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Performance-Based Seismic Engineering (PBSE) for New Buildings Project

Summary:

Structural collapse demand and capacity are not clearly defined or directly simulated in current Performance-Based Seismic Engineering (PBSE) methodology, resulting in a critical gap in structural collapse assessment accuracy. Instead, collapse is assessed indirectly based on analysis results that indicate excessive lateral displacements that exceed predefined limits or implied collapse when the analysis solution algorithm fails to converge. This project aims to develop collapse simulation capabilities through quantifying collapse demand and capacity directly with improved analytical capabilities, and to provide clear and succinct guidelines on collapse assessment methodologies. The outcome will be wider acceptance of PBSE by the practicing structural engineering community.

Description:

Objective: To develop by 2016 accurate models and efficient simulation capabilities for collapse analysis and to provide guidelines on quantifying structural collapse demand and capacity within the assessment procedure that reflects the direct simulation of structural collapse to support implementation of Performance Based Seismic Engineering (PBSE).

The start of a second extramural task in this project, Seismic Analysis and Design of Non-structural Elements in Buildings, has been deferred to 2014 or later because of impacts of increased Institutional Support assessments on extramural projects.

What is the new technical idea? In current performance-based assessment approaches, a common performance objective is the avoidance of building “collapse” from loading by the Maximum Considered Earthquake[1] (MCE) or other significant seismic loading[2]. Accurate collapse modeling is important in the performance-based assessment methodology being developed in the ATC-58[3] project, but the current methodology is usually accomplished by dynamic analysis that does not directly simulate collapse. Instead dynamic analyses are continued until lateral displacement levels become “unacceptable” (based on predefined limits) or numerical solution techniques fail to converge. Collapse thus inferred by drift or convergence issues may simply be a computational problem unrelated to actual collapse. In view of this limitation, this project will focus on assessing structural collapse through direct computational determination of structural collapse and associated demand and capacity. Guidelines will be developed for practitioners to perform collapse assessment, critical to the advancement of PBSE and enhancement of building capabilities to support community resilience. Work that is undertaken will be coordinated closely with the ongoing NEHRP Consultants Joint Venture (NCJV) Task Order 23 Analysis, Modeling and Simulation for PBSE, which is focused on developing a research program that establishes best practices guidelines for practitioners who conduct nonlinear analysis in support of PBSE, using already-established analysis tools.

This extramral project will be managed by NIST EL and performed by the new NIST NEHRP extramural contractor as a task order under the new Indefinite Delivery, Indefinite Quantity (IDIQ) contract to be awarded in FY 2013. The project will synthesize available research results, model building code implications, and practitioner expertise in order to develop guidelines on direct structural collapse assessments. This project directly addresses a critical need identified in the BSSC NIST Research Roadmap workshop held in May 2012. It also addresses a critical need stated in the NIST GCR 09-917-2 Report[4] to improve analytical models and displacement demand assessment for buildings near collapse from seismic loading.

What is the research plan? NIST will award a task order to the new NIST NEHRP extramural contractor that will be designated in FY 2013. The task order will be structured such that leading practitioners and leading researchers in the structural dynamic analysis field will work together to carry out the effort, thus ensuring that both best practices and cutting edge research will be included.

A detailed research plan, including the names of all project participants, will be developed by the contractor during the task order proposal development process. This project description will be revised immediately following task order award to reflect the additional detail that will be provided.

 


[1] Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-10, American Society of Civil Engineers, 2010.

[2] Seismic Rehabilitation of Existing Buildings, ASCE/SEI 41-06, American Society of Civil Engineers, 2006.

[3] Seismic Performance Assessment of Buildings, Volume 1 – Methodology and Volume 2 - Implementation, ATC-58-1, Applied Technology Council, Redwood City, CA, 2012.

[4] Research Required to Support Full Implementation of Performance-Based Seismic Design, NIST GCR 09-917-2, National Institute of Standards and Technology, Gaithersburg, MD, 2009.

 

Major Accomplishments:

Standards and Codes:

The expected project outcome will be a state-of-the-art report on the modeling and computational mechanics aspects of collapse simulation, together with guidelines for implementation of accurate collapse simulation in PBSE evaluations. This document, developed by leading practitioners and researchers, will supplement existing national standards documents (e.g., ASCE 7, ASCE 41, FEMA P695[5]) with needed information for structural engineering practitioners in support of PBSE. It is anticipated that project findings will be used to refine and amplify Section 16.2, Nonlinear Response History Procedure, of ASCE 7, and Section 3, Analysis Procedures, in ASCE 41.

The development and review process for new provisions ultimately incorporated in ASCE 7 begins with vetting via the FEMA-funded Building Seismic Safety Council (BSSC) through its development of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, recently published in 2009 and likely published next in 2014. The “Recommended Provisions” document forms the basis for ASCE to update ASCE 7, with the next ASCE 7 edition anticipated in 2016. NIST EL is represented on the BSSC NEHRP Provisions Update Committee (PUC) by Dr. Jay Harris, who will ensure that proposed provision updates from this project are brought before the PUC.

 


[5] Quantification of Building Seismic Performance Factors, FEMA P695, Federal Emergency Management Agency, Washington, DC, 2009.