Date of Award

August 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Riyad S. Aboutaha

Keywords

column footing, finite element analysis, prestressing, punching shear, strengthening, wrapping

Subject Categories

Engineering

Abstract

Footing enlargement method is widely applied to strengthen bridge footings with structural deficiencies, where dimensions of footings are enlarged by adding new concrete segments. In the traditional method, connections at the contact surfaces are achieved by installing a large number of steel dowels and splicing the flexural reinforcements, which are labor-intensive and time-consuming. To address this problem, five upgraded footing enlargement systems are proposed in this dissertation:

• Circular external prestressing system (CEP);

• Circular external regular reinforcement system (CERR);

• Circular external BFRP wrapping system (CEBW);

• Circular external CFRP wrapping system (CECW);

• Circular external steel jacketing system (CESJ).

In these systems, the connections at the contact surfaces are achieved by the confinement actions provided by different circular external strengthening materials (e.g., prestressing strands in the CEP system, and CFRP wraps in the CECW system). The CEP is an active system, in which the connections are activated during strengthening work. The other four are all passive systems, as the primary connections are activated after the external loads are applied.

By using ABAQUS, a series of finite element models were built to investigate the effectiveness of the five proposed strengthening systems, especially on their improvements in the punching shear capacity. 353 models were built in ABAQUS. For each system, a unique group of parameters were considered and investigated. As an active system, CEP significantly improved the punching shear capacity of RC footings, and the number of prestressing strands had the most significant influence. For the other four passive systems, the improvements in the punching shear capacities were relatively lower. The parameters investigated such as the area of the regular reinforcements (in CERR), the thickness of the FRP wraps (in CEBW and CECW), and the thickness of the steel jackets (in CESJ) had only slight effects on the enhancements.

The analytical models for predicting the punching shear capacities of footings strengthened by the five proposed systems were all developed from the original model adopted by Eurocode 2, with the critical section located at d/2 to the edge of the column. Each analytical model is derived using linear aggression analysis, with the investigated parameters being considered.

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