Location: Massachusetts, USA
Market: Bridge
Product: Hollo-Bolt by Lindapter
Client: Massachusetts Department Of Transportation
Specifier: Vanasse Hangen Brustlin Inc.
Quantity: 50,000

Due to suburban growth and increased vehicle congestion in the 1940’s, the existing bridge over the Mystic River needed to be upgraded. Between April 1948 and February 1950, construction work was undertaken to upgrade the bridge which is now known as the Mystic Bridge (or the Maurice J. Tobin Bridge). The 3,629 metre long bridge spans the Mystic River between Boston and Chelsea. 

With an estimated 225,000 rivets and 50,000 bolts, and a total of around 45,000 tonnes of steel, the bridge is a double-decker span that can carry six lanes of traffic into or out of the city. The Tobin must endure harsh conditions such as 80 mph winds, salt spray, and snow plough blade impacts.

Over 60 years after the first upgrade, regular accidents on the bridge were producing major traffic problems, the demand for more effective traffic management and safer work zones emerged. The client required a durable solution for renovating the bridge including substructure repairs and improvements to safety walkways used by maintenance personnel. 

In 2013, Lindapter proposed a durable design solution to the project engineers Vanasse Hangen Brustlin Inc. (VHB). Meetings and negotiations continued with VHB in 2014 to secure all the phases of the project.

Due to limited and challenging access to the bridge structure, a bolted connection with one-sided access was required for the repair of the safety curbs on the walkway. VHB specified Hollo-Bolt due to its high strength capacity and ability to be installed from one side of the bridge steelwork. 

In addition to these advantages, Hollo-Bolt had just been awarded its first ICC-ES Seismic Approval for Category A, B and C, later approved for use in all Seismic Design Categories A to F.

The renovation of the bridge involved installing new chequer plate walkway covers on the safety curbs on each side of the bridge. The chequer plate covers were formed offsite into “S” shapes and then installed onto the safety curbs using M12 stainless steel Hollo-Bolts with hexagonal head on the vertical sections. M8 stainless steel Hollo-Bolts with countersunk head were then used on the horizontal sections to reduce trip hazards for bridge maintenance personnel and contribute to a safer walkway.

Installation was quick and easy. Each bolt was inserted into pre-drilled holes and tightened with a calibrated torque wrench to the recommended tightening torque to provide the necessary clamping force. In total over 50,000 M12 hexagonal head and M8 countersunk were used to repair the safety curbs.

This project had numerous stages that began onsite in 2017 and continued through to 2022. The safety curbs are an essential feature of the bridge and play an important role in improving the safety of all users including drivers, pedestrians, and cyclists. Hollo-Bolts provided a weld free connection that was quick and easy to install from one side, with no specialist equipment required, proving to be an efficient, secure and long-term solution. 

The Lindapter solution provided many advantages over traditional methods of bolting or welding, including shorter construction schedules, consistent quality control and reduced disruption on-site.

• Fast, convenient installation from one side
• Stainless steel Hollo-Bolts offer a durable and long-lasting solution
• Safer installation as no hot works required
• No bridge closures were needed
• Countersunk Hollo-Bolts reduced potential trip hazards