Use of the capacity curve in the seismic analysis of geotechnical systems

Nonlinear dynamic analysis of soil-structure systems requires advanced and time-consuming computations that may not be feasible for most practical applications. The present research is devoted on conceptualizing and validating simplified procedures that are easier to implement, yet capable of capturing the essential features of the dynamic response of the systems at hand, consistently with modern concepts of seismic performance and capacity design. The geotechnical systems herein considered include retaining structures, bridge abutments, multi-propped excavations, and tunnelling. The seismic capacity of a geotechnical system is studied through nonlinear static numerical analysis (NLSA), in which equivalent inertial forces, proportional to a seismic coefficient, are applied to the system until the activation of a global plastic mechanism. The overall deformability of the system, from static conditions to failure, can be represented by a capacity curve, relating accelerations to seismic displacements of scrutiny points. The capacity curve proves to be a versatile representation of the system response under seismic loading in both displacementbased and equivalent force-based design methods, discussed in the first and second parts of this work. The first part pertains to systems that may accumulate permanent displacements under seismic loading such as earth retaining structures, whereas the second refers to systems that cannot experience important seismic deformations, otherwise, the structural integrity of the entire structure/infrastructure would be compromised. Bridges with integral abutments (IABs) and multi-propped excavations belong to the latter second category. Both methodologies are extensively validated and underscore the essential role of the capacity curve in the seismic assessment of geotechnical systems within the framework of the decoupled approach.