Seismic Risk and Engineering Decisions [antikvár]

Chapter 1 INTRODUCTION EMILIO ROSENBLUETH and CINNA LOMNITZ Instituto de Ingeniería, Universidad Nacional Autónoma de México, Mexico Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico Papers written in the last few years have enriched greatly the literature in earthquake engineering. The discipline is in rapid evolution and revision, more so than most other branches of civil engineering. Several factors incide in thus coloring design to resist earthquakes: the birth and consolidation of the theory of plate tectonics in the 1960s, causing an upheaval in ideas about the origin of earthquakes and opening the possibility of predicting these phenomena; a trend toward explicit optimization in all of engineering, which inevitably gives rise to revision of established approaches, especially in matters so plagued with huge uncertainties; expansion of human settlements and their accompanying structures onto very active seismic zones, raising questions of high economic repercussions in land use and in the effects of earthquake features so far regarded as not significant; need to design structures of ever increasing importance and whose failure would be catastrophic, especially nuclear power plants, with the ensuing public pressure for extreme safety; the advent of efficient methods of analyzing problems in continuum mechanics; and the commercial availability of instruments capable of recording strong motions with unprecedented precision and accuracy, which have made earthquake engineers reexamine their estimates of ground-motion parameters. The avalanche of technical papers has crystallized in some excellent text and reference books covering the areas of geotectonics, seismology, and structural analysis and design. Not all questions have been answered about these subjects, of course, but the state of the art is covered to an extent such as to awaken some confidence in the reader. He feels that he has a reasonable idea of how and why earthquakes originate and evolve as they traverse various geologic formations and of how structures respond to given specific disturbances. He is still much amiss with respect to the disturbances for which he should analyze and design. This is the purpose of the present work: to help bridge the crevasse of decision making between earthquake characteristics and structural behavior. When we say should analyze and design we imply an ethical question. This we shall dodge. Somehow, every engineer will presumably fix his scale of values and choose the path of rational behavior: he will aim at producing