After the storm: load cells in bridge safety testing

Over the late summer of 2017, TV bulletins were filled with images of massive storms swirling across the Caribbean Sea – and the devastating results of their destructive landfalls. 

While some populations had to hunker down and sit it out, others were able to leave. Hurricane Irma forced the residents of the Florida Keys to evacuate their homes, with the result that almost the entire population drove across the chain of road bridges that link the Keys to the relative safety of the Florida mainland. 

Homeward bound

Once the storm had passed,people wanted to return to their homes and to survey the damage. There were grave concerns about the safety of those same road bridges, given the potential for damage by the combination of strong winds and high seas. Luckily all 42 bridges were declared safe, but the inspections took time and considerable effort.

Atorod Azizinamini, director of the Accelerated Bridge Construction-University Transportation Center (ABC-UTC) at Florida International University (FIU) has proposed a more cost-effective way to assess a bridge’s safety by using load cells. 

 

Bridge signature measurement

When a bridge is constructed, it has a signature, defined by the structure’s stiffness. When a bridge sustains damage, this signature changes, and can be measured using a standard impulse-response test (IR). This involves generating stress waves using a small hammer with a load cell at the end to measure the mobility and stiffness of sections of the bridge as a baseline figure. 

For ease of measurement, the bridge is divided into a grid, and measurements taken at each grid point to give a unique signature for that grid square. If subsequent testing after a hurricane or other event show any changes in any given grid, these can be identified and assessed more quickly. 

 

Prior and post testing using load cells

As Azizinamini explains in an article for the FIU website:

“The key is to test bridges prior to the storm, not just afterwards, in order to identify changes, which translates to damage. If there’s no change in behavior of the characteristics of the bridge, nothing happened, but if there is, it will give us a clue on what to do next to fix it.”

Load cells also played a vital part of NASA’s Visible Infrared Imager Radiometer Suite (VIIRS), used to monitor weather and environment changes from space. VIIRS produces detailed aerial images, as well as providing early warning to communities of approaching storms, hurricanes and tsunamis. The load cells in question monitored the force on the cryo-radiator, and were specially constructed to operate in space at temperatures of -300F.

 

Load cells for safety testing

If you have a specific requirement for safety testing structures or equipment, give us a call. We can design and manufacture load cells specific to your requirements, here in the UK.