| Summary: | 碩士 === 淡江大學 === 土木工程學系 === 85 === Due to slenderness and less rigidity of modern building, wind
loads become the dominate lateral force for highrise
building design . The fluctuating wind loads acting on hig-rise
building consist of drag force , periodic acrosswind force due
to vortex shedding and torsional force due to load asymmetry.
The paper studies torsional force on a rectangular prism with
various cross sectional length -to-width ratio in
two simulated atmospheric boundary layer flows .The experiments
were performed by a new pressure-measured system. Through this
system ,pressures at four side of rectangular prisms
can be measured simultaneously, and then relationship between
torsion and drag force ,lift force can be obtained.
The results indicate that torsion will increase with length -to-
width ratio .when length - to-width ratio less then
critical value , 70%~90% of torque comes from asymmetries
pressure distributions on the leeward side . If length
-to-width ratio greater then critical value
,50%~90% of torque comes from the side face ,,the contributions
increase with length -to-width ratio.
The contributions to the torque from the two half forces of each
side are opposite to each other and tend to cancel out
.Therefore , the vortex shedding peak in the pressure spectrum
on side face doesn''t appear in the torque spectrum .However ,
the contributions to the torque from the two leeward half
faces are the same , the effects tend to add up .So the vortex
shedding peak will appear in the torque spectrum .
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