Displaced But Not Moved: Performance-Based Foundation Design

Abstract

Improved understanding of seismicity within New Zealand and globally has led to an increase in seismic hazard for many locations. High seismic acceleration demands (e.g. >1g) for buildings and infrastructure have led to challenges in foundation design and soil-structure interaction. As an alternative to traditional methods, we have utilised 1-Dimensional and 2-Dimensional Site Response Analyses (SRA) as key tools for designing efficient performance-based foundation systems under high seismic demands. This presentation and paper provide an overview into 1D and 2D SRA methods for foundation design. Four case studies are presented where SRA has been utilised to add value to projects. Case Study 1 involves the design of a 300m bridge underlain by 40m of soft and liquefiable soils in which the use of SRA has resulted in a reduction in soil demands. This made the bridge design feasible without extensive ground improvement. Case Study 2 is an example where 1D SRA has been implemented to investigate a potential reduction in seismic acceleration demands for structural assessment of an existing building. Case Study 3 and Case Study 4 are examples where use of SRA has allowed for sliding shallow foundations to be implemented for the design of multiple structures, rather than resolving large lateral seismic demands through expensive piles. This paper also outlines key assumptions regarding simplification of nonlinear soil strength and stiffness modelling for SRA. Large scale friction interface testing for the design of cast in-situ shallow foundations on Wellington Greywacke bedrock is also discussed briefly for Case Study 4.