DUHA Fertigteilbau GmbH
Precast bell towers
The range of Duha Fertigteilbau GmbH includes precast monolithic bell towers delivered to the job site on trucks designed for exceptional loads. This is what happened in two church projects in Germany, namely at the end of 2015 in Cologne Bickendorf and in spring 2016 in the German town of Westerstede near Oldenburg.
Places of worship are getting emptier by the day, and the number of priests is also decreasing. Christian churches in Germany thus have to merge their parishes and withdraw surplus church buildings from religious use. At the same time, however, neighboring churches of roughly the same size need to be altered to accommodate a larger number of churchgoers. For it is often purely pragmatic reasons that give rise to a decision as to which building should be used for worship, including questions such as: Which church is situated in a central location? Which of the buildings is in better condition?
In many cases, churches are chosen that previously did not include a bell tower, but should now be complemented by such a landmark because they become the center of a larger parish. More often than not, the aspect of integration adds to the overall scenario: parishes are usually in favor of relocating the bells of the abandoned church, along with the altar relics, to the remaining building intended for further religious use.
This is what happened at the end of 2015 at the Protestant Church of Cologne Bickendorf, followed by the Catholic Church in the town of Westerstede near Oldenburg three months later. In Cologne, the precast producer headquartered in the North German Emsland region was commissioned by Cologne-based Lepel & Lepel architects. The architects were to modernize and upgrade St. Epiphanias Church and complement it by a free-standing bell tower, a socalled campanile. The design team conceived a monolithic tower structure composed of large-scale angular precast elements, which are separated by continuous joints that form a Latin cross towards all four sides. The upper, vertical part of the cross joint was widened by some centimeters on all sides because these openings make it possible for the sound of the bells to propagate. The L-shaped angles of the upper tower half enclose a cavity that accommodates the bells. The campanile is topped off by a precast pent roof element that again emphasizes its cubic design. The precast elements' sophisticated, bush-hammered white surface and the "cross joint" pattern lend a distinct appearance to the bell tower of the St. Epiphanias Parish Church in Cologne.
Street patterns as a decorative element
Five years before the recent projects, Herz Jesu Church in Westerstede had already been refurbished and upgraded to a large parish church. The merged community opted for an architectural element that corresponded to the situation, namely a new, additional bell tower whose architectural features should, however, not distort or dampen the sound pattern of the bells.
Architect Ulrich Recker chose abstract representations of streets within the local community to design the shape and arrangement of sound openings. The shape of the narrow, incisive openings corresponds to the pattern of streets that becomes apparent to the observer when looking down from the church tower in the respective direction. These expressive forms were to be appropriately implemented in both the detailed design and production phase. To ensure an undisturbed overall appearance, stabilizing features within the sound openings should be as unobtrusive as possible. Furthermore, transfer of vibrational loads to the reinforced concrete structure should be prevented to the largest possible extent.
This is why the Duha team working on the project consulted with the designers of Duha Fertigteil GmbH and decided to use Schöck Combar glass fiber bars as a complement to the steel reinforcement. Besides their structural characteristics, these bars provide the advantage of being completely corrosion-resistant. They are exposed within the sound openings and provide stability to the projecting concrete parts. In line with the architect's aesthetic approach, their slenderness makes them almost invisible from the ground.
Heavy structure, elegant solution
The 57 t, almost 20 m high inner tower structure was preassembled at the factory and transported to the job site. It is composed of an internal steel framework and two intermediate precast floors. The structure was then erected on-site within only three days because the building permit made it possible to block adjacent streets only for a short period. This assembly process also included mounting of the suspended wall panels and of the supporting structure of the reinforced concrete pitched roof. The tower has an almost squareshaped footprint of 3.47 by 3.22 m and extends to a total height of 22 m at the roof level. Four flat bucket foundations were created that transfer loads into rigid corner columns, thus stiffening the structural steel framework.
The first intermediate floor was inserted at a height of 3.29 m and is supported on a coping. This is where the columns also become more slender. The second intermediate floor is located at a height of 12.23 m, and the roof zone begins at a height of 18.37 m. To connect to the structural steel framework, precast columns were fitted with steel plates in a 2 m spacing onto which the prefabricated steel framework was welded. This work step resulted in the 57 t shell structure. This weight required the use of a heavy-duty lifting beam and gantry cranes to move the entire structure and to finally place it on a heavy-haul truck.
The tower's reinforced concrete framework was made from C35/45 concrete with BST 500A reinforcing steel. Dyckerhoff Weiss cement and brightener were added to the concrete mix to achieve the brightest possible architectural concrete surface. Schöck Combar reinforcing bars of 20 mm in diameter were used in the continuous reinforcement zone to retain the aesthetic appeal of the precast wall panels with their many openings. Workers at the precast plant first fabricated sophisticated block-out elements for the openings and then inserted the 9 m long Combar reinforcing bars through the entire steel reinforcement and the block-out elements. This was the only option to ensure correct positioning of the reinforcement in all of the openings. Besides glass-fiber bars, precast elements were reinforced with individual BST 500 A steel bars. The steel framework welded onto the reinforced concrete structure was fabricated to ST 37 minimum tensile strength and then powder-coated. Assembly and welding were carried out at the precast plant to accelerate the project and to ensure sufficient accuracy.
The entire process, including mold-making, precast production, installation of the steel framework and final assembly, had to be meticulously planned - all the more so because the final structure has a total weight of 125.5 t. Robert Mehl, Aachen http://www.bft-international.com