A refined Frequency Domain Decomposition tool for structural modal monitoring in earthquake engineering

Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challenge）, under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames（with variable structural features） are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 ＂Far-Field＂（22 NS, 22 WE） earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.

Numerical analysis of the interaction of soil-structure under earthquake loading

In this paper, the dynamical response of soil structure coupled system was studied by the continuum theory of soild fluid mixtures, the building foundation system subjected to rapid earthquake excitation were calculated by using finite element method.In the results, the deformation patterns and corresponding contour diagrams of pore pressure at various time levels are given, time variations of displacement in a certain node and shear stress in a certain element are also presented. The results of this study have provided an improved understanding of coupled behaviour of porous media. The procedure developed in this paper can be effectively used under a wide range of loading conditions from very slow quasi static to very rapid earthquake excitations.

Earthquake Performance of Bell Towers in the Island of Kefalonia,Greece

The dynamic and earthquake response of bell towers,located at the Island of Kefalonia,Greece,is examined here.These structures were subjected during the winter of 2014 with an intensive earthquake sequence.The dynamic characteristics of two bell towers were measured in situ.Subsequently the dynamic and earthquake response of each bell tower was numerically simulated employing 3-D dynamic elastic numerical simulations taking into account the soil-foundation deformability.It is demonstrated that the soil-foundation-structure interaction influences the dynamic and earthquake response predictions for this structure quite significantly.It also demonstrates the usefulness of such in-situ testing towards formulating realistic numerical models in order to yield realistic predictions of the dynamic and earthquake response of the examined structures.The obtained numerical analyses utilize the earthquake ground motion which was recorded at close distance from both bell towers.The numerical predictions of the earthquake response of both bell towers are utilized to draw conclusions of their actual earthquake performance.It is concluded that the soil-foundation interaction was a critical response mechanism.The newly built RC(reinforced concrete)bell towers performed satisfactorily.

Comparison between Different Shapes of Structure by Response Spectrum Method of Dynamic Analysis

Several procedures for non-linear static and dynamic analysis of structures have been developed in recent years. In this paper, the response spectrum analysis is performed on two different shapes i.e. regular and irregular shape of structure by using STAAD PRO. And the comparison results are studied and compared accounting for the earthquake characteristics and the structure dynamic characteristics. As the results show that the earthquake response peak values and the main response frequencies are very close and comparable. It can be referred to by the engineering applications.

Fast inversion of rupture process of the 14 April 2010 Yushu,Qinghai,earthquake

Four results of the rupture process of 14 April 2010 Yushu, Qinghai, earthquake, obtained by inverting the broadband seismic data of Global Seismographic Network （GSN） based on the inversion method of earthquake rupture process, were compared and discussed. It is found that the Yushu earthquake has several basic characteristics as follows： 1 There exist two principal sub-events which correspond to two slip-concentrated patches being located near the hypocenter and to the southeast of the epicenter. The rupture of the slip-concentrated patch to the southeast of the epicenter broke though the ground surface; 2 The peak slip and peak slip-rate are about 2.1 m and 1.1 m/s, respectively, indicating that the Yushu earthquake is an event with large slip-rate on the fault plane; 3 Overall the Yushu earthquake is a unilateral rupture event with the rupture mainly propagating southeastward. The strong focusing of the seismic energy in the southeast of the epicenter due to the ＂seismic Doppler effect＂ reasonably accounts for the tremendous damage in the Yushu city.

Co-seismic changes of well water level and volume strain meter in capital area and its vicinity,due to the Nov.14,2001 Ms8.1 Kunlun Mountain earthquake,China

The Kunlunshan Mountain Ms8.1 earthquake, occurred in Nov.14, 2001, is the first event with magnitude more than 8 in the China earthquake monitoring history, specifically at the beginning of digital techniques in precursor monitoring networks. Any investigation of recorded data on this earthquake is very important for testing the operation of the digital monitoring networks and understanding the preparation, occurrence, and adjustment of stress/strain of strong continental earthquakes. In this paper we investigated the coseismic response changes of well water level of groundwater and volume strain meter of bore hole in digital earthquake monitoring network of Capital area and its vicinity, due to the Nov.14, 2001 Ms8.1 Kunlun Mountain earthquake. The responding time, shapes or manners, amplitudes, and lasting time of well water level and strain-meters to seismic wave are studied in comparison. Then we discussed the possibility that the response changes of groundwater to strong distant earthquakes can be understood as one kind of observing evidence of stress/strain changes induced by distant earthquake.

The evolution characteristics of positive and negative earthquakes before strong quakes in Kanto area and the Hyugo earthquake in Japan

This paper studies the evolution charateristics of positive and negative quakes before Hyugo earthquake of M =7.2 and several strong quakes in Kanto area in Japan.The results show that the earthquakes over a certain megnitude are mainly positive ones a certain time before the main shock in or near the focal regions of most strong quakes,and form a concentratingintervals of positive quakes,The main quakes generally locate in or near the areas of positive quake distribution.Negative quakes often occur several months before the main shocks (not excluding positive ones), with the decrease of LURR (Loading/Unloading Response Ratio) values.It possibly shows that earthquake generating process has come to a short term stage.These characteristics may help to predict the time and location of the future earthquakes,and have been applied to the preliminary prediction of the time and the location of the earthquake of M =6.6 on Sep.11,1996 in Kanto area.

