Seismic action

Eurocode-8 (2005) BS-EN 1998-1, Design of structures for earthquake resistance - part 1 General rules, seismic actions and rules for buildings. European committeefor standardization, Brussels. 

Seismic action can cause serious accidents to industrial plants as shown in several occasions. The actual worldwide situation of major-hazard plants against earthquakes should be considered as critical. For instance, in Italy about 30% of industrial plants with major-accident hazards are located in areas with a high seismic risk. In addition, in case of a seismic event, the earthquake can induce the simultaneous damage of different apparatus, whose effects can be amplified because of the failure of safety systems or the simultaneous generation of multiple accidental chains. 

During the last years, in order to increase safety against earthquakes, passive control techniques (PCT) have been developed, which are based on the concept of reducing the seismic action instead of increasing the strength (Housner et al., 1997). These techniques that for civil constructions are nowadays considered a consolidated alternative design tool, can also be used for seismic protection of industrial structures. 

Metallic pipes themselves are not particularly vulnerable to seismic actions, but they can suffer the effects of differential displacements, which could not be compatible with the pipe deformations. Moreover, a collapse of the support structure can cause a catastrophic collapse of pipes, as shown in Figure 6b where the breakage of a piping flanged connection is shown. 

Innovative seismic control systems belongs to the world of the vibration control techniques of structures, which includes passive, semi-active, active and hybrid systems (Housner et al., 1997 Spencer, 2003 Christopoulos and Filiatrault, 2007). The experiences acquired during experimental activities and worldwide apvplications have indicated the passive control techniques as the most suitable solutions for the seismic protection of structures. These systems modify the stiffness and/or the dissipative properties of the structure, favoring the reduction of the dynamic response to seismic actions. They can be classified on the basis of... 

The model is a very basic one, with the seismic action represented by an equivalent static horizontal load V. The procedure consists in the calculation of the compressive length through equilibrium, assuming no tensile strength at the interface between the base of the wall and the foundation. A linear distribution of compressive stresses is assumed at the interface. Once the compressive length is... 

As already pointed out above, the main observation on the tests is the generalised rocking behavior of all walls. Rocking is a typical dynamic feature and can hardly be observed in tests where the seismic action is simulated by a static cyclic load (Degee and Lascar 2011a, b). 

This chapter presents the results of shake table tests carried out with the prime objective of characterising the dynamic rocking behavior of high strength clay masonry walls with glued horizontal joints and empty vertical joints subjected to seismic action. The main observation is that rocking occurs for all walls, even for situations where equivalent static models predict an anticipated shear failure. 

To define an adequate concept of repair and strengthening, it is necessary to carry out a detailed analysis of the existing structure, the type and physical-mechanical characteristics of masonry, the dynamic properties of the stmcture, the criteria and the expected seismic action. If this analysis proves that the structure has sufficient load-bearing and deformation capacity, measures for its repair shall be sufficient. Otherwise, depending on the vulnerability level, strengthening should increase the strength of the existing structure or/and its deformabiUty. 

Fig. 18.2 Earthquake spectra and the influence on the first vibration mode of the fixed and isolated buildings, respectively, (a) Original earthquakes, (b) Modified (generic) earthquakes to simulate near field seismic action...

Kato B (1979) Mechanical properties of steel under load cycles idealizing seismic action. CEB Bull D Inform 131 7-27... 

He Y.L. Lu S.Y. 1998. A method for calculating the seismic action in rock slope. Chinese Journal of Geotechnical Engineering. 20(2) 66-68. 

Levels of seismic protection (magnitude of the associated seismic action) Methods of analysis... 

The ultimate deformation capacity of a structure is a measure of its capacity to bear seismic action. It can be evaluated by using the outcomes of a nonlinear static analysis. 

Paulay, T., Park, R., and Priesley, M.J.N. (1978). Reinforced concrete beam-column joints under seismic actions . ACI Journal, Proceedings, 75 585-593. 

The two load distributions are schematically shown in Figure 1. The applied lateral load distributions are increased and the response is plotted in terms of base shear V/, vs. top floor displacement D (for example center of mass of the top floor). This is the so-called pushover curve or capacity curve (also shown schematically in Figure 1). The above load patterns are supposed to reproduce static loads equivalent to the seismic action. The two load patterns correspond to a first-mode dominated behavior and to a bottom soft-story response. Other distributions can be used but are typically non considered. 

A method for considering the randomness of the parameters defining the stochastic model of the seismic action used in the preceding steps. 

Meyer, I.F., Kratzig, W.B., Stangenberg, F. 1988. Damage prediction in reinforced concrete frames under seismic action. EEE-European Earthquake Engineering 3 9-15. 

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