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/306849
Segments were offset by one-half segment length to reduce the out-of-balance moment. Photo: Traylor Bros. The new I-45 Galveston Causeway Bridge, which crosses Galveston Bay in Texas, replaces two existing structures that had outlived their useful service life. The new bridge uses a combination of precast, prestressed concrete I girders and a cast- in-place concrete, variable-depth, double- cell, segmental box girder. Replacing the bridges, however, required overcoming some significant challenges due to the difficult site and the need to remove all existing substructure components down to 2 ft below the mud line. By the time of their replacement, the original bridges featured a complex mix of construction materials and techniques that had been used to make economical repairs to keep the structures in service. The oldest bridge, built in 1938, featured 121 cast-in- place concrete spans plus a steel bascule span at the Gulf Intracoastal Waterway (GIWW). That bridge was supplemented in 1961 with an adjacent structure, consisting of precast, prestressed concrete girders and structural-steel plate girders for the center span at the GIWW. At the time the second bridge was added, a portion of the original bridge had spans replaced with precast, prestressed concrete girders and a steel section to replicate the newer adjacent structure. After some years, due to the high level of exposure to chlorides in the marine environment causing corrosion and the advancing age of the structures, interim repairs to the structures were required. In 1979, footing repairs were completed, and in 1999, temporary repairs were made by installing steel girders beneath the deteriorated superstructure to provide additional support. Ultimately, it was decided that the structures could not be economically rehabilitated and needed to be replaced. In considering options for the new structures, designers focused on the benefits and experience of the local construction community. Bridge projects in the Galveston area rely heavily on the precast concrete industry to provide materials for the bridges, which has resulted in no corrosion issues similar to those that arose on the bridges built many decades ago. The least cost construction method consists of precast, prestressed concrete I-beams, which have an approximate cost of $65/ft 2 . As a result, AASHTO prestressed concrete girders were specified for the long approaches on either side of the waterway, which make up most of the structure's 8592-ft length. A segmental box girder was used for the main spans over the waterway. Twin parallel bridges, built in multiple phases, were proposed in order to maintain traffic flow and avoid major impacts to adjacent right-of-way. Navigation Span Features Box Girders The main section of each bridge over the GIWW features a three-span, 740-ft-long section consisting of a cast-in-place concrete, double-cell box girder varying in depth from 8 ft to 19 ft. The three spans consist of two 195-ft-long end spans and a 350-ft-long center span. Twelve segments were used in the end spans and 19 segments were used in the center span. The bridges were constructed using the balanced cantilever method. The design provided minimum vertical clearance of 73 ft at the edges of the 125-ft-wide navigational channel limits, and 310 ft horizontal clearance to the face of the pier bulkheads. The goal was to open the horizontal clearance as much as possible within the limits available. profile I-45 GALVESTON BAY CAUSEWAY BRIDGE / GALVESTON COUNTY, TEXAS ENGINEER: Texas Department of Transportation PRIME CONTRACTOR (INCLUDING POST-TENSIONING): Traylor Bros. Inc., Galveston, Tex. REDESIGN ENGINEER: Summit Engineering Group Inc., Littleton, Colo. PRECASTER: Traylor Bros. Inc., Galveston, Tex. CONCRETE SUPPLIER: Dorsett Bros. Concrete Supply Inc., Pasadena, Tex. POST-TENSIONING MATERIALS: VSL, Fort Worth, Tex. Utilizing concrete to avoid corrosion issues I-45 Galveston Causeway by Jon Holt, Texas Department of Transportation and Scott Turnpaugh, Traylor Bros. Inc. 22 | ASPIRE , Summer 2009 ASPIRE_Summer09.indb 22 6/5/09 1:51:13 PM