Dissertations

Dissertation

Spring 5-31-2002

Degree Name

Doctor of Philosophy in Civil Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

C.T. Thomas Hsu

Methi Wecharatana

Dorairaja Raghu

Walter Konon

Michael Y. Xing

Abstract

A generalized analytical approach is presented in this research to predict the behavior both of slender and short reinforced concrete columns under sustained biaxial eccentric load.

The present analysis proposes equations established at a cross section of a reinforced concrete column by combining force equilibrium, constitutive law, and compatibility conditions. The strain and curvature of each section and the deflection of the column can then be obtained and resolved.

The established creep computation models, recommended separately by American Concrete Institute (ACI) 209R-92 and the Comite' Euro-International du Be'ton (CEB)-FIP 1990 Model Code have been used to calculate creep and shrinkage for a member under a constant elastic compressive concrete strain for a given period.

This present analysis also proposes a computerized method for time and strain adjustment. The Time and Strain Adjustment of Creep Method, combining a creep calculation with a constant elastic strain such as those mentioned above, the creep strain at each cross section can then be calculated, stored and adjusted to age of concrete, load changes and deflection modifications during each time increment phase.

In the conventional load-deflection analysis process, with projected transformations, a spatial deflection curve is resolved into a couple of planar curves located separately in two orthogonal plans. Based on the force equilibrium equations of inner force at a column section, a set of three simultaneous non-linear differential equations are derived to establish the relationships between the planar curve functions with the eccentric load upon the top of column. Using the Green's Integral Formula, the strain and stress nonlinear functions and column section properties can be solely integrated into a few important coefficients of the differential equations. Thus, it makes the approach also suitable for columns with non-rectangular sections and any kinds of constitutive laws of materials.

The presented rational computer analysis results have been compared with the existing bi-axial and uniaxial experimental data, which are available in literature. They indicate that the results from the proposed analysis correlate with experimental data well.

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