Existing bridges on pile groups: In-situ measurement of stiffness

Abstract Retrofit of existing bridges founded on pile groups can be a challenging, costly, and time-consuming operation, especially when foundation interventions are required. The optimization of retrofit design, and hence of such complicated interventions, may be done by allowing controlled strongly nonlinear response of pile groups and associated energy dissipation mechanisms to develop during seismic loading. Taking advantage of such response may also offer improved seismic performance. Nevertheless, a prerequisite for the application of such rational design concepts is the realistic evaluation of actual stiffness and capacity of pile groups. The latter can be estimated based on in-situ soil testing (e.g. CPT) according to the current state of practice, while the former has been approached until now solely analytically and numerically. This paper proposes a first approach to a simplified stiffness estimation method based on in-situ measurements of lateral vibration response of existing bridges. Estimates of stiffness parameters are obtained with simplified equations of motion, using measurements of the lateral vibration response of a bridge pier and its foundation system to a controlled low-amplitude non-destructive dynamic loading. A numerical study is conducted to evaluate the efficiency of the proposed simplified method and to explore its applicability in real-scale projects.