# Soil-Structure Interaction

## Course Description:

The concept of soil-foundation-structure interaction. Examples of applications to foundations, retaining systems and underground structures. Stiffness matrix for rigid foundations on elastic continuum. Analysis of case studies emphasizing on soil-structure interaction: The Rion-Antirion bridge. Foundation response to combined axial and lateral loading: From quasi elastic behaviour to uplifting and bearing capacity failure. Nonlinear methods for evaluating the seismic performance of SSI systems. Analysis of single piles subjected to axial and lateral loading. Analysis of pile-groups considering pile-to-pile interaction. Seismic kinematic and inertial soil-pile interaction. Case histories focusing on SSI: (1) The collapse of Fukae bridge in Kobe 1995 earthquake, and (2) the leaning tower of Pisa.

• Semester 9
• Teaching hours 4
• Instructors

### Prerequisite Knowledge

Basic knowledge in the following Areas (Courses): Soil Mechanics I, Soil Mechanics II, Foundation Engineering and Matrix Structural Analysis

### Course Units

# Title Description Hours
1 Introduction: The role of Soil – Structure Interaction (SSI) How Soil-Structure Interaction affect the design of civil engineering structures (e.g. high rise building, bridges, underground structures etc.) and the design of their foundation. Examples from real projects. 1Χ4=4
2 Stiffness of a Rigid Foundation in Elastic Soil Determination of the stiffness matrix for soil-structure interaction systems (shallow and embedded footings, caisson foundations). Methods for calculating the stiffness matrix: Rigorous Analysis: The theory of elasticity, Numerical Analysis: The finite element method, Simplified physically motivated analysis. Characteristic solution in the form of closed analytical expressions for the foundation stiffness matrix, accounting for soil layering, inhomogeneity, foundation shape and embedment effects. Numerical Analysis with the use of the F.E code PLAXIS. 2x4=8
3 Analysis of Case Studies emphasizing on Soil-Structure Interaction Analysis of a laterally loaded single-span frame structure with and without considering soil-structure interaction effects. Examples from large-scale projects: Analysis of the foundations of the Rion-Antirion Bridge. Seismic Soil-Foundation-Superstructure Interaction Analysis. 1x4=4
4 Foundation Response Analysis: From quasi elastic behaviour to foundation uplifting and bearing capacity failure Failure mechanisms of shallow and embedded foundations subjected to combined axial and lateral loading. The meaning of progressive failure in bearing capacity problems. Non-linear Soil-Foundation-Superstructure Interaction Analysis. Numerical Analysis with the use of the F.E code PLAXIS 2x4=8
5 A Nonlinear Method for Evaluation the Seismic Performance of SSI Systems The concepts of generalized factor of safety and secant (effective) foundation stiffness matrix. Extending the N2 method to account for SSI effects. Application to case studies with the use of the FE code PLAXIS. 3x4=8
6 Analysis of Single Piles under Lateral and Axial Loading Determination of the stiffness matrix for piles in elastic soil. Laterally loaded flexible and rigid piles. Non-linear horizontal soil reaction on piles: The concept of p-y curves. 1x4=4
7 Analysis of Pile Groups considering Pile–to–Pile Interaction Group of piles under lateral and axial loading. Pile-to-pile interaction and group efficiency: Static and dynamic loading. 1x4=4
8 Seismic Kinematic Soil-Pile Interaction Kinematic and Inertial response of piles. Method of analysis. Group effects. Examples, Case histories. 1x4=4
9 Case Histories of failure and Forensic SSI Analysis The collapse of Fukae bridge in Kobe 1995 earthquake. The leaning Tower of Pisa. 1x4=4

### Learning Objectives

After the successful completion of the course, the students will be able to:

1. Know the role of Soil-structure interaction (SSI) on the performance of civil engineering structures, and its influence on the foundation design.
2. Realize the capabilities of numerical modelling as a design Tool in solving SSI problems.
3. Understand the necessity of characterizing the role of SSI for the safe design of earthquake resistant structures
4. Develop and use simple numerical models, and
5. Analysing real case studies with the use of dedicated PC codes.

### Teaching Methods

 Teaching methods In class lectures. Solving of examples and applications in class. Discussion of case studies. Blackboard presentations. PowerPoint Slide Projection. Calculations in PC using spreadsheets and dedicated software of analysis (e.g. Matlab, PLAXIS). Tutorials for use of numerical modelling software for geotechnical design purposes. Solving of examples with the use of specialized computer codes and spreadsheets. One or two deliverable homework sets for which solving by hands is mandatory and verification by the use of dedicated PC software is optional. Students begin to work in class, independently or in teams of 2 to 3, on 2 term projects and submit technical reports, which are graded according to certain criteria, and returned before the final exam.

### Student Assessment

• Final written exam: 60%
• Problems - Applications: 40%

### Textbooks - Bibliography

1. Potts D.M., Zdravkovic (1999). Finite Element Analysis in Geotechnical Engineering. I: Theory, Thomas Telford Publishing, ISBN-10: 0727727532
2. Potts D.M., Zdravkovic (1999). Finite Element Analysis in Geotechnical Engineering. II: Applications, Thomas Telford Publishing, ISBN-10: 0727727834.
3. Wood D.M. (2004). Geotechnical Modelling, Spon Press, Taylor and Francis Group, ISBN: 0-203-78621-1.
4. Lees A. (2016). Geotechnical Finite Element Analysis: A practical Guide, ICE Publishing, Thomas Telford Ltd, ISBN: 0727760874.
5. Comodromos Em. (2009). Computational Geotechnical Engineering: Soil-Structure Interaction, Klidarithmos Editions, ISBN-13: 9789604612017.
6. Soil-Foundation-Structure Interaction (2015): Gazetas, Anastasopoulos, Garini, Gerolymos, Ed. Tsotras, ISBN: 978-618-5066-24-6 (in Greek)

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