Unique Method for Generating Design Earthquake Time Histories

A method has been developed which takes a seed earthquake time history and modifies it to produce given design response spectra. It is a multi-step process with an initial scaling step and then multiple refinement steps. It is unique in the fact that both the acceleration and displacement response spectra are considered when performing the fit (which primarily improves the low frequency acceleration response spectrum accuracy). Additionally, no matrix inversion is needed. The features include encouraging the code acceleration, velocity, and displacement ratios and attempting to fit the pseudo velocity response spectrum. Also, “smoothing” is done to transition the modified time history to the seed time history at its start and end. This is done in the time history regions below a cumulative energy of 5% and above a cumulative energy of 95%. Finally, the modified acceleration, velocity, and displacement time histories are adjusted to start and end with an amplitude of zero (using Fourier transform techniques for integration).

Hilbert-Huang Transform Based Modal Analysis of Structures

This paper presents a Hilbert-Huang transform based signal reconstruction technique for the modal analysis of structural systems using vibration measurements. The original measured signal is initially undergone a well defined band-pass filter in order to solve the mode confounding problem. After the data preprocessing, each mode of the signal is reconstructed via the proper selection of intrinsic mode functions (IMFs) that are derived from the empirical mode decomposition of the signal’s mode. Through the signal reconstruction mode by mode, the structural parameter such as natural frequency is accurately evaluated, whose accuracy depends on the criterion for selecting the IMFs using the developed component sifting process. Reliable evaluation of systems’ characteristics leads to accurate prediction of systems’ behaviors for structural safety purpose. In this study, data preprocessing is operated to alleviate the problems of mode mixing and noise contaminated signal, as well as to compare with the previous work.

Seismic Mitigation Assessment of Building Using Multiple Direction Optimized-Friction Pendulum System

In order to prevent a building near a fault from earthquake damage, in this study an advanced base isolation system called the multiple direction optimized-friction pendulum system (Multiple DO-FPS or MDO-FPS) is proposed and examined to address its mechanical behavior through the finite element formulation and evaluate its efficiency in seismic mitigation through a series of shaking table tests. On the basis of the finite element formulation, it is revealed that the natural period, the capacity of the bearing displacement and damping effect for the Multiple Direction Optimized-Friction Pendulum System (Multiple DO-FPS) change continually during earthquakes. Therefore, the MDO-FPS isolator can avoid possibility of resonance of enriched frequencies from ground motions and provide an efficient capacity of the bearing displacement and damping during the earthquakes. Simultaneously, the shaking table test results also illustrate that the Multiple DO-FPS isolator possesses an outstanding seismic mitigation capabilities.

Time-Domain Nonlinear SSI Analysis of Foundation Sliding Using Frequency-Dependent Foundation Impedance Derived From SASSI

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using the de-convolution method and/or spatially variable ground motions. For structures that exhibit nonlinearities such as potential base sliding and/or uplift, the frequency-domain procedure is not applicable as it is limited to linear systems. For such problems, it is necessary to solve the problem in the time domain using the direct integration method in programs such as ADINA [2]. The authors recently introduced a sub-structuring technique called distributed parameter foundation impedance (DPFI) model that allows the structure to be partitioned from the total SSI system and analyzed in the time domain while the foundation soil is modeled using the frequency-domain procedure [3]. This procedure has been validated for linear systems. In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used to validate two linear time-domain ADINA models: Model 1 consisting of the mat foundation+DPFI derived from the linear SASSI model and Model 2 consisting of the total SSI system (mat foundation plus a soil block). After linear alignment, the nonlinear springs were added to both ADINA models and re-analyzed in time domain. Model 2 provided the target nonlinear solution while Model 1 provided the results using the DPFI+nonlinear springs. By increasing the amplitude of the vibration load, different levels of foundation sliding were simulated. Good agreement between the results of two models in terms of the displacement response of the mat and cyclic force-displacement behavior of the springs validates the accuracy of the procedure presented herein.

Analysis of the Effective Seismic Support Damping in a Class I Piping System

Based in the existing literature, it is understood that the supports strongly influence the behaviour of piping during earthquake. Given that the level of seismic dissipation depends on the specific support system, the subject of effective damping provided by seismic supports has not been widely explored. This paper investigates this issue for the feeder pipes of a CANDU® reactor. Feeders are numerous class I pipes in parallel, which are separated by frictional spacer elements. The piping system is analyzed using the time history method, taking into account the different damping mechanisms present. By comparing this and a response spectrum analysis of piping, the effective damping in the system is deduced. The effect of specific parameters on the results and the relationship between linear and nonlinear analyses are discussed.

