General design > 20 questions about structural stiffness

20 questions about structural stiffness

1. What is stiffness?

Stiffness is the ability of a structure to resist deformation when subjected to external forces. It is a measure of the amount of force required to cause a certain amount of deformation in the structure. In practical terms, stiffness is the ability of a structure to withstand bending, twisting, compression, or stretching without losing its original shape. A stiffer structure deflects less under a specific load compared to a less stiff structure.

2. How is stiffness measured?

Stiffness can be measured through various practical methods. One common method is testing where a load is applied to the structure and the deformation is measured. Another method is vibration testing, where the natural frequency of the structure is determined and used to calculate stiffness. Specialized tools such as strain gauges and accelerometers can also be used to measure strain and vibration.

However, the stiffness of a single beam under a specific load can be quite accurately calculated using relevant formulas found in standards or literature. Alternatively, stiffness values can also be obtained from tables of section properties. Specially developed programs, or Finite Element Method (FEM), can be used to evaluate stiffness and deflection for more complex structures. 

For example, the stiffness of a horizontal cantilever beam with a vertical point load at the free end can be calculated using the formula below.