Formulation and validation of minimum brace stiffness for systems of compression members

Bracing that is used to reduce the effective length of compressive members, and thereby increase their load carrying capacity, must be designed to provide adequate stiffness and strength. In practice, a targeted minimum or ideal brace stiffness is typically defined, and then this value is increased by a factor of two or three in order to ensure brace strength demands can be satisfied efficiently. While straightforward expressions are available to determine the ideal brace stiffness for single members, the brace stiffness for systems of multiple parallel compression members is more complex. This paper presents the derivation and validation of a simple mathematical expression that is useful for obtaining the ideal brace stiffness of structural systems composed of multiple parallel compression members or sub-assemblages. Use and validation of the proposed expression is explored through a variety of examples. Agreement with results obtained using finite element analyses suggests that the developed expression sufficiently determines the minimum bracing stiffness for systems of multiple parallel members with single and multiple brace points.