Seismic Safety

A method of load increments is presented for the nonlinear static analysis and the determination of second-order limit load and collapse safety of reinforced concrete space framed structures.The method considers the non-linearity caused by both elastic-plastic behavior of reinforced concrete and the effect of geometrical changes on equilibrium equations. The elastic-plastic behavior of reinforced concrete rnembers subjected to combined internal forces is idealized through the concept of plastic sections with limited plastic deformation capability. In the load increments method developed herein, the structural system is analyzed under factored constant gravity loads and proportionally increasing lateral loads. Thus, at the end of the analysis, the factor of safety against lateral earthquake or wind loads can be determined under the anticipated safety factor for gravity loads. At each step of the load increments, internal force-deformation relationships, yield conditions and the effect of geometrical changes on equilibrium equations are linearized by means of special techniques. A fifteen-story reinforced concrete, structure is selected for the illustration of the method.

In recent years, the debate on environmental issues has also extended to constructive principles, evolving into the discussion on the quality of the built environment. It is the opinion of the author that the development of sustainability criteria, drawn up by experts in the field, in the majority of cases can also be functional to the optimization of the basic parameters concerning structural safety. This work examines some of the "natural" methods for increasing structural efficiency, taken from case studies of antiquity. In fact, focusing observations only on the field of seismic activity, it is well known that passive isolation for existing buildings appears to be utopian, too laborious and expensive, as well as having an enormous environmental impact. But the study of certain architectural typologies of antiquity suggests a solution, i.e. an anti-seismic strategy, realized in an intuitive way, through simple devices such as the geometry of the plan, the proportions of the sections and constraints, the distribution of the openings, etc., which do not impose themselves with respect to the architectural and functional harmonies, but which nevertheless perform the task for which they are designed. "Unusual" anti-seismic solutions, coming from the constructive experience of different countries, with constructive methods and traditions that would seem to have nothing similar to each other, but joined by the common denominator of not being regulated, apparently unaware of phenomena such as hysteresis, dissipation, isolation, and born from a "popular" culture, born from the observation of nature, or from the experience handed down. From the examination of the past, it is hoped that the seed of a new philosophy of intervention for safety can emerge: the use of simple and "ancient" ideas, alternatives, translated into modern technology, methods that cannot be generalized, to be developed each time for each individual case.