Seismic response of reinforced concrete frames on monopile foundations

The paper focuses on the effects of soil-structure interaction on the seismic response of reinforced concrete frames on monopile foundations connected by tie beams. Such systems are usually designed by considering fixed restraints at the column bases and the effects of the foundation compliance have not yet been investigated. The soil-foundation system is analysed in the frequency domain by means of a numerical model that allows obtaining the dynamic impedance functions of the system and the foundation input motion necessary for the subsequent nonlinear inertial soil-structure interaction analysis which is performed in the time domain. Tie beams with different stiffness and soil deposits characterised by three different profiles of shear wave velocity are considered. Results of incremental dynamic analyses carried out on frames with monopile foundations are compared with those obtained considering double-pile foundations and the fixed base assumption. Soil-structure interaction is found to affect considerably the response of frames on monopile foundations by increasing the structural deformation and modifying the evolution of the dissipative mechanisms. Analyses accounting for the actual soil-foundation system compliance and the foundation input motion may be crucial for a reliable prediction of the actual distribution of stresses in the superstructure and the foundation elements