Aging infrastructure poses a question that is becoming increasingly important for researchers and infrastructure managers worldwide: How can we reliably assess structures that have been in service for decades when drawings, maintenance records, loading histories, and information about previous repairs are incomplete?
Our recent study, “Condition Assessment of Gerga Steel Railway Truss Bridge,” published in the Journal of Structural Design and Construction Practice by the American Society of Civil Engineers (ASCE), explores this question through the assessment of an operating steel railway bridge in Egypt.
The work formed part of a broader inspection campaign covering more than 75 railway bridges, many of them old and inadequately documented. Rather than treating the Gerga Bridge simply as an individual case, the study was intended to provide a practical framework that could inform the assessment of other aging steel bridges facing similar challenges.
Full-Scale Research Case
The Gerga Bridge provides an unusual opportunity for comparative investigation. It consists of two adjacent bridge systems serving opposite railway directions. One was constructed in 1930, while the other was constructed in 1986. Although they have broadly similar structural configurations, they differ considerably in materials, fabrication techniques, connection details, and bearing systems.
This meant that two generations of steel bridge technology could effectively be studied at the same location and under similar operational and environmental conditions.
Perhaps the most interesting finding was also somewhat counterintuitive: fatigue cracking was observed in the newer bridge but not in the considerably older bridge.
For researchers studying existing structures, this is an important reminder that chronological age alone is not necessarily a reliable indicator of structural condition. Detailing, load paths, fabrication practices, connection configuration, maintenance history, and accumulated loading can be equally—or sometimes more—important.
Assessment Cannot Depend on a Single Source of Evidence
One of the main lessons from the project was the importance of combining several sources of evidence.
The assessment began with document review and detailed visual inspection. A unified inspection procedure was adopted to reduce the subjectivity inherent in visual assessment. Structural dimensions were checked against available drawings, steel members were examined for corrosion, cracking and deformation, concrete elements were assessed for deterioration, and bearings, rivets, bolts, coatings, and connections were systematically examined. Visual evidence represented only the first layer of the investigation.
The research therefore integrated structural analysis, fatigue assessment, static load testing, dynamic testing, modal testing, material testing, and three-dimensional finite-element modelling. Experimental results were subsequently used to validate the analytical models rather than relying on numerical simulation alone.
When Field Testing Meets Numerical Modelling
Full-scale testing provided an opportunity to observe the actual response of the bridge rather than depending exclusively on assumptions. In the study, static and dynamic tests were performed and the resulting experimental data were used to calibrate and verify three-dimensional finite-element models of the old and new bridge systems. The agreement between measured and predicted responses was considered satisfactory, providing confidence that the models could subsequently be used to investigate structural performance beyond the conditions directly measured in the field.
A sophisticated model is most valuable when it is verified against a real structure
Assessment Should Ultimately Lead to Action
Condition assessment has limited value if it ends with identifying defects. The study therefore progressed from diagnosis to intervention. Repair strategies were proposed based on the type and severity of deterioration while also considering economic feasibility.
The interaction between engineering evidence, risk, constructability, economics, and asset-management priorities is itself an important area for further research.
For details refer to:
Hassan, M. M., Abdelnaby, A. E., & Abbas, H. H. (2026). Condition Assessment of Gerga Steel Railway Truss Bridge. Journal of Structural Design and Construction Practice, ASCE. DOI: 10.1061/JSDCCC.SCENG-2052.