- See Article - Beam Design Formulas
Diagram Symbols
Bending moment diagram (BMD) - Used to determine the bending moment at a given point of a structural element. The diagram can help determine the type, size, and material of a member in a structure so that a given set of loads can be supported without structural failure.
Free body diagram (FBD) - Used to visualize the applied forces, moments, and resulting reactions on a structure in a given condition.
Shear force diagram (SFD) - Used to determine the shear force at a given point of a structural element. The diagram can help determine the type, size, and material of a member in a structure so that a given set of loads can be supported without structural failure.
Uniformly distributed load (UDL) - A load that is distributed evenly across the entire length of the support area.
Simple Beam - Two Point Loads Equally Spaced formulas |
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\( R \;=\; V \;=\; P \) \( M_{max} \; ( between\; loads ) \;=\; P \cdot a \) \( M_x \; ( x < a ) \;=\; P \cdot x \) \( \Delta_{max} \; ( at \;center ) \;=\; \dfrac{ P \cdot x }{ 24 \cdot \lambda\cdot I } \cdot l \cdot ( 3 \cdot L^2 - 4 \cdot a^2 ) \) \( \Delta_x \; ( x < a ) \;=\; \dfrac{ P \cdot x }{ 6 \cdot \lambda \cdot I } \cdot ( 3 \cdot L \cdot a - 3 \cdot a^2 - x^2 ) \) \( \Delta_x \; [\; a < x < ( L - a ) \;] \;=\; \dfrac{ P \cdot a }{ 6 \cdot \lambda \cdot I } \cdot ( 3 \cdot L \cdot x - 3 \cdot x^2 - a^2 ) \) |
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| Symbol | English | Metric |
| \( R \) = reaction load at bearing point | \(lbf\) | \(N\) |
| \( V \) = maximum shear force | \(lbf\) | \(N\) |
| \( M \) = maximum bending moment | \(lbf-in\) | \(N-mm\) |
| \( \Delta \) = deflection or deformation | \(in\) | \(mm\) |
| \( P \) = total concentrated load | \(lbf\) | \(N\) |
| \( a \) = length to point load | \(in\) | \(mm\) |
| \( x \) = horizontal distance from reaction to point on beam | \(in\) | \(mm\) |
| \(\lambda \) (Greek symbol lambda) = modulus of elasticity | \(lbf\;/\;in^2\) | \(Pa\) |
| \( I \) = second moment of area (moment of inertia) | \(in^4\) | \(mm^4\) |
| \( L \) = span length of the bending member | \(in\) | \(mm\) |
