Measures of Building Resilience and Structural Robustness Project

Disaster resilience of a building or a community is the capability to quickly restore full functionality following an extreme event.  Buildings play a critical role in achieving community resilience because of their importance in providing emergency response, essential services, and shelter, and because of the significant economic costs and potential loss of life associated with building damage or collapse.  This project will develop the measurement science to assess the disaster resilience of buildings through the use of risk-based assessment and decision methods that are supported by a cost/benefit analysis and performance-based design and rehabilitation methodologies.  A key component of a resilient building is a robust structural system, which limits the spread of collapse when subjected to extreme natural and man-made hazards.  Many U.S. buildings are vulnerable to partial or total collapse under abnormal loads not considered in building design.  At present, there is no accepted engineering methodology to assess and enhance overall structural robustness within a multi-hazard context that considers both design loads and abnormal loads.  This project will address the development of procedures and computational methodologies for assessing overall structural robustness and will provide the measurement science needs for the development of performance-based provisions in U.S. codes and standards for disproportionate collapse resistance that will enhance the disaster-resilience of buildings.

Objective:  By FY 2014, develop the measurement science to assess the disaster resilience of buildings through the use of risk-based assessment and decision methods, and develop performance-based pre-standards for mitigation of disproportionate collapse of steel and reinforced concrete structures.

What is the new technical idea?  Disaster resilience is the capability of a system and its components—such as a community and its buildings and infrastructure—to quickly recover full functionality following an extreme event. Since buildings play a critical role in achieving community resilience, this project will initially focus on developing the measurement science to assess building resilience. This research project seeks to develop performance-based design methodologies for buildings subjected to a wide variety of natural and man-made hazards, and to provide a framework for other hazard-based projects, including earthquake, windstorm, and fire hazards.

The new technical idea is to develop the tools to measure the disaster resilience of buildings using risk-based assessment and decision methods that are supported by a cost/benefit analysis and performance-based design and rehabilitation methodologies. The tools will consider, for a wide spectrum of hazards, a holistic approach to building resilience that includes performance of structural and nonstructural building systems, system damage and loss of functionality following the event, the duration of recovery, and associated economic losses. Of particular interest is the need to develop appropriate design events/scenarios and performance goals and measures for resilience that account for life safety, building usability/functionality during and after an event, and the time and costs required to resume service. Performance criteria and metrics for building resilience will enable the development of decision tools for planners and stakeholders to enhance the performance of buildings during and after extreme events, thus reducing loss of life, injuries, and economic losses. This project will develop (1) performance criteria and metrics for evaluating building resilience, (2) design and retrofit strategies for resilience, and (3) risk-based assessment and decision methods for achieving building resilience that are supported by a cost/benefit analysis and performance-based methods for codes, standards, and practices.

A key component of a resilient building is a robust structural system, which limits the spread of collapse under extreme natural and man-made hazards. Therefore, an important focus of the project is to develop system-level performance metrics for robustness of building structures. Robustness is a key structural property that is related to disproportionate collapse resistance. Both structural redundancy and integrity are key factors that influence the robustness of the structure. The combined influence of these factors must be quantified to express the robustness in a meaningful and measurable manner. The assessment of structural robustness requires simulation of structural behavior under various local failure scenarios. Realistic and efficient simulations require the development and use of advanced and experimentally validated modeling methodologies to examine the structural system performance. Both traditional and new design concepts will be evaluated to determine the relative merits of various structural systems in resisting disproportionate collapse. The project will examine collapse limit states of various structural systems to quantify their reserve capacities, through a combination of push-down and push-over analyses. Reserve capacity measures will support resilience metrics for system damage. The project will also develop design and retrofit methodologies that take explicit advantage of the synergies associated with mitigating disproportionate collapse under multiple hazards to enhance overall structural performance, efficiency, and cost-effectiveness.

What is the research plan?  NIST, through its Disaster Resilience of Buildings, Infrastructure, and Communities goal, is developing the measurement science to assess the performance of structures exposed to earthquake, tsunami, hurricane winds and storm surge, tornados, wind- and water-borne debris, and fire hazards. These efforts have the goal of providing the technical basis for performance-based approaches for the design of new buildings and the rehabilitation of existing buildings for these hazards. This project is cross-cutting with all programs in the Disaster Resilience of Buildings, Infrastructure, and Communities goal and will work closely with NEHRP, NWIRP, and Fire Research Division teams to develop consistent performance criteria and metrics for building resilience.

