### Experimental Study on the Fatigue Performance of Deep Reinforced Concrete Beams Subjected to Simultaneous Reinforcement Corrosion
#### Abstract
This experimental study investigates the combined effects of reinforcement corrosion and cyclic loading on the fatigue performance of deep reinforced concrete (RC) beams. Deep beams are critical structural elements in various types of infrastructure, such as bridges and industrial buildings, where they are subjected to repetitive loading and harsh environmental conditions. Corrosion of steel reinforcement, often caused by the ingress of chloride ions or carbonation, significantly reduces the load-bearing capacity and durability of RC beams. This study presents a comprehensive analysis of the structural behavior, fatigue life, crack propagation, and failure mechanisms of deep RC beams subjected to simultaneous reinforcement corrosion and fatigue loading.
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#### Introduction
The durability and structural integrity of RC structures are major concerns, particularly in corrosive environments. Fatigue loading, resulting from traffic or machinery, combined with reinforcement corrosion poses a serious threat to the longevity of RC structures. While fatigue performance of slender RC beams has been extensively studied, limited research exists on the fatigue behavior of deep RC beams, especially under simultaneous corrosion. This knowledge gap motivates the current investigation.
Deep RC beams differ from slender RC beams because their behavior is typically governed by shear rather than flexure. Corrosion-induced degradation of steel reinforcement in deep beams accelerates crack formation, leading to reduced shear strength and lower fatigue life. By understanding the interplay between corrosion and fatigue, engineers can develop more durable designs and effective repair strategies.
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#### Objectives
The main objectives of this study are:
1. To investigate the impact of reinforcement corrosion on the fatigue performance of deep RC beams.
2. To evaluate the crack propagation, stiffness degradation, and fatigue life under cyclic loading.
3. To determine the influence of varying degrees of corrosion (mild, moderate, severe) on structural performance.
4. To propose practical recommendations for improving fatigue resistance in corroded deep RC beams.
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#### Methodology
**Specimen Preparation**:
Deep RC beam specimens with identical geometric and material properties were cast. The beams had a shear span-to-depth ratio (a/d) less than 2, making shear the dominant failure mode. High-strength concrete and steel reinforcement bars (rebar) were used to ensure durability.
**Corrosion Simulation**:
Accelerated corrosion techniques, such as an impressed current method, were used to achieve varying corrosion levels (e.g., 5%, 10%, and 15% weight loss of reinforcement). Corroded beams were stored in a chloride-rich environment to simulate real-world conditions.
**Fatigue Testing Protocol**:
- A four-point bending fatigue test setup was employed.
- Cycling was applied at a frequency of 2–5 Hz with stress levels ranging from 40% to 80% of the beam's ultimate capacity.
- Crack widths, deflection, stiffness degradation, and energy dissipation were monitored throughout the loading cycles.
**Data Acquisition**:
- Digital Image Correlation (DIC) was used to track crack propagation in real time.
- Electrochemical measurements, including half-cell potential and linear polarization resistance, were conducted to quantify corrosion levels before and after fatigue testing.
- Strain gauges and load cells were used to measure stress distributions and deflections in the beams.
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#### Key Findings
1. **Effect of Corrosion on Fatigue Life**:
- Increasing levels of reinforcement corrosion substantially reduced the fatigue life of deep RC beams.
- Beams with 15% reinforcement weight loss experienced a 35% reduction in fatigue life compared to uncorroded beams.
2. **Crack Propagation**:
- Corroded beams exhibited earlier onset of cracking and faster crack propagation under cyclic loading.
- Corrosion-induced pitting in rebar led to localized stress concentrations, accelerating fatigue failure.
3. **Stiffness Degradation**:
- Beam stiffness decreased significantly with increasing corrosion levels and fatigue cycles.
- Corrosion resulted in a loss of bond strength between steel and concrete, leading to brittleness and reduced energy dissipation capacity.
4. **Failure Modes**:
- Uncorroded beams primarily failed due to diagonal shear cracking.
- Corroded beams exhibited a combination of flexural and shear failure, with severe spalling of the concrete cover.
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#### Practical Implications
The findings underscore the importance of corrosion protection for reinforcement in RC beams subjected to cyclic loading. Enhanced corrosion-resistant materials, such as epoxy-coated rebar or fiber-reinforced polymer reinforcement, may significantly improve fatigue performance. Rehabilitation techniques, including cathodic protection and concrete crack sealing, can mitigate the adverse effects of corrosion.
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#### Recommendations for Future Research
1. Investigate the combined influence of environmental factors (e.g., temperature, humidity) and loading conditions on corroded deep RC beams.
2. Study the long-term effects of different repair and strengthening techniques under simultaneous corrosion and fatigue.
3. Develop predictive models to simulate the fatigue behavior of corroded RC beams, incorporating advanced mechanics and machine learning techniques.
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#### Conclusion
Reinforcement corrosion severely compromises the fatigue performance of deep RC beams, accelerating cracking, reducing stiffness, and decreasing fatigue life. This study highlights the need for rigorous design standards and maintenance strategies to ensure the safety and durability of RC structures in corrosive environments. |
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