Since we need to calculate Iₓ, its moment of inertia would be:Įastern white pine has a modulus of elasticity of 6,800 MPa (6.8×10⁹ Pa), which is the value we obtained from the Wood Handbook.

Given the dimensions of this seat, we can then calculate its moment of inertia, similar to our example above. We can consider this seat as a beam that will deflect whenever someone sits on the bench. Let us say we have a 4-cm thick, 30-cm wide eastern white pine plank that acts as the seat for this bench. Just consult the directions of the arrows in the formula's corresponding image to figure out which directions has a positive load value.įor a sample calculation of beam deflection, let us consider a simple wooden bench with legs 1.5 meters apart from each other at their centers. The formulas in this calculator also consider the moment or torque load, either in a clockwise or counterclockwise direction. Distributed loads are similar to pressure but only consider the beam's length and not the beam's width. The formulas in this calculator only focus on either the downward or upward directions for the point load and distributed loads. Loads can be in the form of a single-point load, linear pressure, or moment load. Downward loads tend to deflect the beam downwards. Loads, on the other hand, affect the beam's deflection in two ways: the direction of the deflection and the magnitude of the deflection. The longer the beam gets, the more it can bend and the greater the deflection. However, by inspecting our formulas, we can also say that the beam's length also directly affects the deflection of the beam. The formulas show that the stiffer the beam is, the smaller its deflection will be. Now that we know the concepts of modulus of elasticity and moment of inertia, we can now understand why these variables are the denominators in our beam deflection formulas. This difference in the moment of inertia values is the reason why we see beams in this configuration – wherein their height is greater than their width. The moment of inertia values we obtained tell us that the beam is harder to bend with a vertical load and easier to bend if subjected to a horizontal lateral load. Since we are considering the deflection of the beam when it bends vertically or around the x-axis, we have to use Iₓ for our computations. That's because we can consider the beam to bend vertically along the beam span (or experience a bending moment around the x-axis) and laterally along the beam span (or bend around the y-axis). Notice how there are two values for the moment of inertia. Using the formulas that you can also see in our moment of inertia calculator, we can calculate the values for the moment of inertia of this beam cross-section as follows: To further understand this concept, let us consider the cross-section of a rectangular beam with a width of 20 cm and a height of 30 cm. The moment of inertia also varies depending on which axis the material is rotating along. The moment of inertia depends on the dimensions of the material's cross-section. The moment of inertia represents the amount of resistance a material has to rotational motion.

On the other hand, to determine the moment of inertia for a particular beam cross-section, you can visit our moment of inertia calculator. You can learn more about the modulus of elasticity by checking out our stress calculator. This difference in the values of modulus of elasticity shows that concrete can only withstand a small amount of deflection and will experience cracking sooner than steel. Concrete's modulus of elasticity is between 15-50 GPa (gigapascals), while steel tends to be around 200 GPa and above. The higher a material's modulus of elasticity, the more of a deflection can sustain enormous loads before it reaches its breaking point. The modulus of elasticity depends on the beam's material. We can define the stiffness of the beam by multiplying the beam's modulus of elasticity, E, by its moment of inertia, I. Calculating beam deflection requires knowing the stiffness of the beam and the amount of force or load that would influence the bending of the beam.

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