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Understanding Beam Bending Stress: Formula and Calculation

beam rolling

Beam bending/rolling stress is a critical factor in engineering and structural design, crucial for determining a beam’s ability to withstand loads. Understanding the formulas and calculations involved in beam rolling/bending stress is fundamental for ensuring structural integrity and safety. Let’s delve into the concepts, equations, and methods used to analyze and calculate beam rolling/bending stress.

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Overview of Beam Bending/Rolling Stress

h beam bending machine
h beam bending machine

Bending/Rolling stress occurs when external forces exert a bending moment on a beam, resulting in stress within the beam’s material. The formula for rolling/bending stress (σ) in a beam can be expressed as:



  • σ = Bending stress (in Pascals or pounds per square inch)
  • M = Bending moment (in Newton-meters or pound-feet)
  • c = Distance from the neutral axis to the outermost fiber of the beam (in meters or inches)
  • I = Moment of inertia of the beam’s cross-sectional area (in meters to the fourth power or inches to the fourth power)

Calculation of Bending Stress

To compute rolling/bending stress in a beam, follow these steps:

  1. Determine the bending moment (M) acting on the beam due to applied loads.
  2. Calculate the moment of inertia (I) for the specific beam cross-section.
  3. Identify the distance (c) from the neutral axis to the outermost fiber of the beam.

Example Calculation

Let’s consider an example: a simply supported beam with a uniformly distributed load. The formula to calculate the bending moment for this case is M=(wL2)/8​, where w is the load per unit length and L is the length of the beam.

Suppose we have a beam with a length of 4 meters and a uniform load of 5 kN/m. The bending moment can be calculated as M=(5×42)/8​=10kNm.

Next, compute the moment of inertia I for the beam’s cross-section. For a rectangular beam, I=(b⋅h3​)/12, where b is the beam’s width and ℎh is its height.

Assuming a rectangular beam with dimensions 0.2 m (width) and 0.4 m (height), (0.2×0.43​)/12=0.0053m4.

Then, determine the distance c from the neutral axis to the beam’s outermost fiber. For a rectangular beam, c=h/2​=0.2m.

Now, apply the rolling/bending stress formula:σ=(Mc)/I​=(10×0.2​)/0.0053=377MPa.

Factors Affecting Bending Stress

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Various factors influence beam rolling/bending stress, including:

  • Beam material properties (e.g., modulus of elasticity)
  • Beam geometry and cross-sectional shape
  • Magnitude and distribution of applied loads


Understanding beam rolling/bending stress and its calculation is pivotal in structural engineering. By comprehending the formulas and concepts behind bending stress, engineers can design beams that efficiently handle loads, ensuring the safety and reliability of structures. The ability to analyze rolling/bending stress aids in optimizing beam designs and material usage, contributing to the overall integrity of engineered structures.