Transit Steel Trapezoidal Box Girder

A few weeks ago I inspected a two span continuous steel trapezoidal box girder which carries the subway over Leveret Circle in Boston. The bridge consists of curved two box girders, a composite deck and reinforced concrete substructure. The viaduct was constructed as part of the Green Line Relocation Project from Haymarket Station to Science Park Station with an original design loading of Green Line Passenger Car.

Constructed in May 2005, The bridge spans 135 feet over gravel and 162.75 feet over Leveret Circle. The bridge has a maximum width of 30 feet out to out. 

The concrete composite deck has hairline cracks in the negative moment region.

A 45' lift truck was used to inspect the span over Leveret Circle and the span over gravel was inspected by ladder. Each girder's interior was accessed by hatches near ground level over the gravel.

When we tried to access the girders we had to cut the locks off with a grinder but one lock was already removed. When then heard and saw movement inside the girder. A homeless man had been living inside the girder. We notified our police details and they helped escort the tenant who left without incident. Inside the girders were filled with an accumulation of homeless peoples debris making for a difficult and unpleasant inspection.

Rules of the hole.....

Concrete Encased Steel Beams

A few weeks ago I did a routine inspection of a concrete encased steel beam bridge. The bridge is located in Tiverton RI. The five concrete encased beams span 35.1'. To access the underside of the bridge we used a small boat which halfway through the inspection sprung a leak. The remaining time was spent in waders, which happened to also have leaks. 

The beams exhibit spalling to the encasement along the undersides exposing the steel bottom flanges. The exposed steel bottom flanges have areas of section loss up to 44% of the original thickness. We were able to find the remaining thickness with a D-meter after spending some time cleaning the surface and making it smooth enough the get a reading.

The concrete deck has several spalls in each bay with exposed and severed rebar.

Just upstream from the bridge there is a spillway with a fish ladder. The damned off pond has large schools of fish and it was a crazy site since they were probably farmed fish and were not afraid of people.

Overhead Tunnel Inspection

The Tip O'Neill Tunnel was opened 10 years ago and carries the Central Artery below Boston's downtown area.  The overhead inspection consists of the exhaust plenums, roof slab, utilities and lighting.

The tunnel's ceiling is has fireproofing throughout the underside which makes it difficult to determine the condition. Areas of the ceiling fireproofing have been removed to access utilities and allow inspectors to view the roof slab. The exposed areas of the slab show localized hairline cracks.

The lighting along the top of the walls have been connected with metal clips which are prone to failing and now have six acetal zip ties. The majority of the metal clips are in place with six ties but a few of the lighting structures have loose clips or broken ties causing displacement and cracked lenses. 

To access the tunnel the we piggybacked with MassDOT as they cleaned the tunnel. It was pretty interesting being able to see how the tunnel was cleaned. First the safety walks were cleaned of debris using some sort of leaf blower. Secondly the walls were sprayed with some type of soap solution at a high pressure. Next they were scrubbed. After that the walls were scrubbed by a dozer with a brush attachment. After the brushing a water truck with attached power washer sprayed off the wall. Finally the lanes were cleaned using street sweepers. The entire time the exhaust fans were blowing to help clear out any dust. It's great to see them maintaining the structures since we don't always get to actually witness it.

Washington bridge collapse

Yesterday a deck truss in Washington state near Mount Vernon collapsed while carrying four-lane Interstate traffic over the Skagit River.

The new mentions a truck present at the time of the collapse and may have struck an overhead member. Typically you would not think of sway bracing or other lateral members when you think of fracture critical bridges like a truss. This collapse has me thinking of a ways that might improve future designs, ratings and inspections of bridges (trusses).

Could the force of a collision cause a gusset plate to fail at a diagonal or vertical member of a truss?

Should gusset plate ratings incorporate checks for these addition collision loads?

Should we design our lateral members to shear at a desired force to not cause a collapse?

As always for inspections we need to check the vertical clearance at the portals and any lateral members over the roadway and verify that signs are in place in advance and at the bridge.

I look forward to hearing more about this collapse (that sounds bad) so that we can improve future designs, inspections and ratings.

Pony Truss in Western Massachusetts

A few weeks ago I did some rigging for the first time out in western Mass. The inspection was for a pony truss with severe section loss to the steel stringers. At first it was a little hairy walking on the 2 foot wide platform but by the end of the day it felt normal. 

The inspection took about 5 hours and the drive was 3 hours each way.

Rigging Weathering Steel Truss

Early in the week I traveled out to Western Massachusetts to do a special member inspection for a truss. The truss has advanced section loss to the steel stringers.

Mississippi Truss Rating

Starting to help our Mississippi office with some truss ratings.

Several of the trusses do not have plans and measurements of all the members and deficiencies had to be taken.

On Friday I started a Truss in Hinds-Warren County which spans over Big Black River and carries Old Highway 80. The bridge consists of ten approach spans to the west and one east. The main truss spans 170 feet and has 8 panels.Currently I'm just checking the net area for the measured members for section properties and dead load calculations.

Trapazoidal Steel Box Girders

Still working on the Central Artery Inspection contract, we have switched from concrete segmental boxes to steel box girders.

Now just north of Boston near Cambridge and Somerville, we are inspecting ramps for Interstate 93 which consist of steel box girders.

Currently I'm working on a bridge which has two steel box girders there for making it a fracture critical bridge as well. The bridge is six span continuous with a cast in place concrete deck. The bridge carries Interstate 93 Ramps NS and SN over Boston Sand and Gravel.

For the exterior of the box we used a manlift to inspect and gain access to the interior of the box. The interior of the box is a permit required confined space so we needed air meters and rescue inhalers.

Two Week Bridge Inspection Course

The past weeks I was taking the NHI Safety Inspection of In-Service Bridges course.

Since I've been doing bridge design, ratings and inspections for a few years now I already had a good grasp on a lot of the topics but it gave me a more in depth knowledge into the appraisal and condition ratings of bridge elements and items.

I'd recommend anyone working in the bridge engineering, construction or maintenance to take a look at the course. It also gives you 60 hours towards your professional development.