1.1 Seismic Loss & Risk Modelling
Alternative Risk Mitigation Techniques for Earthquake Hazards
Z. Aslan, I. Damnjanovic & J.B. Mander
ABSTRACT: The insurance industry has traditionally provided the method of hedging losses from earthquakes plus other natural and human-induced catastrophes. But in the wake of recent catastrophes the insurance industry has demonstrated that it has a limited capacity to absorb large financial losses. Thus, instead of utilising reinsurance, the global capital markets have been used in conjunction with Alternative Risk Transfer (ART) products which provide immediate access to capital for prompt recovery action. However, the pricing of these products has been mostly associated with the hazard frequency and intensity; little recognition is made of the riskiness of the structure to be indemnified. This study proposes a valuation methodology for catastrophe-linked ART products based on a four-step engineering loss model. The approach provides a more transparent method in which the risks and value can be directly linked to the characteristics of the insured portfolio of large constructed facilities. The results show a highly nonlinear relationship between the structural (strength and deformation) parameters and financial parameters.
Economic Analysis of Structures Deficient in Earthquake Resilience
G.R. Walker & R. Musulin
ABSTRACT: The lack of earthquake resilience of many older structures poses a significant disaster risk to many communities in Australia and New Zealand. In considering the future of these structures several options are available including retrofitting to improve the resilience, demolition and replacement, or leaving them as they are. This paper describes the basic fundamentals of cost benefit analysis in respect of these different options, highlighting the importance of including the role of insurance in such analyses. A key input is the annual earthquake risk loss for the different options, the estimation of which is identified as one of the most difficult parts of such analyses. Furthermore there is a significant degree of uncertainty about most of the variables when analysing future costs and benefits. The insurance industry has developed two different tools to cope with these issues in respect of their own management of catastrophe risk. It is proposed that these tools be adapted for the detailed analysis of costs and benefits which is required for reliable decision making in dealing with structures perceived to be deficient in respect of their earthquake resilience. This will require multi-disciplinary research within the engineering, earth science and financial disciplines.
Comparison of Main Shock and Aftershock Fragility Curves Developed for New Zealand and US Buildings
S.R Uma, H. Ryu, N. Luco, A.B. Liel & M. Raghunandan
ABSTRACT: Seismic risk assessment involves the development of fragility functions to express the relationship between ground motion intensity and damage potential. In evaluating the risk associated with the building inventory in a region, it is essential to capture ‘actual’ characteristics of the buildings and group them so that ‘generic building types’ can be generated for further analysis of their damage potential. Variations in building characteristics across regions/countries largely influence the resulting fragility functions, such that building models are unsuitable to be adopted for risk assessment in any other region where a different set of building is present. In this paper, for a given building type (represented in terms of height and structural system), typical New Zealand and US building models are considered to illustrate the differences in structural model parameters and their effects on resulting fragility functions for a set of mains hocks and aftershocks. From this study, the general conclusion is that the methodology and assumptions used to derive basic capacity curve parameters have a considerable influence on fragility curves.
Rapid Modelling of Direct and Indirect Losses for Seismically Damaged Structures
S. Ghorawat, J.B. Mander & I.D. Damnjanovic
ABSTRACT: Earthquake consequences should ideally be reported in terms of 3-D losses: Damage, Death and Downtime. A quantitative risk assessment model is advanced to examine the three loss types. Loss functions are developed from the principles of fragility analysis, cost estimation, plus fault trees. By incorporating the effects of epistemic and aleatory uncertainty, the 3-D loss types are then combined and integrated for all potential earthquakes to give an aggregate expected annual dollar-equivalent loss. To illustrate the comprehensive approach, the utility of the proposed model is investigated and illustrated for the bridges with different detailing classes of non-seismic, ductile seismic, and damage avoidance design. It is shown that indirect losses overwhelm direct damage, typically by an order of magnitude.
Developing Fragilities for Mainshock-Damaged Structures through Incremental Dynamic Analysis
H. Ryu, N. Luco, S.R. Uma & A.B. Liel
ABSTRACT: We present a methodology for developing fragilities for mainshock-damaged structures, “aftershock fragility”, by performing incremental dynamic analysis (IDA) with a sequence of mainshock-aftershock ground motions. The aftershock fragility herein is distinguished from a conventional fragility for an intact structure. We estimate seismic response of a mainshock-damaged building by performing nonlinear time history analysis with a sequence of mainshock and aftershock ground motions (so-called “back-to-back” dynamic analysis). We perform the back-to-back dynamic analyses for a number of levels of mainshock response/damage, and a number of sequences of mainshock and aftershock ground motions. With estimated seismic responses from the back-to-back dynamic analyses, we compute various damage state transition probabilities, the probability of exceeding a higher damage state from aftershock given a damage state due to mainshock. For an illustration of the methodology, we developed an aftershock fragility for a typical New Zealand 5 storey reinforced concrete moment frame. The building is modeled using a single-degree-of-freedom (SDOF) damped nonlinear oscillator with force-deformation behavior represented by a multi-linear capacity/pushover curve with moderate pinching hysteresis and medium cyclic deterioration models. Relative opportunities and challenges associated with the proposed approach are discussed.