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CHAPTER 4: THE CONSTRUCTION PROCESS OF SEGMENTAL BRIDGES - page 28 / 47

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Chapter 4: The Construction Process of Segmental Bridges

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Apart from custom-built timber structures a wide range of steel elements and modules for falsework is available in the construction industry. Liebenberg (1992) gives a range of up to 300 m in length and about 10 m in height for bridges to be built with this method. He also specifically points at the necessity for stable foundations of the falsework, sufficient bracing of the falsework structure, and consideration of the deflection of the falsework in the overall superstructure camber.

Falsework, either stationary or traveling, can also be configured as casting girders that hold the formwork into which the concrete is placed. In that, these girders resemble the erection girders of the span-by-span method, which are used to assemble precast segments. Liebenberg (1992) further distinguishes the girders depending on their location to the bridge superstructure as overhead or supporting it from below, or combination of both. He also reminds that use of major pieces of equipment, such as casting girders needs to be considered carefully because of the high capital investment that is necessary.

4.2.4.1 Stationary Falsework

Stationary falsework is the simplest method of erecting the bridge superstructure. Advantages mentioned by Liebenberg (1992) are that stationary falsework can be erected by less specialized workers to any desired shape. Use of modern standard elements of which the falsework is put together allows uncomplicated erection. There are, however, several disadvantages related to stationary falsework. A lot of material is required for stationary falsework, which requires much time and manual labor to be spent on its erection, in addition to the cost of purchasing or renting the materials themselves. Therefore, Liebenberg (1992) concludes that it needs to be erected some spans in advance to keep up with rates of placement of concrete that can be achieved.

Today, falsework is competitively used e.g. for the complex alignments of highway interchanges, as Cassano (1987) reports for the example California. He states that apart from the feasibility for the highly curved superstructures, use of major falsework systems also allows placement of very large volumes of concrete at the same time and thus speeds up construction. Cassano (1987)

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