The DCR Access Road Bridge over Route 14Winner of 2011 PCI Design Award and Voted "Best Non-highway Bridge" by Aspire Magazine

By Matt Card and Thomas Cyran

The new precast concrete channel bridge (bottom photo) and the original steel l-girder bridge (top photo) and are shown for comparison.The new channel bridge provides nearly 2 ft of additional clearance over the original bridge without increasing the roadway profile on thebridge.

This project involved the replacement of Bridge R-01-012which carries the Department of Conservation and Recreation(DCR) Access Road over Route 24 in the Town of Randolph,Massachusetts. The access road connects two large parcel ofpark land within Blue Hill Reservation that is divided by Route24. The bridge is primarily used byrecreational hikers, horseback traffic andDCR maintenance vehicles. This bridgereconstruction project was administeredby the MassDOT - Highway Divisionand was completed in the Fall of 2010 ata cost of $3.9 million.

Randolph, Massachusetts is located 15miles south of Boston, The town wasoriginally called Cochaticquom by theCochato andPonkapoaq tribes. Thetown was renamed after Peyton Ran-dolph, first president of the ContinentalCongress.

The original bridge, built in 1958, con-sisted of a 247-ft-long, four-span steel I-girder bridge supporting a 7.5-in concrete deck slab and asphaltwearing surface. The substructure featured two concrete stub-type abutments supported on steel piles and three reinforced-concrete piers supported on spread footings.

Partly due to its low 13'-9" vertical clearance over Route 24,the existing bridge had become structurally deficient. In fact, thesteel I-girders had repeatedly been hit by trucks driving belowon Route 24 and had been torn through in numerous areas dueto hit damage. Officials at the MassDOT - Highway Divisionwanted to increase the vertical clearance without having to per-form extensive roadway work either underneath the bridge or atthe access road approaches. Raising the profile of the approach

The I-girders of the original steel bridge were removed andthen reused as temporary erection beams to support theprecast concrete channel segments during erection.

roads beyond the abutments was not an option, as they transi-tion to heavily wood areas and hiking trails within the park. Thehiking trails were also used as horse paths that accommodatehorse-rental farms nearby. MassDOT officials also wanted tocreate a design that would blend with the scenic surroundings,

minimize disturbance to the surround-ing woodlands and minimize long-termmaintenance needs.

To reach those goals, MassDOT engi-neers selected the precast concrete "chan-nel" bridge concept with post-tensioned,segmental construction. In addition tomeeting the immediate goals, the newbridge provides long-term durabilitythrough a minimum service life of 75years. The channel cross-section featuresa precast concrete superstructure with anunusual U-shaped design that provides avery shallow structure depth (12") fromthe bridge deck and it's underside. Thesection consists of two edge beams thatfunction as the main load-carrying ele-

ments, with the roadway slab supported between them. The twoedge beams serve the dual purpose of acting as bridge parapetsas well.

The new DCR Bridge is a 248-ft-long, two-span continuousprecast segmental concrete structure that increases the verticalclearance over Route 24 to 16'5", adding more than 2 ft. to theclearance provided by the previous steel stringer bridge. Thesubstructure consists of two new reinforced concrete stub-type abutments supported on steel piles and a new center pierconsisting of two 59-in.-diameter reinforced-concrete columnssupported on a common concrete spread footing. Utilizing only

16 Pittsburgh ENGINEER

a center pier, the DCR Bridge eliminates the need for side piersalong the edge of the northbound and southbound roadways.This provides added safety for highway users, and also reducesmaterial cost and construction time.

The new superstructureis 29.7 ft wide and 5.38 ftdeep. The precast concreteedge beams are fully post-tensioned using a mix of 12-,15-, and 19-strand tendons.Additional longitudinal ten-dons are provided in the deckslab, using flat 4-strand ten-dons. Transversely, the struc-ture is fully post-tensionedusing flat 4-strand tendons.All reinforcing steel consistsof epoxy-coated bar.

Alfred Benesch & Company(formerly Purcell Associ-ates) served as the Engineerof Record on the project anddesigned the substructureelements. The firm subcon-tracted the superstructuredesign to International BridgeTechnologies (TBT), whichhas experience with the channel concept. It was originally cre-

assembly. Then, groups of 2 to 4 segments were assembledtogether incrementally using post-tensioning bars, starting fromthe center of the bridge and moving towards the abutments ina balanced sequence. Each group of segments was assembledin a one-day shift. Once all of the segments were assembled

together, the permanent post-tensioning was stressed in theedge beams and deck slab,and the temporary steel shor-ing was removed.

When the erection of thesuperstructure segments wascompleted, the contractorfinished casting the abut-ment backwalls and the topof wingwalls and addedthe asphalt riding surface.The bridge's channel shapeprovides a 4-ft-high concreteparapet railing along bothsides of the bridge, to whicha Type II Modified ProtectiveScreen was mounted on eachof the parapets.

ated and patented by the innovative bridge engineer Jean Muller,whose firm designed two such bridges in upstate New York inthe 1990s and others in Europe. Daniel Tassin, IBT's chief tech-nical director, worked with Muller for many years.

Unistress Corp. served as the precaster for the project. Theypurchased forms that were specifically designed for the chan-nel cross section and then shipped them to their precast yard,for assembly and casting. R. Zoppo Corp. served as generalcontractor, with Finley Engineering Group Inc. performingconstruction-engineering services.

Minimizing waste and remaining environmentally aware wereproject goals and resulted in an innovative reuse of materi-als. The steel I-girders of the existing bridge were re-used tofabricate erection beams, thus serving as the temporary shoringneeded while the segments were being erected. Upon comple-tion of segment erection and subsequent grouting and post-ten-sioning, the steel I-girders were removed and recycled for reuse.The existing bridge piles were retained where possible andsupplemented with new ones set between the existing ones. Tominimize excavation needs along the highway, the center pier'sfooting was retained. The contractor removed the existing mate-rial to the top of footing and simply poured the new concrete ontop of the existing footing.

A total of 31 precast concrete channel segments were cast forthe project. Typical segments were 8.2-ft long, with the abut-ment segments being 5.1-ft long. In order to avoid deflectionissues resulting from unequal weight distribution, all of the seg-ments were placed onto the erection beams prior to their actual

The 8.2-ft-long U-shaped segments feature a flange on the top of bothsides that temporarily supported the precast segments on steel erectionbeams.

Timber guard railing andposts were added within theproject limits at all four cor-

ners of the bridge for traffic safety. The guardrail has a specialsteel backing for added strength and safety.

Owners, contractors and engineers are constantly looking forways to build structures that provide longer durability, a faster

Underside view of completed bridge.

speed of construction and pleasing aesthetics. The channeldesign provides a new alternative for achieving these goals. Thechannel design provides a sleek, low-profile appearance thatprovides functional clearance benefits while keeping it unobtru-sive in scenic areas. Best of all, it minimizes long-term mainte-nance needs that will improve safety of construction crews andusers while reducing costs over its service life. EL

Matt Card is a Project Manager at A I/red Benesch & Companyin Boston, and Thomas Cyran is a Bridge Engineer with Inter-national Bridge Technologies in San Diego.

SUMMER 2013 - Special IBC Issue 17