Objective - To establish, maintain, and continually enhance the support infrastructure required to safely conduct measurements on the performance of structures under multiple hazards with quantified uncertainty.
What is the new technical idea? The modular, reconfigurable PERFORM Structural Testbed will enable full-scale experimental evaluation of structural performance under multiple hazards, using state-of-the-art metrology with quantified uncertainty, to promote innovation in the design of robust structural systems by advancing the development of performance-based standards. A roadmap for the structural testbed, to be developed in the initial planning phase of the project, will further articulate the following aspects of NIST’s unique role in measurement of structural performance and will establish an administrative plan to maintain and continually enhance this facility.
- State-of-the-art metrology with quantified uncertainty will establish NIST as the leader in rigorous, transparent, and replicable measurements of structural performance, and in estimating uncertainty in the context of very limited, or non-existent, replicate testing. Quantification of uncertainty is commonly neglected in large-scale structural testing, yet uncertainties in resistance have a key influence on the reliability of structures. Through this project, a framework for quantification of uncertainty in large-scale testing will be developed that integrates replicate testing of materials and targeted structural components with rigorous quantification of measurement uncertainties. The measurement capabilities of the structural testbed will continually be enhanced, and the testbed will enable evaluation of innovative sensor technologies with potential applications in the field, for condition assessment of deteriorating infrastructure or post-disaster evaluation of structures.
- A modular, reconfigurable testbed will provide the flexibility to evaluate structural performance under multiple hazards, including extreme winds and earthquakes, as well as to investigate major challenges facing our nation’s buildings and civil infrastructure, such as the need for mitigation of disproportionate collapse and the need for condition assessment of deteriorating infrastructure. The testbed will also enable the development of new protocols to investigate the interaction of structural and nonstructural systems, which has been identified as a key research need for both windstorms and earthquakes. The investigation of the Joplin tornado (NIST NCSTAR 3) highlighted the need for risk-consistency in the performance of building envelopes and structural systems, because failures of building envelopes were observed to result in extensive damage to building interiors, despite their relatively robust structural systems, thereby rendering the structure incapable of performing its intended function. Noting that current product testing for wind resistance is component-based rather than system-based, the NIST R&D roadmap for windstorm and coastal inundation impact reduction (NIST GCR 14-973-13) stated that new test methods are needed that account for the attachment of cladding components to the building frame. Similarly, one of the highest priorities in the NIST R&D roadmap for earthquake risk reduction (NIST GCR 13-917-23) was development of a new seismic testing protocol for both structural and nonstructural components, to enable the development of consequence functions associated with impacts such as repair costs and repair time.
- Advancement of performance-based design standards was identified as among the four key priority areas in NIST R&D roadmaps for both windstorms and earthquakes (NIST GCR 14-973-13, NIST GCR 13-917-23) and was also one of the key recommendations from the investigation of the Joplin tornado (NIST NCSTAR 3). In contrast with traditional prescriptive standards, performance-based standards promote innovation by allowing designers the freedom to develop new components and systems that meet the specified performance requirements. Experimental data are indispensable in performance-based design, both to establish performance limits for structural and nonstructural components and to validate computational models used to evaluate the performance of complete structural systems. This project will work closely with stakeholders in industry to advance the development of performance-based standards by developing new test protocols and conducting experimental measurements on the performance of structural and nonstructural systems, both for conventional systems and for innovative systems with enhanced robustness.
What is the research plan? This research project will be conducted in three phases. In the initial planning phase, a roadmap will be developed to establish a technical and administrative plan for operation of the structural testbed. A commissioning phase will focus on delivering a fully operational facility that is capable of characterizing structural performance under multiple hazards, including both vertical and lateral loading representative of extreme winds and earthquakes. After commissioning is completed, a third phase of the project will focus on metrology and sustainable operation. Throughout the duration of the project a sustained focus on safety will be maintained. The following paragraphs provide further discussion on each of these aspects of the project.
