Structural Checkup: The Hows and Whys of Bridge Inspection
Inside 7 tags along with a seasoned bridge inspector and comes to appreciate sturdy shoes, metal pokers, and the tonal qualities of 80-year-old concrete.
Whenever there’s a bridge collapse that makes the news – like the one on the Interstate 5 Skagit River in Washington state in May – it doesn’t take long for the phones in Caltrans District 7’s Public Affairs and Media Relations office to start ringing. Frequently the person calling is a reporter wanting to talk about bridges. They want to know if motorists should be worried. They want to know if our bridges are safe. They want to know if it could it happen here.
We’ll get to that in a minute, but let’s get one critical point out of the way first: no Caltrans bridge has ever collapsed due to neglect. Which isn’t to say that bridges don’t collapse. They do. They’re consumed by floods, brought down by fire, leveled by earthquakes, and hit by trucks – as was the case in Washington. But in California, bridges do NOT collapse because they’re not taken care of. In large part, that flawless record is made possible by a special unit created by the department in 1927 to ensure the safety and reliability of the state’s bridge inventory.
Two hundred specially trained engineers, technicians and support staff in Caltrans Structure Maintenance & Investigations (SM&I) are responsible for inspections on over 12,000 state highway bridges and approximately 12,200 bridges owned by local government agencies. Every bridge undergoes regularly scheduled routine inspections performed by licensed engineers with an expertise in bridges. The majority of these inspections are conducted every two years. Steel bridges and structures spanning waterways get additional attention, including inspections of steel elements and underwater inspections of submerged bridge elements. All inspections have one purpose: to ensure the safety and reliability of every bridge open to traffic.
If, during the course of an inspection, inspectors find any issue that could compromise the bridge’s structural integrity, they have the power to do whatever it takes to protect public safety, including closing the bridge or posting the structure for weight limitations until repairs are made.
So what exactly does a bridge inspection involve? Inside 7 decided to tag along on one to find out. On a sunny day in June, we went out with Senior Bridge Engineer Bing Wu of SM&I’s South Office (Los Angeles) and SM&I Chief of Bridge Maintenance Information Jim Drago (Sacramento), who was serving as Bing’s safety second. Bing has been with Caltrans for 24 years, 10 of that doing bridge inspections.
The 40 inspectors and support staff working in SM&I’s South Office are responsible for the investigation, evaluation, work recommendations and documentation for approximately 11,000 city, county, state, and federal bridges in Imperial, Inyo, part of Kern, Los Angeles, Mono, Orange, Riverside, San Bernardino, San Diego and Ventura counties.
On the day we tagged along, Bing and Jim performed a routine biannual inspection, which is a lot like the general physical exam you get from your doctor. You go in not because there’s something wrong, but because you need to get your vitals checked and make sure you don’t have a condition that needs intervention. That’s the basic idea behind a biannual bridge inspection, too – to give the structure a thorough exam and flag anything that might need additional investigation, repair or replacement.
The bridge undergoing inspection on our trip was number 53-0062, the Manhattan Beach Undercrossing on the Pacific Coast Highway (PM 23.79 for those of you who think in postmiles). It’s a concrete I-girder bridge, three lanes in each direction with a turn lane in the middle, built in 1930 and widened in 1972. There are thousands of concrete bridges like this one in California. They’re our structural workhorses, bridges so common we barely notice them and yet vital components of our transportation infrastructure. That, in part, is what makes them so great.
“It’s really kind of beautiful,” said Jim as we viewed the bridge from a nearby parking lot. “The design doesn’t overwhelm the surrounding area. There’s a pathway to the ocean underneath and native vegetation. Bridges like this one are good servants to the public. This one is over 80 years-old and it continues to carry 50,000 vehicles a day safely, reliably and efficiently because it has been well cared for.”
California’s stellar bridge safety record has been built on thorough bridge inspections like this one. One look at Bing and it became clear just how exacting this work is. His safety vest was chock full of inspection supplies: notebook, pens, flashlight, spray paint, hammer, camera, laser ruler, gloves, and a metal poker that appeared to be MacGyvered from a ski pole.
“We see all kinds of things out here, unexpected things waiting for us – wildlife, homeless people, nails, rattlesnakes. I use the pole to let the animals know we’re here before they get to us,” said Bing. Unfortunately, the poker did not impress the colony of surly bees that had evidently chosen this area to build their hive and buzzed around us, giving notice that this was their turf.
