Abstract
Design codes establish seismic site classifications to determine the seismic demand of a structure according to the response of the soil foundation under the action of earthquake ground motions; the site classification can even condition the feasibility of a project. The occurrence of great earthquakes in Chile has tested its design codes, generating much information and experience regarding the seismic design of structures that have allowed researchers to identify variations in seismic demands according to the kind of ground foundation and to propose seismic site classification methods in Chilean regulations since the 1930s; countries in the vanguard of seismic design, such as the USA, Japan, and New Zealand, proposed methods even earlier. In this document, the evolution of methodologies for seismic site classification according to the criteria in Chilean codes is analysed from their implementation in the 1930s to the most recently proposed design code NCh 433, 2018–2021. Although the distinctive features of each country shape the criteria in their design codes, clear knowledge of the evolution of established criteria from their origins is considered an important tool that contributes to the better understanding, interpretation and application of the seismic site classification methodologies contained in a design code with better criteria. Likewise, the review indicates a distinct need to conduct a continuous evaluation of the classification criteria supported by records of new earthquakes, as well as by physical and numerical models that allow incorporating variables which condition the response of the terrain such as topography, lateral heterogeneities, and basic effects.
Highlights
Accepted: 4 November 2021The current main objective of seismic site classification is to assign design response spectra or to define parameters for its establishment according to the non-linear response of the soil foundation to shear waves generated from the bedrock upward to the ground surface by the action of earthquake ground motions.Parameters to carry out seismic site classification remain objects of study and analysis.Despite the discrepancies generated by the geological, geomorphological and laws of each country, some consensus has been achieved at an international level, sometimes indirectly, with respect to parameters that must be applied for such seismic classification
This regulation shows the first approximation to seismic site classification, which is an aspect of design codes that was not considered during this period
Centring the analysis of the proposal only on those revisions related to seismic site classification, one of the main changes proposed by the code committee, taking into account all the antecedents, consists of the incorporation, as a classification parameter of the fundamental period of vibration of the ground, Tg, measured in situ using the H/V spectral ratio method (HVR) method, which is directly linked with the seismic response of the ground and is complementary to Vs30
Summary
The current main objective of seismic site classification is to assign design response spectra or to define parameters for its establishment according to the non-linear response of the soil foundation to shear waves generated from the bedrock upward to the ground surface by the action of earthquake ground motions. Despite the discrepancies generated by the geological, geomorphological and laws of each country, some consensus has been achieved at an international level, sometimes indirectly, with respect to parameters that must be applied for such seismic classification An example of the latter is the known parameter Vs30 proposed by Borcherdt and Glassmoyer [1] and Borcherdt [2], which incorporates many design codes as the main classification parameter [3]. The Chilean seismic resistance design code, named NCh 433, in its most recent modified proposal (version 2018–2021), contains important advances with respect to the methodology of seismic site characterization and would be a pioneering proposal at the international design code level This position is not unprecedented for Chile, as the country has developed normative regulations for construction according to its investigations and experience and had integrated qualifying factors for almost 90 years before similar developments by other countries, such as the USA, Japan, and New Zealand. Having distinct knowledge of the evolution of ruling criteria from their origins is considered an important tool that contributes to understanding, interpreting and applying better criteria for ground classification methodologies contained in a design code
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