Predominant periods of multi-degree-of-freedomsystem analysis and dynamic soil-structure interaction for building structures

Coupled problems of the multi-degree-of-freedom-system (MDOF) or SoilStructure Interaction (SSI) are usually translated to a series of the single-degree-of-freedom (SDOF) equations. In this paper, the predominant periods of MDOF analysis are analyzed without SDOF and the dynamic amplification factors for a sample data of a model building are shown. The analysis method is the assumption that, as well as SDOF analysis, the MDOF analysis is applied to the predominant periods by inelastic analysis. That can give the dynamic amplification factors of the MDOF. At the results, it is cleared that the predominant period of the MDOF is close to be the period by the eigenvalues and in the short period or in the high level modes, the dynamic amplification factors are high which should not be neglected. Moreover, soil-structure interaction with SDOF are also analyzed by elastic analysis for the model building. Some effects to the building structure model by the rocking on the ground are discussed in the sway-rocking models

EACS 2016 paper - Dynamic Behaviour of a Seven-Storey Seismically Isolated Building during the 2011 Tohoku Earthquake

<div>EACS 2016 Paper No. 127</div><div><br></div>The Building Research Institute (BRI) operates a strong motion network that covers buildings in major cities across Japan. In 2010, as one of stations in the BRI strong motion network, the seven-story Tsukuba Town Hall building, which is a precast prestressed concrete frame structure, was equipped with a seismic isolation system consisting of; 11 natural rubber bearings, 45 lead-plugged rubber bearings and 9 steel-damper-combined rubber bearings. The building suffered extremely strong shaking with the Tohoku Earthquake of 11 March 2011. The accelerometer installed on the ground near the building, 334 kilometres far away from the epicentre, red out the peak ground acceleration higher than 1G. Even in this situation, the seismic isolation system successfully reduced the seismic acceleration exceeding 3 m/s2 on the foundation to less than one third. The analysis of the strong motion data obtained during the 2011 Tohoku Earthquake verified the excellent performance of the seismic isolation system. The maximum deformation of the isolation devices reached nearly 70 mm. Based on the analysis of the strong motion data on 84 earthquakes that occurred during the period from 2010 to 2016, dynamic characteristics of the seismic isolation system and the superstructure were discussed. The stiffness of the seismic isolation system showed a clear decline in the large displacement range. The damping effect of the seismic isolation system remained satisfactorily stable. We concluded that the seismic isolation system installed in the Tsukuba Town Hall building worked properly and effectively as expected in the structural design.<br

Kinematic soil-structure interaction effects from building and free-field seismic arrays in Japan

Ground motions at the foundation levels of structures differ from those in the free-field as a result of inertial and kinematic interaction effects. Inertial interaction effects tend to produce narrow-banded ground motion modification near the fundamental period of the soil-structure system, whereas kinematic effects are relatively broad-banded and concentrated at high frequencies. Kinematic interaction effects can be predicted using relatively costly finite element analyses with incoherent input or simplified models. The simplified models are semi-empirical in nature and derived from California data. These simplified models are the basis for seismic design guidelines used in the western United States, such as ASCE-41 and a pending report published by NIST. We compile some available data from building and ground instrumentation arrays in Japan for comparison to these two sets of models. We demonstrate that the model predictions for the sites under consideration are very similar to each other for modest foundation sizes (equivalent radii under about 50 m). However, the data show that both approaches overestimate the transfer function ordinates relative to those from Japanese data. This indicates that the semi-empirical models currently in use are conservative relative to these data sets. We speculate as to possible causes for the observed discrepancies

Recovery of the resonance frequency of buildings following strong seismic deformation as a proxy for structural health

Elastic properties of civil engineering structures change when subjected to a dynamic excitation. The modal frequencies show a rapid decrease followed by a relaxation, or slow recovery, that is dependent on the level of damage. In this article, we analyze the slow recovery process applying three relaxation models to fit real earthquake data recorded in a Japanese building that shows variant structural state over 20 years. Despite the differences in conditions, the different scales and the complexity of a real-scale problem, the models originally developed for laboratory experiments are well adapted to real building data. The relaxation parameters (i.e. frequency variation, recovery slope, characteristic times and their amplitudes, and range of relaxation times) are able to characterize the structural state, given their clear connection to the degree of fracturing and mechanical damage to the building. The recovery process following strong seismic deformation, could, therefore, be a suitable proxy to monitor structural health