Measures of Building Resilience and Structural Robustness Project

Summary

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.

Description

Objective: By FY2014, 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 essential buildings and infrastructure facilities – to quickly recover full functionality following an extreme event. The new technical idea is to develop the tools to measure the resilience of buildings and infrastructure facilities 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 a holistic approach to building resilience that includes the performance of structural and nonstructural building systems, system damage and loss of functionality following the hazard event, the duration of recovery, and associated economic losses. This project will develop (1) performance criteria and metrics for evaluating essential building and facility resilience, (2) design and retrofit strategies for resilience, and (3) risk-based assessment and decision methods for achieving resilience that are supported by a cost/benefit analysis and performance-based methods.

A key component of a resilient building is a robust structural system, which limits the progression of failure 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. Structural robustness is the ability of a structure to withstand local failures without disproportionate collapse. Redundancy, integrity, and ductility are key factors that influence the robustness of the structure. 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. The project will examine collapse limit states of various structural systems to quantify their reserve capacities through push-down analyses. 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? The proposed approach seeks to develop resilience performance criteria and metrics that account for essential building and facility performance during hazard events, including the performance of nonstructural systems, loss of functionality, the duration of recovery, and associated economic losses. The scope includes the performance of structural and non-structural building systems, utility infrastructure housed within or below the building, adjacent transportation facilities, and adjacent buildings or facilities. Data from past hazard events, engineering judgment, and engineering analyses will be used to develop performance criteria and resilience metrics. A case study analysis using HAZUS MH will vary hazard magnitudes and analyze the losses associated with different levels of hazard mitigation, which will be used to demonstrate how to apply cost/benefit analysis to promote more cost-effective design/rehabilitation approaches.

The project also proposes to develop metrics to quantify the robustness of various structural systems. 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 be used by design professionals to design for disproportionate collapse resistance. 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:

• A research needs assessment for developing guidelines and standards for the disaster resilience in essential buildings and infrastructure facilities that considers performance criteria and metrics, and identifies gaps and needs for addressing resilience in codes, standards, and practices.
• Guidelines for assessing building resilience, with performance criteria and metrics for building performance under multiple hazards that address 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.
• 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:

• Best Practices Guide for design and rehabilitation of buildings (complete)
• Computational methodologies to evaluate the disproportionate collapse potential of building structures based on the following experimental and computational work:
• • testing of full-scale subsystems to validate detailed computer models (complete)
  • testing of 3D multi-story frames to validate reduced 3D computer models (complete)
  • development of reduced 3D models of various structural systems (near completion)
    
  • comparative assessment of robustness of various structural systems (near completion)
  • evaluation of structural systems capable of resisting disproportionate collapse (near completion)
• Guidelines for assessing disproportionate collapse vulnerability, including both rapid and comprehensive evaluation guides (near completion)
• Guidelines for design of new buildings to resist disproportionate collapse 
• Pre-standards for design of new buildings to resist disproportionate collapse
• Dissemination of project research results through a dedicated website  (complete)
  

Major Accomplishments

Research Outcomes:

• Main, J.A. (2013). "Composite floor systems under column loss: Collapse resistance and tie force requirements." Journal of Structural Engineering, ASCE, in review.
• Bao, Y., Lew, H.S., Sadek, F., and Main, J.A., (2013). "A Simple Method to Enhance Catenary Action Development in Beams of R/C Frame Structures." ACI Concrete International, in review.

Potential Research Impacts:

• Lew, H.S., Bao, Y., Pujol, S., and Sozen, M.A. (2013). "Experimental study of RC assemblies under a column removal scenario." ACI Structural Journal, in press.
  
• Main, J.A. and Sadek, F. (2013). "Modeling and analysis of single-plate shear connections under column loss." Journal of Structural Engineering, ASCE, in press.
  
• Bao, Y., Lew, H.S., and Kunnath, S.K. (2013). "Modeling of reinforced concrete assemblies under a column removal scenario." Journal of Structural Engineering, ASCE, in press.
  

Realized Research Impacts:

• Lew, H.S., Main, J.A., Robert, S.D., Sadek, F., and Chiarito, V.P., (2013). "Performance of steel moment connections under a column removal scenario. I: Experiments." Journal of Structural Engineering, ASCE, 139(1), 98-107.
  
• Sadek, F., Main, J. A., Lew, H.S., and El-Tawil, S. (2013). "Performance of steel moment connections under a column removal scenario. II: Analysis." Journal of Structural Engineering, ASCE, 139(1), 108-119.
• 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.
  
• Khandelwal, K., El-Tawil, S., and Sadek, F. (2009). "Progressive collapse analysis of seismically designed steel braced frames." Journal of Constructional Steel Research, 65(3), 699-708.
  
• Sadek, F., El-Tawil, S., and Lew, H.S. (2008). "Robustness of composite floor systems with shear connections: Modeling and evaluation." Journal of Structural Engineering, ASCE, 134(11), 1717-1725.
• Khandelwal K., El-Tawil, S., Kunnath, S., and Lew, H.S. (2008). "Macromodel-based simulation of progressive collapse: Steel frame structures." Journal of Structural Engineering, ASCE, 134(7), 1070-1078.
  
• Bao, Y., Kunnath, S., El-Tawil, S., and Lew, H.S. (2008). "Macromodel-based simulation of progressive collapse: RC frame structures." Journal of Structural Engineering, ASCE, 134(7), 1079-1091.

Impact of Standards and Tools:

• A new ASCE/SEI Standards Committee on disproportionate collapse mitigation of building structures has been established, based on a proposal by NIST. NIST is leading the development of a chapter on acceptance criteria for structural performance and making substantial contributions to a chapter on design and analysis approaches. Project team prepared white papers outlining the scope and content for both chapters. (FY13)
• A new PCI Task Committee has been established to develop guidelines for design of precast concrete frame structures to resist disproportionate collapse based on the outcome of NIST research that revealed a vulnerability of precast concrete connections.  NIST is participating in the committee and is tasked with examining the effectiveness of proposed connection configurations in reducing vulnerabilities to disproportionate collapse. (Committee established in FY12)
• Developed evaluation tools, acceptance criteria, and performance metrics to be used in a performance-based design approach to mitigate disproportionate collapse. (FY12)
• Developed "A Guide to Assessing Vulnerability of Buildings to Disproportionate Collapse" in collaboration with industry. (Draft completed in FY12, to be published in FY13)
• McAllister, T.P. (2013) "Developing Guidelines and Standards for Disaster Resilience of the Built Environment: A Research Needs Assessment", TN 1795.
• ASTM E2506 Guide for Developing a Cost-Effective Risk Mitigation Plan for New and Existing Constructed Facilities (Revisions adopted 2012)
• Project team wrote a section on structural systems for the ASCE/SEI Standard 59-11 on Blast Protection of Buildings. (published in FY11)
• 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. (published in FY09)
• Structural integrity requirements proposed by the Ad Hoc Joint Industry Committee on Structural Integrity have been adopted for the 2009 IBC (published in FY09)
  
• Best practices guide for preventing progressive collapse in buildings (NISTIR 7396) published and widely cited, including adoption in the ASCE 7-10 Standard as part of the commentary section on general structural integrity. (published in FY07)