Earthquake Performance Rating Systems: SEAOC Perspective and Future Directions

Over the past year, significant developments related to earthquake performance rating systems for buildings have occurred, including the release by the Structural Engineers Association of Northern California (SEAONC) of the SEAONC Earthquake Performance Rating System (EPRS), and the launch of the US Resiliency Council (USRC). In addition, work by a Structural Engineers Association of California (SEAOC) Ad Hoc EPRS Committee continues, supported by efforts in each SEAOC Member Organization (MO). With activity by multiple organizations, questions have arisen as to what has been occurring and how the efforts relate. These “frequently asked questions” are intended to inform members of SEAOC and other interested persons of SEAOC’s perspective on recent developments and future directions regarding earthquake performance rating systems. This discussion has been developed by members of the SEAOC Board with input from a variety of others, and has been reviewed by the SEAOC Board.

1. What is an earthquake performance rating system?

An earthquake performance rating system is a ‘common language’ to communicate expected seismic performance of a building to a nontechnical audience.  This communication is intended to allow understanding of performance expectations and to facilitate comparison of performance between different buildings.  The ‘words’ in the ‘language’ are specifically chosen to be widely-understood.  A rating cannot exist without an underlying structural evaluation.  The rating ‘translates’ the findings of that evaluation into the ‘common language.’

2. What earthquake performance rating system resources exist?

Over the years various public and private institutions have developed in-house earthquake evaluation and performance rating systems that they have used to evaluate buildings they lease, purchase, hold, or sell from their building portfolios.  Relatively recently, earthquake performance rating systems and implementation organizations have become available for general use in both the public and private sectors:   

  • The SEAONC EPRS is the original work of a SEAONC committee, developed over a period of approximately eight years, including both a rating system for existing buildings and translation of structural evaluation results to ratings.  SEAONC EPRS resource documents are published and available to SEAONC members. Documents can be made available to others upon request.
  • A SEAOC EPRS is in discussion.  A SEAOC committee is currently considering development of a SEAOC EPRS resource document, to be based on the SEAONC document but modified as found appropriate by the SEAOC committee. This process of elevating the technical work of one SEAOC regional MO to the state level is consistent with SEAOC’s bylaws and standard committee practice.
  • The USRC is an independent non-profit organization formed to serve as an implementation body and an issuer of ratings that have consistency.  USRC ratings are based on an adaptation of the SEAONC EPRS, used with permission, to suit the USRC’s specific purposes. The USRC allows the use of a variety of evaluation methods in establishment of a USRC rating, including FEMA P-154, FEMA P-58, ASCE-31, and the ARUP REDi System.
  • FEMA P-50, prepared by the Applied Technology Council (ATC) for the Federal Emergency Management Agency (FEMA), is a system for seismic assessment of existing one- and two-family wood frame dwellings, with a rating assigned to reflect a combination of regional seismic hazard and dwelling vulnerability to seismic damage. The primary focus of FEMA P-50 is identification and retrofit of vulnerabilities.
  • The REDi System, developed by ARUP, provides a proprietary performance criteria for new construction, rather than rating existing buildings.

3. What are the differences between the SEAONC EPRS and the USRC?

The SEAONC EPRS is a technical resource that provides the ‘common language’ (rating descriptions), plus the methodology for selecting an appropriate rating based on results of a structural evaluation.  The USRC is an implementation organization that has developed processes to generate and document USRC ratings, with a primary aim to provide consistency across ratings.  USRC processes include qualification of persons to perform USRC ratings, as well as quality assurance for USRC ratings themselves.  USRC ratings are an adaptation of the SEAONC EPRS.

4. Besides the USRC, has any other organization adopted or adapted the SEAONC EPRS and developed processes around it?

Not to our knowledge.  It is possible that other implementation organizations will emerge in the future.

5. Are the various building rating systems mentioned above in conflict or competition?

No, SEAOC does not view the various rating systems and implementation efforts as being in conflict or competition, as each rating system suits its specific purpose. The SEAONC (and possible future SEAOC) documents are technical resources, while the USRC is an implementation organization. Earthquake performance rating systems are very much in their infancy, and SEAOC and MO technical committees will continue to develop rating system resources, much as our seismic design and retrofit provisions continue to develop. SEAONC and SEAOC plan to make future developments of our rating systems available to USRC and any other implementers of rating systems for their use (with appropriate agreements between organizations).

6. When might one seek out a rating from the USRC or other implementation organizations?

The main point is fitness for purpose.  If a building owner seeks information for private decision-making, a SEAONC EPRS rating or other rating might be well-suited.  If a rating will be disclosed to or relied upon by a third party or the public, the building owner might want the USRC added benefits of rater qualification and quality assurance processes to assure consistency.  These measures provide a level of confidence that a different rater would assign the same or similar rating. It should be noted that a USRC rating is issued and tracked by USRC. In contrast, a rating using a system other than USRC and issued directly by the engineer performing the rating, would likely not be tracked or verified except by that engineer’s firm.  Whatever rating system is used, it is important that the rater document and communicate to the client the evaluation and translation methodologies used to arrive at the assigned rating. This includes any limitations or restrictions regarding use of the evaluation and ratings.

7. What is the best way forward using rating systems, both for individual practitioners and organizations?

Anyone seeking to perform building ratings is advised to look at available resources and judge what best suits their building stock and their needs for disclosure, verification and tracking. For those investigating a small to moderate number of existing buildings, an approach like those currently available through SEAONC and USRC may be most practical.  For those with a large stock of buildings and with resources and reason to do so, it could make sense to develop special-purpose rating methods and/or implementation procedures.

The SEAOC Board has voted for and reaffirmed support in concept of the USRC; the board has taken no position regarding the USRC rating system as currently implemented. With the SEAONC EPRS currently under review by a SEAOC committee, the SEAOC Board has not taken a position on the SEAONC EPRS. SEAOC anticipates that earthquake performance rating systems and implementation will continue to develop over coming years. SEAOC members interested in involvement are encouraged to contact their local MO office for information on local activities. SEAOC hopes to have collaborative relationships with other organizations involved in rating system development and implementation.

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