Design for low/moderate seismic risk
The increase of knowledge about seismic hazard worldwide, associated to an increase of awareness of the potential losses due to earthquakes, and economic progress allowing for policies of risk reduction, have led several countries in which seismic hazard was formerly ignored to pay greater attention to seismic design. The paper deals with a number of aspects related to this increased interest. It is first discussed, with reference to the solutions adopted in a few countries, the problem of where to put the lower limit to seismic intensity for which explicit seismic design is worth being carried out. It is shown that the limit varies considerably among countries, depending on economic conditions and on the general quality of the constructions. Based on the results of analytical simulations illustrated in the paper, it is concluded that modern RC buildings can have a substantial capacity to resist earthquake motions, if they have a regular configuration and are correctly designed for gravity loads only. In terms of PGA, this capacity may go up to 0.15 - 0.25g for structural damages still far below the ultimate state. This stresses the greater importance, especially in regions of moderate seismicity, of providing the profession with documents of good practice, rather than with analytically sophisticated codes. Looking at the future, ample space is given in the paper to discuss about which one of the two design methods, the established force- based or the emerging displacement-based is best suited to the needs specific to L/M risk zones. In their present state, they are both less effective for L/M areas than in ones of high seismicity. The DBD approach offers better perspectives for being extended to the L/M case on more rational bases.
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Copyright (c) 2000 Paolo E. Pinto
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