The Unstressed Pre-camber Setting Method for Steel Truss Bridge

Abstract

This paper focuses on the method of setting pre-camber for steel truss girder bridge with the known pre-camber curve. The relative elevation between two adjacent joints is taken as the input variable to deduce the mathematical expressions of the length variation of each member based on the mechanical equilibrium equation of structure formed in stages. Considering the characteristics of pre-camber setting of through steel truss girder bridge, the length variation formula of each member is further developed here in three cases: (1) changing the length of upper chord member bar only,(2) changing both the length of upper chord and diagonal wed member bar, and (3) changing the length of upper chords, diagonal wed and vertical member bar simultaneously. An example study is carried out to illustrate the application of the method. The analysis results show that the unstressed pre-camber setting method is an absolutely geometrical method, which will not generate stress in members and supports during the pre-camber setting. This method, of which the concept is clear and reliable, deserves being developed to be used in the other types of bridges.