Life Cycle Management of Steel Bridges Based on NDE and Failure Analysis

The finite element method is used to investigate failure mechanisms in pin-hanger connection in aging highway bridges. Bridge pins and hangers are typically considered as critical elements whose failure may result in partial or entire collapse of the structure. The primary function of a pin-hanger connection is to allow for longitudinal thermal expansion and thermal contraction in the bridge super-structure due to temperature changes (daily or seasonal). The induced movements, due to thermal effects, have considerable impact on bridge design and performance. Thus, in addition to the applied mechanical loads (dead load and traffic), the thermal load due to temperature changes is also included. A key goal was also to relate original design calculations (before the bridge was built) to the current analysis which accounts for the entire bridge structure under combined loads and extreme environmental conditions. Many bridges in use today have deteriorated due to aging, misuse, or lack of proper maintenance. After years of exposure to atmospheric environments (deicing salts and load variations), corrosion and wear tends to produce at least a partially fixed (or locked up) condition. Pack-rust (or corrosion buildup) can have two detrimental effects on the pin:

  • First, the cross-section of the pin can “decrease” because of corrosive section loss. The corrosion can produce pitting that may act as crack initiation sites.

  • Second, pack-rust can effectively “lock” the pin within the connection, so that no rotation is permitted. This may produce a likely location for the development and propagation of cracks.

Furthermore, bridge structure is nonlinear especially when the pin is in the locked condition and an elastic-plastic analysis is required to model the bridge behavior when the pin is locked. One of the main focuses in this study is on the determination of the three-dimensional (3D) crack growth in the pin, since the lifetime of the entire structure is dependent on the behavior of cracks. Due to the accessibility of 3D finite element programs and the comparatively low cost of computing time, it is state of the art to perform 3D analyses of complex engineering problems. The finite element program ABAQUS has been used throughout the investigation, which essentially includes:

  • stress analysis

  • thermal effects

  • elastic-plastic analysis

  • determination of the mixed-mode stress intensity factors (KI , KII , and KIII)

  • fatigue crack growth simulation

Furthermore, since analytical solutions are not available in many cases, especially for this 3D problem (with complex geometry and loading conditions), a series of validation tests were performed on bridge components.