Experimental Assessment of Rocking and Torsion in Civil Engineering Structures Using 3C and 6C Sensors

Date: 4/24/2019

Time: 09:30 AM

Room: Grand Crescent

In this abstract, an experience is presented related to the rotations observed in the City-Hall building in Grenoble (France), a 12-story reinforced concrete building. This building is permanently monitored since 10 years, with 3 components accelerometers located at the bottom and the top. Modal decomposition including soil-structure interaction was done using ambient vibration and dozen earthquakes recordings and compared with iXblue 6C rotational sensor data, temporarily installed at the top then at the bottom. Dynamic response of structures to a seismic loading produce rotational forces that may generate considerable stresses. These rotational forces are essentially related (1) to the rotational deformation around the two horizontal axes (rocking) and resulting from soil-structure interactions considering the structure as rigid body; (2) the rotation around the vertical axis (torsion) essentially when the center of mass (i.e., where the inertia seismic forces apply) is shifted from the center of stiffness (i.e., where the elastic forces apply). Simplified models including rotations of the soil-structure interaction are based on the modal decomposition. In this case, each component of the motion is assumed to be independent of the others. Thus, in the structures, only translation sensors are generally installed and the rotation components are evaluated via the spatial derivatives of the horizontal and vertical components. For example the torsion is usually calculated as the relative difference between two horizontal sensors placed at the same floor and the rocking between two vertical sensors placed at the foundation level. However, combinations of translations and rotations exist which can only be evaluated with the measurement of the 6 motion components (3 translations and 3 rotations). In this study, an extensive comparison between the direct measurement of rotation and the spatial derivative rotation is done, validating the classical soil-structure interaction models used in civil engineering.

Presenting Author: Philippe Guéguen

Authors