Effect of Modeling Uncertainty in Loss Estimation and on Financial Decision Variables - 1302005

Project Title—ID Number Effect of Modeling Uncertainty in Loss Estimation and on Financial Decision Variables - 1302005
Start/End Dates 10/1/05 – 9/30/06
Funding Source PEER-NSF
Project Leader (boldface) and Other Team Members Eduardo Miranda (Stanford/F), Carlos M. Ramirez (Stanford/GS), Felix Cheong (UCB/US), Tim Schrotenboer (Calvin College/US)
F=faculty; GS=graduate student; US=undergraduate student; PD=post-doc; I=industrial collaborator; O=other

Project goals and objectives

The main goal of this project is to develop fragility/loss information and tools that will enable practicing structural engineers to conduct loss assessments of buildings using PEER's performance-based loss estimation methodology. Specific objectives of this research are: (a) development of fragility functions for generic nonstructural components; (b) development of generic loss curves for building stories; (c) development of computer tools to facilitate loss estimation calculations and delivering loss information to decision makers.

Role of this project in supporting PEER's mission (vision)

While PEER's methodology provides a rational way of estimating losses produced by earthquakes, concerns have been expressed in the sense that, in its present form, it cannot be easily used by practicing engineers. Hence, there is a need to develop information and tools that will facilitate its adoption and that at the same time facilitates the visualization and interpretation of loss estimation results. The main objective of the project is development of such tools.

Methodology employed

PEER has developed a general framework to estimate the performance of structure in future earthquakes. PEER's approach is distinctively different from existing performance based approaches currently being used by some practicing structural engineers (e.g., FEMA 356). Namely, it provides measures of seismic performance that are directly relevant to stakeholders such as dollar losses, downtime and casualties/fatalities. Another distinct feature is that it provides a fully probabilistic framework which permits the incorporation and propagation of all relevant uncertainties involved in the estimation of the ground motion, the structural response, the damage and the losses.

Brief Description of previous year's achievements, with emphasis on accomplishments during last year (Year 8)

The toolbox will have two main components. The first one will permit the calculation of story fragility/loss functions that will permit the estimation of losses in building stories as a function of scalar Engineering Demand Parameters (EDPs) such as interstory drift ratio or peak floor acceleration.. Main input to this toolbox will be on one hand the specification of performance groups present in each story, and on the other hand the damage state, EDP-sensitivity, fragility parameters and loss parameters for each performance group present in the story. The second one will conduct loss estimation calculations by using story fragility/loss functions; simulation results from OpenSees or another simulation tool; and seismic hazard curve at the site.

One of the main challenges of the proposed research is the lack of data necessary to develop detailed fragility functions for various damage states for structural components, but particularly for nonstructural components. For this purpose this project is complementing existing experimental information with building performance data collected by structural engineers following the 1994 Northridge earthquake as part of the ATC-38 project (Database on the Performance of Structures Near Strong-Motion Recordings: 1994 Northridge, California, Earthquake). As part of the ATC-38 project, the Applied Technology Council developed and implemented a standardized procedure for systematically documenting the performance of buildings (both damaged and non-damaged) located in the vicinity (within 1000 feet) of strong- motion recording sites. The ATC-38 project involved the inspection of more than 500 buildings resulting in a statistically rigorous database of building characteristics and documented seismic performance which provides extremely valuable data to develop the proposed generic story loss functions. In addition to the ATC-38 data, 20 buildings that were inspected as part of the SAC project and that were located within 1,000 feet of a recording station will also be used. As part of a CSMIP-sponsored project these datasets were used to develop damage probability matrices and empirical fragility functions using ground motion parameters. In the proposed study structural motion based fragility functions are being developed by using simplified building models developed by the PI and his research students. The simplified building models are defined by a very small number of parameters which are treated as non-deterministic. Computer analysis tools were developed during Year 8 and the models were validated by comparing the displacement and acceleration response computed with the simplified model and those recorded in a very large set of buildings that are instrumented and have been subjected to various earthquake of various levels of intensity.

During Year 9 the development of empirical fragility functions will be finalized and a report explaining the methodology, data used, processed and final curves will be written to be published as a PEER report.

A small group of industry practitioners will be involved as an oversight committee during the development of the loss estimation toolbox. It is anticipated that during early stages of the development some portions of the code will be developed in Matlab, however the finish product will be a stand-alone product running in MS Excel which is a tool available and commonly used by structural engineers and other stakeholders. In particular, in is anticipated that interaction with ATC-58 project participant will take place. It is anticipated that the proposed loss estimation toolbox will not only provide an excellent tool for students and investigators within PEER but can become a major outreach vehicle for implementing PEER's methodologies.

Chart - Example of empirical fragility function for acceleration sensitive nonstructural components

Other similar work being conducted within and outside PEER and how this project differs

The ATC-58 generated an example to illustrate the use of the loss estimation methodology. The proposed work differs from that effort in the sense that correlations between repairs and fragilities in that effort were neglected. The only correlations that were considered were those between response parameters of different floors. In the proposed approach all level of correlation are considered. Therefore, the proposed project compliments and provides improvements of this outside work.

Describe any instances where you are aware that your results have been used in industry

Fragilities and damage methodologies were used by John Martin and Associates for implementing an automatic damage detection system for instrumented structures.

Expected milestones & deliverables

There are three major milestones in the proposed research investigation:

  1. Development of structural motion-seismic performance pairs from ATC-38 and CSMIP datasets. This involves first modeling each of the buildings and then computing peak responses on each story. Software tools were developed specifically for this purpose during Year 8 and a significant progress was made in processing each of the building. It is anticipated that this activity will be developed during Year 9.
  2. Development of generic empirically-based fragility functions for nonstructural components. One will be for drift-sensitive components while the other one will be for acceleration-sensitive components.
  3. Development, testing and calibration of the PEER loss estimation toolbox. It is anticipated that this activity will be initiated in Year 9, particularly the design of the user interface, and generation of expected annual losses and disaggregation of expected annual losses. The rest of the development and testing will be done in Year 10.

There will be three main deliverables from the proposed investigation:

  1. A research report and papers documenting the development of the generic story loss functions;
  2. A database summarizing computed responses and observed seismic performance of buildings located within 1000 ft of a recording station, and corresponding structural motion-performance data points
  3. The Excel-based PEER loss estimation toolbox

Member company benefits

Craig Comartin, CDComartin, Inc.

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