THE CONCRETE BRIDGE MAGAZINE

SUMMER 2017

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/844035

Contents of this Issue

Navigation

Page 52 of 55

ASPIRE Summer 2017 | 51 Construction The temporary support system (TSS) was supported by four 48-in.- diameter drilled shafts for each pier. These were installed using a full-containment system to prevent any discharge of excavated materials or turbid water into the waters of the sanctuary. Due to the local scarcity of structural ready-mix concrete suppliers approved by the FDOT in the Florida Keys, as well as the distance of the plants from the project, concrete was difficult to obtain. A tremie system was fabricated to allow rapid discharge of the concrete into the shafts to reduce on-site truck time. By eliminating the need for boom- pump trucks, the tremie system also allowed concrete to be placed from the Long Key Bridge superstructure during the daylight hours without lane closures. This enabled a more flexible pour schedule while also reducing the impact on the traveling public. A stanchion system was designed and installed on the barges to allow the TSS to be assembled in two halves prior to mobilization to the piers. Each half of the TSS was hung from the two sides of the barge, at which time the barge was pushed into place next to the drilled shafts. The TSS was then lifted onto the shafts using two cranes. A 45-ton rough-terrain crane had to be used on the front of the barge so that its boom could be lowered to get underneath the bridge and then boomed up between the newer Long Key Bridge and the historic Flagler East Coast Railroad Bridge, which is now used as a fishing pier. The TSS was then lifted off the barge brackets and secured on top of the drilled shafts with the embedded anchor rods. The barge would then move to the other side of the pier and repeat the process for the second half. This process eliminated the need for the TSS to be fully disassembled and reassembled for each pier, reducing the set-up and break-down times. Removal of the existing V-piers was facilitated by a removal frame—designed by the general contractor's specialty engineer, A2B Engineering—that supported the four column legs that formed the V. After jacking operations removed the compressive stresses on the columns, the legs were chipped out, and cut at locations under the superstructure and just above the pier cap at the hinge points. They were then rolled out in pairs and lifted to a demolition barge for removal. The pier cap was separated from the existing 42-in.-diameter drilled shafts by wire sawing, then rolled out and lifted by crane onto the demolition barge. The removal frame allowed the existing piers to be disengaged and then removed from under the Long Key Bridge superstructure with only 15-minute traffic closures during the actual jacking operations. The replacement precast concrete V-piers were required to be positioned with high precision in relation to the existing drilled shafts and the existing Long Key Bridge box-girder superstructure. Four pedestals cast integrally at the top of each precast concrete V-pier needed to be placed directly underneath the diaphragms inside the substructure's expansion joint segments, while also aligning the 16 dowel holes in the pier cap with the reinforcement cages of the existing drilled shafts. Alignment of the precast pier dowel holes with the existing drilled shaft reinforcement cage was critical to allow coring of the dowel holes through the pier cap into the drilled shafts without damaging the structural integrity of the shafts or damaging the coring equipment. The V-pier was placed on four hydraulic jacks mounted on high-capacity rollers. This allowed the pier to be rolled into place and then adjusted in small increments to the precise position. After alignment of the V-pier and preparation of the existing drilled shafts, custom-fabricated aluminum grout forms were clamped to the top of the existing drilled shafts and adjusted to exact elevation. The drilled shaft tops and cored dowel bar holes were cleaned, then the V-pier was lowered by hydraulic jacks onto a seal on the top of the clamps. Once the clamps and V-pier were sealed, grouting was begun. After the grout reached its design strength, neoprene bearing pads were slid into location between the pedestals and the bridge superstructure. The overall movement of the superstructure was less than 1 /8 in. The project was completed safely and successfully, allowing the Long Key Bridge, the only land access to the Lower and Middle Florida Keys, to remain open during construction. _____________ James Charles is a project engineer, John Meagher is vice-president of operations, Tom Charles is an area manager, and Wayne Wheeler is general superintendent, all with Johnson Bros. Corporation, a Southland Company, in Orlando, Fla. For more information on the Long Key Bridge V-pier replacement, see the Winter 2017 issue of ASPIRE SM . V-pier being lowered from Long Key Bridge to the construction barge at night. Note holes for dowels to drilled shafts. Temporary support system in place and removal frame installed on existing V-pier. Jacking system can be seen. New V-pier being lifted and placed onto the temporary support system. Hydraulic jack and roller assembly is mounted on the column legs. EDITOR'S NOTE

Articles in this issue

Archives of this issue

view archives of THE CONCRETE BRIDGE MAGAZINE - SUMMER 2017