ATC-99-1

PROJECT OVERVIEW

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

Project Status: Complete

Client: Federal Emergency Management Agency (FEMA)

PROJECT SUMMARY

A reasonable alternative seismic design approach would be to use non-linear response analysis results in a simplified displacement-based approach.  Rather than calculating an equivalent lateral force for the to-be-designed simple building as prescribed in ASCE/SEI 7, such an approach could utilize the assessed nonlinear response characteristics of the initially proposed simple building for selection and sizing its seismic lateral force-resisting systems.  The challenge in implementing such an approach is that it would need to be validated against the performance of standard code-designed buildings and shown to meet the seismic performance intent of the standard seismic design procedure.  

The recently published FEMA P-695, Quantification of Building Seismic Performance Factors, and the FEMA P-58, Seismic Performance Assessment of Buildings, provide methodologies that can be used to validate the performance equivalency of alternative design procedures.  To be generally useful and nationally applicable, an alternative procedure would also need to be verified to be applicable to: (a) any selected lateral force resisting system, (b) any seismic hazard site, and (c) a reasonable range of building configurations.

This project seeks to complete three aspects, including:  (1) development of a methodology based on simplified nonlinear response analysis to assess and verify that building designs will meet the seismic performance intent of building codes and standards; and (2) development of a tool, based-on this methodology, to assist and improve seismic designs of low-rise buildings; and (3) consideration of the potential consequences of earthquake damage in the design decision process.

Task 1: Continue Development of the Canadian Methodology for Application to U.S. Practice

Under this task, the project team will investigate further extrapolation of the Canadian Methodology and available data to U.S. applications for new construction.  As developed under Task 17.2 in the initial phase of work, the preliminary scope of U.S. application for low-rise buildings is six stories or less, with the systems identified in Table 1.

Table 1.  Preliminary Structural Systems for U.S. Low-Rise Construction

Table 1 also identifies systems for which partial data are available from the Canadian work.  A key limitation is that the Canadian Methodology developed data for 2-story systems and extrapolated it to 3-story systems, while a U.S. application of the methodology may need to extend as high as 6 stories.  A basic assumption of the Canadian Methodology presumes shear behavior, while taller systems will need to be investigated for flexural and cantilever behavior in addition to shear behavior.  

Also investigated under Task 17.2 during the first phase of work was the effect of ground motion characteristics on the predicted response.  Results from this study will be used to refine additional investigations in the current phase of work. 

Selected studies will be targeted to verify the concept and to refine the framework of the proposed U.S. application of the methodology.  At this time, it is envisioned that the U.S. application will be patterned primarily after the Canadian Methodology, but might also be patterned after work leading to the development of the FEMA P-807 methodology for weak story wood frame buildings, which was similar in concept to the Canadian project.  It is assumed that prior design and analytical work will be leveraged to conduct the current work.  The actual number of studies that can be performed will depend on the degree of difficulty and the resulting variations in construction types, seismicity, and building configurations covered.  The extent of validation studies that can be conducted using available project resources will be determined in collaboration with the FEMA Task Monitor and the Project Management Committee. 

Task 2: Complete the Framework of the Methodology with Performance Measures

Based on the developmental work conducted under Task 17.5, the project team will revise the initial report on the outline of the methodology developed under Task 17.3 of the prior phase of work.  The revised report will be prepared by the Project Director and members of the Project Management Committee, and will be reviewed by the Project Review Panel as proposed under Task 17.7, below.  The report will include an assessment of the Project Work Plan, and recommendations for the level of effort of future developmental phases.