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Bridge Replacements on MD 28 and MD 450, Frederick County and Anne Arundel County, Maryland
Two single-span bridge replacement projects in Maryland were selected as a recipient of a HfL grant. The first bridge is located on MD 28 over Washington Run, in Point of Rocks, Maryland in southern Frederick County. The second bridge is located on MD 450 over Bacon Ridge Branch, east of Annapolis, Maryland, in central Anne Arundel County. The project locations of these bridges are shown in Figure 14, and pictures of the preexisting bridges are shown in Figure 2, respectively.
Figure 1 . Locations of MD 28 bridge over Washington Run (left) and MD 450 bridge over Bacon Ridge Branch (right).
Figure 2 . Preexisting condition of MD 28 bridge over Washington Run (left) and MD 450 bridge over Bacon Ridge Branch (right).
The original bridge on the MD 28 project was 78 years old and rated as "structurally deficient and functionally obsolete". The bridge was 37 feet long and 25 feet wide and carried approximately 11,000 vehicles per day. The MD 28 limit of work represents an approximate total roadway length of 0.1-mile, including approach and intersecting pavements.
The original bridge replaced on the MD 450 project was reported as 82 years old and "structurally deficient and functionally obsolete". The bridge was 36 feet long and 24 feet wide and carried approximately 8,000 vehicles per day. The MD 450 limit of work was approximately 0.3-miles in length, including approach and intersecting pavements. In addition to the bridge replacement, it was desired that an elevated surface profile could help resolve an existing flooding problem immediately east of the bridge, as illustrated in Figure 3.
Figure 3 . Flooding on pavement at east approach of MD 450 bridge.
Each bridge was constructed as a single span bridge over a small stream, utilizing precast PCC bridge elements for the superstructure. The substructure of each bridge was also removed and replaced, utilizing cast-in-place integral abutments on piling. Additional construction elements include the placement of a special mix PCC overlay over the precast slabs, upgrading approach roadway barrier systems, and performing adjacent roadway tie-ins.
All construction for this effort at each project site was conducted under full roadway closure with detoured traffic. The elements were fabricated at the Schuylkill Products, Inc. casting facility located in Pottsville, PA. The contract was awarded to Concrete General, Inc. The following subsections highlight the innovations features of this project.
MDSHA adopted and enforced the following mission statement for this project: "Get In, Get Out QUICK, Stay Out". Several new or rarely used methods of achieving the greatest efficiency in construction were employed for this effort. These methods are described within this section.
A single bundled contract was granted to one low bidder to perform both bridge projects. MDSHA often bundles multiple projects in a single contract, but such contracts generally apply for area-wide roadway maintenance contracts (i.e. crack sealing, patching, surface treatments) and the multiple project sites are bounded within a single maintenance district. This project marks the first time in MDSHA that multiple significant bridge construction projects are joined as one and awarded to a single contractor. Figure 4 shows the cover sheet of a single set of project plans for both bridges combined in MDSHA Contract No. AX4695180.
Figure 4 . Cover sheet of MDSHA Contract # AX4695180.
Additional considerations come into play on administering this contract because the project sites are in two different districts. Since MDSHA generally executes project management and oversight at the district-level, certain trade-offs were realized throughout the contract performance. For instance, while certain benefits (such as consistent quality control, project coordination, and schedule performance) were realized by having a single contractor, the need for two different teams to execute both on the agency side and the contractor side concurrently raised some difficulties in contract management and project accounting.
The decision to perform this project under full roadway closure affords the opportunity to exercise additional innovative contract methods and many benefits were realized throughout the project as a result. As stated previously, safety in the work zone was greatly increased by the use of full detours routing traffic away from the site, and the project duration was greatly reduced from the typical duration of similar projects performed with temporary MOT. An aggressive field completion schedule was established through use of an innovative incentive/disincentive policy.
The contractor had a window for completion of both projects within 60 calendar days to receive full incentive or within 75 calendar days prior to receiving a disincentive. This incentive program ensured that the contractor would meet the aggressive schedule requirements so that all work would be completed within the summer months and not impact school bus routes during the school year. Figure 5 illustrates the signage posted to indicate full bridge/road closure to begin "on or about 6/17/2008", within 2 weeks of the end of the school year.
