Advancing Performance Based Design through Full-Scale Simulation of Wind, Water and Structural Interaction

Sponsor: National Science Foundation Partnership for Advancing Technology in Housing (CMMI- 0729739).

Investigator: Forrest Masters

UF has constructed a 2800 hp hurricane simulator capable of replicating turbulent wind and rain loads on a full-size low-rise structure. Four 700 hp engines spin eight hydraulic actuated vaneaxial fans to produce 35+ psf stagnation pressures. Air passes through specially designed venture inlets force the air to travel perpendicular to the fan disc for maximum efficiency. Test with a 1:18 scale model produced a 14% over an open fan configuration). The system was designed to be portable—the inlets and contraction duct shown in Figure 1b can be removed and stowed for travel. Air travels accelerates though the contraction and passes through a series of custom designed neutral shape NACA airfoils designed to discharge water at the trailing edge to simulate wind-driven rain. The airfoils are connected to a hydraulic rotary actuator, which creates the changes in wind directionality. To recreate hurricane conditions, an active computer control system modulates wind speed by varying fan RPM, creates directional effects by articulating the airfoils at the exit, and injects water into the flow field to simulate rain. The control system utilizes a fast running PID-control operated in the Labview environment.

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The target wind field characteristics were established from analysis of surface wind field data collected by the Florida Coastal Monitoring Program during recent tropical cyclone landfalls. Through collaboration with industry and government, a series of experiments will be conducted to investigate (1) vortex suppression technologies for low-slope roofs, soffit failures and design remedies, and measures to reduce water penetration in building walls and sub-systems and (2) the accuracy of existing components and cladding testing procedures that simulate wind loading and wind-driven rain effects. An additional aim is the development of relationships between the complex test methods employed by the Hurricane Simulator and simpler, less expensive test methods that can be routinely used for product certification.

Quantifying Wind-Driven Rain Intrusion through Fenestration/Wall Systems

Sponsor: American Architectural Manufacturers Association

Investigator: Forrest Masters

Water intrusion remains one of the most critical, recurring issues during hurricane impacts.  Although most homes/businesses survive structurally, a significant number experience enough rain penetration to require massive interior restoration and occupant displacement / business interruption until the completion of repairs.  As a result, critical, controversial knowledge gaps have emerged.  These include:

1. Do the most intense rains occur in the highest winds, when pressure loading is the most severe? What percentage of the design pressure should be prescribed? What spectrum of wind buffeting and rain loading should be applied?
2. What is the distribution of raindrop sizes as a function of wind speed, terrain and topography, and proximity to the coast (to account for ocean spray)?
3. What quantity of rain field traveling in the undisturbed flow field wets the building façade? How much travels around the structure? Should a corner window be designed to the same specifications as a window in the middle of the wall?

To answer these questions, the FCMP has begun deploying a new wind-driven rain sensor with its towers. The precipitation imaging probe (PIP) is one of two commercially available sensors that can accurately characterize wind-driven rain in extreme winds, and it is also an airborne instrument used on hurricane (hunter) reconnaissance aircraft. It is unique in that similar, less expensive ground-based instruments (e.g., disdrometers, spectropluviometers) are not functional in wind speeds greater than the terminal velocity of falling rain. No such data has been collected near the earth’s surface. This research will result in world’s first repository of surface hurricane wind-driven rain data.

Reduction of Wind-Driven Rain Intrusion through the Building Envelope

Sponsor: Florida Catastrophic Storm Risk Management Center

Investigators: Forrest Masters, David Prevatt, Kurtis Gurley and Greg Kopp (UWO)

The investigation team will develop a representative test matrix of soffit configurations that encompass various (a) soffit styles and materials, (b) substrate and exterior finishes, (c) fastening and support systems and (d) overhang lengths and rafter shapes. Using a Pressure Loading Actuator from the University of Western Ontario’s Three Little Pigs Project, fluctuating wind loads will be applied from wind tunnel pressure data to the specimen to quantify their resistance to dynamic pressure loading. In this regard, the experiment will unambiguously apply the basis wind pressure time histories used by ASCE 7 and the Florida Building Commission to the soffit assemblies. This, by far, is the most accurate representation of dynamic load conditions available today.

Following the dynamic pressure testing, the test matrix will be subjected to hurricane-force wind-driven rain (WDR) loads. A series of WDR scenarios spanning multiple storm intensity levels will be developed to form the basis of a general purpose WDR testing methodology using a Hurricane Simulator recently competed at the University of Florida.

