The huge umbrellas put up by crane-building specialist Liebherr will in future protect the pilgrims in Mecca against the sun. With a span of 53 m, a single umbrella shades an area roughly equivalent to half a football field. The ribs of the umbrella were made from premium tubes using FineXcell® grades of steel from Vallourec so as to keep the structure as light and delicate as possible despite the extremely high static loads. The product package included specific proof of ductility for the material in addition to documentation of the specific material properties.
The project is a very special form of infrastructure: the Saudi royal house commissioned Liebherr via its general contractor to provide the Mecca pilgrims with an effective form of protection against the sun through the construction and installation of a total of eight “sunshades”. To speak of these complex shading systems as umbrellas or sunshades is an understatement, to put it mildly. The term “convertible roof” applies much better, according to the statement from Jürgen Appel, department manager and responsible for the project at Liebherr in Ehingen. Because, unlike the rigid umbrella structures at the departure terminal of Abu Dhabi, these structures here are movable and can be folded up.
Protection from the sun by day – cooling off by night
While during the daytime the sandy colored fabric made of synthetic fibers largely reflects the heat of the sun and thus provides shade, at sunset the unit is retracted to allow the natural stone floor underneath it that had been warmed up during the day to cool down again. This is a highly valid and even crucially important action to take in view of temperatures that not infrequently reach values of 50° C in the shade.
Liebherr is primarily thought of in connection with modern high-performance cranes, excavators and special vehicles, but the production of such “special constructions” already has a tradition of more than 25 years in the company and is managed by a separate department. In particular, the comprehensive know-how from crane construction is used here to produce units of this kind with their complex technology.
Combination of building and machine
The dimensioning of the shade-providing systems that are rated by experts as a hybrid of a building and a machine is done on the basis of the requirements as defined in the Eurocode. However, since the designers at Liebherr wanted to work with fine-grain steel tubes of strength class S770QL for technical reasons, whose use is not mandatorily regulated in the standards that are applied to buildings and structures, Vallourec was required to provide special forms of verification: “In the construction that we developed the tubes for the weight-transferring ribs at the sub-structure must exhibit high strength, perfect straightness and good weldability. A further prerequisite was that the tube diameter should be well under 300 mm for design reasons”, confirms Jürgen Appel. The almost tolerance-free wall thickness over the entire length of the tube was extremely important so as to allow precise connections.
The first of eight planned huge sunshades on the Liebherr test field at the Ehingen location: A filigree construction with a span of 53 m and a total weight of 600 t. The ribs, which bear a significant proportion of the weight, were produced by Vallourec using FineXcell780® tubes made of fine-grain steel.
Proof of ductility provided
Vallourec provided the required verification for the shaping ability in the form of so-called ductility verification so as to be able to warrant the usability of the premium tubes made from fine-grain FineXcell®780 steel. In addition to this, the customer received further documentation of the specific material properties and for the recommended procedures for welding FineXcell®780 that had been verified by standard-related tests.
The scope of supply for the rib tubes is 30 t per umbrella. The thick-walled tubes were produced at the radial forge in Aulnoye, whose innovative production technology guarantees maximum precision and dimensional compliance. Overall this was an order- and customer-specific product package that was created in a solution-oriented way in close cooperation with the customer. It thus went way beyond the mere provision of some premium tubes.
High-tech tube for top construction performance
FineXcell® tubes are among the most demanding products from Vallourec in terms of material science. These tubes made of high-strength fine-grain steels have a homogenous, fine-grained, material structure as a result of the application of modern metallurgical production procedures, their carefully controlled chemical composition, and the very latest heat treatment methods. FineXcell® tubes reach yield point values of up to 1000 MPa. They combine high strength, good impact toughness and very good properties for welding to a very capable material for slender constructions that can withstand high loads, such as in crane construction and the production of hydraulic cylinders.