But what about highway and transit bridges in the state, that number in the thousands? Where do inspectors even start? The state has 6,820 road bridges and NJ Transit has 691 bridges of varying types.
State Department of Transportation inspectors went to the epicenter in Hunterdon County and worked outward, said Steve Schapiro, a New Jersey Department of Transportation spokesperson.
The DOT advised other transportation agencies and local bridge owners to inspect their bridges and to inform the agency of the results, Schapiro said. The state also updated the Federal Highway Administration about inspections and what they found, he said.
“These inspections found no observable damage to NJDOT bridges and there were no damage reports from other agencies or local bridge owners,” Schapiro said. “Immediately following the earthquake, NJDOT sent in-house inspection teams to the field to inspect NJDOT’s bridges near the earthquake epicenter.
“The teams were assigned to inspect all the bridges along interstate and state highways working systematically outward from the epicenter.”
While DOT Operations staff checked bridges, the Movable Bridge Engineering Group inspected and tested NJDOT’s draw and lift bridges to ensure they were operating properly, he said.
NJ Transit had a 30-minute systemwide delay while rail and light rail bridges were checked on April 5.
Making the call on which bridges to check first
“It’s up to the authority, Department of Transportation or NJ Transit how they prioritize bridge inspections,” said Matthew J. Bandelt, a professional engineer and associate dean for Research and Graduate Studies at the New Jersey Institute of Technology.
Typically, state transportation departments have a system in place where the most heavily-traveled bridges and the oldest and structurally deficient bridges would be checked first, Bandelt said.
New Jersey has 442 structurally deficient bridges. That doesn’t mean a bridge is in danger of collapsing, but that it has deteriorated over time and can’t carry the same load or weight it was designed to when new.
“They go from the most import and highest risk … down to the lowest risk bridges,” he said.
What inspectors looked for
Engineering experts and the DOT said post-earthquake inspections look at damage to bridge components that take lateral or side loads, similar to what wind storms exert.
DOT inspectors looked at bridge columns, rocker bearings that support bridge structures, anchor bolts, bridge seats, curved girders, long bridge spans and other components that could be affected by ground movement, Schapiro said.
Typically, inspectors would look for signs of damage such as cracking in concrete bridge piers and abutments and distortion or bending in steel and damage to the bearings between support structural steel and bridge piers, Bandelt said.
Those inspections can go beyond what inspectors can see and require more technical tests and equipment, said Mohammad Ilbeigi, an assistant professor at Stevens Institute of Technology in Hoboken .
“They may use different methods, including visual inspection, acoustic and thermal devices, and ground-penetrating radars,” he said.
N.J. bridges are designed to handle earthquake-like forces
While the East Coast isn’t as prone to the same frequency and force of earthquakes on the West Coast, there are two types bridge design standards in place that provide some earthquake protection here.
One is that bridges and buildings in New Jersey are already designed to withstand lateral, side to side forces exerted by windstorms, Bandelt said.
“They’re designed for wind forces – they’re similar to earthquakes because of a lateral push on the side of a building or bridge,” he said. “Winds tend to govern (design) in New Jersey.”
All new bridges built in New Jersey since at least 1991 have included seismic design provisions, and new DOT bridges follow American Association of State Highway and Transportation Officials load and resistance standards for bridges, Schapiro said.
Those specifications have been updated at various points as research provides additional information, explained Patricia Bush , program manager for Bridges and Design at the American Association of State Highway and Transportation Officials.
The April 5 quake will help in the design of future bridges
Seismic design standard updates also are influenced by recent earthquakes, engineering experts said.
The April 5 earthquake will serve as a data point when design standards are updated, which happens every five years, Bandelt said.
“A bridge built in a state with a high probability of a strong earthquake would look different that a bridge built in a state with a low probability of a small earthquake, even though both may be designed to the same specifications,” Bush said.
The Federal Highway Administration requires that all new bridges on the National Highway System be designed to the American Association of State Highway and Transportation Officials specifications in place at the time of the design, Bush said.
Standards for bridge rehabilitation projects depend on how much of the bridge is being rebuilt, the type of rehab work being done and whether they have to be updated to meet the new specifications, she said.
What drivers need to know
Should drivers be concerned about structurally deficient bridges withstanding earthquakes such as New Jersey’s 4.8 magnitude event?
“Not if routine inspections, guided by the Federal Highway Administration are performed carefully and deteriorated bridges are maintained,” Ilbeigi said.
The stresses and loads put on a bridges ability to carry weight are different than components that resist lateral forces in an earthquake, Bandelt said.
“They still remain resilient against potential earthquakes and other extreme events considered in their design” he said. “If a bridge deteriorates significantly and transportation agencies are unable to maintain it, they will close it before it becomes unsafe.”
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Larry Higgs may be reached at lhiggs@njadvancemedia.com. Follow him on X @CommutingLarry
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