Applied Technology Council A Nonprofit Corporation Advancing Engineering Applications for Hazard Mitigation California - Washington, DC Area

In September 2004 the Applied Technology Council (ATC) was awarded a "Seismic and Multi-Hazard Technical Guidance Development and Support" contract (HSFEHQ-04-D-0641) by the Federal Emergency Management Agency (FEMA) to conduct a variety of tasks, including one entitled "Quantification of Building System Performance and Response Parameters" (ATC-63 Project). The purpose of this project is to establish and document a recommended methodology for reliably quantifying building system performance and response parameters for use in seismic design. A key parameter to be addressed is the response modification coefficient (R factor), but related design parameters such as the system overstrength factor (W₀) and deflection amplification factor (C_d) are also addressed. Collectively these factors are referred to as "Seismic Performance Factors". 

R factors are used to estimate strength demands on systems that are designed using linear methods, but are responding in the nonlinear range. Their values are fundamentally critical in the specification of seismic loading, and original values were based largely on judgment and qualitative comparisons with other known systems. The recommended methodology is intended to provide a rational basis for determining building seismic performance factors that, when properly implemented in the seismic design process, will result in:

"Equivalent safety against collapse in an earthquake, comparable to the inherent safety against collapse intended by current seismic codes, for buildings with different seismic-force-resisting systems."

The Methodology consists of a framework that involves development of detailed system design information and probabilistic assessment of collapse risk. It utilizes nonlinear analysis techniques, and explicitly considers uncertainties in ground motion, modeling, design, and test data. The technical approach is a combination of traditional code concepts, advanced nonlinear dynamic analyses, and risk-based assessment techniques. Studies have been conducted on collapse simulations using nonlinear dynamic analyses modeled in OpenSees (Open Systems for Earthquake Engineering Simulation) and SAWS (Seismic Analysis of Woodframe Structures). Sample results from analytical studies are shown in the figures below.

To date the ATC-63 Project has reviewed relevant research on nonlinear collapse simulation,  developed a draft recommended methodology for assigning Seismic Performance Factors, conducted benchmarking studies on selected structural systems, obtained feedback from a group of experts and potential users, and evaluated selected structural systems to verify the technical soundness and applicability of the approach.   This effort has led to the development of the ATC-63 Project - 90% Draft report, FEMA P695 Quantification of Building Seismic Performance Factors, which is now available for immediate download.  Download PDF file here.

This draft is being released for public comment and interim use.  It will be the focus of a set of workshops intended to review the document, provide feedback, and collect information that will used as a guide in the preparation of a finalized version of the recommended methodology, and eventual publication by FEMA.

Figure 1 – Incremental Dynamic Analysis Results for 4-story Special Concrete Moment Resisting Frame (source: Deierlein, Haselton, Liel, Stanford University )

Figure 2 – Sample cumulative distribution function based on incremental dynamic analysis results (also known as a collapse fragility curve). This curve expresses the probability of collapse given the intensity of ground motion, in this case measured by spectral acceleration.

Figure 3 – Variable Collapse Mechanisms in a four-story Special Concrete Moment-Resisting Frame (source: G. Deierlein, C. Haselton, and A. Liel, Stanford University )

Figure 4 – Sample Results of Incremental Dynamic Analysis to Collapse for Two-Story Wood Light-Frame Archetype without Gypsum Wallboard (source: A. Filiatrault, University at Buffalo).

Figure 5 – Sample Collapse Fragility Curve for Two-Story Wood Light-Frame Archetype without Gypsum Wallboard (source: A. Filiatrault, University at Buffalo )

* If clip doesn't play, download by right clicking on link and selecting Save target as.. then double click on downloaded file.

			Comments or suggestions are welcome: webmaster@atcouncil.org
					Information on how to read our PDF documents