Aging civil engineering structures can be severely damaged by strong earthquakes. Due to the potential risk of seismic damage to structures, there is a growing need for investigative methods to assess the structural integrity and risk of damage. The authors have developed a device that accurately measures vibration data in structures. This device has been installed in the headquarters office building of Chuo Kaihatsu Corporation and used for observations over three years. In this paper, the focus is on analyzing the building's natural frequencies calculated from transfer functions (amplification ratios of building response to input ground motion) using several recorded strong motions from past seismic observations. By observing seismic characteristics such as the building's natural frequencies over an extended period, an assessment of the safety of the office building was conducted based on the results of post-earthquake structural health detection.

T-BAGS system developed by Takeuchi Construction Inc. is a seismic base isolation and vibration control system that uses two stacked layers of sandbags which slide between them. Numerical dynamic analyses of a typical residential five-story building with and without the T-BAGS system are conducted. The building and the T-BAGS system are integrated and modeled as a three-dimensional series of masses and nonlinear springs. The shear force vs. shear deformation behavior of the sandbags is modeled using the Ramberg-Osgood model based on experimental results. The slippage at the interface between the upper and lower sandbags is assumed to follow the Mohr-Coulomb friction law. It is shown from the analytical results that the response acceleration of the building induced by severe earthquakes can be considerably attenuated using the T-BAGS base isolation and vibration control system. It is emphasized that the hysteretic shear behavior of the sandbags contributes to the vibration control efficiently

Seismic earth pressure is a major action to design semi-underground structures. Previous studies numerically calculated the seismic earth pressures acting on semi-underground structures, but they used the elastic-perfectly plastic constitutive model with Mohr-Coulomb for the elasto-plastic model of soil, which may not represent the general behavior of soil ground. In this study, an elasto-plastic model that can consider the strain dependence of stiffness and cyclic stiffness reduction is used to obtain the seismic earth pressure acting on the semi-underground structure. The effects of the presence or absence of vertical degrees of freedom at the bottom and the shear wave velocity dependence on the confining pressure on the seismic earth pressure are also investigated. Comparing the earth pressure distributions with those obtained in previous studies, the increment from the initial soil pressure in this study was small. That could be explained by the influence of the gradual decrease in the stiffness due to the elasto-plastic behavior.

The rapidly growing offshore wind energy industry is expanding to areas with difficult soil conditions such as seismically active regions offshore Japan and Taiwan. Pile foundations, whether as a monopile or in jackets or tripods are mainly used to support offshore wind turbines. However, designers face numerous challenges related to predicting long-term performance of these foundations in problematic soils, especially under cyclic loading, with the risk of significant accumulated displacement or tilt. These risks are exacerbated by occasional storm surges and possibly seismic events. This paper presents an experimental device that models a miniature instrumented pile segment in sand under cyclic loading and can measure the soil reactions and excess pore pressures that may develop. The device allows the simulation of storm events and the study of various mechanisms that may occur in the soil, including cyclic degradation, strain degradation, pore pressure generation, rate effects, gapping and ratchetting. The soil reaction curves obtained during the testing could be adopted to calibrate finite element or other models

The renewable energy sector is rapidly expanding worldwide, with offshore wind playing an increasingly prominent role. After over two decades of European developments, the offshore wind industry is expanding to America and, beyond China, into the Asia-Pacific (APAC) region. Wind farm developers are currently facing the challenge of designing/building earthquake-resistant support structures for offshore wind turbines (OWTs), which requires reliable seismic analysis of the whole structural system and the soil. In the common case of bottom-fixed OWTs founded on large/stiff monopile (MP) foundations, serious challenges are introduced by the complexity of non-linear MP-soil interaction, which may be accompanied by dynamic amplification phenomena, permanent soil deformations and, possibly, ground liquefaction. Notwithstanding the continual advances in the field of earthquake geotechnical engineering, several gaps must be filled for the optimisation of OWT support structures, to avoid over-conservatism in designing and, consequently, overusing steel for fabrication. Such overuse will be unsustainable from a resource perspective and may prevent economic exploitation of offshore wind energy in seismic regions. This paper describes the background, objectives, and methodology of DONISIS (Design of Offshore moNopiles Including Seismic Interaction with Soil), a recent research project led by Delft University of Technology in collaboration with 17 academic and industry partners and supported through Carbon Trust’s Offshore Wind Accelerator programme. DONISIS will enhance the fundamental understanding of seismic soil-structure interaction mechanisms in tall, MP-founded OWTs, with emphasis on the role of non-linear soil behaviour and pore water pressure effects. The adopted research approach is described herein, particularly with regard to four distinct work packages on: (a) constitutive modelling of soil behaviour during earthquakes, with emphasis on the relevant case of sandy soils; (b) physical testing of seismically loaded OWTs using one of the largest centrifuge facilities in the world; (c) 3D Finite Element (FE) modelling of seismic OWT-MP-soil interaction; (d) engineering seismic analysis of MP-supported OWTs, based on efficient 1D modelling of soil reactions. The knowledge acquired throughout the research programme will feed into the development of a new 1D seismic design model for MP foundations, which will retain high accuracy while allowing fast design computations and swift research-to-practice transition in collaboration with the participating industry partners. The goal is to develop a set of OWT seismic design recommendations and best practice guidelines for seismic MP design.

Pier is a key member in the bridge structure as it must transfer superstructure loads to the foundation safely. However, there is always risk of it getting damaged under the events of ground excitations and this makes researchers find new ways of designing a ductile, lightweight, and economical pier along with its foundation. This study presents such a pier consisting of multiple steel pipes integrated by shear links. It is supported by either a conventional pile group foundation with a footing (F-type) or by connecting column pipes directly to piles interconnected by an underground beam (S-type). The study focuses on the dynamic soil-structure interaction to determine the influence of kinematic and inertial effects on the behaviour of both types of structures. A series of dynamic simulations are conducted by using a sinusoidal wave of amplitude 200 gal and frequency of 2Hz. Comparison of pile’s response at key instances such as corresponding to maxima of inertia, ground deformation and pile head bending moment identifies the influence of kinematic and inertial action. The qualitative action of inertia force and far-field ground deformations is established by applying inertia force and ground deformation profile as loadings in separate static analysis. A match of correlation of inertial or kinematic action with corresponding dynamic analysis determines the dominant action. The contribution of kinematic action towards pile moment is discovered by the dynamic analysis without superstructural mass and columns. Kinematic action has a maximum contribution of 30% only towards pile bending moment for D-S and 17% for D-F type. Inertial action is determined as most influential for both types of structures for an input motion of 2Hz; however, the kinematic action should be deemed serious as well due to the similar direction of action of inertia and earth pressure in F-type structures.