By Bilal Hussain
 
The bridge over the two lines of railroad tracks is very complicated by more than 70° degrees of skew between the railroad lines and the highway. The bridges allow uninterrupted flow of traffic over the highway. There is on average daily traffic of more than 10,000 vehicles over different bridges depending upon route and it ensures smoother and faster travel by eliminating potential delays and safety concerns associated with rail-road crossing.

After making the bridge, the possibilities of accidents between more than 10000 vehicles and the trains will be removed and thus improving the safety concerns of the associated population. The highways are vital route for commercial traffic with more than 1000 trucks on average or even more depending upon location, daily transport goods across different bridges and the bridges ensure the efficient and timely delivery of the goods across the United States. They also play important role in supply chain management.

The bridges are also important to the freight trains prospective that carries goods across the country. The bridge ensures the uninterrupted and efficient movement of the freight trains across different parts of United States.

For the longevity of the bridge, the bridge needs to be inspected regularly after a certain period. There are many structural health monitoring techniques available for bridge inspection. One of the most widely used methods is acoustic based Non-Destructive testing.

Acoustic emission is a type of structural health monitoring used to detect damage in civil infrastructure and mechanical parts.

Acoustic emission is a feature-based machine learning approach to detect damage in parts/structures, where different feature selection is very critical in damage detection.

One of the approaches used in feature selection is Pearson Correlation, this approach selects the features that have low correlation with each other. Alternatively, researchers/engineers have used single feature to avoid feature selection and subsequently machine learning.

The single feature used by most researchers/engineers is the peak amplitude of the waveform.
When cracks are detected through Non-Destructive testing, we need to know the cause of these cracks.
In the case of bridges, there are four possible causes of the damage. First the mechanical loads due to cars and trucks, second aerodynamic loads due to wind, and third are thermal fatigue loads due to extreme weather conditions (thermal expansion during summer and thermal contraction during winter when temperature goes below -20°C in cold areas).

The fourth is the combination of these three loads.

I am currently in the process of analysing the bridge structure due to thermal and combined loading. After visual inspection of the bridge cracks, the most probable cause of the damage is contributed to thermal fatigue loads in extremely cold areas. The bridge is made of steel and concrete materials. The thermal expansion of steel is more than concrete, so when designing for composite (Steel and concrete) structures, we must take into consideration the differential thermal expansion and contraction of two materials.

The bearings and expansion joints can accommodate the movements caused by thermal stresses. The fixed and movable supports can also take care of these movements without inducing excessive stresses.
So, the purpose of this project is that engineers should consider variations in thermal loads in combination with live (cars and trucks), dead and wind loads without compromising structural integrity of the bridge over the life span.

Bilal Hussain, a researcher, wrote from Ohio University.