Field Testing and Load Rating Railroad Bridges

Many railroad bridges are facing increased service loads due to heavier locomotives and rolling stock, and a live load test can help determine if safe stress levels are being exceeded. BDI uses specially-designed structural testing equipment and corresponding analysis software that helps develop accurate ratings for the Cooper design loads. We can also monitor eyebar members during heat-shortening operations, measure various track and rail forces, and install long-term monitoring systems to help track changes over weeks, months, or years.

Accurate Ratings for Cooper E Loads

Many older and unique rail structures were designed for significantly different loads than they are currently experiencing. In order to quantify their actual behavior, we instrument the superstructure with our Wireless Structural Testing System (STS-WiFi) and continuously record data as a locomotive crosses the structure at crawl speed. Typically, a field test of up to 64 sensors can be completed in one day! Next, a relatively simple finite element model is developed and compared to the collected data. This model is then modified until its response matches that of the bridge, which in turn allows accurate rating values to be developed. Often, ratings are significantly increased, although there can be cases where heavier loads may need to be restricted.

BDI can help evaluate live load responses such as guiderail forces around curves, out-of-plane bending forces in girders and axial members, responses from eyebar members before and after heat straightening, in-situ residual stresses and various deflections. Since our testing equipment is so flexible and simple to use, it can be adapted to all types of live load scenarios. Our overall approach is to find the simplest, most cost-effective way to perform evaluations so that the owner can determine appropriate retrofit schemes if required. Since we don’t perform design or inspection services, we often complement the capabilities of design firms.