# Railway Overhead Wiring Structures in Australia: Review and Structural Assessment
## 3 OWS in Australia
### Inspections and Assessments of Existing OWS  
OWS are exposed structures and environmental effects accelerate their deterioration over time. A reliable train network requires proper inspections and assessment of these structures. The AS4292 Railway safety management [55] provides the overarching requirements and Part 2 of the standard [56] covers requirements on civil infrastructures. However, a standardized method of inspections or assessment criteria is unavailable, and the procedures are commonly an \"in-house\" practice, i.e., train companies have their own internal procedures to safeguard reliability of their assets. Detail procedures of inspection and assessment differ from company to company, but they can be divided into planned maintenance which is carried out on a regular time interval, and condition-based maintenance which is carried out only when necessary. Regardless of jurisdictions, maintenance work often follows similar considerations:  
1. A historical archive is maintained, and information includes structural drawings, design loads, year of construction, failure histories, previous inspection reports and maintenance records, etc.
2. A planned inspection schedule, e.g., every two years.
3. Several \"levels of inspections\" are prescribed. An example is shown in Table 3. A low-level inspection involves visual inspections without disruption to train service. Inspectors typically look for signs of deterioration such as corrosion, plumb deviation or deflection, loosening of bolts, cracks, erosion of soil around foundation, conditions of electrical fittings, nearby vegetations, etc. A score will be assigned to different components and recorded. If remedies are deemed required, the defects are further categorized into different priorities for scheduled maintenance. A significant defect will flag an urgent repair which may require suspension of train service. A poor result from a low-level inspection will trigger a high level of inspection.
4. A higher level of inspection requires engineering assessments by experienced engineers. The use of destructive or non-destructive testing to gather quantitative data  
Figure 7: Construction of a new OWS next to a decommissioned one.  
is required. Assessment may include estimation of thickness loss due to corrosion, measurement of paint thickness, etc.
* Once determined necessary, remedial works on existing OWS are determined by engineers. Remedial works such as application of surface coatings, replacements of foundations, partial replacement of structural members, or complete replacement of OWS structure.  
Figure 8a shows an example of retrofitting of an OWS by replacement of foundation. Extensive spalling of concrete was observed in the original foundation and new reinforced concrete is cast around an existing laced column of a signal gantry. Figure 8b shows partial replacement of corroded steel members in a signal gantry with new galvanized sections. The heavily corroded portion is patched up with a steel plate.  
Although steel OWS are simple structures and their assessments are less complex than the assessment of steel bridges, due to the amount in a rail network a more scientific approach to assessment may deem more cost-effective. The authors have proposed a time-dependent structural reliability approach to assess OWS. Readers who are interested in this approach may refer to [57].