Ultra-high performance fiber-reinforced concrete in incremental bridge launching

Abstract

Incremental bridge launching is one of the many ways in which a bridge can be constructed. In The Netherlands this method is not often used. This may be explained by the fact, that there are not many suitable locations for application of this method. Incremental bridge launching is profitable for long bridges and can only be used for straight bridges or when the superstructure has a constant horizontal and vertical radius throughout the length. However, when the preconditions for use of this method are met, incremental bridge launching can be a great solution for bridge design. Ultra-high performance fibre-reinforced concrete (UHPFRC) is a new concrete. In contrast to regular reinforced concrete, UHPFRC contains fibers to provide for the capacity that is necessary when the concrete is loaded in tension. However, as for incrementally launched bridges, its application is limited as of yet. One explanation for the reluctance to use the material, is that compared to regular concrete, the cost of production are many times higher. To make economical designs using UHPFRC, the high cost of production need to be recovered by material savings, when a structure is executed or during its lifetime. The aim of this thesis is to identify whether a superstructure designed in UHPFRC can increase the application range of incremental bridge launching in The Netherlands, and to explore whether the concept can compete with other bridge designs. In order to make a statement, a case study approach is used. It concerns the launch of the eastern approach bridge of the bridge over “Het Pannerdensch Kanaal”, designed in UHPFRC. The location suits incremental bridge launching perfectly, as there is a constant horizontal and vertical curvature in the alignment for over 550 meters. The most favorable cross-section for incrementally launched bridges is a box girder. A comprehensive analysis on the cross-sectional capacity of a prestressed box girder, designed with different concrete strength classes, is performed to optimize the shape. The design of a box girder takes a special procedure, where both the transverse and longitudinal directions are considered separately. Transverse bending moments and shear forces, due to mobile loading, are obtained with influence surfaces and the differential equation of the Euler-Bernoulli bending beam. For the longitudinal direction, a spreadsheet is developed to identify the bending moments and shear forces that occur during launch and service life. The force method for analysis of indeterminate structures is used to determine the governing bending moments for this multiple span bridge. Also, the sheet contains parts to determine the required amount of central and continuity prestressing and to optimize the length of the steel nose to reduce the peak moments during launch. The use of UHPFRC in the design of a structure requires a special approach. Requirements regarding quality control are strict and need to be prescribed to allow on-site production. The typical characteristics of UHPFRC have an important impact on the execution and production cycle of the incrementally launched bridge, which is therefore investigated. The case study is used to investigate the competitiveness of the design. Cost of production and execution are integrated into a price per cubic meter of concrete and compared to the design of The Zeeburgerbrug, which was launched and built with regular concrete. Efficient use of UHPFRC allows a light box girder design, which can be launched without auxiliary supports. Conventional and shear reinforcement are not necessary. Transverse and longitudinal prestressing provide sufficient bending moment capacity, while the fibers contribute to a huge shear capacity that is more than enough to withstand the shear forces. The required amount of central and continuity prestressing does not fit in the concrete cross-section. Therefore, all tendons are applied externally. The anchors and deviators will not fit in the concrete cross-section either. The cost comparison shows, that a lot of the higher cost of production of UHPFRC can already be compensated during the design and construction phases. The remaining part of the higher cost of production of UHPFRC need to be compensated differently, for instance by savings in maintenance cost due to better durability properties or by a lighter substructure, as we are able to generate proper savings in the amount of concrete for the superstructure. The case study proves that when the superstructure is considered only, it might be hard to design and execute the UHPFRC box girder more economically than the design of The Zeeburgerbrug. However, when we consider the total bridge over the entire service life, we might have a competitive design. Alternative bridge designs, that use different construction techniques should be developed to assess the competitiveness of the incrementally launched UHPFRC box girder for that location.