The proposed approach will be to develop resilience performance criteria and metrics that account for building performance under multiple hazards, including the performance of structural and nonstructural building systems during a hazard event, system damage and loss of functionality following the event, the duration of recovery, and associated economic losses. The primary focus will be the performance of structural and non-structural building systems (e.g., architectural, mechanical, and life safety systems), utility infrastructure housed within or below the building (such as water, wastewater, gas, power, and communications), adjacent transportation facilities (e.g., subway, roads, etc.), and adjacent buildings or facilities. To develop resilience metrics, the project will use data from past events, engineering judgment, and engineering analyses to evaluate the performance of building systems. The project will consider scenario-based events (events that exceed typical design requirements), including a variety of natural and manmade hazards, as candidates for evaluating building resilience.  In addition, the project will provide a technical basis for cost/benefit analysis of design or rehabilitation approaches to enhance the resilience of buildings. In 2011, a DHS-NIST sponsored workshop, organized with ANSI-HSSP, was held to identify gaps in our current codes, standards, and practices related to resilience and to identify candidate metrics for resilience. A roadmap for NIST research in building and community resilience is being formulated based on input from this workshop.

This project will conduct a comprehensive comparison and assessment of current structural design provisions in standards and codes, including loads and material-specific (steel and reinforced concrete) design. The comparison will include current U.S.-based codes and standards including the International Building Code, ASCE standards, ACI standards, and AISC standards, as well as international codes and standards including ISO standards, the Eurocode, and codes and standards from Japan, New Zealand, Australia, etc. The code comparison and assessment will include steel and reinforced concrete structures and will address the following loads or hazards: (1) fire, (2) wind, (3) earthquake, and (4) coastal flooding (storm surge and tsunami), along with their combinations in a multi-hazard context. The comparison and assessment will have the following objectives: (1) identify differences between codes and standards for the U.S. and other countries/regions, (2) identify gaps in codes and standards and associated research needs, and (3) use the results from (1) and (2) to drive changes to improve U.S. or ISO standards. In addition, test cases (or case studies) of design loads for selected types of construction (e.g., low, medium, and high rise) will be evaluated for various codes and standards to quantify differences in design requirements, including magnitude, mean recurrence intervals (MRI), and associated risk (probability of failure) levels where appropriate. In FY 13, this task will focus on fire loads and effects on structures.

A case study analysis using HAZUS MH will vary the magnitude of the hazard and analyze the losses associated with different levels of hazard mitigation, as reflected in selected building codes. The case study findings will be used to demonstrate how to apply cost/benefit analysis to promote more cost-effective design/rehabilitation approaches.

Because resistance to disproportionate structural collapse is crucial for achieving building resilience, this project also addresses the measurement of structural robustness. The recommendations from a national workshop formed the basis for a coordinated national plan for problem-focused research on mitigation of disproportionate collapse of buildings. The project proposes to develop metrics to quantify the robustness of various structural systems to assess their disproportionate collapse potential. These metrics will be based on experimentally validated computational models of structural systems incorporating the predominant behaviors and failure modes of components and connections. Such models can also be used by design professionals in design for disproportionate collapse resistance. A key component in the development and evaluation of robustness metrics will be a series of push-down and push-over analyses to assess the reserve capacity of a variety of structures with different systems and materials. The project will develop performance objectives, acceptance criteria, and evaluation methods for both new and existing structures, which will be used to develop guidance documents and pre-standards for design and rehabilitation of structures to mitigate disproportionate collapse. The work on building resilience will produce the following outcomes in the near term:

1. A roadmap for research in building resilience that considers performance criteria and metrics, and identifies gaps and needs for addressing resilience in codes, standards, and practices.
2. Guidelines for assessing building resilience, with performance criteria and metrics for building performance under multiple hazards that addresses the performance of structural and nonstructural building systems, system damage and loss of functionality following an event, the duration of recovery, and associated economic losses.
3. Guidelines for conducting a cost/benefit analysis with a technical basis for design or rehabilitation approaches to enhance the resilience of buildings.

