ATC-120, Seismic Analysis, Design, and Installation of Nonstructural Components and Systems - Background and Recommendations for Future Work
Client: National Institute of Standards and Technology (NIST)
NIST GCR 13-917-23, Development of NIST Measurement Science R&D Roadmap: Earthquake Risk Reduction in Buildings (developed by the Building Seismic Safety Council (BSSC) of the National Institute for Building Sciences (NIBS) for NIST in 2013) identified nonstructural issues as a top priority need for problem-focused studies related to earthquake engineering for new and existing buildings. The report identified four critical areas related to nonstructural design criteria needing focused study: (1) the vertical distribution of nonstructural design forces over the height of a building, Fp; (2) the response modification coefficients for nonstructural components; Rp; (3) the overstrength factors used in the design of nonstructural anchorage; and (4) nonstructural component and system performance metrics.
Nonstructural components and systems can account for a significant percentage of the construction cost of a building (depending on occupancy), and significant economic losses resulting from downtime and loss of functionality have been observed in past earthquakes, even when the structure is not severely damaged. With recent advancements in performance-based design methodologies, and the development of concepts for community resilience, there has been an increased emphasis on economic losses resulting from downtime and loss of building function due to nonstructural components and systems, and an increase in research and testing in this area. Development of new research results, and the availability of new international standards, makes reexamination of U.S. nonstructural design criteria possible at this time.
The goal of this project is to improve technical aspects of nonstructural system design in the areas that will have the largest impact for public safety and economic welfare. This project addresses work to investigate current nonstructural design criteria, with an emphasis on determining whether or not a disconnect exists between current design requirements and observed (or expected) performance of nonstructural building systems and components, and to propose technical solutions where significant gaps exist. The project work was split into two phases. Under Phase 1, the project team conducted a background investigation to understand the current state-of-knowledge and practitioner needs related to seismic design of nonstructural components and systems, evaluated the current design framework, and developed a report outlining a list of recommended problem-focused studies to further investigate and eventually improve nonstructural design criteria. The purpose of on-going Phase 2 is to implement the two highest priority recommendations from the Phase 1 report: (1) conduct a holistic assessment of current code design approaches; and (2) develop nonstructural component and system performance objectives.
Efforts to improve the seismic performance of nonstructural components have been underway for decades. These efforts have involved engineers of various disciplines, industry trade organizations, contractors, component and material suppliers, building officials, and legislative bodies. The efforts of these groups come together at only a few points; the building code and the job site. Most of their work is done in parallel, with little intercommunication. Information on the compatibility of their efforts is sparse, and it is unclear whether the sum of all their efforts produces the desired seismic performance. Assessments of current code requirements and methodologies, while valuable, are narrowly focused, and fail to capture the overall effectiveness of the nonstructural design process.
The effectiveness of various ASCE/SEI 7 force equations to estimate seismic force demands for nonstructural components and systems, and whether the ASCE/SEI 7 requirements provide cost-effective protection of nonstructural components and systems has been difficult to evaluate from recorded earthquake data. This evaluation has not been possible primarily because earthquakes that generated design-level or greater ground motions in populated areas have not occurred in regions with many structures designed using modern codes (last edition of the Uniform Building Code or the subsequent editions of the International Building Code). This problem is expected to persist in the near future because even in the event that a populated area was exposed to design-level ground motions, few, if any modern buildings will be instrumented. Even when instrumentation is present, nonstructural components, their supports, and attachments are generally not instrumented.
Therefore, it is important to evaluate analytically the effectiveness of design force equations for nonstructural components and systems and to assess the need for further development of the code provisions, propose improved design force equations for nonstructural components when needed, and to provide guidance in terms of when to implement different design options for nonstructural component and system. An evaluation of design force equations for nonstructural components and systems in the context of the different requirements for nonstructural components is needed. Assessing the lateral force design procedures is also important because of the relationship between the code equations and seismic qualification approaches used for acceleration-sensitive nonstructural components and systems.
While there is general agreement about the importance of protecting nonstructural components from damage that results in life-threatening damage and falling hazards in earthquakes, there is no consensus about what constitutes acceptable performance, particularly in ordinary buildings. Minimum code requirements are intended to protect life safety, but should also offer protection from property losses in some levels of earthquake shaking. Explicit performance objectives for nonstructural components and systems should be developed to provide a transparent basis for code requirements.
Future advances in design procedures for nonstructural components and systems require explicit definition of the performance objectives that underlie them. Without clarity in the objectives, nonstructural designs will not be consistent and building owners, tenants, and designers may not understand the intended level of performance. ASCE/SEI 41 contains component-specific nonstructural performance goals, which clarify the desired performance objectives. However, ASCE/SEI 7 provides only general building performance expectations. Thus code compliance for new buildings can vary widely based on interpretation. For example, how much damage is acceptable in cladding in the Design Earthquake? Does it need to prevent water infiltration? Is it acceptable for glazing to crack or pieces of cladding to become dislodged? Should there be any nonstructural performance requirements at the MCE level? The answers to these questions can have a significant impact on design and construction.
As currently envisioned, this work will include collection of available results from FEMA P-58 nonstructural assessments for damage and functionality conducted to date on the ATC-63-2 Project, ATC-63-3 Project, and ATC-58-2 Project, but will exclude performance of additional FEMA P-58 assessments. Work will include coordination with the ATC-58-2 project team to leverage the results of that work with the problem-focused studies on nonstructural design forces conducted on this project to develop potential nonstructural performance criteria. Development of nonstructural performance objectives will require building consensus across a broad group of stakeholders. The process should begin with a small team of experts, representing a broad spectrum of experience and perspective, tasked with creating a framework for defining performance objectives. Stakeholders should be brought together to explore options, express perspectives and find common ground. Representation from code and standard organizations will be essential to the process.
S. McCabe (Contracting Officer’s Representative)
M. Hoehler (Technical Point of Contact)
Jon A. Heintz, Program Manager
Scott D. Schiff, Project Manager
Project Technical Director
Phase 1 Participants:
Project Technical Committee: S. Fathali, J. Gillengerten, T. Hutchinson, R. Medina
Project Review Panel: R. Bachman, D. Honegger, E. Miranda, M. Mahoney, K. Ryan, D. Watkins
Working Group: X. Wang
Phase 2 Participants:
Project Technical Committee: J. Gillengerten, W. Holmes. B. Lizundia, R. Medina, E. Miranda, R. Pekelnicky
Project Review Panel: R. Bachman, A. Filiatrault, J. Harris, M. Mahoney, M. Rodriguez, S. Rose, J. Soulages, J. Tauby, C. Tokas
Working Group: D. De La Rosa, M. Halligan, M. Leon, J. Silva