Prefabricated systems can provide the time required for concrete to cure and reach full strength before the bridge is in place, thereby allowing traffic to continue flowing over the existing bridge while the prefabricated system is constructed and left to cure. If the bridge substructure and superstructure are not built in the same location during ABC, and the ABC prefabricated systems do not bear on the substructure during construction, then the substructure and the superstructure can be built simultaneously. That would condense the construction schedule for ABC even more. While bridge building can occur during winter, as concrete can be cured during the winter with some additional equipment and special provisions, the temperature constraints of paving ensure that the majority of roadwork generally occurs from April to October. The two types of temperatures that affect asphalt installation are the ground temperature and the ambient temperature. While the weather influences the ambient temperature, the ground temperature is often lower than the ambient temperature and can dictate the construction period. Temperature extremes at either end of the spectrum are problematic for laying asphalt as the extreme cold reduces asphalt malleability, and the extreme heat causes asphalt to melt. Ideally, the ground and air temperatures would be above 50 degrees and below 90 degrees Fahrenheit. These temperatures generally occur in the late spring through summer and early fall, although high summer temperatures often result in early morning construction. Most of the bridges built in Utah with ABC are single-span bridges. During bridge replacements, limited space makes it difficult to construct interior bridge supports for multi-span bridges. There is often not enough room to construct a new support in the space between the travel lanes beneath a bridge because the support for the existing bridge already occupies the space. As a result, some bridges with multiple smaller spans are replaced with a single larger span when ABC is used for the bridge replacement. Small jump spans occasionally occur on each end of a bridge when supports are located near abutments. These 20-foot to 30-foot spans are used when the bridge abutment is sloped away from the roadway beneath the bridge. The new bridge support is located at the base of the existing bridge abutment. When no existing traffic has to be considered, the average time required to construct a new single-span bridge with traditional construction is three months. That time increases to six or seven months for bridge replacements where existing traffic has to cross the bridge during construction due to the complexities of construction phasing for the bridge and traffic. For a bridge replacement with traditional construction, all of the traffic would be shifted to one-half of the bridge while the other bridge half was demolished and a new bridge was constructed. Once the new bridge section was in place, traffic would be shifted onto the new bridge while the remaining section of the existing bridge was demolished and rebuilt. The six to seven months required for a traditional bridge replacement with active traffic is roughly the length of time available during the roadway construction season from April to October. Some bridges built with traditional construction and traffic phasing require over a year and a half of construction time to accommodate the two different construction seasons and complete the asphalt paving used for the road surface past the approach slabs at the end of the bridge. ABC makes it possible for a new bridge to be moved into place in hours using lateral slides, SPMTs or bridge launches. The rest of the road closure time is often spent removing the original bridge, securing the new bridge to its supports, and paving approach slabs. The Utah Department of Transportation (UDOT) has used Accelerated Bridge Construction with remarkable success for over two decades and is considered a leader in the field. ABC PROJECTS IN UTAH UDOT started to implement ABC when they began to reconstruct I-15 for the 2002 Winter Olympics. The aggressive schedule for the 17-mile corridor was completed ahead of schedule in four and a half years. That project used prefabricated bridge elements, including partial-depth precast prestressed concrete deck panels. Subsequent ABC projects in Utah used a variety of prefabricated elements for projects that spanned from bridge deck replacements to the widening or replacement of entire bridges.7 This includes the 2004 I-215 bridges over 3760 South and 3900 South that used multiple precast elements for the replacement of the whole bridge over 3760 South and precast panels for the deck replacement of the bridge over 3900 South.11, 12 The 4500 South bridge over the I-215 East Loop in Salt Lake City in October 2007 was the first bridge in Utah that was intended to be ABC from the beginning and was designed to be moved by SPMTs. Ralph L. Wadsworth (RLW) Construction built the 172-foot long and 1,500-ton steel girder bridge with a concrete deck in a staging yard less than 600 feet from the bridge location.5, 13 Bridge superstructure construction took four months. Workers built the abutments for the new bridge underneath the existing bridge without closing any roads during the foundation construction. Throughout the project, 4500 South was closed for 10 days, but I-215 was only closed for a weekend so that SPMTs could remove the existing bridge on Saturday and place the new bridge on Sunday. The grade and slope of the site, bridge, and terrain made the 4500 South bridge, designed by Michael Baker Jr., Inc. (Baker), now Michael Baker International (MBI), one of the most complex bridge moves with SPMTs in the United States at that time. However, the road was reopened Monday morning six hours ahead of schedule.5 While using SPMTs added nearly $80,000 to the project cost, the weekend ABC bridge move replaced a minimum of six months of road closures and detours, saving more 36
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