Located in Hartford, Vermont, the Hartford I-91 Improvement project
replaced the north- and southbound bridges carrying Interstate 91 over US
Route 5. The existing bridges with suspended-span steel connections were
built in 1966, and were determined by the Vermont Agency of Transportation
to be fracture critical, meaning that if one steel member of the
bridge were to fail, a portion of or the entire bridge was likely to
collapse. Both bridges needed to be replaced immediately, with limited
inconvenience to travelers.
PCL used the innovative accelerated bridge
construction method of a lateral slide to replace
fracture-critical bridges in Hartford, Vermont.
A birds-eye view of the north- and southbound I-91
bridges sliding into place.
Through the use of the innovative accelerated bridge construction
method of a lateral bridge slide, PCL’s Transportation Infrastructure
Group replaced the north- and southbound bridges and successfully
completed Vermont’s first major lateral bridge slide.
SLIDING
TO SUCCESS
With nearly 15,000 vehicles traveling over the north- and southbound
bridges each day, it was essential that the project team limit the effects
of construction on the traveling public.
One of the Vermont Agency of Transportation’s goals was to
replace the bridges during only two weekend closures of I-91, and with no
full closures of US Route 5, thus allowing weekday travelers to keep to
their regular routes. To meet this goal, PCL used the innovative
accelerated bridge construction method of a lateral slide to replace the north
and south bridges. Accelerated bridge construction shortens project
schedules and significantly minimizes traveler inconvenience.
To complete the replacement, the team first built the new superstructures
adjacent to the existing bridges. The bridges remained open without the
need for a long-term Interstate closure or detour.
Once the existing bridges were demolished, the team used
hydraulic jacks placed underneath the new bridges to push, or slide, each
bridge into place over the course of two closure weekends. Without using
this slide-in bridge technique, the project would have resulted in
mobility impacts lasting upwards of six months.
ACCELERATED
EXPERIENCE
For the project to be a success, the Vermont Agency of Transportation
needed a contractor with experience in accelerated bridge construction
methods—specifically with lateral slide bridges—who could be responsible
for the design, construction, and overall performance of the bridges.
PCL’s Transportation Infrastructure Group has extensive experience
using accelerated bridge construction methods, including lateral slide
bridge technique, to replace bridges. The lateral slide bridge method in
combination with the construction manager / general contractor (CMGC) alternative
delivery method enabled PCL to become involved in the project early on,
during preconstruction. PCL’s preconstruction services on this project
enabled the team to modify the design to accommodate constructability features
for the lateral slide technique and improve the project’s schedule before
construction began.
Once
the closure weekends ended, the Vermont Agency of Transportation surveyed
local residents to ask their opinion about the bridge slides. Survey
results showed that 100 percent of the respondents were satisfied with how the
new bridges turned out, and 99 percent liked how the project was
delivered, using accelerated bridge construction methods. The two bridges
were completed ahead of schedule and are estimated to last, at a minimum,
for the next 80 years.