Wood Beam Deflection Calculator | Span Check

Deflection is teh technical term for the bending or sagging that occur in a wood beam when a load is applied to the wood beam. Deflection is a significent factor to consider when use wood beams in construction because it is possible for the wood beam to not break under the load but to sag too much for the desired use of the wood beam. While many peoples focus on the strength of the wood beam to ensure that it will not break under the applied load, deflection is the factor that will determine whether or not the building project are successful or whether the wood beam will sag too much to appear unsteadily.

The dimensions of the wood beam and the type of wood that is used in the construction of the wood beam can determine the stiffness of a wood beam. The most important dimension to consider for increasing the stiffness of the beam is the depth of the wood beam. Increasing the depth of the wood beam will have a more greater impact on the stiffness of the wood beam than increasing the width of the wood beam.

Why Wood Beams Bend and How to Reduce Sagging

This is due to the fact that the moment of inertia of the wood beam, which is a measure of how the material of the wood beam is distribute within the wood beam, increases significanly if a builder increase the depth of the wood beam. If the depth of a wood beam is doubled, the stiffness of that beam will increase 16 folds. However, if the width of a wood beam is doubled, the stiffness of the wood beam will only double.

Using this information, it is possible to design a beam that is tall and narrow rather than wide and shallow to increase it’s stiffness. The type of load that is applied to a wood beam will have an impact upon how that wood beam deflects. A point load is a type of load that is applied to one specific location on a wood beam.

A point load will cause more deflection in a wood beam than a uniform load. A uniform load is a load that is applied evenly along the length of the wood beam. A load placed at the center of the wood beam will cause the beam to deflect more than a load placed closer to one of the support of the beam.

In addition to these factor, the type of wood that is used will also have an impact upon the deflection of a wood beam. For example, beams made out of hardwoods or engineered wood product like Laminated Veneer Lumber (LVL) will have more stiffness in their deflection than beams made out of softwoods like pine. There are service limit for wood beams that determine the deflection limits of the wood beam.

One common limit is set at L/360. This means that the deflection limits of a wood beam should not exceed the length of the beam divided by 360. These limits should be strict limits, such as L/360, for any visible structure in a construction project. Any deflection limits can be set to be looser limits, such as L/180, for structures that is hidden from view or structures that do not require the wood beams to have high level of stiffness.

For example, floors need to have deflection limits of L/240 since floors that deflect too much will feel “bouncy” to the individual that walk on those floors. When wood beams are selected for a construction project, it is important to remember that the actual dimensions of the wood beams are slightly different than the dimensions of the wood beams that is name or labeled. For example, a wood beam that is labeled 2×10 is actualy 1.5 inch in width by 9.25 inches in depth.

These actual dimensions should be used when calculating the specifications of the wood beam since using the nominal dimensions will result in incorrect calculation of the deflection and strength of the wood beam. In order to calculate the specifications of a wood beam, the actual dimensions of the wood beam, the type of load that will be place upon it, the species of wood from which the beam is made should be considered to determine if it will meet the service limits of the construction project. Finally, another factor to consider for the performance of a wood beam is the impact that the environment will have upon the beam.

Humidity level will impact wood beams because wood expands when the humidity levels are high and contracts when the humidity levels are low. This change in dimension will change the stiffness of the wood. Wood beams may also be affected by the phenomenon of creep.

Creep is the slow and permanent sagging of a wood beam under a constant load over an extended period of time. This phenomenon should of been considered for wood beams that will be use outdoors or beams with a constant load. Finally, the supports for the beam must be sufficiently strong since the wood beams may fail at the ends of the beams if the supports are not able to handle the load created at these ends of the beams.