Collapse-Resistant Building Standard Released
The American Society of Civil Engineers recently released the first national building standard of its kind, providing guidance to mitigate disproportionate collapses in buildings. The new standard was reportedly developed over a decade, using information from the National Institute of Standards and Technology research.
“Many different loads are considered in designing a building, but if there’s an unanticipated load that you didn’t explicitly design for, it shouldn’t cause the whole building to collapse,” said NIST research engineer Joseph Main, a member of the ASCE committee that developed the standard.
About the Standard
ASCE/SEI 76-23, Standard for Mitigation of Disproportionate Collapse Potential in Buildings and Other Structures, describes minimum requirements for planning, assessment, analysis, material selection, design and detailing, construction and qualification testing to mitigate disproportionate collapse of new and existing buildings and other structures.
Additionally, the guidance provides risk assessments and avoidance, as well as characteristics that enhance collapse resistance including the strength, ductility, deformation capacity and robustness necessary to resist collapse without exceeding relevant limit states. It includes threat-specific and non-threat-specific methodologies and identifies direct design and indirect design approaches.
According to NIST, disproportionate collapse is a phenomenon when small, isolated failures in a structure propagate with the potential to bring down an entire building and is a risk for larger buildings.
Based on a proposal from the institute, ASCE formed a new standards committee of building experts from industry, academia and the federal government. The committee reportedly then decided to set performance goals for structures, giving engineers independence to come up with their own design solutions.
“The standard points towards solutions but doesn’t prescribe them,” said Donald O. Dusenberry, consulting engineer and chair of the ASCE committee. “It offers proven methods to analyze and design structures for disproportionate collapse but allows for cost-effectiveness and creativity.”
NIST reports that the required performance and level of hazard varies depending on the size, occupancy and utility of a building. NIST researchers also looked at the mechanics of what happens when sections of a structure are removed, which was previously not considered, to inform the requirements.
“Those designing government buildings or any buildings that are critical for communities, I think, would be the first groups looking carefully at this standard,” said NIST research structural engineer Fahim Sadek, a member of the same ASCE disproportionate collapse committee.
“The loading scenario for the connections is quite different from what you would typically get under wind, earthquake or gravity loads that people are used to designing for,” Main said. “It’s a much more complex condition.”
Over the past decade, researchers reportedly carried out numerous computer simulations of building components giving out. In one of the simulations, they removed the middle of three columns from a structural frame and applied forces above the missing column until connections fractured.
Afterwards, the team replicated many of these scenarios in the real world by building and destroying either fractions of or entire building structures to produce data to ensure that their simulations were realistic.
According to NIST, the experiments were useful for identifying the degree that beams and connections can rotate and bend before a structure is overwhelmed and crumbles. The researchers also used the findings to develop simplified modeling approaches for evaluating the susceptibility of buildings to disproportionate collapse.
A separate ASCE technical committee, led by Main, is currently working to release guidelines that help designers harness computer modeling tools for disproportionate collapse mitigation.
“Different modeling approaches are already available, from powerful models suitable for detailed analysis of individual building components to simplified models meant for the evaluation of entire buildings,” wrote the NIST.
“Engineers could use these types of resources to test the integrity of their designs under various hazard scenarios described in the standard.”
ASCE notes that the standard is intended to address the same structures covered by ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, and is written in mandatory language, with the expectation that it could be referenced by building codes or contracts documents.
The code was prepared by the Disproportionate Collapse Mitigation of Buildings and Other Structures Standards Committee of the Codes and Standards Activities Division of the Structural Engineering Institute of ASCE.