S. Harichandran, Ph.D., P.E., F.ASCE
2006 - December 2009
In bridge design practice, little attention has been paid to the secondary components in steel girder bridges and their effect on overall system behavior. However, if these components are not treated cautiously, the bridge service life may be significantly influenced and even catastrophic failure may occur. A large number of steel girder highway bridges have suffered from this unaccounted behavior, exhibiting, among other problems, the locking of pin-hanger hinge details, fatigue cracks on girder web at diaphragm-to-girder connections, and substructure cracking due to the thermal movement restraint as a result of transversely restraint or unintended fixity of bearing supports. The behavior of three secondary components was covered in this study. The selected components were: ( 1) pin-hanger details, (2) diaphragm-to-girder connections, and (3) bearing restraints. The objective of this research work is to investigate the behavior of these secondary components and their influence the overall behavior and service life performance of steel girder bridges and to assess repair approaches that might reduce maintenance and extend their service life. The specific tasks included: a) performing global and local structural analysis to evaluate the behavior of secondary structural elements and their interaction with the complete bridge system; b) assessing the effectiveness of current and proposed solution schemes through similar analyses; and c) providing recommendations for the retrofit or modification of existing structures and the design of new steel girder bridge systems.
Figure 1. Pin-Hanger Connection Detail
Figure 2. Diaphragm-to-Girder Connection Detail
Analytical studies to evaluate the behavior of the specified bridge secondary components were conducted. A global finite element model for an existing bridge was generated for assessing stress demands of pin-hanger details and refined local finite element model was developed to evaluate service and fatigue life of the pin-hanger component. For diaphragm-to-girder connections, two simple analytical models were developed to evaluate the maximum out-of-plane stresses at the small gap of the girder web. The models were validated using 3D finite element models. Fatigue stresses were evaluated and different diaphragm patterns and rehabilitation measures were assessed using the validated approach. In order to evaluate the effect of bearings on bridge system performance, 3D finite element models of a set of hypothetical simple span bridges were generated. Different values of shear modulus of the elastomeric bearing pads were considered and the effect of skew angles were considered.
Figure 3. Stress Along Net Section of Hanger Plate
Figure 4. Effect of Bearing Shear Stiffness on Maximum Live Load Deflection
The analysis results have provided considerable insight on the effect of secondary components on the serviceability of steel girder bridges. The fatigue category E for pin-hanger details was found to be adequate for pin-hanger details. Diaphragm patterns were shown to influence the fatigue stress and the overall bridge behavior, and the shear stiffness of bearing elastomeric pads was found to have a significant influence on bridge performance.
The research evaluated of the influence of secondary bridge components on the behavior and serviceability of steel girder bridges. The study evaluated the efficiency of solution schemes currently followed by the Michigan Department of Transportation to solve problems associated with the studied connection details. The study provided answers to serviceability issues and concerns currently being faced in MDOT’s steel girder bridge inventory. Design modifications and/or retrofit recommendations are being developed accordingly.
- Elewa, M.A., "Influence of Secondary Components on the Serviceability of Steel Girder Highway Bridges", Ph.D. Dissertation, Michigan State University, East Lansing, MI, in progress.