The work on structural robustness will produce the following outcomes:

1. Best Practices Guide for design of new buildings and rehabilitation of existing buildings (Complete)

2. Computational methodologies to evaluate the disproportionate collapse potential of building structures for practicing engineers based on the following work:

   Experimental:

   1. testing of full-scale subsystems to validate detailed computer models (Complete)
   2. testing of 3-D multi-story frames to validate reduced 3-D computer models (Nearing completion: 2012)

   Computational:

   1. development of reduced 3-D models of various structural systems (Nearing completion: 2013)
   2. comparative assessment of reserve capacities of various structural systems (Underway: 2013)
   3. evaluation of structural systems capable of resisting disproportionate collapse (Underway: 2013)
3. Guidelines for assessing disproportionate collapse vulnerability, including both rapid and comprehensive evaluation guides (Nearing completion: 2012)
4. Comprehensive guidelines for design of new buildings to resist disproportionate collapse (Underway: 2013)
5. Pre-standards for design of new buildings to resist disproportionate collapse (2014)
6. Dissemination of project research results through a dedicated website that will include reports, papers, models, data, etc. (2013)

Recent Results:

Outputs, Building Resilience:

• Resilience Roundtable on Standards for Disaster Resilience for Buildings and Physical Infrastructure Systems, sponsored by the DHS, NIST, and ANSI-HSSP, was held September 2011 to identify gaps in our current codes, standards, and practices related to resilience and to identify candidate metrics for resilience.
• Workshop for Standards for Disaster Resilience for Buildings and Physical Infrastructure Systems, sponsored by the DHS, NIST, and ANSI-HSSP, was held November 2011 and further developed technical input and guidance from participants for creation of a roadmap for developing resilience standards.
• A White Paper on the Resilience of the Built Environment, presented at the 2011 Roundtable and Workshop.

Outputs, Structural Robustness:

• Completed testing of a half-scale 3-story reinforced concrete building through a cooperative agreement with Hunan University. NIST developed the design, test sequence, and instrumentation plan, and performed pre-test predictions. Test results are currently being used to validate NIST 3-D system models of RC buildings.
• Completed testing of two precast concrete beam-column assemblies to characterize their behavior under column loss scenarios and to provide experimental data for validation of computational models.
• Organized a technical session and made two presentations at the Structures Congress 2012.
• Organized a technical session at the Structures Congress 2011, including three presentations by Lew, Main, and Sadek.
• Two presentations at 2011 World Congress on Advances in Structural Engineering and Mechanics, Seoul, Korea.
• Reports:
• • Main, J.A. and Sadek, F. “Robustness of steel gravity frame systems with single-plate shear connections.” NIST Technical Note, National Institute of Standards and Technology, Gaithersburg, MD, in WERB review.
  • Lew, H.S., Bao, Y., Sadek, F., Main, J.A., Pujol, S., and Sozen, M.A., (2011), “An Experimental and Computational Study of Reinforced Concrete Assemblies under a Column Removal Scenario.” NIST Technical Note 1720, National Institute of Standards and Technology, Gaithersburg, MD, October 2011.
  • Sadek, F., Main, J.A., Lew, H.S., Robert, S. D., Chiarito, V, and El-Tawil, S., (2010). “An Experimental and Computational Study of Steel Moment Connections under a Column Removal Scenario.” NIST Technical Note 1669, National Institute of Standards and Technology. Gaithersburg, MD, September 2010.
• Journal Papers:
• • Bao, Y., Lew, H. S., and Kunnath, S. K. (2012). “Modeling of Reinforced Concrete Assemblies under a Column Removal Scenario.” submitted to Journal of Structural Engineering, ASCE.
  • Lew, H. S., Main, J. A., Robert, S. D., Sadek, F., and Chiarito, V. P., (2012). “Performance of steel moment connections under a column removal scenario. I: Experiments.” Journal of Structural Engineering, ASCE, in press.
  • Sadek, F., Main, J. A., Lew, H. S., and El-Tawil, S. (2012), “Performance of Steel Moment Connections under a Column Removal Scenario. II: Analysis,” Journal of Structural Engineering, ASCE, in press.
  • Sadek, F., Main, J. A., Bao, Y., and Lew, H. S., (2011), “Testing and Analysis of Steel and Concrete Beam-Column Assemblies under a Column Removal Scenario,” Journal of Structural Engineering, ASCE, 137(9), pp. 881-892.
  • Alashker, Y., El-Tawil, S., and Sadek, F., (2010), “Progressive Collapse Resistance of Steel-Concrete Composite Floors,” Journal of Structural Engineering, ASCE, 136(10), pp. 1187-1196.
  • Bao, Y., Kunnath S.K., (2010). “Simplified Progressive Collapse Simulation of RC Frame-Wall Structures,” Engineering Structures, 32(10), 3153-3162.
• Conference Proceedings:
• • Liu, J., Main, J.A., and Sadek, F. (2012). “Modeling of double-angle shear connections for evaluation of structural robustness.” Proc., 6th Congress on Forensic Engineering, San Francisco, CA.
  • Main, J. A., and Sadek, F., (2011), “Modeling of Bolted Connections for Collapse Analysis of Steel Structures,” Proc., 14th International Symposium on Interaction of the Effects of Munitions with Structures, Seattle, WA.
  • Main, J. A., Bao, Y., Sadek, F., and Lew, H. S., (2011), “Experimental and Computational Assessment of Robustness of Steel and Reinforced Concrete Framed Buildings,” Proc., 11th International Conference on Applications of Statistics and Probability in Civil Engineering, Zurich, Switzerland.