Study on Key Technology of Using Shell Sand as Backfill for Sea Reclamation

The results of a study on the key technology of using shell sand, a kind of sea sand, as backfill for sea reclamation are described briefly. Iaboratory tests show that the physical and mechanical properties of shell sand are as good as normal quartz sand. Based on the chemical test and durability test of shell sand it could be concluded that the influence of corrosion of shell sand by acid rain and sea water might be ignored in the evaluation of the safety and durability of the engineering project. The results of field improvement tests show that the bearing capacity of shell sand backfill foundation is more than 200 kPa after vibmflotation improvement or dynamic compaction improvement. The shell sand is a good backfill material for sea reclamation.

Control Effects and Material Parameters of Piezoelectric Smart Moment Controllers

The control using piezoelectric smart moment (PSM) controllers for seismically excited structures was studied.The radical principle of PSM controller was introduced firstly and then the different formulae of control shear force for different structures were derived with the stiffness ratio of columns taken into consideration.With the active control algorithm based on the theory of modern optimal control,this study proposes a simulative computation on the frame structure and mill structure respectively,and the results indicate that the installation of this smart controller with proper parameters can significantly reduce seismic responses of different structures. The optimal parameters of the damper can be identified through a parameter study.

FEEDBACK CONTROL OPTIMIZATION FOR SEISMICALLY EXCITED BUILDINGS

A feedback control optimization method of partially observable linear structures via stationary response is proposed and analyzed with linear building structures equipped with control devices and sensors. First, the partially observable control problem of the structure under horizontal ground acceleration excitation is converted into a completely observable control problem. Then the It6 stochastic differential equations of the system are derived based on the stochastic averaging method for quasi-integrable Hamiltonian systems and the stationary solution to the Fokker-Plank-Kolmogorov （FPK） equation associated with the It6 equations is obtained. The performance index in terms of the mean system energy and mean square control force is established and the optimal control force is obtained by minimizing the performance index. Finally, the numerical results for a three-story building structure model under E1 Centro, Hachinohe, Northridge and Kobe earthquake excitations are given to illustrate the application and the effectiveness of the proposed method.

Fast magnitude determination using a single seismological station record implementing machine learning techniques

In this work a Support Vector Machine Regression（SVMR） algorithm is used to calculate local magnitude（MI） using only five seconds of signal after the P wave onset of one three component seismic station. This algorithm was trained with 863 records of historical earthquakes, where the input regression parameters were an exponential function of the waveform envelope estimated by least squares and the maximum value of the observed waveform for each component in a single station. Ten-fold cross validation was applied for a normalized polynomial kernel obtaining the mean absolute error for different exponents and complexity parameters. The local magnitude（MI） could be estimated with 0.19 units of mean absolute error. The proposed algorithm is easy to implement in hardware and may be used directly after the field seismological sensor to generate fast decisions at seismological control centers, increasing the possibility of having an effective reaction.

Application of Finite State Machine Theory to the Simulation of Reversed Non-Linear Hysteretic Relationships

This paper presents the application of finite state machine (FSM) theory to the programming of nonlinear hysteretic model simulation for both known and newly created rules. The complicated reversed internal paths involved in the nonlinear relationship which not only depend on material properties, but also on load history, often confuse rule creators and scholars. In this paper, we first describe the development of past hysteretic models. Then we introduce the FSM theory conceptually, and explain how it is applied to reversed and diverse routes. Next, state definitions and procedures are explained with a specific data example using the bilinear model. Finally, the successful application to UC-win/FRAME (3D) is described and several characteristics are summarized. By using FSM’s states and the linkages to represent a hysteresis model, we can quickly realize the programming of the defined complex model rules, and the nonlinear modeling becomes more efficient and feasible.

Three-Dimensional Modeling of Shallow Shear-Wave Velocities for Las Vegas, Nevada, Using Sediment Type

A three-dimensional model of near-surface shear-wave velocity in the deep alluvial basin underlying the metropolitan area of Las Vegas, Nevada （USA）, is being developed for earthquake site response projections. The velocity dataset, which includes 230 measurements, is interpolated across the model using depth-dependent correlations of velocity with sediment type. The sediment-type database contains more than 1 400 well and borehole logs. Sediment sequences reported in logs are assigned to one of four units. A characteristic shear-wave velocity profile is developed for each unit by analyzing closely spaced pairs of velocity profiles and well or borehole logs. The resulting velocity model exhibits reasonable values and patterns, although it does not explicitly honor the measured shear-wave velocity profiles. Site response investigations that applied a preliminary version of the velocity model support a two-zone ground-shaking hazard model for the valley. Areas in which clay predominates in the upper 30 m are predicted to have stronger ground motions than the rest of the basin.