👉How Vertical Force Create Diagonal Crack in Beam?

💫Vertical force (load) creates diagonal cracks in a reinforced concrete beam because it produces shear stress together with bending stress. The interaction of these stresses causes principal tensile stress that acts diagonally.

🏷Here is a clear step-by-step explanation:

⭐️1. Effect of Vertical Load on a Beam

⏺When a vertical load acts on a beam: It creates bending moment and It also creates shear force, especially near the supports

⭐️2. Stress Distribution Inside the Beam

⏺Inside the beam section: Flexural (bending) stress causes Compression at the top Tension at the bottom
⏺Shear stress is maximum near the neutral axis Concrete is weak in tension, so cracks form where tensile stress is highest.

⭐️3. Combination of Stresses

🔰Principal Tensile Stress
⏺At any point in the beam:
Vertical shear stress (τ)
Horizontal flexural tensile stress (σ) These two stresses combine to form principal tensile stress, which acts at an inclined (diagonal) direction.

🔹 Concrete cracks perpendicular to the direction of maximum tensile stress
🔹 Therefore, cracks appear diagonally

⭐️4. Why Diagonal Cracks Start Near Supports

⏺Shear force is maximum near supports
❇️Bending tension still exists
This combination causes diagonal tension cracks to start at the bottom of the beam near the support and move upward toward the load

⭐️5. Typical Crack Angle

⏺Diagonal cracks usually form at 30°–45° to the beam axis This angle depends on:
❇️Shear force magnitude
❇️Beam depth
❇️Material properties

⭐️6. Types of Shear-Related Diagonal Cracks

📍Flexure-shear cracks

⏺Start as vertical flexural cracks Turn diagonal as shear increases

📍Web-shear cracks

⏺Form suddenly without prior flexural cracks Occur in deep beams or short spans

⭐️7. Role of Stirrups (Shear Reinforcement)

⏺Diagonal cracks are controlled by stirrups

❇️Stirrups: Carry shear force
⏺Prevent sudden brittle shear failure
⏺Limit crack width and propagation

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