Concrete beams, crucial components in building structures, can experience two main types of failures: flexural failure and shear failure. These failures can lead to serious consequences, making it essential to comprehend their nature and mechanisms.
Flexural tension failure happens when the load on a beam surpasses its flexural capacity. This occurs when the steel reinforcement yields, followed by the crushing of concrete at the compression side of the beam. Recognizing this failure involves observing vertical cracks at the tension side, extending towards the compression side, and noticeable deflection. Flexural tension failure, a gradual and ductile process, is a desired outcome in beam design.
Flexural compression failure initiates with concrete crushing at the compression side, followed by steel yielding at the tension side. It occurs in over-reinforced beams and is a sudden, brittle failure without warning. Avoiding over-reinforcement or enhancing concrete compression strength can prevent this undesired failure.
Balanced failure results when concrete crushes and steel yields simultaneously, happening when the amount of steel equals the balanced reinforcement ratio.
Shear failure occurs when a beam’s shear resistance is lower than its flexural strength, and the shear force exceeds the capacity of materials. This abrupt, brittle failure has undesirable consequences.
Diagonal tension failure begins with vertical flexural cracks at the beam’s bottom, progressing diagonally as the load increases. It culminates in sudden concrete failure in shear. Common in beams with low or no web reinforcement, this failure occurs typically for shear-span to depth ratios greater than 2.
Shear compression failure initiates with cracks in the beam’s cross-section, progressing to penetrate the compression zone. The final stage involves concrete crushing when compressive strength is exceeded. This failure is associated with high shear reinforcement and can occur in beams with a span to depth ratio of less than four.
Splitting shear failure is expected when the shear span to depth ratio is less than one, common in deep beams. Sometimes, compression failure near supports may occur instead.
Anchorage failure involves the splitting of concrete along the longitudinal reinforcement due to small diagonal cracks, occurring when the main reinforcement is inadequately anchored beyond the crack. Vigilance is crucial to prevent this type of failure.
Understanding these failure modes is vital for designing robust concrete beams and ensuring the safety and stability of structures.