The advances in computer hardware and the software capabilities are ever increasing the domain of physics and engineering simulations. However, the non-linear time domain SSI analyses are still rarely seen outside of research projects as they are expensive, require increased awareness and judgement from the analyst, and are somehow seen as exotic from utilities and regulators. In this paper we present a practical approach for two-stage SSI and SSSI analyses of safety-related structures at sites with complex stratigraphy.
In the first stage the impedance functions of a rigid massless foundation are obtained using ACS SASSI and are used for sensitivity analysis of the soil-foundation response to establish a representative best estimate soil profile from a suite of candidates. In the second stage a full 3-D model of the soil and the structures including material non-linearity and gapping/sliding is developed in PLAXIS 3D. The analysis is based upon Section 5 of ASCE 4-16 together with supporting information from other sections of this standard. The direct method described in Section 5 of ASCE 4-16 is used for analysing the combined soil-structure system in a single step, without invoking superposition for the structure or the soil separately.
The PLAXIS soil domain properties are calibrated against 1-D site response analysis results and the boundary conditions are simulated using the free field boundary elements. A comparison of the results of the time domain analysis is presented against the output of a full 3-D analysis in the frequency domain using ACS SASSI. It is show that these advanced software’s can handle soil non-linearity and gaping and provide results in realistic time frames.