Earthquake excitation

Using the quantified uncertainty obtained from Bayesian methods, there are two important types of applications. The first category is robust reliability analysis. Under severe earthquake excitations, buildings and bridges may exhibit significant nonlinear behavior. With a stochastic representation of the anticipated ground motions [96,130,237], one important reliability problem is to determine the first passage probability of some response quantities of interest in a... 

Aldemir U, Bakioglu M (2000) Semiactive control of earthquake-excited structures. Turk J Eng Environ Sci 24 237-246... 

In seismic design practice it is common to neglect the influence of soil-pile interactimi oti the motimi applied to the superstructure (i.e. the earthquake excitation is assumed to be equal to the free-field ground motion), except for important structures (NEHRP 2003 Eurocode 8 2004 Norme Tecniche per le Costruzioni 2008 Greek National Code, EAK 2000). It is worth discussing the relevant clauses from Eurocode 8 (EN 1998-5, 2004). The code prescribes that kinematic effects... 

Finally, the response of Configuration 2 to harmonic and earthquake excitation with PGA = 0.17g presented in Fig. 27.9, exhibits a similar behavior to both Configurations 1 and 3, resulting to simultaneous sliding and rotational failure. As seen from both the acceleration time histories (Fig. 27.9a) and the failure mechanisms (Fig. 27.9b) the sliding failure mode prevails, which is consistent to the critical accelerations estimated in Table 27.2. 

A free standing configuration for the Reactor Pool, resting on a common foundation mat, but structurally decoupled from the RB, designed for a RG. 1.60 Safety Shutdown Earthquake excitation anchored to 0.3 g, presents reasonable wall thicknesses and reinforcing bar densities. 

The response of distribution systems (piping, cable trays and cable conduits) to earthquake excitations tends to be quite non-linear. Computations of stresses and support reactions by means of linear elastic analyses provide approximate indications of stresses and support loads that are suitable for comparison with acceptance criteria to determine the adequacy of the design, but such computations should not be applied for deriving accurate values of actual stresses and support reactions. Nominally fixed supports for distribution systems with some limits on deflections may be considered rigid for modelling purposes. 

In general functional requirements should be estabUshed for active items (i.e. those items that move or otherwise change state) in advance, as part of the test procedure. In most cases active items are required to perform their active function after the earthquake excitation has ceased. However, if they have to perform such active functions during the earthquake excitation or during potential aftershocks, this should be considered in establishing functional test requirements. Care should also be taken that functionality tests are consistent with the required safety functions in service. ... 

Figure 7.50 Time histories for acceleration, speed, and displacement through earthquake excitation [7-691.

Wang, A.P. Lin, Y.H. 2007. Vibration control of a tall building subjected to earthquake excitation. Journal of Sound and Vibration, 299, 757-773. 

The dynamic response of civil engineering structures subjected to earthquake excitation can be reduced by using passive control systems such as energy dissipation devices (e.g. viscous dampers, etc.). The advantage of these systems with respect to active and semi-active control systems consist in the fact that they don t require any power supply, therefore are quite reliable and they require least maintenance. 

The seismic response of structures subjected to earthquake excitations may be effectively reduced by incorporating any of various kinds of available passive energy dissipation devices (Soong and Dargush 1997). Niunerous are the studies related to optimal placement and capacity of damping coefficient for linear multistory buildings. 

Four different earthquake leeords have been considered to investigate the dependence of the optimal locations on the stochastic nature of the earthquake excitation. 

Due to the great uncertainties in the nature of the earthquake excitations, using different earthquake records can yield differentoptimal locations. Therefore there is need for further research in developing statistical methods that can overcome the weaknesses of the above approaches. 

Paik, J., Reed, D. (2001). Analysis of uniformly and linearly distributed mass dampers under harmonic and earthquake excitation. Engineering Structures, 23, 802-814. doi 10.1016/S0141-0296(00)00095-X... 

Wang, A.-R, Fung, R.-F. (2001). Dynamic analysis of atall building with atune-mass-damper device subjected to earthquake excitations. Journal of Sound and Vibration, 244 ), 123-136. doi 10.1006/jsvi.2000.3480... 

Wong, K. K. F., Chee, Y. L. (2004). Eneigy dissipation oftuned mass dampers during earthquake excitations. Structural Design of Tall and Special Buildings, 13, 105-121. doi 10.1002/tal.244... 

Multi-Objective Optimization Design of Control Devices to Suppress Tall Buildings Vibrations against Earthquake Excitations Using Fuzzy Logic and Genetic Algorithms... 

One of the most important tasks in stmctural engineering is to reasonably minimize the undesired vibrations of the stmctures due to the environmental dynamie loads such as earthquake excitations. Various strategies and theories have been investigated and developed to approach this goal over the years. Use of the control systems is one of these methods to enhance the stmctural performance against vibration excitations. The main purpose of these methods is to reduce the stmctural responses such as displacement, velocity and acceleration. Control systems are divided to four groups of passive, semi active, active and hybrid systems based on the performance and rate of the eneigy consumption and the kind of their installation to the main stmcture. 

The main building is assumed to remain within the elastic limit during the earthquake excitation. As the control systems reduce the building response to a relatively low value, therefore this assumption would be reasonable. 

The response of the building is depended on its mode shapes and natural frequencies and can be simulated by dominant modes. According to the reference (Zuo Nayfeh, 2003) the first mode shape is dominant in earthquake excitation if modal frequencies are well-separated. But in this study, three first frequencies of the example building are very close, thus, three first modes of the main structure are considered for accurate modeling of the building therefore, the displacement vector can be expressed as... 

Table 9. Ratio of maximum displacement, velocity and acceleration of the STMD to the TMD and the percentage of reduction of them in seven earthquake excitations...

Pourzeynali, S., Esteki, S. (2009). Optimization of the TMD parameters to suppress the vertical vibrations of suspension bridges subjected to earthquake excitations. Iranian International Journal of Engineering. IJE Transaction B (Application), 22(1), 23-34. 

Earthquake Excitation Earthquake excitation is light or intense vibration and movement of the ground beeause of releasing of the eneigy of quick rupture in the earth s emst fault which is happened quiekly. 

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