A numerical study on the structural integrity of self-anchored cable-stayed suspension bridges

Paolo Lonetti,Arturo Pascuzzo

doi:10.3221/igf-esis.38.46

Abstract

A generalized numerical model for predicting the structural integrity of self-anchored cable-stayed suspension bridges considering both geometric and material nonlinearities is proposed. The bridge is modeled by means of a 3D finite element approach based on a refined displacement-type finite element approximation, in which geometrical nonlinearities are assumed in all components of the structure. Moreover, nonlinearities produced by inelastic material and second order effects in the displacements are considered for girder and pylon elements, which combine gradual yielding theory with CRC tangent modulus concept. In addition, for the elements of the suspension system, i.e. stays, hangers and main cable, a finite plasticity theory is adopted to fully evaluate both geometric and material nonlinearities. In this framework, the influence of geometric and material nonlinearities on the collapse bridge behavior is investigated, by means of a comparative study, which identifies the effects produced on the ultimate bridge behavior of several sources of bridge nonlinearities involved in the bridge components. Results are developed with the purpose to evaluate numerically the influence of the material and geometric characteristics of self-anchored cable-stayed suspension bridges with respect also to conventional bridge based on cablestayed or suspension schemes.

Highlights

Cable supported bridges are frequently employed to overcome long spans, because of their aesthetic, structural and economic properties, if compared to conventional and standard bridge schemes [1, 2]
As a matter of fact, several studies, based on formulations, which involve both geometric and material nonlinearities, have shown that material inelastic behavior of structural members highly affects the nonlinear static behavior of the bridge structure [8,9,10,11]. Both geometric and material nonlinearities were considered in the modified Bifurcation Point Instability (BPI) approach proposed by Yoo and Choi [12, 13] in which the effect of material inelasticity in the structural members was reproduced by means of classical tangent modulus theory and column–strength curves provided by current design codes
It is worth noting that the above referred studies, involved in the framework of cable supported bridges, take in account mainly material nonlinearities in both girder and pylons, without introducing any source of nonlinearities in the constitutive elements of the cable system. Such contributions are considered only in rare cases and mainly in the framework of cable-stayed bridges [16, 24]. Such effects should be taken into account especially in those bridge configurations mostly dominated by the cable system configurations, such as of pure suspension or combined cable-stayed suspension, in which, typically, the cable system plays an important role in the cable force distribution and in the ultimate bridge behavior

Summary

INTRODUCTION

Cable supported bridges are frequently employed to overcome long spans, because of their aesthetic, structural and economic properties, if compared to conventional and standard bridge schemes [1, 2]. Since girder and pylons are mainly subjected to axial forces and bending moments, the nonlinear material behavior can be taken into account by a gradual yielding theory based on the combination of the Column Research Council (CRC) tangent modulus concept and a plastic hinge model [33] The former is suitable to take into account for gradual yielding along the length of an axially loaded element between plastic hinges, whereas the latter is used to represent the partial plasticization effect associated to bending mechanisms. It is worth noting that the structural response for each load increment is obtained by means of an iterative and incremental procedure, which considers both geometric and material nonlinearities arising from bridge constituents For this reason, the finite element model of the structure is coupled with several equation-based models, each of them related to definition of the inelastic properties of cables, pylons and girder. Current stiffness matrix as well as load vector are updated on the basis of the values arising from the previous converged step

RESULTS

Findings

CONCLUSIONS