ASCE 4-16

Abstract

Scope: Types of Structures Covered by This Standard. This standard is intended for use in the seismic analysis of all safety-related structures of nuclear facilities, including but not limited to above- and below-ground structures, buried piping, vertical liquid storage tanks, distribution systems, anchored and unanchored components, and structures with seismic isolation systems. Analysis of caisson and pile-supported foundations, unlined tunnels, and floating structures are not covered by this standard. However, nothing in this standard precludes the use of these structures and structural elements. FoundationMaterial Stability. The analysis procedures provided herein assume that the foundation media adequately support the structures analyzed and that no soil or rock failure occurs that would modify or void the seismic analysis. Purpose. This standard provides minimum requirements and acceptable methods for the seismic analyses of safety-related structures of a nuclear facility. The standard provides methods for calculating seismic responses in structures and for deriving input motions for use in the seismic design and qualification of electrical and mechanical systems and components. The purpose of the analytical methods is to provide reasonable levels of conservatism to account for uncertainties. The following areas for deterministic seismic analyses contain conservatism: 1. The spectra of acceleration histories used in analysis envelop the design response spectra, thus introducing some level of conservatism. 2. For soil-structure interaction, a minimum of three soil cases are analyzed using a range of soil properties, and the results are enveloped. 3. For in-structure response spectra, the peaks are broadened. 4. For structural damping, generally conservative values are specified. 5. The use of response-spectrum analysis and equivalent static methods generally results in conservative demand estimates. For certain special structures covered in Chapters 7–12 of this standard, added conservative assumptions are incorporated into the analysis process to account for highly variable physical properties and analysis parameters. The goal of the added conservatism is to preclude underestimation of response that may lead to unacceptable behavior. Given the seismic design response spectra, the goal of the standard is to develop seismic responses with 80% probability of nonexceedance. For probabilistic seismic analyses, the response with 80% probability of nonexceedance is selected.