Award Date

5-1-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Ying Tian

Second Committee Member

Nader Ghafoori

Third Committee Member

Samaan Ladkany

Fourth Committee Member

Ryan Sherman

Fifth Committee Member

Zhiyong Wang

Number of Pages

199

Abstract

Columns are critical components resisting the collapse of a reinforced concrete (RC) frame structure subjected to high sustained loads. Research on columns under sustained high stresses is very limited. At material level, past creep tests were focused either on concrete with ages less than 90 days or under a sustained stress less than 70% of short-time strength. At structural component scale, virtually no experimental data can be found for the response of axially loaded RC columns subjected to high sustained loads exceeding 75% of column short-time strength with loading age greater than 200 days. Even if a few experiments were conducted to examine the sustained eccentrically loaded columns under high sustained loads, the experiments were conducted predominantly within three months of concrete casting. The goals of this research were to (1) understand the behavior of aged reinforced concrete frame columns with ages greater than 200 days and under high sustained loads no less than 75% of short-time loading capacity caused by sustained concentric and eccentric loading, (2) examine the effects of transverse reinforcement ratio on the creep behavior of RC columns, (3) examine and explore a numerical method based on an existing nonlinear creep model for aged concentrically loaded concrete columns under high sustained stresses. To achieve the research goals, thirteen columns were tested after 209 to 629 days of concrete casting. The sustained loading lasted 2 to 120 days. Test variables included sustained load level, eccentricity ratio, and transverse reinforcement ratio. Eight of the thirteen columns were subjected to concentric loads. Among them, one plain concrete and one RC column, as control specimens, were tested to failure in a short time; two plain concrete and four RC columns were subjected to sustained concentric loads ranging from 76% to 98% of code-defined nominal short-time strength. No concentrically loaded column failed even the sustained load was as high as 98% of column short-time strength. Five RC columns were tested under sustained eccentric loading. These columns were initially loaded to cause the bending moment at the column mid-height to reach 77% to 100% of nominal flexural capacity after considering axial force-moment interactions. The columns showed high resistance to large sustained loads, and only one eccentrically loaded column failed during sustained eccentric loading. For concentrically loaded columns subjected to 98% code-defined nominal short-time strength, higher transverse reinforcement ratio decreased concrete creep during the early stage of sustained concentric loading but diminished over time. For eccentrically loaded columns, higher transverse reinforcement ratio increased flexural stiffness and resulted in lower creep deformation, thereby reducing failure risk due to second order effects. A numerical method for predicting concrete column creep under high axial sustained stresses and older loading ages is explored based on existing creep models. The experimental results of short column tests were compared with the predictions.

Keywords

Aged concrete; High sustained load; Nonlinear reinforced concrete creep; Numerical simulation model; Reinforced concrete creep experiments

Disciplines

Civil Engineering

File Format

pdf

File Size

11300 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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