Outcomes, Building Resilience:

• A report with a framework/roadmap for research needed to support the development of building and community resilience standards, based on the 2011 Roundtable and Workshop/industry review and input (Sep 2012).
• An ASTM-based approach for developing standards that model losses and help stakeholders assess disaster resilience built around ASTM’s E06 Committee on Performance of Buildings and ASTM’s E54 Committee on Homeland Security.

Outcomes, Structural Robustness:

• Developed innovative approach for enhancing disproportionate collapse resistance of RC structures using local debonding of reinforcing bars (patent disclosure filed)
• Demonstrated a weakness of current precast concrete connections that negatively affects the robustness of precast buildings; industry (PCI) has committed to supporting continued research aimed at improving precast concrete connections
• Established new criteria for tying of structures to achieve robustness
• Developed “A Guide to Assessing Vulnerability of Buildings to Disproportionate Collapse” in collaboration with industry, to be finalized in 2012.
• Developed experimentally validated 3D models of steel and reinforced concrete frame buildings for assessment of reserve capacity and vulnerability to disproportionate collapse
• Developed a methodology for assessing robustness of steel and concrete framed buildings based on the quantification of reserve capacity and the ability of the structural system to redistribute loads using a series of push down analyses
• Developed evaluation tools, acceptance criteria, and performance metrics to be used in a performance-based design approach to mitigate disproportionate collapse

Standards and Codes:

Building Resilience:

• Revisions to two ASTM Standards (ASTM E2506 Guide for Developing a Cost-Effective Risk Mitigation Plan for New and Existing Constructed Facilities and ASTM E2541 Guide for Stakeholder-Focused, Consensus-Based Disaster Restoration Process for Contaminated Assets) have been balloted and approved by ASTM’s E06 Committee on Performance of Buildings and ASTM’s E54 Committee on Homeland Security. (Outcome)

For assessment of building resilience, the project plans to develop the following:

• Performance criteria and metrics for evaluating building resilience.
• Design and retrofit strategies for resilience.
• Risk-based assessment and decision methods for achieving building resilience that are supported by a cost/benefit analysis and performance- and scenario-based methods for codes, standards, and practices.

The appropriate standards and/or codes for these resilience assessment and decision tools will be identified as the research progresses.  EL staff participation in the standards and codes committees includes:

• Therese McAllister – (1) ASCE 7 Standard Main Committee (Subcommittees: (1) General Requirements for Structural Stability and (2) Load Combinations); (2) SEI-ASCE Technical Council on Life-cycle Performance, Safety,  Reliability, and Risk of Structural Systems, Task Group 3, Risk Assessment of Structural Infrastructure Facilities and Risk-Based Decision Making; (3) ASCE Fire Protection Committee; (4) IBC-Structural Committee member for 2012 Code Development Hearings.
• Robert Chapman – (1) ASTM E06 Committee on Performance of Buildings; (2) ASTM E54 Committee on Homeland Security.

Structural Robustness:

• A new ASCE/SEI Standards Committee on disproportionate collapse mitigation of building structures has been established, based on a proposal by NIST. (Impact)
• Structural integrity requirements for tie reinforcement submitted by NIST based on experimental and analytical research have been incorporated in the ACI 318-09 Building Code. (Impact)
• Best Practices Guide (NISTIR 7396) adopted by ASCE 7-10 Standard as part of the commentary section on General Structural Integrity. (Impact)
• Structural integrity requirements proposed by the Ad Hoc Joint Industry Committee on Structural Integrity have been adopted for the 2009 IBC. (Impact)
• Project team wrote a section on structural systems for the ASCE/SEI Standard 59-11 on Blast Protection of Buildings. (Impact)

In the area of structural robustness, project team members plan to work with the following standards committees to implement the guidelines and pre-standards resulting from this project into standards for structural integrity and disproportionate collapse resistance:

• ASCE/SEI Standards Committee on disproportionate collapse mitigation of building structures (newly established)
• ASCE 7, Subcommittee for General Structural Requirements (structural integrity)
• ACI 318, Subcommittee C: Safety, Servicability and Analysis (concrete structures)
• AISC Specification, Ad-Hoc Committee on Structural Integrity (steel structures)