Statics: Direct Force Path

Direct Force Path

Stiffness of a structure is the ability of the structure to resist deformation.
Stiffness of a structure represents the efficiency of the structure to transmit loads on the structure to its supports.
Internal forces in members are induced when they transmit loads from one part to another part of the structure. The internal forces can be tension, compression, shear, torque or bending moment, or a combination of all or some of them.

There are three inter-related concepts relating to the internal forces in a structure:

  • The more direct the internal force paths, the stiffer the structure.
  • The more uniform the distribution of internal forces, the stiffer the structure.
  • The smaller the internal forces, the stiffer the structure.

Following the first concept, five simple criteria can be adopted for arranging bracing members in frame structures to achieve a direct force path leading to a stiffer structure.

  • Bracing members should be provided in each storey from the support (base) to the top of the structure.
  • Bracing members in different storeys should be directly linked.
  • Bracing members should be linked in a straight line where possible.
  • Bracing members in the top storey and in the adjacent bays should be directly linked where possible. (Suitable for temporary grandstands and scaffolding structures where the number of bays may be larger than the number of storeys)
  • If extra bracing members are required, they should be arranged following the above four criteria.