ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306162
Span 1 Span 2 Span 3 Span 4 Kentucky project's 325-ft-long main span sets record for spliced, precast, prestressed, concrete girders The Route 22 Bridge over the Kentucky River near Gratz, Ky., was initially planned as a steel structure, but officials at the Kentucky Transportation Cabinet allowed a concrete alternative to be designed. That option resulted in the creation of a spliced, post-tensioned, precast concrete girder bridge that features a 325-ft-long main span, the longest span of this type in the United States. It also produced a cost savings of more than $800,000. The bridge was designed to replace the existing steel-girder structure, which will be demolished after the new bridge is in place. Upon release of the initial drawings, which featured a steel-plate girder design, engineers at a precasting firm asked if they could provide a precast concrete alternative for consideration. Long Spans Required The company realized that to span the river as required would necessitate long spans. But it knew it could produce the segments required, and it had access to special barge-loading facilities that would allow it to deliver the girders via the river. The 325-ft length was necessary to s p a n t h e r i v e r w i t h o u t c h a n g i n g the pier locations from the original design, which located them along the riverbank. Moving them closer to shorten the span lengths would h a v e re q u i re d p l a c i n g a p i e r i n the river, which would have caused encroachment on the waterway and environmental concerns. The bridge has four spans and four girder lines were used throughout the bridge. The center span features haunched bulb-tee pier segments varying from 9 ft deep to 16 ft deep. The haunched pier segments were each 138 ft long and weighed 169 tons. Between the two cantilevered pier segments, a 9-ft-deep drop-in girder, 185 ft long completed the 325- ft main span. Segments were joined with 1-ft-wide cast-in-place concrete closure joints. Spliced Approach Spans There are two approach spans on the west side with lengths of 175 ft and 200 ft and an approach span on the east side of 200 ft. The precast beams for the three approach spans consist of 9-ft-constant-depth, bulb-tee beams. Span 1 consists of two segments with lengths of 90 ft 9 in. and 84 ft 3 in. that were set on falsework at their splice. Span 2 comprised one end of the haunched pier segment and a drop-in girder segment, 131 ft long. Span 4 comprised two segments, 57 ft 6 in. and 73 ft 6 in. set on falsework with one end bearing on an end bent and the other supported with a strongback from the cantilevered end of the haunched pier segment. In all, eight girder segments were used in each beam line. Materials Selection The girder segments used concrete with a specified 28-day compressive strength of 7500 psi. All segments used normal weight concrete except for the main- span, drop-in girders, which used a profile ROUTE 22 BRIDGE OvER THE KENTUCKY RIvER / GRATZ, KENTUCKY E NGINEER : Kentucky Transportation Cabinet, Lexington, Ky. PRIME CONTRACTOR: Haydon Bridge Co., Springfield, Ky. PRECASTER: Prestress Services Industries LLC, Lexington, Ky., a PCI-certified producer PRECAST SPECIALTy ENGINEER: Janssen & Spaans Engineering Inc., Indianapolis, Ind. ERECTION CONTRACTOR: C.J. Mahon Construction Co., Columbus, Ohio by Brian Slagle, Janssen & Spaans Engineering Inc. GoinG to RecoRd LenGths Schematic of the framing of the spans on the Route 22 Bridge over the Kentucky River near Gratz, Ky. 24 | ASPIRE , Winter 2011 Book_Win11.indb 24 1/4/11 2:34 PM