Background
The single most comprehensive work towards earthquake risk calculation until today is condensed in HAZUS, a software system prepared for use in the United States by the Federal Emergency Management Agency (FEMA). The pushover analysis approach behind this software is physical-analytical (and hybrid), and large resources had been used to define fragility curves for different building types and categories for various levels of shaking. From an engineering perspective this analytical approach is very attractive, however, it quickly becomes complex even for simple buildings, and a calibration to the historical damage record is necessary. While HAZUS previously was an inaccessible software, NORSAR has recently developed the HAZUS methodology into a stand-alone software that can be applied anywhere in the world, and also includes a logic tree-based weighting of input parameters that allows for the computation of confidence intervals. The new software package from NORSAR is termed SELENA – Seismic Loss Estimation using a Logic Tree Approach.
The SELENA/HAZUS approach is often called the capacity-spectrum method since it combines the ground motion input in terms of a response spectrum (spectral acceleration versus spectral displacement) with the building’s specific capacity curve. The philosophy behind this is that any building is structurally damaged by its permanent horizontal displacement (and not by the acceleration itself). For each building and building type the inter-story drift (relative drift of the stories within a multi-story building) is a function of the applied lateral force that can be analytically determined and transformed into building capacity curves (capacity to withstand accelerations without permanent displacements). Building capacity curves naturally vary between different building types, and also between different regions, reflecting on building code regulations and local construction practice.
Highlights
- SELENA is a Matlab™ based computer tool that will assist you in computing damage scenarios.
- The damage probability for any specific structure follows the computation principles of HAZUS
- GIS-based software (e.g., Arcview) can be utilized at multiple levels of resolution to display predicted losses graphically.
- SELENA was developed through support from the International Centre for Geohazards, Norway.
SELENA principles.
Technical main points
While the HAZUS approach is attractive from a scientific/technical perspective, the fact that it is tailored so intimately to US situations and specific GIS software makes it difficult to apply in other environments and geographical regions. Aware of the importance of a proper seismic risk estimation, the International Centre for Geohazards, through NORSAR and the University of Alicante (Spain), has developed a Matlab™ based tool in order to compute the seismic risk in urban areas using the capacity spectrum method, -- SELENA (SEimic Loss EstimatioN using a logic tree Approach). SELENA can compute the probability of damage in each one of the four damage states (Slight, Moderate, Extensive and Complete) for defined building types.
The user must supply built area or number of buildings in the different model building types, earthquake sources, attenuation relationships, soil maps and corresponding ground motion amplification factors, capacity curves and fragility curves corresponding to each of the model building types and finally cost models for repair or replacement. This probability is subsequently used with the built area or number of buildings to express the results in terms of damaged area (square meters) or number of damaged buildings. Simple models for computing economic damages and casualties are also included.
The algorithm is based on the HAZUS methodology, and 144 predefined vulnerability curves detailed in the HAZUS manual can be applied in SELENA. The main innovation of SELENA is the implementation of the computation in a weighted logic tree scheme, allowing epistemic uncertainties of the different input parameters to be properly included, and the final results are provided with corresponding confidence levels. The method has been successfully applied to the city of Oslo (Molina and Lindholm, 2005).
Disclaimer
The SELENA software package can be downloaded and distributed free-of-charge.
Although we have done our best to find and remove bugs and weaknesses, the software is used at your own risk and neither the authors nor their organizations have any responsibility for the results that are obtained with the software or the use of these results. Users that appreciate the software may reference the paper by Molina and Lindholm (2005): A logic tree extension of the capacity spectrum method developed to estimate seismic risk in Oslo. Vol. 9, pp. 877-897, J. Earthq. Eng. doi:10.1142/S1363246905002201
Changes and improvements as well as suggestions are appreciated by the author.
Contact
Please contact Conrad Lindholm or Domink Lang for further information.
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