Date of Award

8-1-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Riyad S. Aboutaha

Keywords

Column, Concrete, Corrosion, Deterioration, Finite Element Analysis, Lateral Strength

Subject Categories

Engineering

Abstract

Corrosion of reinforcing steel bars is the primary durability problem that causes degradation of reinforced concrete structures located in aggressive environments. Severe corrosion of steel bars decreases the lateral load-carrying capacity of reinforced concrete members, causes loss in the mechanical properties of reinforcement and cross-sectional area of steel bars and concrete cover, bond deterioration, reduces anchorage of steel bars, and decreases the confinement by transverse reinforcement. Consequently, corrosion results in drop in the lateral strength of columns. Therefore, studying response of corroded reinforced concrete columns subjected to lateral loads is necessary.

According to the Federal Highway Administration (FHWA) report in 2013, 25.9 percent of the total inventory of highway bridges are deficient or functionally obsolete. Corrosion damage caused by deicing salts is considered one of the main problems that cause a bridge structure to be structurally deficient (FHWA, 2004). However, absence of a practical model for assessment of the residual lateral strength of severely corroded RC columns as well as the lack of research on ultimate lateral capacity of deteriorated concrete structures shows the need to develop a practical method to calculate the current lateral capacity of corroded reinforced concrete bridge columns.

A new methodology was developed in this research, to evaluate the current lateral strength of severely corroded RC columns, which can be adapted to existing bridge condition evaluation methods. A Finite Element Analysis (FEA) model to simulate severely corroded columns was created and verified against experimental data conducted by other researchers. After being verified against experimental data, a total of 308 Finite element models were developed to investigate several variables that affect the lateral response of corroded columns. A series of 24 in×24 in square column sections having different material properties were modeled as cantilevers. Location of corrosion within the cross-section (Compression-side corroded, Tension-side corroded, All-sides corroded), corrosion level (CR=25%, 30%, 35%, 40%, 45%, 50%), length of corroded zone along the column height (1H=24in, 2H=48in), axial load ratio (NR=P/(f'c.Ag )=0%,5%,15%,25%), compressive strength of concrete (f'c=4ksi,7ksi), steel reinforcing ratio (ρ=2%,3%,4%) and shear span to depth ratio (L/d=2.5, 5) were the variables investigated in this study. For severely corroded RC columns, stirrups were assumed to be completely deteriorated and the concrete cover spalled off. Therefore, concrete cover and stirrups were removed at corroded locations. The corroded bars were assumed to be completely un-bonded to the surrounding concrete.

Based on results obtained from the finite element analysis, a practical model was developed. The proposed practical method considers all the changes in material and geometry properties including area loss of corroded steel bars and concrete cover, bond deterioration and its consequences on corroded bars’ buckling, location of corroded zone, length of corroded zone along the column, compressive strength of concrete, reinforcing ratio of RC column section, axial load ratio, and shear span to depth ratio. This study also provides engineers better understanding of lateral response of severely corroded RC bridge columns with detailed force-displacement diagrams based on finite element analysis.

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