By GATE Wallah - ME, CE, XE & CH
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Get instant insights and key takeaways from this YouTube video by GATE Wallah - ME, CE, XE & CH.
Bending Stress Distribution Assumptions
🧊 The material must be Isotropic, Homogeneous, and Elastic, implying it follows Hooke's Law.
⚖️ Young's Modulus (E) must be the same in both tension and compression for consistent stress calculation across the beam.
📏 The cross-section must be symmetric in the plane of loading to ensure pure bending (bending without torsion).
✈️ Plane sections remain plane after bending, which leads to a linear strain profile across the beam's depth.
Flexural Formula
⚙️ The fundamental formula for bending stress is σ/y = M/I = E/R, essential for civil engineers.
📊 σ represents bending stress at a distance y from the neutral axis, M is the bending moment, I is the moment of inertia (second moment of area), E is Young's Modulus, and R is the radius of curvature.
Section Modulus (Z)
💡 The Section Modulus (Z) is defined as Z = I / y_max, where `y_max` is the maximum distance from the neutral axis to the extreme fiber.
📈 It directly relates to maximum bending stress: σ_max = M / Z.
🏗️ In design, a higher section modulus (Z) is desirable as it reduces the maximum stress for a given bending moment, making the structure safer.
➡️ Maximize Z by distributing the cross-sectional area as far as possible from the neutral axis.
📐 Key Section Modulus values include:
* Rectangular: bd²/6
* Square: a³/6
* Circular: πD³/32
* Hollow Circular: **(π/32D) * (D⁴ - d⁴)**
* Triangular (base at bottom): bh²/24 (where `y_max = 2h/3`)
Key Points & Insights
➡️ Calculate maximum bending stress (σ_max) by dividing the maximum bending moment (M_max) by the section modulus (Z) for prismatic beams.
➡️ For eccentric axial loads, decompose the effect into an axial stress (P/A) and a bending stress (M/Z) due to the induced moment.
➡️ When determining stress states on elements within a beam, remember that shear force is zero at the mid-span of a uniformly loaded simply supported beam, meaning shear stress is also zero at that section.
➡️ An element on the neutral axis at a point of zero shear force will be free from all stresses (no normal stress from bending, no shear stress).
➡️ For deflection calculations in complex beams (e.g., cantilever with an overhanging free end), use superposition by combining standard deflection formulas for different segments or conditions (e.g., `Δ_total = Δ_load_point + θ_load_point * L_extension`).
➡️ Macaulay's Method is primarily suitable for prismatic beams and can handle several concentrated loads, extendable to uniform distributed loads.
➡️ The first integration in the Double Integration Method yields the slope of the beam's elastic curve.
📸 Video summarized with SummaryTube.com on Sep 24, 2025, 17:42 UTC
Full video URL: youtube.com/watch?v=NFhFWopRJOk
Duration: 1:31:25
Get instant insights and key takeaways from this YouTube video by GATE Wallah - ME, CE, XE & CH.
Bending Stress Distribution Assumptions
🧊 The material must be Isotropic, Homogeneous, and Elastic, implying it follows Hooke's Law.
⚖️ Young's Modulus (E) must be the same in both tension and compression for consistent stress calculation across the beam.
📏 The cross-section must be symmetric in the plane of loading to ensure pure bending (bending without torsion).
✈️ Plane sections remain plane after bending, which leads to a linear strain profile across the beam's depth.
Flexural Formula
⚙️ The fundamental formula for bending stress is σ/y = M/I = E/R, essential for civil engineers.
📊 σ represents bending stress at a distance y from the neutral axis, M is the bending moment, I is the moment of inertia (second moment of area), E is Young's Modulus, and R is the radius of curvature.
Section Modulus (Z)
💡 The Section Modulus (Z) is defined as Z = I / y_max, where `y_max` is the maximum distance from the neutral axis to the extreme fiber.
📈 It directly relates to maximum bending stress: σ_max = M / Z.
🏗️ In design, a higher section modulus (Z) is desirable as it reduces the maximum stress for a given bending moment, making the structure safer.
➡️ Maximize Z by distributing the cross-sectional area as far as possible from the neutral axis.
📐 Key Section Modulus values include:
* Rectangular: bd²/6
* Square: a³/6
* Circular: πD³/32
* Hollow Circular: **(π/32D) * (D⁴ - d⁴)**
* Triangular (base at bottom): bh²/24 (where `y_max = 2h/3`)
Key Points & Insights
➡️ Calculate maximum bending stress (σ_max) by dividing the maximum bending moment (M_max) by the section modulus (Z) for prismatic beams.
➡️ For eccentric axial loads, decompose the effect into an axial stress (P/A) and a bending stress (M/Z) due to the induced moment.
➡️ When determining stress states on elements within a beam, remember that shear force is zero at the mid-span of a uniformly loaded simply supported beam, meaning shear stress is also zero at that section.
➡️ An element on the neutral axis at a point of zero shear force will be free from all stresses (no normal stress from bending, no shear stress).
➡️ For deflection calculations in complex beams (e.g., cantilever with an overhanging free end), use superposition by combining standard deflection formulas for different segments or conditions (e.g., `Δ_total = Δ_load_point + θ_load_point * L_extension`).
➡️ Macaulay's Method is primarily suitable for prismatic beams and can handle several concentrated loads, extendable to uniform distributed loads.
➡️ The first integration in the Double Integration Method yields the slope of the beam's elastic curve.
📸 Video summarized with SummaryTube.com on Sep 24, 2025, 17:42 UTC
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