United States Department of Transportation
i
LRFD software for design and actual ultimate capacity of confined rectangular columns.
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2013-04-01
[PDF-1.95 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-HIGHWAY/ROAD TRANSPORTATION-Design;
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Abstract:The analysis of concrete columns using unconfined concrete models is a well established practice. On the
other hand, prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear
analysis. Modern codes and standards are introducing the need to perform extreme event analysis. There has been a
number of studies that focused on the analysis and testing of concentric columns or cylinders. This case has the highest
confinement utilization since the entire section is under confined compression. On the other hand, the augmentation of
compressive strength and ductility due to full axial confinement is not applicable to pure bending and combined
bending and axial load cases simply because the area of effective confined concrete in compression is reduced. The
higher eccentricity causes smaller confined concrete region in compression yielding smaller increase in strength and
ductility of concrete. Accordingly, the ultimate confined strength is gradually reduced from the fully confined value fcc
(at zero eccentricity) to the unconfined value f’c (at infinite eccentricity) as a function of the compression area to total
area ratio. The higher the eccentricity, the smaller the confined concrete compression zone. This paradigm is used to
implement adaptive eccentric model utilizing the well known Mander Model.
Generalization of the moment of area approach is utilized based on proportional loading, finite layer procedure and
the secant stiffness approach, in an iterative incremental numerical model to achieve equilibrium points of P- and M-
response up to failure. This numerical analysis is adapted to assess the confining effect in rectangular columns
confined with conventional lateral steel. This model is validated against experimental data found in literature. The
comparison shows good correlation. Finally computer software is developed based on the non-linear numerical
analysis. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings,
capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and
reinforcement selection are seamlessly integrated as well. The software generates 3D failure surface for rectangular
columns and allows the user to determine the 2D interaction diagrams for any angle between the x-axis and the
resultant moment. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO
LRFD are made. This study is limited to stub columns.
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