Nonlinear Seismic Correlation Analysis of the JNES/NUPEC Large-Scale Piping System Tests

The Japan Nuclear Energy Safety Organization/Nuclear Power Engineering Corporation (JNES/NUPEC) large-scale piping test program has provided valuable new test data on high level seismic elasto-plastic behavior and failure modes for typical nuclear power plant piping systems. The component and piping system tests demonstrated the strain ratcheting behavior that is expected to occur when a pressurized pipe is subjected to cyclic seismic loading. Under a collaboration agreement between the U.S. and Japan on seismic issues, the U.S. Nuclear Regulatory Commission (NRC)/ Brookhaven National Laboratory (BNL) performed a correlation analysis of the large-scale piping system tests using detailed state-of-the-art nonlinear finite element models. Techniques are introduced to develop material models that can closely match the test data. The shaking table motions are examined. The analytical results are assessed in terms of the overall system responses and the strain ratcheting behavior at an elbow. The paper concludes with the insights about the accuracy of the analytical methods for use in performance assessments of highly nonlinear piping systems under large seismic motions.

Repetitive Control Based Disturbance Cancellation Using Iterative Basis Function Feedback With Wavelet Filtering

This paper presents repetitive control laws in real time using matched basis functions. These laws adjust the command given a feedback control system in order to eliminate tracking errors, resulting from in general a periodic disturbance and a non-periodic disturbance. The periodic error can be reduced by linear basis functions while the non-periodic error by the projection algorithm along with the wavelet filtering. The control laws do not use a system model, but instead the control action is chosen to be a linear combination of chosen input basis functions, and the corresponding output basis functions are obtained, nominally by experiment. The repetitive control laws use the projection algorithm to compute the output components on the output basis functions, and then the corresponding input components are adjusted accordingly. The output signals are reconstructed via the wavelet filtering before they are feedback to the controller. Numerical experiments show that the repetitive controllers are quite effective. In particular, the output tracking errors are further reduced because of the introduction of the wavelet filtering when compared to the previous work. In general, the repetitive control laws developed here can be used for the purpose of precision machinery control.

Study on Reducing Relative Displacement of Isolation Device With Friction Surface of Inclination

This paper deals with an isolation device by using friction force. An isolation device decreases response acceleration and external force. Therefore, earthquake damage is reduced. However, an isolation device has a demerit for large relative displacement. The purpose of this research is to decrease the relative displacement by using the friction force. Then, an analytical model in consideration of the friction force is proposed, and a simulation is analyzed with well-known earthquake waves. Consequently, it is thought that optimal friction force exists, and this force decreases both the response acceleration and the relative displacement. This is considered to change with the properties of earthquake waves. Then, it analyzed using the regular random wave. The result, the proportional relation was seen between relative displacement and the optimal coefficient of friction. Then, by changing a friction coefficient according to relative displacement, it is thought that both response acceleration and relative displacement can be reduced. However, it is difficult to change a friction coefficient. So, in this research, reduction of response acceleration and relative displacement is aimed by changing the angle of a friction surface and friction force. Furthermore, an angle is changed in the middle of a slope. It is thought that it becomes possible to reduce response acceleration and relative displacement further. An experimental device is made under the same conditions as the proposed analytical model. The experimental results are compared with the analytical results.

Shaking Table Tests of Static Dynamics Interchangeable-Ball Pendulum System for Motion Sensitive Equipment

Recently, the high-tech industry has become a key industry for economic development in many countries. However, motion sensitive equipments located in these industrial buildings are vulnerable during earthquakes, which may cause huge economic loss. In this study, an isolator for safeguarding the motion sensitive equipment, namely, the static dynamics interchangeable–ball pendulum system (SDI-BPS) is proposed and investigated to examine its protective capability for the motion sensitive equipment during earthquakes through a series of shaking table tests. The experimental results illustrate that the SDI-BPS isolator can provide significant damping to reduce the large bearing displacement and size, and avoid the stress concentration, which can cause damage or scratches on the sliding surface of the isolator, to prolong its life span of service. The SDI-BPS isolator also provides excellent capability in protecting the motion sensitive equipment and exhibits a stable behavior under long terms of service loadings and earthquakes.

An Approach for Assessing Structural Uplifting Using Blast Motions

When a nuclear power plant (NPP) structure is subjected to beyond-design-basis seismic motions, a localized nonlinear effect on the soil-structure system is attributed to separations between the structure and the surrounding soils such as basemat uplift. Experiments involving field tests for real seismic events are usually difficult because of the low probability for large earthquakes at any particular site. To this end, the magnitudes of blast-induced ground motions at a coal mine have been found to be predicatable and can reach very large values. An approach has been developed to investigate whether the strong ground motions recorded at this coal mine can be used to evaluate the basemat uplift effect. This approach involves the use of a scaled ground motion to establish the relationship between the basemat uplift and the peak ground acceleration (PGA). This paper summarizes the field measurements for the ground motions at a coal mine by the Japan Nuclear Safety Organization (JNES) and a method using large scale finite element analyses for basemat uplift assessment performed by Brookhaven National Laboratory for the US Nuclear Regulatory Commission.