BEHAVIOR OF CONCRETE COLUMNS UNDER VARIOUS CONFINEMENT EFFECTS by AHMED

427 Pages·2012·7.75 MB·English

BEHAVIOR OF CONCRETE COLUMNS UNDER VARIOUS CONFINEMENT EFFECTS
by

AHMED MOHSEN ABD EL FATTAH
B.S., Cairo University, 2000
M.S., Kansas State University, 2008

AN ABSTRACT OF A DISSERTATION

Submitted in partial fulfillment of the requirements for the degree

DOCTOR OF PHILOSOPHY
Department of Civil Engineering
College of Engineering

KANSAS STATE UNIVERSITY
Manhattan, Kansas
2012
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 f (at zero eccentricity) to the unconfined value f’ (at infinite eccentricity) as a
cc c
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 and Lam and Teng 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-ε and M-ϕ response up to failure. This numerical analysis is
adaptod to asses the confining effect in circular cross sectional columns confined with FRP and
conventional lateral steel together; concrete filled steel tube (CFST) circular columns and
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 2D interaction
diagrams for circular columns, 3D failure surface for rectangular columns and allows the user to
determine the 2D interaction diagrams for any angle α 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.
BEHAVIOR OF CONCRETE COLUMNS UNDER VARIOUS CONFINEMENT EFFECTS
by
AHMED MOHSEN ABD EL FATTAH
B.S., Cairo University, 2000
M.S., Kansas State University, 2008

A DISSERTATION
Submitted in partial fulfillment of the requirements for the degree

DOCTOR OF PHILOSOPHY
Department of Civil Engineering
College of Engineering
KANSAS STATE UNIVERSITY
Manhattan, Kansas
2012
Approved by:

Major Professor
Hayder Rasheed
Copyright

AHMED MOHSEN ABD EL FATTAH
2012
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 f (at zero eccentricity) to the unconfined value f’ (at infinite eccentricity) as a
cc c
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 and Lam and Teng 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-ε and M-ϕ response up to failure. This numerical analysis is
adaptod to asses the confining effect in circular cross sectional columns confined with FRP and
conventional lateral steel together, concrete filled steel tube (CFST) circular columns and
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 2D interaction
diagrams for circular columns, 3D failure surface for rectangular columns and allows the user to
determine the 2D interaction diagrams for any angle α 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
Table of Contents
List of Figures…………………………………………………………………………………...xiii
List of Tables……………………………………………………………………………....…...xxv
Acknowledgements…………………………………..…………………………..…….....…...xxvii
Dedication…………………………………..…………………………..……..................…...xxviii
Chapter 1 - Introduction .................................................................................................................. 1
1-1 Background ............................................................................................................................... 1
1-2 Objectives ................................................................................................................................. 1
1-3 Scope ........................................................................................................................................ 3
Chapter 2 - Literature Review ......................................................................................................... 4
2-1 Steel Confinement Models ....................................................................................................... 4
2-1-1 Chronological Review of Models ......................................................................................... 4
2-1-1-1 Notation.............................................................................................................................. 4
2-1-2 Discussion ........................................................................................................................... 50
2-2 Circular Columns Confined with FRP.................................................................................... 56
2-2-1 Past Work Review ............................................................................................................... 56
2-2-2 Discussion ......................................................................................................................... 115
2-3 Circular Concrete Filled Steel Tube (CFST) Columns ........................................................ 118
2-3-1 Past Work Review ............................................................................................................. 118
2-2-2 Discussion ......................................................................................................................... 134
2-4 Rectangular Columns subjected to biaxial bending and Axial Compression ....................... 135
2-4-1 Past Work Review ............................................................................................................. 135
2-4-2 Discussion ......................................................................................................................... 194
viii
Chapter 3 - Circular Columns Confined with FRP and lateral Steel .......................................... 196
3-1 Introduction .......................................................................................................................... 196
3-2 Formulations ......................................................................................................................... 197
3-2-1 Finite Layer Approach (Fiber Model) ............................................................................... 197
3-2-2 Present Confinement Model for Concentric Columns ...................................................... 197
3-2-2-1 Lam and Teng Model ..................................................................................................... 197
3-2-2-2 Mander Model for transversely reinforced steel ............................................................ 199
3-2-3Present Confinement Model for Eccentric Columns.......................................................... 206
3-2-3-1 Eccentric Model Based on Lam and Teng Equations .................................................... 209
3-2-3-2 Eccentric Model based on Mander Equations ............................................................... 210
3-2-4 Moment of Area Theorem ................................................................................................. 212
3-3 Numerical Formulation......................................................................................................... 216
3-3-1 Model Formulation ............................................................................................................ 216
3-3-2 Numerical Analysis ........................................................................................................... 219
3-4 Results and Discussion ......................................................................................................... 226
3-4-1 Stress-Strain Curve Comparisons with Experimental Work ............................................. 226
3-4-2 Interaction Diagram Comparisons with Experimental Work ............................................ 236
Chapter 4 - Circular Concrete Filled Steel Tube Columns (CFST) ............................................ 245
4-1 Introduction .......................................................................................................................... 245
4-2 Formulations ......................................................................................................................... 246
4-2-1 Finite Layer Approach (Fiber Model) ............................................................................... 246
4-2-2 Present Confinement Model for Concentric Columns ...................................................... 247
4-2-2-1 Mander Model for transversely reinforced steel ............................................................ 247
ix
4-2-2-2 Lam and Teng Model ..................................................................................................... 254
4-2-3Present Confinement Model for Eccentric Columns.......................................................... 255
4-2-3-1 Eccentric Model based on Mander Equations ............................................................... 258
4-2-3-2 Eccentric Model Based on Lam and Teng Equations .................................................... 260
4-2-4 Moment of Area Theorem ................................................................................................. 262
4-3 Numerical Model Formulation ............................................................................................. 265
4-3-1 Model Formulation ............................................................................................................ 265
4-3-2 Numerical Analysis ........................................................................................................... 273
4-4 Results and Discussion ......................................................................................................... 279
4-4-1 Comparisons with Experimental Work ............................................................................. 279
Chapter 5 - Rectangular Columns subjected to biaxial bending and Axial Compression .......... 293
5-1 Introduction .......................................................................................................................... 293
5-2 Unconfined Rectangular Columns Analysis......................................................................... 294
5-2-1 Formulations...................................................................................................................... 294
5-2-1-1 Finite Layer Approach (Fiber Method).......................................................................... 294
5-2-1-2 Concrete Model .............................................................................................................. 295
5-2-1-3 Steel Model .................................................................................................................... 296
5-2-2 Analysis Approaches ......................................................................................................... 296
5-2-2-1 Approach One: Adjusted Predefined Ultimate Strain Profile ........................................ 296
5-2-2-2 Approach Two: Generalized Moment of Area Theorem ............................................... 300
5-2-2-2-a Moment of Area Theorem .......................................................................................... 300
5-2-2-2-b Method Two ............................................................................................................... 304
5-2-3 Results and Discussion ...................................................................................................... 313
x