In the September 2022 issue of this newsletter, Ashley Bomely, PE described the complete streets elements of the Memorial Avenue project. The details of the bridge that integrated so artistically with the network of streets at both ends are explored here. At the time when a potential replacement bridge was being considered for the aging Morgan Sullivan Bridge carrying Route 147 over the Westfield River, little did we imagine that this project would become a template for other projects in its vicinity to expand the complete streets network.
Evolution of a Bridge Replacement Project
The Morgan Sullivan Bridge, completed in 1946, carried four lanes of traffic over the Westfield River with four spans supported on three wall piers. The roadway width between the curbs was 44 ft. providing four 11 ft. lanes. The roadway widened to 78 ft. at the south abutment to account for vehicle turning at the adjacent intersection. The cantilevered brackets supporting the sidewalks on both sides had begun to show signs of advanced deterioration. The residents of the community talked about how the bridge bounced while they sat in traffic on the bridge. In addition to the structural deficiencies which would have eventually downgraded the bridge to a ‘poor’ condition, there were gaps in ADA compliance in the sidewalks with stretches of Springfield Street without any sidewalks. The lack of bicycle lanes meant that bicyclists were limited to sharing the roadway with vehicular traffic, making it a dangerous proposition. There was no convenient access to the local businesses in the immediate vicinity with frequent traffic backup further blocking entrance to the businesses. Moreover, the two-week-long Eastern States Exposition held annually in West Springfield creates a surge of pedestrian traffic in the area. The vehicular traffic on the bridge had increased significantly and it was the traffic study to address congestion in the area from where the project began. Subsequently, it evolved into a bridge widening project, then to a superstructure replacement project and finally into a full bridge replacement project.
Benefits of Utilizing High Strength Steel for Girders
The FEMA Flood Insurance Study for the Westfield River put the 500-year flood below the bottom of the beams of the old bridge in Spans 1 through 3 but 1 ft above in Span 4 while the 100-year flood was determined to be almost 5 ft below the bottom of beams. Using hybrid steel plate girders with 70 ksi steel flanges made it possible to keep the beam depths similar to the existing beams while using longer span lengths and reducing the number of piers from 3 to 2.
Bridge elevation - three-span configuration to reduce the number of piers
Bridge Abutment as Flood Protection
Additionally, an earthen flood dike along the northerly embankment of the Westfield River had a line of vertical steel sheeting buried within the dike to prevent seepage. The existing north abutment of the bridge, which was incorporated into dike, was also constructed with vertical steel sheeting extending below the footing. The existing abutment itself had been found on steel piles. The existing piles were cut-off below the proposed footing but not extracted as to minimize disturbance to soil and dike. The existing vertical stee sheeting was left in place and new piles were driven clear of the existing sheeting and cut-off piles to support the proposed abutment which is now part of the dike.
Several utilities required needed consideration for maintenance during bridge construction. Utilities on the existing bridge included a 16 in. high pressure gas pipe attached to the west fascia, two low pressure gas pipes, six transite telephone conduits in the interior bays and a 2 in. fiber duct encased in the west sidewalk. These all have to be maintained or temporarily relocated during construction and replaced onto the new bridge.
The replacement bridge consists of a three-span continuous plate girder superstructure supported by two reinforced concrete pier bents founded on drilled shafts with rock sockets. The span lengths are 104 ft, 125 ft and 104 ft. This span configuration allowed for the elimination of one pier support from the original bridge. The superstructure cross-section has ten lines of 40 in. deep steel plate girders spaced at 8 ft. 6 in. on center that support an 8 in. thick reinforced concrete deck slab with a 3 in. thick Superpave wearing surface. The minimum roadway width is 62 ft., carrying five 11 ft. wide lanes with a 5 ft. shoulder on the west and a 2 ft. wide shoulder on the east side. An 8 ft. wide bidirectional bike lane is located adjacent to the 5 ft. 6 in. wide east sidewalk and is separated from the roadway by a crash tested bridge railing as well as a bicycle railing. The west sidewalk is 6 ft. wide. To accommodate these provisions for a complete street, the bridge structure needed to be widened. The minimum out-to-out bridge width is 86 ft. 4 in., a considerable increase compared to the 60 ft. width of the bridge it replaced. At the south abutment, the bridge width increased from nearly 95 ft. to approximately 133 ft. to account for turning lanes at the adjacent intersection.
Splayed Beams to Support Turning Lanes and Sidewalks
The bridge is located between two four-way intersections. The original bridge had two lanes in each direction without designate left turn lanes which created significant back-ups over the bridge. The new bridge will have a fifth lane along the center that will provide for a left turning lane at each intersection avoiding the blocking of the through traffic. The south end of the bridge is widened even further to support to slip lanes provided for free right turns heading both on and off of the bridge.
Figure 2 - Partial framing plan showing raker beams in span 1 and ange
in the south abutment
Supporting these slip lanes required raker beams to be incorporated into the bridge. These raker beams have one end supported on the abutment and the other end on the continuous exterior beam. Due to the required turning radius for trucks and the bike path and sidewalk, these raker beams were approaching 90 ft. in length and added a significand amount of load onto the continuous exterior beam. A 35-degree bend was introduced in the south abutment to help shorten the span of the longest raker beam down to 72 ft and greatly reducing the load on the exterior girder allowing utilization of a shallower beam for the raker and avoiding an increase in depth of the continuous exterior beam.
Figure 3 - Bridge pier stage 1 construction
The existing bridge is routinely inspected using an Under Bridge Inspection Unit. This unit consists of a truck that parks on the bridge and has a mobile arm with a basket supports inspectors while they extend over the side of the bridge and swing under the bridge to perform the inspection. The crash tested railing along the east curbline, combined with the 8 ft. wide bike lane and 5 ft. 6 in. wide sidewalk would prohibit the use of this type of equipment. An opening in the railing was provided at the south end and the combined bike path and sidewalk was designed to be wide enough to allow the inspection vehicle to drive on the sidewalk during the biannual bridge inspections. The geometry is difficult due to the curve from the slip lanes. The MassDOT Bridge Inspection Unit laid out the curve and ensured that they could drive the vehicle onto the sidewalk so that the bridge could be constructed with the assurance that it would be able to be inspected.
Bridge Substructure and Impactful Construction Phase Decisions
Each of the two bridge piers is founded on five 4 ft. diameter drilled shafts. A 10 ft. high x 4 ft. 6 in. wide pier wall caps the drilled shafts over which five 4 ft. diameter columns are constructed which line up with the drilled shafts. The 4. ft 6 in. wide x 4 ft. deep pier cap supports the steel girders on elastomeric bearings. The pier wall provided a buffer for any alignment issues that could have arisen during construction. The pier construction was proposed in two stages, with the first stage comprising construction of a partial pier with three columns and drilled shafts to support the newly constructed west half of the bridge. However, during construction, the contractor was able to install all five drilled shafts and construct the entire width of the pier wall as well as five pier columns in the first stage itself leaving only the construction of pier cap for the second stage. A low clearance rig was used for drilled shaft construction under the existing superstructure on the east side of the bridge and the drilled shaft subcontractor only had to be mobilized once during construction of the entire bridge. This was elemental in completion of the project ahead of schedule and also avoided delays as the work was performed during the first construction season which had favorably low water levels and the second construction season was met with unusually high water levels.
Completing the projects of this scale on schedule is typically challenging and completing it ahead of schedule thus a feat. In this case, it was attributed to the contractor’s means and methods, their timely execution and a relatively low water levels in the River. The drilled shaft cages were short enough to be installed under the existing superstructure by using the low clearance rig in the first stage of construction which positively impacted the construction schedule.
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