Seismic Fragility of Code-conforming Italian Buildings Based on SDoF Approximation

ABSTRACT

The paper presents and discusses seismic fragility functions of code-conforming buildings in Italy. The structures under consideration are taken from those considered by a large Italian research project (RINTC), aiming at evaluating the seismic reliability of new-design buildings. Design refers to a variety of structural typologies (i.e. un-reinforced masonry, reinforced concrete, steel, and precast concrete buildings) and configurations (e.g. number of stories, floor plan, and the presence of infills), as well as to sites with different hazard levels and local site conditions. The seismic fragility of the structures is evaluated via multiple-stripe nonlinear dynamic analysis using the equivalent-single-degree-of-freedom (ESDoF) systems calibrated based on pushover analysis of the three-dimensional structural models. The seismic response of the ESDoF models is also validated in terms of demand-capacity ratio and risk of failure compared to those of the three-dimensional structural models. Along with providing fragility curves for the buildings located at high-hazard sites, the study discusses the issues that significantly affect the fragility assessment for those located at low-to-mid hazard sites.

KEYWORDS:

• Performance-based earthquake engineering
• seismic risk
• vulnerability
• nonlinear dynamic analysis
• collapse risk

Acknowledgments

The study presented in this article was developed within the activities of the ReLUIS-DPC 2014–2018 research program, funded by Presidenza del Consiglio dei Ministri – Dipartimento della Protezione Civile; however, opinions and conclusions do not necessarily reflect those of the funding entity. Data and technical supports from the RINTC workgroup are gratefully acknowledged. The authors are also thankful to the two anonymous reviewers who helped to greatly improve the quality of the paper.

Notes

1. In general, the choice of analysis methods for structural design of masonry buildings is made depending on the regularity of the structure and the hazard level at the site.

2. Applying the same damping ratio (5%) for the three different structural types/configurations (RC, steel, and PRC) could be discussed; however, this study rather prioritized the agreement between the ESDoF systems and the corresponding 3D structural models avoiding the discrepancies due to arbitrary adjustments of the damping ratios. For the details of the typology-specific modeling, see the cited papers.

3. In fact, 20 two-horizontal-component accelerometric waveforms were selected from the record set used in the cited paper, which contains the 30 single-component GM records.

4. At these IM levels, the scaling factors were quite large; this is inevitable due to the acceleration values to observe a significant number of failures in the buildings designed at the low-to-mid hazard sites. In fact, the average of the scaling factors at the IM level corresponding to $T_R=4.4\times {10}^7$ years was 17 for the CS-based record set and 26 for the PEER GM set. The effects of scaling on structural response are discussed in literature; see for example Luco and Bazzurro (2007), where similar ranges of scaling factors are investigated. However, note that very large accelerations may have a limited impact on the failure rate because of their small exceedance rates (i.e. Eq. (1)).