The almost 90 m high pylons for a new cable‑stayed bridge across the Ohio River are characterized by their complex shapes and massive legs and cross beams. PERI provided a comprehensive overall concept for its construction – consisting of a planning solution with perfectly matched formwork, climbing, shoring and scaffolding systems along with extensive on‑site support. With this PERI solution, the construction crew were able to realize the two bridge pylons in Louisville within the specified construction period and with low dimension tolerances.
The 762 m long cable-stayed bridge over the Ohio River connects the states of Kentucky and Indiana. The new bridge is part of the nearly 14 km long Louisville-Southern Indiana Ohio River Bridge Project which offers new possibilities for the river crossing and thereby counteracting congestion problems in the region. Through the project, among other things, the Interstate 64 highway has been re‑routed to the north of Louisville
The span of the main bridge section reaches 365 m, and the carriageway is carried by means of stay cables supported by two reinforced concrete pylons each 90 m high. The lower part of the pylon legs inclines in an outwards direction and is designed as a solid construction while, above the carriageway, the pylon legs are inclined inwards and feature hollow box cross‑sections. In the process, the cross‑sections taper in an upwards direction, and a slight curvature caused a continuous change in the angle of inclination from casting segment to casting segment. Two 3.65 m thick cross beams connect the pylon legs – one at road surface level and the other at the upper pylon reinforcement. Therefore, each construction section presented a particular challenge not only regarding the geometry but also in terms of the load transfer. In addition, it was important to find the optimal formwork solution in the area of boxes for accommodating the stay cables.
A German‑American PERI project team developed and delivered a complete solution for the individual construction sections. A number of formwork and scaffolding systems from the extensive PERI rental pool were used: the variable VARIO GT 24 Girder Wall Formwork, a combination of ACS, RCS and SCS Self‑Climbing Formwork, heavy‑duty shoring on the basis of the VARIOKIT Engineering Construction Kit and PERI UP Scaffolding were combined to create a complete solution which ensured fast cycle sequences, high load‑bearing capacities and a maximum level of safety during all stages of construction.
The pylons were divided into five construction sections: the outwardly inclined and tapering lower section of the massive pylon legs were followed by the hollow box cross beams at the level of the carriageway as the second section. The following inwardly inclining and likewise tapering part of the pylon leg in turn was again divided into two sections as the boxes for the stay cables at the top of the pylons had to be integrated. The upper cross beam for reinforcement of the pylon formed the fifth and final phase of execution. Due to the tremendous differences in the individual construction stages, each area required separate new sets of formwork and scaffolding.
The lower pylon legs were realized in four casting segments, each around 18 m high. As the concrete required prolonged curing time, PERI provided two sets of formwork per pylon leg which were used by the construction team implementing the so‑called leapfrog process. By means of custom connections at the corners, the formwork could be easily adapted to suit the extreme inclinations as well as the tapered sections. Through the use of appropriate reinforcement featuring system components from the VARIOKIT Engineering Construction Kit, the formwork was sufficiently strengthened here so that the concreting loads from the reversed inclined areas could be transferred into the foundations.
The "knuckles" in the pylon leg required a particularly tricky solution whereby the lower cross beam was also to be accommodated. Construction of this area took nearly four months. The formwork for the hollow cross beams – likewise realized using VARIOKIT system components – was supported on six VST Heavy‑Duty Shoring Towers each with a load-bearing capacity of over 270 t. The use of mobile hydraulics on the head spindles guaranteed easy striking. The fact that all customized system components could be rented from PERI resulted in a high level of cost‑effectiveness for the solution.
Parallel to the time‑consuming and complex realization of the cross beam, the construction team began with the third construction section – the further rising pylon legs. The RCS Rail Climbing System was used on the inside of the hollow construction whilst the ACS Self‑Climbing System raised the VARIO formwork on the outside. The combination of climbing systems facilitated fast construction process with crane requirements kept to an absolute minimum. Through the planned possibility of dividing the climbing formwork in construction section number 4 (means the upper area of the pylon), installation of the steel stay anchor boxes could be carried out without any interruption to the formwork and concreting operations. For the final cross beam of the pylon at a height of around 90 m, formwork featuring VARIOKIT components was planned, pre‑assembled and flown in according to the construction progress.
By pre‑assembling of the formwork sets in the PERI rental facility in the South of Chicago, the required assembly time on the construction site could be minimized. Another special feature: the Walsh / Vinci Construction consortium commissioned PERI to incorporate insulation between the girders of the VARIO GT 24 Wall Formwork. As a result, concreting operations could also continue throughout the winter – without incurring any loss of time for the corresponding time‑consuming and elaborate measures on site.
Not least, thanks to the comprehensive PERI support with technical planning as well as on-site project assistance, the jobsite team was able to realize the project with all its complexity within the tight schedule. Completion date and the opening to traffic are scheduled for the end of 2016.