Custom formwork „Made in Germany"

In the construction of highly sophisticated shapes and surfaces with cast-in-situ concrete, even flexible system formwork eventually arrives at the geometric limits to its use. This is where custom formwork carpenters take over, fabricating tailor-made wooden forms with time-honored carpentry skills. This traditional craft is now on the ascendant as a result of the trend toward building elements with increasingly elaborate geometries.

For formwork suppliers aspiring to supply complete solutions from a single source, custom formwork construction is a must as one of the services offered. The demand for accurately dimensioned one-off forms has been growing in the last two decades - which is why the two Harsco Infrastructure locations for custom formwork construction in Radebeul (near Dresden) and Irxleben (near Magdeburg) have been continually expanding. The two teams with operations beyond the immediate region always go in to action when formwork challenges cannot be met with shuttering "off the peg" alone. In close cooperation with their designer colleagues in applications technology, the custom formwork carpenters craft the computed and drawn one-off designs with extreme precision. Although the structures of timber and steel fabricated by the eastern German experts are in particularly strong demand for bridge and tunnel engineering projects, specially built forms supplementing system formwork are required again and again for other construction projects as well.

Wooden one-offs with a precision fit
Each custom form is unique in its shape and size and therefore imposes new challenges on designers and craftsmen. Wood and wood-based materials are mainly used, although the formwork structures are usually combined with steel elements (walers, couplers etc.) to give them the requisite stability. Compliance with dimensional and shape tolerances, during both the construction of the individual components and the assembly of these parts to create the custom form, calls for exceptional exactitude, craftsmanship and a wealth of experience. This is not least because wood is a "living" material whose size and shape can change according to the ambient conditions. Custom formwork is constructed with the aid of conventional woodworking machines such as table and belt saws etc., as the use of CNC machine tools is not worthwhile owing to the small volume of jobs. Vocational training in woodworking and experience with wood are therefore ideal credentials for a custom formwork carpenter.

When a request for custom formwork is received, everything has to move quickly. The fabrication and assembly plans drawn up by the formwork designers in consultation with the formwork carpenters serve as a basis for a precise calculation of the materials required and for the job-related order. Keeping materials available on site only makes sense to a limited extent, as each job calls for different quantities and different materials. In Radebeul, for example, only those items are stocked in the so-called „semi-finished product store" that are actually regularly used. Once the materials have arrived, the various components of the custom formwork are crafted by hand and subsequently assembled into the ready-to-use form. The average processing time from receipt of the request through to delivery in Radebeul amounts to a mere two to three weeks - despite the procurement of materials for the specific job, which constitutes the biggest bottleneck time-wise.

Complex geometries
One reason for the growing demand for custom formwork is the increasing complexity of geometric shapes created with cast-in-situ concrete. "Bridge piers, for instance, are getting more and more complicated," says someone who ought to know. Dietmar Lehnert, in charge of the formwork carpentry team in Radebeul, has been following the growth in the standards of quality and geometry expected of bridge supports. His most sophisticated custom formwork projects include, for instance, a recently constructed bridge structure in southern Germany. For its corkscrew-shape pier heads, the custom formwork carpenters supplied a 4.5 m high H20 timber beam structure (8.7 x 3.2 m) inclusive of walkway bracket, work bracket, support and Protecto guardrail. A total of 20 differently shaped arc segments of 21 mm thick Maritime Pine made up the substructure of the intricate form, which was covered with a plastic-coated board lining. The finished custom form was supplied ready-for-use to the construction site where it only needed to be set up and supported.

Similarly convenient because it was also supplied in its ready-to-use state was the custom formwork solution for the construction of the two abutments for the new traversing bridge at Leipzig/Halle Airport. Harsco Infrastructure developed and fabricated the required tailor-made timber beam forms:
• 1110 m² of formwork elements consisting of 24 cm beams - pre-assembled wall-high with board linings for the fair faces
• Roughly 220 m2 of custom elements of GF20 large-area formwork to shutter the movement joints, return walls and pier cap (service access)
• Roughly 60 running meters of ID15 stationary shoring and insert boxes resting on them on the earth side
• 8 m high support frames for the one-sided shuttering of the movement joints during the first application.
This custom formwork was supplemented by further components from the company's own product range. Edge protection was provided by components of the Protecto system, the Bosta 70 frame scaffold was used for the working and protective scaffolds, and the Super 10 aluminum aligning strut, extensible at both ends, (up to 25 kN load uptake) was employed to align the formwork.

The examples illustrate why the leading formwork manufacturers run their own custom formwork operations. Today's complex building projects often demand the combined use of system and custom solutions. In some cases, custom formwork has to be supplemented with system formwork in order to yield ready-to-use forms. On the other hand, many a system formwork assignment has to be backed up with custom formwork services in order to efficiently realize a formwork task. Tailor-made ribs and bulkheads for geometrically elaborate slab shapes, oblique-angled recesses for curved wall surfaces - the range of possible examples could be continued ad libitum. And all this confirms that there will be no shortage of work for custom formwork carpenters in the foreseeable future.

Captions:

Custom forms are the showcase activity of formwork construction and are only ever required when system formwork arrives at its geometric limits. This is a component of the pier head form described in the article.

Form for the pier substructure.

Accurately dimensioned one-off forms are crafted in wood with traditional carpentry skills.

Custom form for the abutments of the new traversing bridge at Leipzig Airport.

Download: Sonderschalungsbau en.rtf

Christian Henkel
Marketing/PR Hünnebeck GmbH
chenkel@harsco.com

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