LAUSR

Abstract The unpredictable out-of-plane buckling of the upper chords is an important problem of half-through truss bridges widely used in many places. Many specifications adopt the theory of elastic stability as a means to obtain the critical buckling force of the upper chord. In these specifications, the axial force in the upper chord is simplified to parabolic or equivalent force distribution in the span. However, the calculation results of these simplified models can not always satisfy calculation precision in practical projects. To obtain a critical buckling load of the upper chord, using energy method, a mechanical model with trapezoidal axial force distribution is put forward to establish an elastic theoretical model with higher precision. Three bridges with different span are analyzed and theoretical results are in good agreement with buckling analysis by use of finite element method. The trapezoidal axial force distribution model has higher precision than equivalent and parabolic axial force distribution models used in the current specifications. Meanwhile, the effective length coefficient of the upper chord is derived by use of Euler's Formula, and a simplified table based on TAFDM is presented to obtain aluminum half-wave number and the effective length coefficient of the upper chord.