Also planned are a series of experiments to evaluated aged window and wall systems. Existing performance metrics are determined only for newly installed products, with no consideration for the thermal and mechanical stresses caused by solar radiation and moisture pressure. Experimental research to date has not directly coupled hygrothermal and structural aging to wind and wind-driven rain resistance of products intended for high-humidity, hurricane-prone areas. The ultimate goal will be to identify and resolve competing design requirements for extreme weather and day-to-day conditions as they emerge.

Composite Structural Insulated Panels (CSIPs) for Hazard Resistant Structures

Sponsor: National Science Foundation (CMMI- 0825938)

Investigators: Nasim Uddin (UAB), Fouad Fouad (UAB), Heshmat Aglan (Tuskegee), Forrest Masters, and Talat Salama (UAB)

Building construction systems, such as Structural Insulated Panels (SIPs) have demonstrated the capabilities for energy efficient and affordable housing but with inadequate resistance against wind storm loading and floods. The objective of the project is to, for the first time ever, adapt a new preforming process and low cost thermoplastic technology to develop innovative multifunctional envelop systems for sustainable housing and storm shelter through the evolution of Composite SIPs (CSIPs) concepts that will provide better energy efficiency, inherent flood resistance and substantially higher strength with much thinner structural panels. Adaptation of inexpensive natural fiber reinforced composite to replace conventional building materials will receive emphasis. Numerous issues regarding basic materials science and engineering, joining (including mechanical attachments and bonding), structural testing and analysis, and environmental performance modeling will be addressed to determine if the potential of CSIPs can be fully realized. The potential payoff for success of this program could be rapid technology insertion into building systems needed for the rebuilding of homes in the gulf coast states and in flood prone areas since the approach builds upon existing construction systems concepts. The potential for these technologies to lead to low cost, energy efficient housing with superior resistance to natural hazards such as floods, hurricanes, and tornados is tremendous with excellent potential for transition into commercial applications. The spirit of interdisciplinary engineering education will be encouraged through cross-disciplinary educational program including web casting of large-scale tests and engaging the composites industry in the construction market.

Reduction of Wind-Driven Rain Intrusion through Residential Fenestration/Wall Systems

Sponsor: Residential Construction Mitigation Program, State of Florida Department of Community Affairs

Investigator: Forrest Masters

The purpose of this project is establishing performance benchmarks for existing water intrusion standards. Test results were used to evaluate the load intensity and duration stipulated in the existing test protocols as well as those in development. Static and pulsating pressures were applied over a spectrum of intensities to determine how well a product performs in severe wind driven rain. The results of this research will be translated back to the cost-effective and repeatable test methods in commercial testing facilities. This research was developed to support and expand the activities in the NSF-PATH project.

Development of a Probabilistic Insurable Hurricane Loss Model

Sponsor: Florida Office of Insurance Regulation, 2001-2008

Investigator: Kurt Gurley et al.

The Florida Public Hurricane Loss Projection Model (FPHLPM) is supported by a research grant from the Florida Office of Insurance Regulation. It is being developed by a consortium of Florida universities and NOAA’s Hurricane Research Division of the Atlantic Oceanographic and Meteorological Laboratory. The model estimates the annualized expected insurable losses to residential structures in the state of Florida due to hurricane wind damage. The four major components of the model are: 1) Hurricane wind model headed by Mark Powell and researchers from FSU, 2) a structural damage prediction model headed by Jean-Paul Pinelli at FIT and Kurt Gurley at UF 3) a financial/actuarial team headed by Shahid Hamid at FIU, and 4) a computer platform development team headed by Shu-Ching Chen at FIU.

Modeling and Simulation of Wind Loads for Wind Hazard Mitigation

Sponsor: National Science Foundation (NSF) CAREER Award, 2000-2005

Investigator: Kurt Gurley

The research offers advancements in the accurate representation of natural hazard loads for application in structural reliability assessment. The focus is on the modeling and simulation of highly correlated non-Gaussian extreme wind loads on building components. Modeling efforts focus on the probability content, spatial and temporal coherence, integral effects over large areas, transient, and higher-order phenomena associated with extreme wind forces in the building envelope. Robust simulation methods will adopt these models, and provide a consistent frame­work for applications in reliability analysis. This will enhance the impact of reliability methods on hazard resistant design through a more realistic treatment of severe loading. Concurrent FCMP efforts in full-scale hurricane wind measurement near ground level provide necessary data to advance this research.