
5. Recent Research Results and How To Implement Them into Practice.
6. Needed Additional Research.
7. Needed Additional Observational Arrays and Testing Facilities.

Discussions

Group A

1. It is necessary for the researchers, to definitely recognize the current status of the SSI-related researches
2. To identify the available data in both countries etc. A proposal was posted to publicizing the data available and introduced during this workshop in both countries as data libraries.
3. The possibility to conduct the blind prediction test utilizing these publicized data. It was also acknowledged to pursue the possibility of such activities.
4. The group members discussed the necessity of dense instrumentation, such as to investigate the rotational components of the ground motions. It is indispensable for the advancement of the methodology in SSI effect.
5. The group member also discussed on the future organization of the workshop to bring the benefit from the workshop.
6. Other items such as the followings should draw further attentions.
   Non-linearity issues: currently insufficient in experiments and analyses
   1. Identification issues
   2. Seismic margin entangled in SSI phenomena, unexpected seismic margin in low-to-mid rise buildings
   3. Energy dissipation mechanism in SSI phenomenon

Group B

1. Construction of database on in-situ measurement or earthquake recordings and experiments. The action should be taken to construct the database from the instrumentations in real size structure including foundation and ground. Some problems will be anticipated, however, it might cause less conflict that some organization in public position such as BRI or AIJ for Japan side, and NEES (Network for Earthquake Engineering Simulation) for U.S. side takes the leading role.
2. Enhancement of seismic performance of pile foundation.
   Pile cap connections: There are number of research works concerning pile cap connections recently in Japan. They say that the semi-rigid connection might be better. On the issue, the technique should be verified with experiments.
   In earthquake recording in structures not only sensors attached in superstructures, foundations and soils, but also strain gauges, sensors such as optical fibers in piles so that the transfer of forces in the foundations can be detected. These ideas are important for improving the seismic performances of pile foundations.
3. Important topics in future will be as follows;
   1. Efficiency of pile group
   2. Influence of soil non-linearity (Liquefaction-countermeasured soil, ground deformation)
   3. Non-linearity in SSI (modeling in uplift and its effect on response of superstructure)
   4. Elucidation of kinematic interaction (analysis method and observation system)
   5. Mechanical property of piles (strength and deformability)
   6. Effectiveness of oblique piles
   7. Effectiveness of embedment
   8. Simple procedure for introducing SSI effect in Seismic Design

General discussions

1. Definition of SSI is changing.
   Originally: how soil compliance influences dynamic response of superstructures (buildings, nuclear contained structures)
   Today, anything related to soil response during earthquakes (e.g., deformation, wave propagation, lateral spreading, liquefaction, etc, that in any way influences the earthquake response and performance of structures, whether they are directly supported on, or partially or totally embedded within the soil (kinematic and inertial effects).
2. Significant progress was observed since the 1^st UJNR workshop on SSI, such as the sophisticated tools, which allow one to incorporate complex soil, and structural behavior into analyses improved the understanding of basic phenomena on SSI
   1. Elastic analysis vs. inelastic soil and structural response
   2. SSI evaluation by microtremor: how to extrapolate to design levels: dynamic stiffness; radiation and material damping
   3. Foundation compliance affects distribution of inertial response
   4. Limitations of analysis
   5. Bridges: Joints, pounding, abutments
   6. Buildings: infills, overstrength, etc.
   7. Mixed foundations
   8. Load transmission

Recommended actions

1. SSI research must address needs of practitioners.
2. We need to bring SSI to building and code level design (situation different from nuclear industry).
3. We need to develop simple yet sufficiently accurate physical and mathematical models for obtaining realistic estimates of SSI effects
4. We need to gain sufficient physical insight to develop these models.
5. We need to recognize that the instrumentation and model test (both in the lab and in the field) most play an essential role.
6. We need to compile/summarize existing data
7. We need to conduct experiments to calibrate and compile models - tests an centrifuges and shake tables
8. Specific topics need further studies. Those are,
   1. Pile group for either stable or unstable soils
      It is essentially very complex behavior.
      The response of foundation highly sensitive to small changes in configuration and material properties
      No simplified analysis tools are available yet.
   2. Pile connections (fixed vs. pinned design); bridges vs. buildings; retrofit vs. design
   3. Damage Inspection
      It is very difficult to access for inspection after earthquake. (It is necessary to develop suitable instrumentation techniques)
   4. Non-linearity
      Geometric: uplift; contact gaps
      Material behavior: soil and structural
      Kinematic loading
      Damage in soft or liquefied soils
      Examine damage evidence in other conditions; tunnels vs. bridges vs. pipelines vs. buildings.
   5. Liquefaction issues
      Site response when liquefaction is involved.
      Prediction of magnitude of displacements
      Restraint on lateral spreading

Exchange of research information concerning SSI

Construction of Database