Date of Graduation

5-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor

Rathinam P. Selvam

Committee Member

Rick J. Couvillion

Second Committee Member

Darin W. Nutter

Third Committee Member

Uchechukwu C. Wejinya

Fourth Committee Member

Richard A. Coffman

Abstract

The study of the conventional Straight Line (SL) wind flow dominates research into wind loads on structures. Most structure design takes into account only research into SL flow. Few researchers have studied tornado forces on buildings and attempted to distinguish between tornadic wind loads and SL flow loads. Using a computer simulation, this research addresses and distinguishes between the tornadic forces and SL forces on structures. In the numerical simulation, tornado forces and SL forces will be compared on large structure plan areas and on thin structure plan areas. Additionally this research investigates how the increase in the vortex strength (α) affects tornado forces on a cubic structure. The large structure plan areas are dimensionalized by the structure height: (1h x 1h, 2h x 2h, 4h x 4h and 8h x 8h) where h is 20.3 (m) and tornado maximum radius (rmax) is 61(m). The structure plan areas are a multiple of factor two. The thin structure plan areas are obtained by dividing the large structure plan areas by a factor of ten.

This research has three key findings. First, when the same maximum reference velocity (Vtrans.) was used and when the large structure plan area characteristic length was approximately twice the tornado maximum diameter, the force and pressure coefficients had the same values as Straight Line (SL) flow. Second, the thin structure plan areas are more likely collapse faster in the presence of a tornado compared to SL flow due to the high differentials pressure in tornado between the windward wall and the leeward wall. In addition, on the thin structure plan areas, the tornado force coefficients were twice the SL flow force coefficients. The final key finding is that when the vortex strength (α) increased, the tornado force coefficients increased exponentially.

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