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Seismic Design For Pressure Vessels As Per ASME SEC VIII Div 1, 2: Equations For Seismic Forces

The American Society of Mechanical Engineers (ASME) has established standards for the seismic design of pressure vessels, which are important for ensuring their safety and reliability in areas with seismic activity. This seismic design is covered in Section VIII of the ASME Boiler and Pressure Vessel Code, which provides guidelines for designing pressure vessels to withstand the effects of earthquakes and other seismic events.


When designing a pressure vessel for seismic loads, engineers must consider the vessel's size, shape, location, and the seismic hazards that may be present in the area. This involves both an analysis of the vessel's structural properties and an assessment of the seismic hazard at the site. The design should ensure that the vessel can withstand the expected seismic forces while maintaining its safety and integrity.


The seismic design of pressure vessels is covered in both ASME Section VIII Division 1 and ASME Section VIII Division 2. Division 1 provides requirements for the use of seismic coefficients to calculate the equivalent static force that must be applied to the vessel to simulate the effects of the seismic event. The seismic coefficients are based on the peak ground acceleration expected at the site and take into account the vessel's weight, height, and other structural properties.


The equation for calculating the seismic force using the seismic coefficient method is as follows:

F = W × Ss × S1

where F is the seismic force, W is the weight of the vessel, Ss is the site-specific seismic response coefficient, and S1 is the spectral acceleration parameter. The seismic force is calculated for each direction of seismic loading (vertical, horizontal, and torsional), and the maximum value is used in the vessel's design.


ASME Section VIII Division 2 provides more comprehensive requirements for analyzing the response of the vessel to seismic loads, including both elastic and inelastic behavior. This involves using advanced methods such as finite element analysis (FEA) and nonlinear time history analysis to model the behavior of the vessel under seismic loading conditions.


The equation for calculating the seismic force using the dynamic analysis method is as follows:

F = m × a

where F is the seismic force, m is the mass of the vessel and its contents, and a is the acceleration of the ground motion. The mass includes the weight of the vessel and its contents, as well as any attached equipment or piping that may contribute to the vessel's dynamic response.


In addition to these equations, ASME also provides guidelines for selecting seismic response spectra, determining the effective mass of the vessel, and other aspects of the seismic design process. Compliance with these guidelines can help ensure that pressure vessels are designed to withstand seismic loads and provide reliable and safe operation for their intended use.


In conclusion, seismic design for pressure vessels as per ASME Section VIII Division 1 and ASME Section VIII Division 2 is an important consideration for ensuring the safety and reliability of pressure vessels in areas with seismic activity. The equations for calculating seismic forces using the seismic coefficient method and the dynamic analysis method are key components of the seismic design process, and engineers must carefully evaluate the potential seismic hazards at a given site to ensure that pressure vessels are designed to withstand these forces.

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