Finite element evaluation of modal stresses in cantilever highway sign structures

Abstract

The dynamic properties of the cantilever sign structures such as its mode shapes and frequency for different modes are being studied under wind load. The analysis considered the dead loads of the structure principally the self-weight of the truss, sign, and walkways, and the wind load. Finite element analysis are conducted to evaluate the modal stresses in the truss and compared to the total stresses. The first three mode shapes in the wind load direction and the gravity load direction are modeled. The modal participating mass ratios of the sign structure for different mode shapes are also calculated. Results show that in chord members with 24 inch length, 50 percent and in chord members with 48 inch length, almost all the stresses (bending + axial) are modal stresses. In interior diagonal members 40 percent, in horizontal diagonal members 75 percent and in column part almost 75 percent of stresses (bending + axial) are modal stresses. The purpose of the study is a modal and static analysis in critical members of a cantilever sign structure under wind loading using finite element method.