Earthquake Proof Efficiency of Sliding Base Isolator With Dog-Bone Type Damping

In recent years, there have been more and more seismic retrofit applications of using base isolators in seismic prone regions. In the past, the focuses of researches on the efficiency of various base isolators have been aimed at their behavior under earthquakes without long predominant periods. The doubts of efficiency of the base isolator nearby active faults or located at a soft deposit soil have been raised by researchers. It is revealed from previous studies that the seismic responses of the base isolated structure are significant due to the influence of resonance. In order to minimize the inherent shortcomings of base isolators, various base isolators with dog bone type of friction behavior have been proposed in this study. In the meanwhile, the exact solutions used to describe the behavior of the proposed isolators have also been derived in this study. The numerical studies show that the displacement responses of proposed isolators under near fault earthquakes and ground motions with long predominant periods are much lower than those of the traditional FPS and VCFPS devices. Hence, the required dimensions of proposed isolators can be smaller than those for the FPS and VCFPS isolators.

Cyclic Performance of Two-Story Ductile RC Frames With Infill Walls

This paper presents the results of the experimental and analytical investigations conducted on four 0.8 scale 2-story one bay ductile reinforced concrete frames with infill nonstructural walls subjected to cyclically increasing loads. The material properties and the member sizes of beams and columns in the four RC frame specimens are identical, but with different types of infill nonstructural wall. These four frames are the pure frame, frame with short column, frame with short beam and frame with wing walls. The four RC frame specimens were designed and constructed according to the general prototype building structures in Taiwan. Test results indicate that the ductility behavior of the frames with infill wall is similar to those of the pure frame. The ultimate base shear strength of the frames with infill walls is higher than those of the pure frame. Analytical results show that the proposed simplified multi-linear beam-column element implemented in a general purpose structural analysis program can accurately simulate the cyclic responses of the RC frame specimen incorporating the elastic flexural stiffness computations suggested by the model building codes.

Visual and Versatile Hybrid Seismic Testing System Incorporated With Non-Linear Finite Element Analysis

Hybrid simulation/testing systems have been developed incorporating a non-linear finite element method with a pseudo-dynamic test. In order to ensure stability and efficiency for time integration, the incremental formulation of the α-OS method has been implemented on this system. Visualization system has also been integrated to recognize both numerical simulation for whole systems and laboratory testing for local parts. Numerical hybrid examinations of the soil structure interaction problem have been conducted on this system. By these results, validity and effectiveness of this system has been demonstrated.

On Selection of Control Parameters for H∞ Output Feedback

In this paper, an H∞ direct output feedback control algorithm through minimizing the entropy, a performance index measuring the tradeoff between H∞ optimality and H2 optimality, is employed to design the control system in reducing structural responses due to dynamic loads such as earthquakes. The control forces are obtained from the multiplication of direct output measurements by a pre-calculated time-invariant feedback gain matrix. To achieve optimal control performance, the strategy to select both control parameters γ and α is extensively investigated. The decrease of γ or increase of α results in better control effectiveness, but larger control force requirement. For a single degree-of-freedom (SDOF) damped structure, exact solutions of output feedback gains and control parameters are derived. It can be proved analytically that the LQR control is a special case of the proposed H∞ control. Direct velocity feedback control is effective in reducing structural responses with very small number of sensors and controllers compared with the DOFs of the structure. In active control of a real structure, control force execution time delay cannot be avoided. Relatively small delay time not only can render the control ineffective, but also may cause system instability. In this study, explicit formulas to calculate maximum allowable delay time and critical control parameters are derived for the design of a stable control system. Some solutions are also proposed to increase the maximum allowable delay time.

Three Dimensional Seismic Isolation System for Next-Generation Nuclear Power Plant With Rolling Seal Type Air Spring and Hydraulic Rocking Suppression System

Three dimensional (3D) seismic isolation devices have been developed to use for the base isolation system of the heavy building like a nuclear reactor building. The developed seismic isolation system is composed of rolling seal type air springs and the hydraulic type springs with rocking suppression system for vertical base isolation device. In horizontal direction, the same laminated rubber bearings are used as horizontal isolation device for these systems. The performances and the applicability have already been evaluated by the technical feasibility tests and performance tests for each system. In this study, it was evaluated that the performance of the 3D base isolation system with rolling seal type air springs combined with hydraulic rocking suppression devices. A 1/7 scaled model of the 3D base isolation devices were manufactured and some performance test were executed for each device. For the rolling seal type air springs, dynamic loading test was executed with a vibration table, and pressure resistant ability test was executed for reinforced air springs. In the dynamic loading test, it is confirmed that the natural period and damping performance were verified. In the pressure resistant ability test, it is confirmed that the air springs had sufficient strength. For the hydraulic rocking suppression system, forced dynamic loading test was carried out in order to measure the frictional and oil flow resistance force on each cylinder. And the vibration table tests were carried out with supported weight of 228 MN in order to evaluate and to confirm the horizontal and vertical isolation performance, rocking suppression performance, and the applicability of the this seismic isolation system as the combined system. 4 rolling seal type air springs and 4 hydraulic load-carrying cylinders with rocking suppression devices supported the weight. As a result, the proposed system was verified that it could be applied to the actual nuclear power plant building to be target.

