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Nonlinear Static Analysis of Continuous Multi-span Suspension Bridges
최동호,권순길,유훈 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.1
This paper performs the static analysis of multi-span suspension bridges using the deflection theory. Applying the deflection theory conventionally used in three-span suspension bridges to multi-span suspension bridges, the horizontal forces of the main cables due to live loads are obtained by converting the suspension system to the equivalent beam system and using the compatibility equation of cables for four spans. Iterative computations are used due to nonlinearity of the differential equations. The results, such as deflections and moments of girders and horizontal forces of the main cable, are compared with the finite element analysis for verification. The resultant values from two methods are almost the same. Finally, using the linearized deflection theory, parametric studies are performed by influence line analyses for parameters such as the side-to-center span ratio, the tower stiffness ratio and the sag to span ratio. From the parametric studies, alternatives to reduce displacements of girders in the center span and girder moments of all spans are investigated.
Tension Force Estimation of Extradosed Bridge Cables Oscillating Nonlinearly under Gravity Effects
최동호,박완순 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.3
Extradosed bridges have loose and sagged cables that are different from those used in cable-stayed bridges. The total tension force of an extradosed bridge cable estimated using the existing formulas is not accurate. Although the existing formulas are widely used in the field, they do not consider the exact deflection curve, features of nonlinear oscillation, and stretching force due to self-weight. In this study, a new method was developed to calculate the total tension force of the cable. In the new method, the total tension force of the cable includes the applied axial load and the stretching force due to self-weight. For the exact estimation of the applied axial load to the cable, the vibration of the cable was treated as a conservative nonlinear oscillation system, and a new formula was derived using the perturbation technique. The new formula was used to clearly explain the hardening effect due to the initial amplitude of the initial excitation, the presence of imaginary number of frequencies, the correlation with the stretching force due to self-weight, and the softening effect of the slenderness ratio on nonlinear natural frequency. For calculating the stretching force due to self-weight, the stretching of the cable for the static deformation was considered. A field test showed that it is necessary to add the stretching force due to self-weight to the estimated axial load for extradosed bridge cables and that the new method can be used to calculate the total tension force of loose and sagged cables.