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Evaluating, Benchmarking, and Improving Performance-Based Earthquake Engineering Loss Predictions

Graduate Researcher(s): 
Gemma Cremen (gcremen@stanford.edu)
Faculty Advisor/PI: 
Jack Baker
Project Sponsor: 
Stanford Graduate Fellowship
John A. Blume Research Fellowship

Performance-based earthquake engineering (FEMA P-58) has in many ways revolutionized the thinking about seismic engineering design and acceptable performance of buildings in earthquakes. It is now making its way into commercial engineering design and risk analysis practice, as engineers aim to design better-performing buildings, and holders of mortgage or insurance instruments try to better understand the risk they face from damage to associated buildings. Some inputs to the calculations (e.g. structural response predictions) have been extensively studied. There are few studies however, that specifically examine the loss predictions.  The purpose of this research was to evaluate, benchmark, and improve these loss predictions, using various statistical techniques.

  1. We developed a methodology for quantifying the errors in FEMA P-58 damage and loss predictions, when different numbers of buildings are used to capture the response of a building in a given seismic event. We found that errors decrease as the number of building instruments is increased and that the reduction in error is substantial as soon as more than a small number of floors are instrumented (Figure 1).

Figure 1: Errors in FEMA P-58  repair cost predictions, for different levels of building instrumentation.

  1. We developed a methodology for evaluating P-58 component-level loss predictions across buildings subjected to given seismic events, which involved ranking the loss predictions according to categorical component damage information recorded on post-earthquake damage surveys. We used a ground shaking benchmark to determine whether P-58 analyses provide more insight into damage than variations in ground shaking between buildings. We found that FEMA P-58 provides benefit over simply using ground shaking intensity measures as a predictor of component-level damage (Figure 2).

Figure 2:  Comparing observed damage with (a) FEMA P-58  repair cost predictions and (b)  ground shaking intensity at each building.

  1. We made several recommendations for improving P-58 non-structural mechanical component fragility functions and associated loss predictions. For example, we recommended refining the current P-58 procedure for computing anchored mechanical component loss predictions, such that damage is predicted directly in line with the component and anchorage fragility functions. The proposed procedure leads to repair cost predictions that vary smoothly as a function of median anchorage capacity (Figure 3).

Figure 3: Variation of P-58 repair cost prediction with median anchorage capacity, using the proposed and current P-58 procedures for computing  anchored mechanical component losses.

Publications: 
  1. Cremen, G. & Baker, J. W. (2018). Improving non-structural component fragility functions and loss predictions in FEMA P-58 (journal publication in preparation).
  2. Cremen, G. & Baker, J. W. (2018). A methodology for evaluating component-level loss predictions of the FEMA P-58 seismic performance assessment procedure. Earthquake Spectra, (in press).
  3. Cremen, G. & Baker, J. W. (2018). Quantifying the benefits of building instruments to FEMA P-58 rapid post-earthquake damage and loss predictions. Engineering Structures, 176, 243-253.
  4. Cremen, G. & Baker, J. W. (2018). Quantifying the benefits of building instruments to FEMA P-58 damage and loss predictions, 11th U.S National Conference on Earthquake Engineering, Los Angeles, California, USA.
  5. Baker, J. W., Cremen, G., Giovinazzi, S., & Seville, E. (2016). Benchmarking FEMA P-58 performance predictions against observed data-A preliminary evaluation for the Canterbury earthquake sequence, 2016 Annual Conference of the New Zealand Society for Earthquake Engineering, Christchurch, New Zealand.