Pressure vessels seismic loads

At the very top of the vessel there are no induced stresses introduced by wind or seismic loads the only considerations are the functional design of the vessel and the stress considerations when the vessel is operating either under partial vacuum or under a pressure greater than atmospheric. Furthermore, at the very top of the vessel, there is usually little static dead weight to consider in the stress analysis except when condensers, heat exchangers or other auxiliary apparatus are attached to the top. 

We will now consider the special problems in tall tower design which are not described in the ASME Code for Unfired Pressure Vessels. As discussed previously, circumferential stresses control the design of cylindrical vessels if external loads are of small magnitude. In tall vertical vessels, four major factors (wind load, seismic loads, dead weight and vibration) may contribute to axial stresses — in addition to axial stress produced by the operating pressure or vacuum of the vessel. 

The MCSS is designed for high stiffness in order to maintain structural integrity during an SSE event. The seismic analysis indicates that the fundamental frequency is 32 Hz and a spectrum load of approximately 0.5 g. Comparison with ASME Boiler and Pressure Vessel Code Section III, Div. 1, Subsection NG stress criteria demonstrates that failure of the structure is not credible. 

Pressure vessels and their supports must be designed to resist the forees and loadings anticipated during a seismic event... an earthquake. The seismic design is not defined by the ASME Code but by building codes (previously NBC, SBC, and UBC, but now IBC) that reference technical standards such as ASCE/SEI 7, ACI 318, and AISC 360. Many countries have their own seismic standards and there are international standards as well. The ASME Code states in UG-22 that the vessel and support structure must be designed to withstand the forces from a seismic event. 

The loading conditions that are generally considered for the design of pressure vessels include pressure, dead weight, piping reaction, seismic, thermal expansion and loadings due to wind and snow. The ASME Boiler and Pressure Vessel Code delineates the various loads in terms of the following conditions ... 

Major loads that induce compressive stresses in the containment vessel are internal and external pressure and crane and seismic loads. 

NUREG-0800, Standard Review Plan Section 3.9.5, Reactor Pressure Vessel Internals Provides guidelines and information to address the design arrangements of all reactor internals structures and components and the loading conditions that provide the basis for the design of the reactor internals to sustain normal operation, anticipated operational occurrences, postulated accidents, and seismic events. [6.8]... 

Pappa P et al (2012) Structural safety of industrial steel tanks, pressure vessels and piping systems under seismic loading (INDUSE). RFCS project final report, Brussels, www.mie.uth.gr/induse Peek R (1988) Analysis of unanchored liquid storage tanks under lateral loads. Earthq Eng Struct Dyn 16 1087-1100... 

Wind, seismic and vibrational stresses and accumulated dead weight compression loadings primarily affect the axial stress and produce only a small effect as a result of Poisson s relationship on the circumferential stress. Therefore, the shell thickness of the upper portion of a tall vertical vessel designed to operate under either internal pressure or vacuum is determined by the circumferential stress. 

The procedure for designing a simple cylindrical vessel to Code Case 2286 or Section VIII, Division 2 is to first establish geometry as weU as determine shell thickness values to begin with. Typically, some thickness is estab-hshed from, say, internal pressure and those thickness values are used for starting the procedure in Code Case 2286. External loads from wind and seismic design criteria must be estabhshed to complete the procedure. 

As a loading, wind differs from seismic in that it is more or less constant whereas, seismic is of relatively short duration. In addition, the wind pressure varies with die height of die vessel. A vessel must be designed for the... 

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