1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

In the countries of the former Yugoslavia, the first regulations for the design of seismically resistant structures date back to 1964, and the reason for their adoption was the Skopje earthquake in 1963. The next, much more advanced structural code dates from 1981 with a few additions. Many RC multi-storey buildings were designed and built according to the mentioned code for high-rise buildings from 1981, especially in larger cities. Some of the reasons were that they are mainly calculated according to their bearing capacity and global displacements values, and not according to the interstory lateral deformations. However, there was no possibility to correlate their reliability to resist earthquake actions with modern International documents (starting from ATC 40 (1996) - until the latest one from 2017, EC 8-part 3, FEMA 273, etc.), nor was it checked later. Recent earthquakes, including the Montenegrin (1979) earthquake, shortly before the 1981 Regulations, showed the vulnerability and even progressive collapse of reinforced concrete (RC) structures.
In many countries, for more significant structures, an assessment of their condition from the aspect of vulnerability and/or robustness is performed. It is significant that many seismically resistant structures have shown less sensitivity to progressive collapse because their integrity is, to some extent, a barrier against the occurrence of progressive collapse. Such analyses precede the reinforcement detailing of existing structures to the calculated seismic action characterized, above all, by the intensity and return period.
In this paper, a brief application of nonlinear modern methods of analysis and reliability assessment of these structures, with risk analysis according to the performance limit states of the building is performed. The robustness and seismic vulnerability of two models of an RC building with the same geometric characteristics were analysed, with one building designed according to European building design standards and the other according to Yugoslav regulations from 1981. The goal was to establish the difference in the performance of the two structures, because there is a large number of a reinforced concrete buildings designed by applying old codes in this region.
The methodology of calculation and design of RC buildings, necessary for the mentioned analyses, is described in the paper. Numerical analyses were conducted on RC building designed according to Yugoslav standards from 1981 and according to the mentioned modern norms (Eurocode) with a comparison of the important indicators in the obtained results.