Abstract Summary
In most civil engineering applications, the seismic Soil Structure Interaction (SSI) is assessed by performing blind numerical analyses with no detailed verification of the accordance between numerical results and in situ observations of SSI. The most widespread way to account for dynamic SSI is to associate a set of Impedance Functions (IF) to the structure’s foundation. The implementation of this method is simple and widely used in practice since it allows to describe the relationship between efforts and displacements at the soil-foundation interface for harmonic stresses depending on the frequency of interest. However, this method is based on many simplifying assumptions, such as rigid foundation and homogeneous and horizontal soil layers amongst others. The purpose of this paper is to present a measuring methodology which aims at acquiring in situ data to characterize the IF and therefore, allowing a prior validation of numerical analyses of IF within the following framework: • a linear behaviour of the soil, of the foundation and of their interface; • a relatively rigid and superficial foundation (compared to a considerably softer soil). The main difficulty of such a task is the measurement of the evolution of the forces at the soil-foundation interface. To overcome this difficulty, in this work, we propose to induce the ground-foundation motion with applied forces. At this point, it is sufficient to measure the displacements of the foundation with traditional devices (velocimeters and/or accelerometers) to get the knowledge of the in situ IF. Indeed, within this framework, one can derive an explicit function relating the measured displacements to the FIs terms based on the mechanical equilibrium of the soil-foundation interface using the principles of rigid body dynamics. For the foreseen device, the forces are generated by mechanical vibrations applying unidirectional sinusoidal forces which frequency is to be monitored. Eventually, this paper presents a reduced scale experimental mock-up of the proposed set-up and the set of equations leading to the measurement of in situ SSI in the absence of material and interface non linearities. This is a first step towards the validation of SSI calculations in numerical models. Forthcoming work will cover the evidence of feasibility at a full structural scale before aiming at the extension of the framework to include material and interface non linearities.
