Building portfolio fragility functions to support scalable community resilience assessment

Abstract

Community resilience planning, risk mitigation, and recovery optimization must assume a system perspective at the level of the overall community built environment. While engineers can quantify the performance of individual buildings and facilities, such information must be aggregated to reflect the vulnerability of the building portfolio as a whole to support resilience-based decisions at the community level. This study presents a methodology for building portfolio analysis that relates the performance of individual buildings exposed to natural hazards to the overall performance of a building portfolio. We introduce the concept of building portfolio fragility function (BPFF), defined as the probability that a building portfolio, as an aggregated system, fails to achieve prescribed performance objectives conditioned on scenario hazards, to characterize the vulnerability of a building portfolio and to directly inform resilience-driven decisions at the community level. The paper concludes with an illustration of the development of BPFFs to the Centerville community.

Keywords:

• Community resilience
• portfolio fragility function
• risk
• spatial correlation
• system performance objectives

Acknowledgment

The research reported herein was supported by the National Institute of Standards and Technology (NIST) (Award No. 70NANB15H044). This support is gratefully acknowledged. The views expressed in this paper are those of the authors and do not necessarily reflect the views of NIST. The authors would also like to acknowledge Dr. Xianwu Xue at University of Oklahoma for his effort in preparing the GIS figures of Centerville presented in this study.

Notes

1. The appropriate scenario event for resilience assessment of a real community should be identified based on the hazard frequency analysis and the risk tolerance of the specific community under investigation. For example, ASCE 7 (ASCE, 2010) is based on an earthquake (MCE) with a return period of 2475 years (2%/50 years). For Memphis, TN, for example, the dominant contributors to this return period hazard come from two faults that are 35 and 65 km from Memphis (Reelfoot Fault System), either of which is capable of generating scenario earthquakes of this magnitude.

2. Ground motion intensity is the ground motion characteristic that can be related to the response of structural systems, nonstructural components, and building contents through engineering analysis, such as peak ground acceleration, peak ground velocity, peak ground displacement, or a spectral response quantity such as spectral displacement, velocity or acceleration.

3. The damage state categorizes the extent of damage to structural and nonstructural components by different damage levels (often related to the structural system deformation or acceleration). In HAZUS-MH (FEMA, NIBS, 2003), four damage states (i.e. slight, moderate, extensive, and complete) to structural and nonstructural components of a building and their relationship with building response threshold are identified.

4. The damage value is defined as the functionality loss to individual buildings with respect to the portfolio functionality of interest as a result of its physical damage. The damage values often are categorized as direct dollar losses, downtime (or restoration time), and deaths (causalities) (FEMA, 2012).

5. The structural components refer to the main load-resisting system; In HAZUS, the nonstructural components are grouped as either ‘drift-sensitive’ or ‘acceleration-sensitive,’ in order to assess their damage due to an earthquake.