Roadmap: Full-scale structural testing is a vital, yet resource-intensive activity that requires careful planning to ensure that adequate programmatic resources will be available for years to come. A roadmap will be developed to articulate NIST’s unique role in state-of-the art measurements of structural performance and to establish administrative plans to ensure that adequate resources are available for sustained operation and continued enhancement of the structural testbed.
Safety: Safety considerations in structural testing must be given high priority and require focused and sustained attention. This project will be responsible for coordinating the development of safety documentation and for maintaining records of authorized users of equipment in the PERFORM Structural Testbed. By integrating those key personnel in the division with prior experience in testing of large-scale structures, this project will provide a holistic perspective on safety to help ensure safe execution of structural testing activities.
Commissioning: The PERFORM Structural Testbed currently incorporates a reinforced concrete strong floor, a state-of-the-art hydraulic power distribution and control system with an integrated 220 kip capacity servohydraulic load frame, and multiple servohydraulic actuators for application of structural loads. This project will identify and prioritize the investments required to bring the structural testbed to full-operation, taking proactive steps toward realizing a fully-functioning facility. Commissioning tests, which will be staggered as new equipment becomes operational, will verify the performance of newly added experimental capabilities to ensure safe and effective execution of tests and other laboratory activities. A key product of the commissioning phase will be a modular system of structural reaction blocks that will be integrated with the existing strong floor using post-tensioning rods. These reaction blocks, together with the strong floor, provide a reconfigurable reaction system for application of vertical and horizontal loads, as well as for bracing of test specimens. Commissioning tests of the reaction system will be planned to characterize the stiffness of the system for loads applied at different heights and along different axes of the blocks. A second key product of the commissioning phase will be an instrumentation and data acquisition system with state-of-the-art sensors for measurement of structural deformations and strains associated with nonlinear structural and material performance.
Operations: Following the successful completion of the commissioning phase, this project will continually maintain the support infrastructure required to conduct large-scale structural testing and ancillary testing of materials and structural components. Sustainable operation of the PERFORM Structural Testbed, including the hydraulic power distribution and control system and the integrated servohydraulic load frame, will require long-term coordinated planning and investment. Budgeting for costs associated with procurement and maintenance of equipment will be coordinated with current and future users of the equipment. An up-to-date equipment inventory will be maintained, and regular maintenance will be scheduled to ensure uninterrupted operation of the equipment and quality of the experimental measurements. This project will facilitate the scheduling and planning of testing activities, equipment usage, and space usage in the structural testbed and will maintain authorization records for the facility’s personnel.
Metrology: After procurement of the initial instrumentation and data acquisition system in the commissioning phase, project staff will continue to pursue the identification and development of innovative sensor technologies in an effort to further enhance the measurement capabilities of the facility and provide opportunities to develop richer, more meaningful datasets. Innovative sensor technologies with potential applications in the field are of particular interest (e.g., for condition assessment of deteriorating infrastructure or for post-disaster evaluation of structures). A specific measurement challenge that this project will address is the quantification of concrete cracking and damage progression in the nonlinear performance of reinforced concrete structures. Measurement approaches to be considered for this purpose include techniques currently being explored based on fiber-optic sensors and ultrasound measurements, as well as techniques based on image processing and electrical resistivity.
NIST (2014a). Measurement Science R&D Roadmap for Windstorm and Coastal Inundation Impact Reduction, NIST GCR - 14-973-13, prepared by the NEHRP Consultants Joint Venture for the National Institute of Standards and Technology, Gaithersburg, MD.
NIST (2014b). Development of NIST Measurement Science R&D Roadmap: Earthquake Risk Reduction in Buildings, NIST GCR - 13-917-3, prepared by the National Institute of Building Sciences for the National Institute of Standards and Technology, Gaithersburg, MD.
Kuligowski, E., Lombardo, F., Phan, L. and Levitan, M. (2013). Technical Investigation of the May 22, 2011, Tornado in Joplin, Missouri, NIST NCSTAR 3, National Institute of Standards and Technology, Gaithersburg, MD.