Roebling Suspension Bridge. I: Finite-Element Model and Free Vibration Response

This first in a 2-part series on the John A. Roebling suspension bridge (1867) over the Ohio River is an analytical investigation, whereas Part II focuses on the experimental investigation of the bridge. The primary objectives of the investigation are to assess the bridge's load-carrying capacity and compare this capacity with current safety standards. Dynamics-based evaluation is used, requiring the combining of finite-element (FE) bridge analysis and field testing. A 3D FE model is developed to represent the bridge and to establish its deformed equilibrium configuration due to dead loading. Starting from the deformed configuration, a modal analysis is performed to provide the frequencies and mode shapes. Transverse vibration modes dominate the low-frequency response. It is demonstrated that cable stress stiffening plays an important role in both the static and dynamic responses of the bridge. Inclusion of large deflection behavior is shown to have a limited effect on the member forces and bridge deflections. Parametric studies are performed using the developed FE model. The aim of the investigation is to provide structural information that will assist in the preservation of the historic John A. Roebling suspension bridge, though the methodology proposed could be applied to a wide range of cable-supported bridges.