NEW PERUVIAN REGULATION FOR SEISMIC DESIGN OF UNDERGROUND STRUCTURES

This paper describes a proposal for the new Standard for earthquake-resistant design of underground structures for road and railway infrastructure in Peru. The considered structures are: road and railway tunnels, by-passes, and, mainly, metro and railway stations. Other buried structures not corresponding to road and railway infrastructure (underpasses for pedestrians, foundations, building basements, mining infrastructure, industrial facilities, pipes, culverts, sewers, rainwater storage tanks, sewage treatment stations, etc.) are not contemplated. This Norm will incorporate the best of international documents (ISO [1]) and regulations of advanced countries (China [2], Japan [3], New Zealand [4], European Union [5], USA [6]), but has a clear Peruvian vocation; this means to be harmonized with the legislation and construction practices of the country, and to fit the usual level of knowledge, expectations and mentality of its potential users. Of course, the Standard cannot contradict any Peruvian legal text. The Code will be developed to be easily updated in order to incorporate the latest research advances, to include the conclusions derived after observed seismic damages, and to benefit from the experience acquired by its application. Many norms propose discrete classifications; then, small changes generate abrupt changes in the design parameters. This occurs in the soil classification into categories (A, B, C, D, etc.), and in the territory partition into seismic zones. To avoid this problem, continuous categories will be proposed instead: soil can be classified according to the shear wave velocity (or other equivalent parameters), and the site seismicity through the bedrock acceleration (PGA). Regarding this last issue, the Peruvian institutions (CISMID, IGP, SENCICO, among others) provide extensive information on the seismicity of each point inside the national territory. The Design Life of the analyzed structures is stated as 100 years. The importance of the analyzed structures is organized in levels that express the severity of the failure consequence; three levels are considered (low, normal and high). This regulation lies in the context of the PBD (Performance-Based Design). In this sense, five Damage Levels (equivalent to Limit States or Performance Requirements) are considered; four of them are structural (correspond roughly, to FO, IO, LS and CP in the American documents) and the fifth one is related to functionality (refers especially to derailment). For important structures (high importance), resilience will be considered; it is understood as the capacity of the construction to be repaired and put back into operation within a reasonably short time. Each Damage Level and Importance Level is associated with a certain seismicity, quantified in terms of return period (probability of being exceeded during the construction Design Life). As well, the seismic action during the construction stage is defined. The main analysis and design strategy will be displacement-based static equivalent formulations. The use of more sophisticated strategies (e.g. nonlinear dynamic analysis) will only be allowed if carried out properly. In any case, simplified analyses (approaches based on forces or displacements) will be required, and large reductions with respect to them will not be permitted.