Dynamic Soil-Structure Interaction (SSI) and Structure-Soil-Structure Interaction (SSSI) is the study of the effects of ground motion on structures. The ground motion can be derived from seismic events or motions present in a structure supported by the soil. SSI studies examine the transmission of motion into a structure, and/or the effects of the motion on the properties of the soil. In this context, soil is any material making above competent rock level. This can include sands, gravels, weathered rock, clays, alluvium and random fill material.
In the case of severe ground motion, most usually associated with earthquakes, the passage of the motion can cause the soils to strain sufficiently for their properties to change. For cohesion less materials with low SPT values it is possible that the material will liquefy and act as a fluid.
Large structures can influence the properties of the materials due to the presence of the stress bulb beneath the foundations. This in itself leads to different transmission properties.
SSSI is the study of the effects of the adjacent structures on each other where ground transmitted motion is concerned. This takes two principal forms:
In the case of seismic loading, the presence of a heavy structure adjacent to a light structure can lead to a change in response of the lighter structure.
Nuisance vibration can be characterised as vibrations transmitted from structure to structure via the ground. Examples would be reciprocating plant vibrations being felt in neighbouring homes and offices, vibration from pile driving and road/rail vibration. Another consideration would be vibration induced in structures that contain sensitive equipment, such as precise measuring equipment or scientific apparatus.
CREA uses a mix of traditional methods and advance computer aided calculation to carry out SSI studies. Software includes CLASSI, FLUSH, SHAKE, WinSSI and ANSYS.
CREA is involved in the development of WinSSI which is a version of the SMACS CLASSI suite run from user friendly GUI. WinSSI is marketed by our associate company Soil and Structure Dynamics Limited.