Make no mistake: bridge inspecting is not a job for the faint of heart – and not just because of the bees, critters, nails, exposure to live traffic and other hazards. This is physically taxing work: climbing steep slopes, crouching in enclosed areas, reaching high and bending low. You need quick reflexes and an excellent sense of balance. A long day of bridge inspecting will leave you tired, achy and in need of a shower. A bridge roughly the size of number 53-0062 takes about an hour and a half to inspect. An experienced inspector can do about eight of these inspections in a day. A big bridge (think Gerald Desmond in the Port of Long Beach) can take several weeks.
Bing began his inspection of 53-0062 by reviewing the pre-inspection report, which provides details about the bridge and previous inspections, issues that were identified in the past and repairs that were made. This is important because if, for example, a two-foot long crack was noted in a previous inspection, Bing will document any growth in the crack. Based on his findings, he may recommend that the crack continue to be monitored or that District 7 Maintenance staff repair the crack.
Bing began his inspection by taking a sweeping general overview of the structure from the ground below the bridge. He looked for any signs that might indicate potential problems that would prompt further investigation when he performs his detailed inspection of the bridge deck, superstructure and substructure later. We then climbed a steep slope to the deck.
Bing scanned the full length of the bridge rails to check that the alignment of the bridge remains true. He then examined the bridge rails for spalls. He gently tapped the rails with his hammer, looking for areas of loose concrete. He listened for a hollow sound that would denote delamination, separation of the concrete from the rebar. In some places the concrete fell away when he hit it. He circled these areas with spray paint so that repair crews can find them easily later.
Bing also noted an uneven sidewalk slab that could pose a trip hazard and measured cracks he spotted, including a large one – a couple feet long and a few inches wide – in the two-inch-thick asphalt concrete overlay that exposed the concrete deck beneath it. This wasn’t a safety hazard, but it would need to be repaired soon to smooth out the ride for motorists and prevent a pothole from forming. There were also transverse cracks in the asphalt concrete above the bent caps, which are common on bridges like these. Bing photographed the cracks and noted them in his report so the condition can be tracked in future inspections.
With the deck thoroughly inspected, we headed back down the slope to check out the superstructure and substructure. This involved more climbing and crouching under beams by the abutment, the metal poker getting a workout as a cobweb-clearing and dirt-removal tool. Bing hammered the concrete. He measured cracks. He shined his flashlight into dark corners looking for any signs of water intrusion permeating the concrete from the deck. He scanned the substructure looking for signs of settlement or erosion.
Hanging from one of the girders was a sheet of black plastic, about three feet by three feet, a makeshift doorway. Someone had made a home here, tucked away under 53-0062 in the heart of Manhattan Beach, invisible to everyone except spiders and bridge inspectors. There was a welcome mat outside. A flower pot with a petunia, recently watered. Bing was unfazed. This is a common occurrence in his line of work.
“This is a healthy bridge,” he said, closing his notebook when the inspection was complete. “Spalling, cracks, some corrosion – that’s not unusual. It doesn’t affect the integrity of the structure. If we see a pattern of cracks or cracks that are growing, that’s something we need to look into. We document our findings in the Bridge Inspection Report, figure out what’s causing the condition, and get it repaired.”
Caltrans spends about $450 million annually on bridge maintenance, preservation and inspection, most of which comes from the State Highway Operation and Protection Program (SHOPP). Small repairs, like the ones Bing and Jim noted today, will likely be handled by the District 7 Bridge Crew. Contractors are enlisted to perform more extensive repairs.
Many of California’s older bridges, like 53-0062, are in good shape but functionally obsolete, a term broadcasters love to repeat in scary-sounding teaser headlines. But the term tells us more about the age of a bridge than its structural integrity. Functionally obsolete simply means that the bridge was built using different standards than are used today. For example, 53-0062 has almost no shoulders and narrow lanes. Would we build a bridge like this today? No. Is it unsafe? No. It’s actually holding up really well.
Another term that doesn’t serve us well is structurally deficient. Like the label functionally obsolete, structurally deficient doesn’t mean a bridge is unsafe. Rather, it indicates that a bridge is in need of maintenance, such as filling minor cracks or repainting. It’s also used to determine eligibility for federal funding of bridge replacements and major rehabilitation. But telling viewers/readers/listeners that a bridge is functionally obsolete or structurally deficient is more provocative than saying it’s an older bridge with some minor maintenance issues that can be handled fairly easily and inexpensively.
“We do the best job, the most diligent job we can to inspect our bridge inventory, to identify the conditions of every bridge in the state, and when necessary, to perform repairs to ensure safety and reliability,” Jim said. “This is something we’ve been doing since 1927, and our record is solid. It’s one that we work hard at every day to keep intact.”