Akwasi F. Mensah

Akwasi F. Mensah

Akwasi joined the graduate program of the CCE Department of University of Florida in August 2008.  Akwasi who hails from Ghana, West Africa graduated in 2006 from Kwame Nkrumah University of Science and Technology, Kumasi, Ghana with a BSc (Honors) degree in Civil Engineering. Prior to joining UF, he worked as a structural engineer in Accra, Ghana.

Mr. Mensah been primarily engaged in developing wind load time histories from existing 1/3 wind tunnel data, developed previously by the PI. The time histories from 386 pressure taps distributed on a 1:50 scale wind tunnel model will first be scaled to provide full-scale wind pressures at the design wind speed of 130 mph, 3-second gust.  Then the roof to wall reaction load time history will be generated by combining the pressure time histories with experimentally derived influence functions using Database Assisted Design (DAD) methodology. Akwasi is again responsible for developing a DAD software using MATLAB for the methodology.

The time histories have also been provided to Oregon State University (Dr. Gupta) for his use in an analytically generated influence functions using SAP 2000 to generate the roof –wall connection loads.

Akwasi has also been charged with studying and testing the wind measuring instruments to be used for testing the 1/3 scale house with UF Hurricane Simulator (to be performed in July 2009) to validate the DAD.  The main instruments to be used include several Model 265 differential pressure transducers (range ± 10 in. water column) manufactured by Setra Systems, Inc. (http://www.setra.com) and a Cobra Probe wind flow measuring device by Turbulent Flow Instrumentation, Australia, (http://www.turbulentflow.com.au).  The Cobra Probe is a multi-hole pressure probe built, Australia) and it is used for the measurement of complex turbulent flows. The probe which is pre-calibrated and comes with its custom-built data acquisition software measures four pressures from four surfaces cut into the head of the probe.  The probe has a frequency response of up to 5,000 Hz.

The Cobra Probe results will be used for characterizing the wind flow during the Hurricane Simulator testing and to obtain simultaneous measurements of the wind speeds, roof pressures and structural load time histories during the Simulator testing.

A Setra Datum 2000 digital meter was also acquired with NIST-traceable calibrated display. The pressure transducers will the convert pressure differences to a proportional high level analog output for both unidirectional and bidirectional pressure ranges. The pressure transducers will be installed on the roof and walls of the 1/3 scale wood-framed model house to measure tributary area pressure for one of the roof-truss to wall plate instrumented connections.

Specific tasks that Akwasi performed include:

  • Wind Tunnel Data Processing
    • Developed MATLAB scripts to convert raw wind tunnel pressure data to pressure coefficients scaled to design – level wind load time histories. Files were stored as binary files.
    • Corrected for tubing response and low-pass filtered the wind tunnel data to be used with assistance from Peter Datin.
    • Developed expertise in the use of Hierachchial data format (HDF) designed by National Center for Supercomputing Applications (NCSA) for manipulation of huge data sets (http://www.hdfgroup.org/).
    • Archived the wind tunnel data and its experimental information in HDF format. Achieved by consultations with Dr. Joseph Main of NIST, Drs Eric Ho and David Morrish of the University of Western Ontario.
  • Database-assisted design (DAD) software
    • Reviewed previous literature on database assisted design (DAD) methodology.
    • Downloaded, tested and studied the DAD software, ‘windPRESSURE’ developed by National Institute of Standards and Technology (NIST) for evaluating structural loads on rigid, gable-roofed buildings (http://www.itl.nist.gov/div898/winds/wind_pressure/wind_pressure.htm)
    • Currently developing purpose-built MATLAB script for the DAD analysis for this project, which will combine wind tunnel data with the structural influence functions (developed by Datin).
  • Cobra Probe and Setra Transducers Validation and Usage
    • Reviewed previous literature on the design, calibration, and operation and computation analysis of the cobra probe.
    • Currently validating the Cobra Probe measurements against other established wind flow measuring techniques, such as the Scanivalve hot-wire anemometry and Laser Doppler velocimetry (LDV).
    • Validation experiments included experiments on wind flows using existing boundary layer wind tunnel facilities at UF’s Hurricane Research Laboratory.
    • Other experiments to investigate the effect of roof slope (ramp) on velocity profile in wind tunnel using the probe.
    • Design of a Traverse system: A motorized traverse system is being fabricated to support the Cobra Probe and move it within a 10 ft by 20 ft grid during Simulator testing.
    Conference Proceedings and Presentations

    1. Datin, P.L., Mensah, A. F., Prevatt, D.O., Martin K., Gupta R., Thang D., Lindt J., “Performance Based Wind Engineering and Structural Load Paths in Wood-Frame Residential Structures”, 1st International Conference on Structures & Architecture – ICSA 2010 in Guimaraes, Portugal.
    2. Datin, P.L., Mensah, A. F, Prevatt, D.O., Martin K.,  Gupta R., Thang D.,  Lindt J., “Performance-based Wind Engineering of Light-framed Wood Residential Structural Systems”, World Conference on Timber Engineering, WCTE 210 at Riva del Garda, Trentino, Italy
    3. Mensah, A. F., Datin, P.L., Prevatt, D.O., “3D Flow Characterization of Simulated Hurricane Wind Flow Around a 1/3-Scale Light-Framed Wood Structure Using a 4-hole Pressure Probe Sensor”, Structural Engineering Institute’s 2010 Structures Congress joint with the North American Steel Construction Conference in Orlando, Florida.
    4. Datin, P.L., Mensah, A., Prevatt, D.O., “Experimentally Determined Structural Load Paths in a 1/3-Scale Model of Light-Framed Wood, Rectangular Gable Roof Structure”, Structural Engineering Institute’s 2010 Structures Congress joint with the North American Steel Construction Conference in Orlando, Florida.
    5. Datin, P.L., Prevatt, D.O., Mensah, A. F., “Performance Based Wind Engineering (PBWE): Interaction of Hurricanes with Residential Structures”, Proceedings of 2009 NSF Engineering Research and Innovation Conference, Honolulu, Hawaii.

    6. Mensah A. F. (2009), “Determining Vertical Reactions in a Typical Residential Building based on a Performance Based Methodology”. Research presentation to the faulty and graduate students of Structures group, University of Florida, November 2009.

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