C-130 testings on low-rising buildings
Investigations of wind-induced building damage have shown that roof and roofing systems are the most vulnerable parts of the whole building envelope to fail. Damages to the roof typically initiate around the roof corners and edges where extremely high suctions occur due to the flow separation. In an effort to improve the structural performance of buildings in strong wind events we studied building behavior at near ultimate wind loads. This work focuses on controlled full-scale experiments using the propellers of a C-130 aircraft to generate the flows. Testing was carried out on two low-rise residential constructions, in particular, a manufactured home and a modular home. In this test, a Hercules C-130 aircraft was used to generate simulated wind events. The flow characteristics, induced external and internal pressures, and selected structural responses were measured during each event. In order to obtain the influence of building on the reference pressure, barometric and wind speed measurements, two wind tunnel tests were performed in Texas Tech Wind Tunnel.
The experiments confirmed some differences in turbulence intensities, roughness length, integral scales and spectra of flows existed between C-130 generated flows and atmospheric boundary layer (ABL) flow in open terrain. In general, the C-130 flow was less turbulent than the ABL flow. As to the pressure distribution over the manufactured home and modular home, some scatter of the data is evident for runs conducted at lower flow speeds, but data from runs at higher flow speeds show little scatter.
Compared to ASCE 7-02, it was found that ASCE7-02 (MWFRS) provided an upper limit to current results. However, a few exceptions occurred on the roof leading edge. The results of full scale C-130 tests were consistent with that of wind tunnel tests, full scale natural wind tests and other similar research.
The existence of the test specimens had a significant influence on the wind speed measurement especially when the wind speed anemometers were close to the buildings. When wind speed anemometers were behind the building, the measured wind speed decreased almost 50%. When wind speed anemometers were in the front of windward walls, the recorded wind speed was about 10-15% less than non-influenced wind speeds. While, with wind speed anemometers located on the side of building models, the influenced of the buildings can be ignored.
In the full scale tests, the influence of the buildings on reference pressure measurements needs to be considered and the correction of its influence is necessary. When the reference pressure pit was located directly in front of windward wall, the reference pressure pit experienced pressures higher than that in the free stream flow field. Whereas if the reference pressure pit was located beside the sidewall, the reference pressure pit experienced lower pressures. As to the influence of buildings on barometric pressure measurements, it only influences the calculation of air density less than 1%, so it is reasonable to ignore it.
This work was performed under the Department of Commerce NIST/TTU Cooperative Agreement Award 70NANB3H5003.