Rotational Components of Seismic Motion Based on Surface Wave

In this paper, the appropriate methods are presented to obtain the seismic rotational components caused by the arrival of the surface waves applying the theory of elastic wave propagation. The rocking component around a horizontal axis and the torsional component around a vertical axis are generated respectively by the Rayleigh and Love waves. At the same time, the calculation formulations of phase velocities about these waves with frequent dispersion are derived and introduced to the rotational components, which may be more suitable for engineering practice. A procedure is developed to compute the time histories. Finally, numerical results have shown that the rotational motions have more energy than the translatonal motions in high frequent range by using the given methods.

Stability and Accuracy for Nonlinear Systems

Stability and accuracy of the Newmark method for solving nonlinear systems are analytically evaluated. It is proved that an unconditionally stable method for linear elastic systems is also unconditionally stable for nonlinear systems and a conditionally stable method for linear elastic systems remains conditionally stable for nonlinear systems except that the upper stability limit might vary with the step degree of nonlinearity and step degree of convergence. It is also found that numerical accuracy in the solution of nonlinear systems is highly related to the step degree of nonlinearity and the step degree of convergence although its general properties are similar to those of linear elastic systems. Analytical results are confirmed with numerical examples.

Verification Test for Hybrid Seismic Experimental Method Using Nonlinear Finite Element Method

An improved substructure hybrid seismic experimental method has been developed. This method consists of numerical computations using a general-purpose nonlinear finite element analysis tool and a pseudo-dynamic vibration test. Therefore, it enables seismic testing of large-scale structures that cannot be loaded onto a shaking table. The method also visualizes both data measured by sensors placed on the specimen and the results of the numerical analysis, and it helps us to understand the behavior of an entire structure consisting of a specimen and a numerical model. We performed verification tests for a piping system, in which we used a numerical model including supports, valves, and a branch pipe, and a specimen including two elbows. As results of tests, we conclude that the developed system has enough accuracy to be used as a seismic testing method.

Study on the Seismic Load Coupling Effects Due to Horizontal and Vertical Excitation for the Newly Developed 3-Dimensional Base Isolation System

Recently, many huge earthquakes occurred in many places, such as Hyogo-ken Nambu earthquake in 1995, Kocaeli earthquake and Chi-Chi earthquake in 1999 and Niigata Chuetsu earthquake in 2004 etc., and huge earthquakes are also considered to occur in near future. Therefore, many horizontal isolation structures have been proposed and constructed. In addition to the horizontal isolation, 3-dimensional isolation systems are under development as well. For these reasons, the authors also have developed a new 3-dimensional base isolation system and evaluated the effectiveness of the system. This isolation system employs sliding pads and laminated rubber bearings for horizontal isolation as some other isolation systems do. Thus, the vibration response of the upper structure depends on the friction force between sliding pads and the floor. In the actual seismic events, these sliding type isolation systems suffer from both horizontal and vertical seismic excitations simultaneously. For these reasons, the friction force in the horizontal direction has two components; one depends on the self weight and the other depends on the vertical seismic response. The latter will change time-dependently. Therefore, it can be said that the coupling effects between the horizontal and vertical seismic excitations become predominant. In this study, the coupling effects of the horizontal and vertical seismic excitations are investigated analytically as for the rocking motion, response displacement and response acceleration for the various seismic wave inputs. The effects of the phase difference between the horizontal and vertical seismic input and the amplitude of the vertical excitation are clarified and the design guide lines for the sliding type base isolation systems exposed to the horizontal and vertical simultaneous seismic excitations are proposed.

Study on Isolation Device for Decrease of Displacement by Using Control of Friction

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. A low horizontal natural frequency decreases the response acceleration. Therefore, in this research, a soft spring is attached to the base of the structure. 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, as the friction force increases, the results show that the relative displacement decreases. However, it is found that the response acceleration increases. But 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. Therefore, it is thought that the response acceleration and the relative displacement are decreased by changing the friction force to the most suitable value for earthquakes. This isolation device is examined with simulation analysis. An experimental device is made under the same conditions as the proposed analytical model. The analytical results are compared with the experimental results, and the validity of an analytical program is examined.