ABSTRACT

It is well known that the seismic structural reliability is not explicitly controlled in design carried out according to seismic contemporary building codes; that is, those enforcing a simplified version of performance-based design. This is even more true for structures designed with obsolete seismic codes or without any seismic provisions at all, which constitute most of the building stock in countries such as Italy. Between 2019 and 2021, a large research project, RINTC – Rischio Implicito delle Norme Tecniche per le Costruzioni (i.e. implicit risk of existing buildings designed according to the Italian codes), has addressed, in a coherent manner, the inherent seismic structural reliability of existing Italian structures built according to evolving codes, which have now been superseded by multi-limit-state-based provisions. To this aim, five structural typologies of residential and industrial buildings have been considered, that is, reinforced concrete, pre-cast reinforced concrete, base-isolated reinforced concrete, masonry, and steel structures. The building design accounts for the evolution of codes within the last century or more. Structures are supposedly located at five sites in the country, representative of different seismic hazard, both currently and at the time of design. Nonlinear state-of-the-art three-dimensional numerical models for the considered structures have been analyzed via multi-stripe nonlinear dynamic analysis, the results of which, in turn, have been used to evaluate the annual failure rate as a measure of seismic reliability with respect to two performance levels defined within the project and named global collapse and usability-preventing damage. These rates, finally, allowed to appreciate the variation of seismic safety with the evolution of codes and to compare with that implied by current design. The results of the study allowed to conclude that the evolution of seismic codes clearly tends to enhance the seismic reliability with the largest average improvement attributable to the enforcement of the current code.

摘要

众所周知，在根据现代抗震建筑规范进行的设计中，抗震结构可靠性并未得到明确控制；也就是说，那些强制执行基于性能的设计的简化版本。对于使用过时的抗震规范或根本没有任何抗震规定设计的结构来说更是如此，这些结构构成了意大利等国家的大部分建筑存量。2019 年至 2021 年间，一个大型研究项目 RINTC – Rischio Implicito delle Norme Tecniche per le Costruzioni（即根据意大利规范设计的现有建筑物的隐性风险)，以连贯的方式解决了根据不断发展的规范建造的现有意大利结构的固有抗震结构可靠性，这些规范现在已被基于多极限状态的规定所取代。为此，考虑了五种住宅和工业建筑的结构类型，即钢筋混凝土、预制钢筋混凝土、基础隔震钢筋混凝土、砖石结构和钢结构。建筑设计考虑了上个世纪或更长时间内规范的演变。据推测，结构位于该国的五个地点，代表了当前和设计时的不同地震危险。通过多条纹非线性动力学分析，对所考虑结构的非线性最先进的三维数值模型进行了分析，全局崩溃和防止可用性损坏。最后，这些比率允许了解地震安全性随规范演变的变化，并与当前设计所暗示的进行比较。研究结果得出的结论是，抗震规范的演变显然倾向于提高抗震可靠性，其中最大的平均改进归因于当前规范的实施。