Miami bridge collapse: What is accelerated bridge construction?

The University City Bridge, the pedestrian bridge on the campus of Florida International University that collapsed on Thursday, apparently leaving several dead, was built under a process called Accelerated Bridge Construction.

The bridge, a 950-ton structure, slammed down onto 8th Street, the roadway known as the Tamiami Trail, landing on at least eight vehicles in addition to hitting some pedestrians who were crossing the road at the time.

The bridge was put in place about a week ago but had not been opened to pedestrian traffic. The bridge was designed by FIGG Bridge Group, a Boston firm, and built using the ABC method.

What is Accelerated Bridge Construction and how does it work? Here’s a look at ABC:

• ABC projects are constructed offsite and moved to the site to be put together and anchored in place.
• From the Federal Highway Administration: "The most common form of ABC is the use of prefabricated bridge elements. These elements can be fabricated in a controlled environment off-site and assembled in place at the bridge site. This construction method can best be described as building blocks. The prefabricated elements are connected at the site to form a complete bridge. Prefabrication of beams is not a new concept. Virtually all bridges are currently built with prefabricated beams and girders."
• According to a website post from FIU on a page that has since been taken down, but was cached by Google, ABC was used to build the bridge to help minimize the disruption to traffic on the eight-lane roadway it went over. "To keep the inevitable disruption of traffic associated with bridge construction to a minimum, the 174-foot portion of the bridge was built adjacent to Southwest 8th Street using a method called Accelerated Bridge Construction (ABC) and was driven into its perpendicular position across the road by a rig in only six hours on Saturday, March 10."

• From the FIU post: "Civil engineering doctoral student Dewan Hossain said: "I would say this is magic. In five hours using that ABC technology and sensors, the bridge is already there. In the classroom, we learn about the design, the construction, the safety – that's a big issue – and here we're seeing it actually happening. Here we are establishing a real, practical application of what we learn in the classroom. I would encourage more students to come view these types of projects to enhance what they learn."
• The FHA says ABC "uses innovative planning, design, materials, and construction methods in a safe and cost-effective manner to reduce the onsite construction time that occurs when building new bridges or replacing and rehabilitating existing bridges."
• The FHA also said about ABC: "A common reason to use ABC is to reduce traffic impacts … because the safety of the traveling public and the flow of the transportation network are directly impacted by onsite construction-related activities. However, other common and equally viable reasons to use ABC deal with site constructability issues. Oftentimes long detours, costly use of a temporary structure, remote site locations, and limited construction periods present opportunities where the use of ABC methods can provide more practical and economical solutions to those offered if conventional construction methods were used."
• FIU hosts the Center for Accelerated Bridge Construction, a national center for education about and promotion of ABC.
• The University City Bridge, built by the Munilla Construction Management, was designed to survive a Category 5 hurricane.