Figure 5 . Notice of bridge closure at MD 28 over Washington Run.
The focus of this subsection is the innovative utilization of prefabricated bridge superstructure elements, namely precast, prestressed PCC slabs and how they were used to expedite construction, improve safety, and provide a high quality finished bridge. Similar elements have been used rarely by MDSHA in past projects, but not as a generally available option for similar projects, and past projects have not been performed within the same aggressive construction schedule as achieved in these projects.
The MD 28 superstructure was constructed as ten 4’ x 41’ precast PCC beams, simply spanning 40 feet between abutments. The MD 450 superstructure was constructed as ten 4’ x 56’ and one 3’ x 56’ precast PCC beams. Transverse tie-rods for post-tensioning and grouted shear keys between beams were used to provide strength and stability between the prefabricated elements. Figure 6 illustrates the typical section and plan view for the MD 28 project, and Figure 7 illustrates the same for the MD 450 project.
Figure 6 . Typical superstructure section and plan view of slab layout – MD 28 bridge.
Figure 7 . Typical superstructure section and plan view of slab layout – MD 28 bridge.
The prestressed slabs were cast off-site in a controlled environment and then shipped to the site via conventional semi-trailers. Extreme care was used to ensure proper placement and alignment of tie-rod holes, curb rebar, anchor bolts, etc., such that all elements would fit properly and securely in the field. Drilling, coring, or other corrections to placement errors in the field would result in rejection of the slab by MDSHA. MDSHA further required that the contractor assemble all slab units for each bridge at the casting plant prior to shipping slabs to the project sites in order to ensure that there was no misalignment of the tie-rod holes. Any such misalignment would result in rejection of the slab by MDSHA. Figure 8 illustrates precasting activities during the fabrication of elements for the MD 28 project.
Figure 8 . Precasting of MD 28 bridge slabs.
Following successful demonstration of assembly, the delivery of the precast slabs was simple for these projects due to the full closure, causing no additional impact to traffic during the critical stage of construction. Upon delivery to the project sites, the precast slabs were transferred by crane from semi-trailer to the abutments and placed carefully for longitudinal and transverse alignment. Figure 9 through Figure 11 illustrate the placement of precast slabs on the MD 28 project.
Figure 9 . Crane placement of Slab No. 4 at MD 28 project.
Figure 10 . Alignment of elastomeric bearing pads for Slab No. 6 at MD 28 project.
Figure 11 . Completion of slab placement at MD 28 project.
Upon proper alignment and placement of the slabs, the contractor can apply tension to the lateral tie rods. Figure 12 shows a contractor preparing for post-tensioning, and Figure 13 contains the section details, elevation, and general notes regarding tie rod and hole locations.
Figure 12 . Preparation of post-tensioning on tie rod at MD 28 project.
Figure 13 . Typical section detail, elevation, and notes for tie rods on MD 450 project.
Following the post-tensioning application, the remaining superstructure construction activities directly related to the use of prefabricated slabs include grouting the shear keys, finalizing the integral abutment, and pouring the finish surface. Figures Figure 14 and Figure 15 illustrate a picture (at the beam end) and detail of the shear key between beams.
Figure 14 . Aerial view of shear key at end of beams.
Figure 15 . Shear key detail for MD 28 project.
Figure 16 details the connection of the precast beams at each abutment. Figure 10 had previously shown the alignment of the elastomeric bearing pads with preformed holes in the beams. At this stage, prior to completion of the superstructure, dowel holes are drilled through the precast beam holes and into the abutment for connecting. Finally, the pour of the MDSHA Mix No. 8 PCC overlay as the deck finish surface will also incorporate the pouring over beam-end reinforcement as part of the integral abutment. The utilization of the integral abutment allows for a smoother ride with no expansion joints as well as minimizing future bridge maintenance needs. Approach pavement on either side of each bridge was resurfaced with a standard hot-mix asphalt (HMA) surface lift.
Figure 16 . Slab detail at abutment for MD 28 project.
4 Map illustrations of project locations derived from Google Maps.