My research experience and areas of interest involve seismic response of deteriorated concrete bridge components and rehabilitation of deteriorated reinforce concrete structures, with a focus on finite element analysis and estimation of residual capacity of deteriorated RC members.
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. One of the main problems that cause a bridge structure to be structurally deficient is corrosion damage caused by deicing salt (FHWA, 2004). 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.
Recent strong earthquakes have shown that the primary cause of collapse in many existing older structures is column failure. However, absence of a practical model for assessment of the residual lateral strength of 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. My research aim is investigating the response of corroded columns subjected to transverse loading in addition to compressive axial load, and proposing a model to predict the behavior of corroded reinforced concrete columns.
During my Ph.D. program, I have investigated the effect of severe corrosion on lateral strength of square RC bridge columns. A Finite Element Analysis (FEA) model to simulate severely corroded columns was created in ABAQUS and verified against experimental data conducted by other researchers. A total of 308 Finite element models were developed to investigate several variables that affect the lateral response of corroded columns. 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 research is in preparation to be published in ACI Journal of Structural Engineering. There are also one technical report (granted by The University Transportation Research Center (UTRC)) and three conference papers presented out of this work.
My future research area will focus more on lateral capacity of RC columns with rectangular sections (a/b>2) and circular sections and also columns which have corroded un-symmetrically. Although my previous research has simplified the process of finite element simulation of corroded columns and proposing a practical model to estimate the lateral strength of corroded columns, there are still many remaining research challenges I hope to address. In an aggressive environment, the corrosion is typically non-uniform. It means that, a column is most probably corroded partially which makes its cross-section un-symmetrical. For an un-symmetrical cross-section subjected to loads, neutral axis is not perpendicular to plane of loading anymore. Therefore, flexural capacity of cross-section is varied due to change in location of inclined neutral axis other than loss of concrete and steel area due to corrosion. From another perspective, lateral load applied (centric on the original section) to an un-symmetric cross-section produces torsional moment which creates shear stresses in the cross-section. The column already carries shear stresses due to shear forces, additional shear stresses due to torsion leads the column face with wider shear cracks and most probably premature shear failure.
Ultimately, my research aims to enable structural engineers to better understand lateral response of severely corroded RC bridge columns with detailed force-displacement diagrams based on finite element analysis, as well as use a practical model to estimate the residual capacity of deteriorated reinforced concrete columns.