Objective - To develop next-generation methods and tools to better characterize extreme wind hazards and associated loads, and response of structures to extreme winds, including tornadoes, thus enabling performance-based standards for designing structures that resist extreme winds.
What is the new technical idea? The technical ideas include (1) determination and quantification of extreme wind hazards, including tornado hazards, (2) development of methods using state of the art measurement and computational technologies for determining wind loads on the building envelope and main wind force resisting system, and (3) development of performance-based design methods for tornado-resistant design. These technical ideas support topics that have all been identified by the professional community in the new Measurement Science R&D Roadmap for Windstorm and Coastal Inundation Impact Reduction (NIST 2014) as being high priority.
The project uses the capabilities of numerical computation, existing data, and spatial and temporal statistics to develop new procedures to estimate wind hazards with superior accuracy, and for any mean recurrence interval required for the development of the ASCE 7 Standard or other standards. An improved hazard estimation will not only help reduce losses, it can also reduce costs through more efficient structural designs.
Tools for accurate characterization of tornado hazards (extreme wind speeds and wind-borne debris impacts) and development of tornado hazard maps, as well as methodology for performance-based tornado-resistant design of conventional buildings subject to tornado hazards will be developed.
New methods for estimation of wind loads on both the building envelope and the main wind force resisting system (MWFRS) will be developed, based on modern aerodynamic test data, to replace the multiple existing methods in the current ASCE 7 standard, which are based on 30-50 year old data and often yield very different answers for the same building. The new methods will be based on analysis of data from the NIST, the Tokyo Polytechnic University (TPU), and other aerodynamic databases.
Progress will be achieved in the development of Computational Fluid Dynamics algorithms and software consistent with models of separated flows around bluff bodies, supported by aerodynamics testing in the newly developed NIST civil engineering wind tunnel. The software will be capable of simulating effectively the aerodynamic loads on buildings immersed in atmospheric flows. This effort will substantially reduce the need for time-consuming and expensive wind tunnel testing; eliminate uncertainties due to Reynolds number violation effects; and allow the routine production of “on-demand” detailed estimates of wind loads for Database-Assisted Design and other structural design applications, including performance-based design that considers non-linear (post yield) behavior.
What is the research plan? Tornado-resistant design: (a) perform comprehensive review of existing tornado databases and current methods for tornado risk estimation; (b) develop tornado risk metrics, with appropriate consideration of spatiality, for a pilot midwestern municipality; (c) develop risk-consistent performance-based tornado design methodology to ensure that the performance of all components and systems that make up a building meet the same performance objective when subject to tornado hazards.
Aerodynamic loading: (a) Synthesize comprehensive aerodynamic database from published and publicly available wind tunnel and field data (2015); (b) use analysis of the synthesized database to develop improved methods for estimation of wind loads on the MWFRS , building envelope (i.e., components and cladding), and building elements that act as or support both the envelope and the MWFRS, such as exterior load bearing walls and roof trusses; (c) develop pre-standard provisions for the ASCE 7 standard for wind loads on the MWFRS, building envelope, and building elements acting as both; and (d) enhance the previously developed Database-Assisted Design software to enable use of the much larger TPU aerodynamic database, which will greatly expand the range of building geometries.
Computational Wind Engineering (CWE): (a) Perform state-of-the-art review to summarize simulations of the planetary boundary layer; (b) develop inflow boundary conditions for engineering models of turbulent flows; (c) use publicly available open source CFD software and experimental design techniques to assess the sensitivity of aerodynamic pressures on a rectangular cylinder induced by uniform, smooth flow to parameters of the simulation (time step, grid type, configuration and size, type and order of numerical scheme, computational domain size, turbulence model); (d) perform comparison between CFD time series pressure estimates and wind tunnel pressure measurements for rectangular cylinder in uniform smooth flow; (e) develop method for simulating shear flow with Atmospheric Boundary Layer target turbulence and mean flow characteristics by using item (b) above at inflow boundary and appropriate conditions at other boundaries; (f) repeat the items (c) and (d) above for simulation of flow over a rectangular cylinder immersed in shear flow by using item (e) above; (g) revise modeling of flow near separation lines in light of results of comparisons (such as tuning turbulence model parameters); (h) develop methods for reducing computational resources and times via development of wall functions and simplified flow models.
ASCE - American Society of Civil Engineers
CFD - Computational Fluid Dynamics
CWE - Computational Wind Engineering
C&C - Components and Cladding
MWFRS - Main Wind Force Resisting System
NIST (2014). 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.