NW 17th Avenue Bridge Rehabilitation Over the Miami River, Miami ...

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HMS 12 th Biennial Movable Bridge SymposiumNW 17 th Avenue Bridge RehabilitationWhat can be done in 213 days!IntroductionIn light of the recent bridge failure of the I-35W Interstate Highway Bridge in Minneapolis and theshockwaves it caused, it was not surprising that when a South Florida local TV station ran an article onthe NW 17 th Avenue Bridge in downtown Miami, it caught the attention. The bridge was on the Florida’slist of “structurally deficient” bridges and is one of the major crossings over the Miami River, while beingnear a major hospital and court houses. Excerpts of the article that was posted on the TV station’s websitestated:“NBC 6’s Jeff Burnside looked at one of the 50 listed bridges Friday with an engineer from FloridaInternational University. The bridge was visibly in poor shape – it shook when cars crossed over it. To besure, Luis Prieto, a highly-credentialed FIU professor, inspected the bridge. “It’s a potential danger, Prietosaid. Trieto said, for 20 years, he’s been bringing students to the NW 17 th Avenue Bridge as an exampleof a dilapidated bridge. “I personally, if I were a director of public works, I would shut it down rightnow,“ Prieto said, “I think it is a serious situation.””The week this ran, the Miami-Dade County had announced a weight restriction on the bridge for 5 Tons,which was initially being enforced by police officers. However, once they were removed, the loadrestriction was not obeyed which forced the County to completely close the bridge. This caused majordelays especially when the adjacent NW 12 th Avenue Bridge and the NW 5 th Street Bridge werepartially/completely closed for replacement. Further it was observed that many motorists would not stopon the bridge during red lights due to fears from the bridge vibrating and deflecting.The bridge, a double leaf, simple trunnion type bascule span bridge constructed in 1928, was certainlyshowing its age.Project OverviewProject LocationBridge DescriptionNW 17 th Avenue Bridge1
HMS 12 th Biennial Movable Bridge SymposiumNW 17 th Avenue Bridge RehabilitationWhat can be done in 213 days!The NW 17 th Avenue Bridge, built in 1928, is a six span bridge with adouble leaf bascule span carrying four lanes of traffic, two northboundand two southbound. The nearest bridges over the Miami River are theNW 12th Avenue Bridge to the east and NW 22 nd Avenue Bridge to thewest.The existing bascule span was a three girder system with floorbeamsthat support a two level stringer system and an open deck roadwaygrating with filled concrete grating cantilevered sidewalks. The threegirder system was a design developed by Harrington, Howard and Ash.John Lyle Harrington was the former partner of John Waddell –founder of Hardesty &Hanover, LLP. There are onlyabout five known bridges ofthis type still in existence,four in Florida (one is being replaced currently, NW 5 th StreetBridge) and one in New Jersey. The original floor systemconsisted of transverse floorbeams, longitudinal stringers andtransverse timber ties supporting timber planking. The timberportions of the deck system were later replaced with transversesteel substringers (channels) and an open steel grating.Mechanically, the existing machinery facilitated the rotation ofeach leaf and consisted of trunnion assemblies, rear live loadanchors, and automatic mechanical latching span locks. The twoseparate cantilevered leaves of the moveable span are supported bytrunnion shafts, through the bascule plate girders, seated in sleevebearing assemblies. Moment on the leaf is reacted against by thelive load anchors located betweenthe bottom flange of the flankingspan floor beam and the top of thebascule girders at the rear of thecounterweight (there are no forward live load shoes). The tip of each northspan girder at the channel side had an automatic mechanical latch. Duringmovable span operation the north (near) leaf must be seated first and thenthe south (far) leaf bar engages with the north leaf latches (3 total). Thelatches transfer the shear force from traffic live loads crossing the span.The existing operation was achieved byan electric motor energized to providetorque to the main drive rack pinionthrough 5 stages of an open gear train.The main drive pinion was fixed to thepier in the shaft sleeve bearings and thepinion engaged with the circular rackbolted to the center bascule girder. Theleaf rotated as the drive pinion walked the rack.2
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NW 17th Avenue Bridge Rehabilitation Over the Miami River, Miami ...

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