| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
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| Initial Amendment Date: | January 9, 2015 |
| Latest Amendment Date: | January 9, 2015 |
| Award Number: | 1453960 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Gianluca Cusatis
CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | June 1, 2015 |
| End Date: | May 31, 2021 (Estimated) |
| Total Intended Award Amount: | $500,000.00 |
| Total Awarded Amount to Date: | $500,000.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
300 TURNER ST NW BLACKSBURG VA US 24060-3359 (540)231-5281 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
750 Drillfield Drive Blacksburg VA US 24061-1051 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Structural and Architectural E |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
This Faculty Early Career Development (CAREER) Program grant will pursue research to create new enhanced structural systems by strategically removing material (i.e. introducing engineered cutouts) in constituent steel plates. Structural systems subjected to extreme lateral loads due to earthquake or wind resist collapse when they can sustain large deformation without breaking. This property, known as ductility, protects the lives of inhabitants because buildings can deform without collapsing. Typical structural systems that rely on shear deformations in steel plates to develop ductility are challenged by shear buckling and the potential for fracture. This research attempts to revolutionize structural systems that rely on ductile shear deformations. The innovative approach is to improve ductility and energy dissipation ability by strategically removing material from the plates rather than adding more material. This project will develop cutout patterns, and the underlying science, to convert shear deformations into smaller ductile mechanisms that resist buckling. The new structural systems have the potential to improve the performance of the built environment when subjected to extreme lateral loads.
The project's approach involves converting global shear deformations into local ductile yielding mechanisms in a way that can resist buckling, develop increased stiffness, exhibit stable and full hysteretic behavior, and allow structural behavior to be tuned. The computational and experimental studies will lead to a new understanding of the mechanics of ring-shaped and yielding link hysteretic elements. Fundamental knowledge about approaches for creating ductile shear behavior will be discovered by 1) computationally exploring size, shape, and layout of cutouts for buckling resistant mechanisms, 2) developing methods to tune behavior, 3) validating concepts through small- and large-scale experiments, and 4) structural system level modeling. A related educational plan will inject visual demonstrations and hands-on activities into structural engineering curricula by 1) conducting and videotaping hands-on activities for K-12 outreach, 2) creating well-produced videos of the outreach activities, experiments, and key demonstrations, and then 3) creating an online warehouse for videos and instructions related to structural engineering.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Structural systems subjected to extreme loading such as earthquakes often rely on inelastic yielding of steel components to maintain the load-carrying capacity of the building while allowing the building to survive the large imposed displacements. If the yielding steel components are replaceable, they are sometimes referred to as structural fuses, of which, one category involves steel plates subjected to shear deformations. Shear-acting structural fuses that have specialized cut-out patterns convert shear deformations into local yielding mechanisms and can have improved behavioral characteristics. A relatively limited number of shapes have been previously proposed and investigated for shear-acting structural fuses and several of these are prone to buckling which impedes the ability of the structural fuse to absorb seismic energy. Advances in manufacturing technology open the door to more complex structural fuse shapes and thus invite innovation.
The goals of this research project were to a) develop new approaches and concepts for shear-acting structural fuses, b) explore new shapes for structural fuses, c) understand the mechanics of these structural fuses through derivation of governing equations, experiments, and computational simulations, d) create validated design procedures for the structural fuses, and e) create and collect educational demonstrations related to the research and other topics. The research consisted of several phase including computational exploration of the design space, developing methods for tuning and controlling structural fuse behavior, both large-scale and small-scale experimental programs, computational simulation of buildings having the structural fuses subjected to earthquakes, and the development of design procedures based on all previous phases. The research led to several key outcomes as described in the following paragraphs.
New approaches for identifying structural fuses shapes were formulated. Topology optimization is a tool for finding the distribution of material in a design space that best satisfies a particular performance objective (referred to as the objective function). A new type of objective function was created that controls buckling as a function of two computationally efficient analyses, one that finds the yield strength of the structural fuse assuming it doesn?t buckle, and a second that finds the elastic buckling strength. Using this approach, the computer was asked to find the best shapes for structural fuses so that they resist buckling while yielding. Additionally, new concepts for structural fuse shapes were found by exploring shapes that naturally resist buckling (e.g., ring shape), transforming the optimized buckling-resistant shapes into a regular geometry that also resists fracture (e.g., coupled butterfly-shape), and others approaches.
As a result of the exploration, six shapes were selected for further study in shear-acting structural fuses including the butterfly-shaped link, optimized shapes, coupled butterfly shape, hourglass shape, links between elliptical holes, and ring-shaped. Validated design procedures were developed for each structural fuse shape by deriving equations that govern their behavior and then checking and refining the procedures against two experimental programs, computational studies on individual structural fuses, and computational simulations of buildings that use these structural fuses.
This research created fundamental knowledge about structural fuse behavior and about how local yielding mechanisms behave as part of a larger shear panel. The properties of structural fuse shapes that make them resist buckling and/or resist fracture were discovered. It was found that localized shear stresses and axial stresses interact to affect the distribution of yielding and ways to control this interaction through proportioning were derived. Methods for predicting elastic buckling of the shapes using differential equations as well as methods for predicting strength using assumed collapse mechanisms were developed. Challenges found in matching the derived equations to experimental or computational simulation data led to discoveries that helped refine the design equations.
Educational videos were created based on topics related to the research such as buckling and the role of ductility in earthquake engineering and timelapse videos were created from each of the experiments to demonstrate concepts related to structural fuses. Educational videos and demonstrations were collected into a website. The project impacted hundreds of students through the educational videos and demonstrations, as well as provided training for four graduate students and more than a dozen undergraduate students that participated directly in this research. It is hoped, that the results of this research will have an impact on reducing losses and improving the resilience of buildings subjected to extreme hazards such as earthquakes.
Last Modified: 09/11/2021
Modified by: Matthew Eatherton
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