An analytical algorithm for the pylon saddle pushing stage and distance during the suspension bridge construction

Abstract

During the construction of suspension bridges, the stress state of the pylon (tower) is improved by pushing the pylon saddle by an appropriate distance at the proper time. An analytical algorithm for the assessment of the required timing and displacements for the pylon saddle pushing at particular construction stages is proposed and verified in this study. The timing calculation is based on the assessment of current hanger tensile forces at each construction stage and the pylon stress state, while the pushing distance/displacement is derived from the conditions of elevation difference closure and the conservation of unstrained length of the main cable segments. This algorithm was successfully applied during the construction of a particular suspension bridge in China with a main span of 730 m. The results obtained strongly indicate that the bending moment in the pylon bottom is contributed by both horizontal and vertical forces of the main cable. The horizontal constituent is dominant and its share gradually increases in the bridge construction process. In a suspension bridge with side spans of various lengths, the stresses in the pylon bottom on the side with a larger side span is more likely to exceed the limit. Therefore, the respective strength criterion controls the pylon saddle-pushing schedule. The proposed analytical algorithm is quite straightforward and is recommended for wider application.

Improved algorithm for determining cable saddle pre-offsets considering the coupling effect of tower and splay saddles

“…The calculation of the cable saddle preoffsets requires solving several coupled non-linear equations composed of Eqs. (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and reaching up to 19. The simultaneous equations can then be worked out by the Newton-Raphson method.…”

“…In Ref. 18 , the cable configuration in the unloaded state was calculated based on the principle that in the basic equation of the main cable alignment, the unstrained length of any cable segment remained constant during the structural construction and after its completion. The tower saddle’s pre-offsets were then solved.…”

“…Although Refs. 17 , 18 derived the nonlinear equations of the main cable saddle offsets, these algorithms aimed to solve the tower saddle pre-offsets without considering the joint action between the splay saddle and tower saddle offsets.…”