ATC-99

PROJECT OVERVIEW

Title: Methodology to Assess and Verify the Seismic Capacity of Low-Rise Buildings

Project Status: Completed

Client: Federal Emergency Management Agency (FEMA)

PROJECT SUMMARY

This project seeks to conduct the first phase of a multi-phase project to eventually develop an alternative seismic design approach for low-rise construction in the United States that similarly utilizes non-linear response analysis results in a simplified displacement-based approach.  The approach would ideally incorporate a computing tool or analytical engine (similar to the tool developed for FEMA P-807) using the large amount of dynamic analysis data that has already been generated.  Rather than calculating an equivalent lateral force as prescribed in ASCE/SEI 7, such an approach would utilize the assessed nonlinear response characteristics of the building to select and size the seismic-force-resisting system.  

One challenge in implementing such an approach would be to validate it against the performance of standard code-designed buildings and demonstrate that the seismic performance intent of current U.S. model building codes and standards are met.  The FEMA P-695 report, Quantification of Building Seismic Performance Factors, provides a methodology that can be used to validate the performance equivalency of alternative design procedures.  To be generally useful and nationally applicable, an alternative design procedure would need to be verified for a variety of: (a) seismic-force-resisting systems; (b) site classes and seismic hazards; and (c) range of building configurations.  This validation effort would require the pre-determination of applicable building heights and structural system types, and a comparison of these parameters with the Canadian study parameters to determine which of the Canadian study data can be used, and what, if any, new data must be developed.

Task 1: Develop Initial Methodology for Validation on Selected Systems.  This task involves the investigation of the development of an initial methodology for simplified design of low-rise buildingsbased on the methodology developed on the Canadian project. 

Subtask 1.1 – Review Information from Related Projects

The Project Management Committee will review the work conducted on the Canadian project to understand the technical basis, and consider what adaptations would be needed for U.S. design and construction practice.  The PMC will also review work from other relevant projects including: FEMA P-807Seismic Evaluation and Retrofit of Weak-Story Wood-Frame Buildings, FEMA P-440A Effects of Strength and Stiffness Degradation on Seismic Response (ATC-62 Project), NIST GCR 10-917-9 Applicability of Nonlinear Multiple-Degree-of-Freedom Modeling for Design (ATC 76-6 Project), Static Pushover to Incremental Dynamic Analysis, SPO2IDA, as developed by Vamvatsikos and Cornell (2006).  Work will include the following milestones:

  • Initial review of Canadian Methodology (February 8, 2012)
  • Identify potential scope of consideration for U.S. practice based on the issues listed below (April 30, 2012)
    • Performance level/definition
    • Definition of low rise
    • Construction types (prototypes)
    • Damage patterns
    • Earthquake sources/regions of seismicity
    • Behavioral limitations/acceptable modes of behavior
    • New buildings with an eye toward existing buildings
    • Analytical engine
    • Modeling sophistication
    • Gravity system drift capacities
    • Torsional considerations
    • Case study analyses as required for validation of scope
  • Focused review of Canadian Methodology (June 15, 2012) relative to the above (bulleted) task breakdown
    • Develop ideas for U.S. methodology
    • Review Canadian methodology for solutions
  • Summarize the Canadian Methodology (June 30, 2012)
    • Identify what is applicable to U.S. practice
    • Identify necessary adaptations for U.S. practice

Subtask 1.2 – Develop Initial Methodology for Validation Studies

Based on available information, the Project Management Committee will develop an initial methodology targeted to U.S. applications and perform limited proof-of-concept studies.  In developing the initial methodology, the PMC will consider: (1) selected lateral systems that are popularly used in U.S. construction; (2) defined seismic environments and appropriate earthquake ground motion records for intended nonlinear responses analysis and performance measurement; and (3) necessary restrictions on building configuration (e.g. number of stories, height, vertical/ horizontal irregularities). 

At this time, it is envisioned that the U.S. methodology will be closely patterned after the Canadian Methodology.  It is assumed that prior design and analytical work conducted on the Canadian project will be leveraged to conduct proof-of-concept studies.  The scope and extent of studies that can be performed will depend on the degree of similarity or difference between the U.S. methodology and the Canadian Methodology and the resulting variations in construction types, seismicity, and building configurations covered.  Workwill include the following milestones:

  • Confirm scope of low-rise applications in U.S. (May 31, 2012)
  • Perform limited investigation of technical adaptations (July 15, 2012)
    • Choose one prototype (e.g. wood); attempt solution; identify issues
    • Investigate multistory wood systems; explore modes of behavior including structural and nonstructural elements
    • Check a FEMA P-807 building using the Canadian Analyzer
  • Refine list of necessary adaptations for U.S. practice (July 31, 2012)

Task 2: Prepare Draft Outline of the Methodology.  This task involves the preparation of an early draft (20% complete) report outlining the initial methodology, including a summary of the Canadian methodology, adaptations necessary for U.S. construction practice, and recommendations for study in future phases of work.  The report will be prepared under the direction of the Project Technical Director, with assistance from selected members of the PMC.  Workwill include the following milestones:

  • Development of a preliminary Outline (June 30, 2012)
  • Develop future plan (scope/level of effort/schedule) for adaptation of the Canadian Methodology to develop a FEMA methodology for low-rise buildings in the U.S. (August 15, 2012)
    • Compare with current US practice (IEBC, ASCE 41)
    • Consider implementation ideas (incentives/liability/training)
    • Consider verification
  • Submissionof draft report to FEMA (September 14, 2012)

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