Surveying 3,000 Metric Tons of Steel
October 1, 2006
Munich-based BMW is a world-renowned manufacturer of dynamic, high-performance and aesthetically irresistible cars. But the respected automobile company has also become known for its architecturally exciting buildings. Thirty years ago, the BMW headquarters known as "Four Cylinders" became famous throughout the world for its innovative design that dominates the Munich skyline. Today, the company is constructing an architectural masterpiece--BMW Welt (BMW World), a new multi-functional event and delivery center--that symbolizes the innovative characteristics associated with the BMW brand name. This extraordinary steel and glass structure exhibits precision and quality reminiscent of the renowned BMW engineering legacy, which is why the surveying work involved in its construction is critical to the entire project.
Located between BMW's headquarters and the Olympic Complex in Munich, BMW Welt has emerged from a 14-meter-deep (46 ft) structural excavation site as a mesh of interlaced steel girders. Scheduled to open to the public in spring 2007, the filigree-steel-skeleton structure creates the impression of a futuristic apparition or space station, rather than the multipurpose building it will become: a business center for meetings and conferences, a delivery center for BMW automobiles with personal customer support, shops and restaurants with first-class culinary specialties and a center for car accessories. BMW Welt is designed to unite the many dimensions associated with the BMW brand--tradition and innovation, emotion and precision, dynamics and aesthetics, exclusiveness and openness--under a single roof.
In 2001, BMW held an architectural competition for the BMW Welt building. The architectural duo of Professor Wolf D. Prix and Helmut Swiczinsky of COOP HIMMELB(L)AU, an established firm in the international architectural scene (with offices in Vienna and Los Angeles) known for its avant-garde buildings, was awarded the design contract. During the initial design phase for the BMW Welt building, COOP HIMMELB(L)AU remained faithful to its inherent adage: "architecture is a reflection of now, as buoyant and variable as clouds and a pointer to the future." The firm's futuristic design includes a 28-meter-high (92 ft) double cone structure (two cones placed apex to apex) with a diameter of 45 m (148 ft). Steel construction work began in January 2005. The double cone, erected using approximately 1,000 metric tons of steel, is not only aesthetically appealing, but functional as well. The building's spiral-shaped ramp allows cars to be driven directly into the structure for easy delivery purposes. One side of the cone supports the cloud-like 16,000 m2 (172,224 ft2) curved roof, which appears to float over the multi-dimensional building structure; the other side utilizes "fish belly girders" (named after their characteristic shape) to form the framework of a self-supporting lounge in the roof. Architect Prix calls the design a "chess game set on a digital plane." The architectural visions of BMW Welt can become a reality thanks to sophisticated computers and CAD software. And the utilization of high-accuracy electronic surveying instruments, including total stations, has been vital to the implementation of the complex design.
Setting-out in the Midst of ChaosOn the BMW Welt site, where construction operations seem chaotic, where engineers and construction workers hurry from one destination to the next, and where suspended loads and reverberating construction machinery would distract many, the surveying teams of Vokal + Partner (Munich, Germany) do their job of precision measuring. Vokal + Partner is a family business run by the Vokal brothers, Mario and Norbert. Their firm specializes in surveying for steel and faÃ§ade construction, and began working on the BMW site in June 2005.
For the construction of the roof, the crews directed their Trimble (Sunnyvale, Calif.) S6 robotic total station and two Trimble 5601 Direct Reflex (DR) total stations towards points to be set out for the roof of the future building.
The steel roof structure, which weighed 3,000 metric tons, originally rested on 26 scaffolding towers. Using hydraulic presses, each section of the roof was gradually lowered by 6 cm (2 in) and positioned on 11 concrete columns. Slowly, the complete steel structure of the roof moved downward at the pace of a few millimeters a day.
During the process, which took several weeks, Vokal + Partner surveyors ensured every 10 minutes that the roof was brought steadily and precisely to its 200 predefined support points. The semi-automatic target detection and tracking system, as well as the servo-driven control, guaranteed that they could track each horizontal and vertical movement of the 10 points in focus with millimeter accuracy and immediately contact the staff responsible for the roof placement in case of discrepancies.
Along with real-time monitoring during the roof lowering process, the surveyors conducted geodetic network and settlement measurements at approximately 200 points in predefined time intervals, using two or three crews, each consisting of two surveyors. Equally critical, the crews transferred points in two dimensions and three dimensions to be set out onto the site for the steel structures or from the site into CAD plans. Vokal + Partner surveyors also checked the accuracy of the steel, faÃ§ade and shell construction work.
"We need precise instruments with an angle precision of 1" and distance accuracy of +/- 1 mm for the demanding tasks required on the projects we undertake," Mario Vokal says. "The passive prism tracking provided by the Trimble S6 is an excellent extension to our Trimble 5600 series, which uses active prisms. The S6 also enables us to import and export CAD data into the TCU controller, which has proven itself in daily use. This allows us to effectively manage the survey operations and the large complexities of the site. The next sensible step would be the activation of our S6 series tool for automatic settlement and deformation monitoring."
Many pieces of the project, including the panels for the solar system on the lounge, restaurant area and side roofs, must first be marked out with high accuracy for assembly and precise installation by individual assembly companies. These are also measured and documented with as-built surveys to ensure that they are positioned correctly. The installation tolerances are +/- 2 mm horizontal, +/- 3 mm vertical; if these are exceeded, online adjustment is necessary.
Other important tasks include geometric control and documentation to prove that the construction of the steel structure meets specifications after completion. During the entire project, data of all junctions and intersections of the lower edges of the binding girders are collected three-dimensionally and evaluated in a chart. The results not only serve as proofs and for archiving, but also can be used for further static computations. Vokal's surveyors also provided additional measurements to the design engineers to confirm that the construction conformed with the design. During production in the factory, Vokal + Partner supervised and examined the areas of the glass-cut faÃ§ades, the bridge hangings anchored in the side roof, the console panels for mounting the front faÃ§ade, the unique stairs in the area of the double cone, and even the individual finished sections of the bridge construction that run inside the building. All of these measurements were taken so that the components could later be aligned and documented onsite.
Reliable Service"We've been using Trimble instruments since we took over the company from our father seven years ago," Mario Vokal says. "We particularly appreciate their accuracy, reliability and robustness."
These characteristics have been shown to be essential on the BMW Welt site. Often, rain lashes against the total station's lens, particularly when it is located on one of the scaffolding towers or hydraulic lift platforms. When the Vokal team is stationed in a crane cabin 40 m (141 ft) off the ground to set out points that are otherwise inaccessible, gusts of wind may sway the crane cabin and cause the men and their instruments to move up against the parapet. Additionally, trains rumble along the nearby underground line. In all of these circumstances, the +/- 6' dual-axis automatic compensation of the Trimble 5601 is more than sufficient to maintain measurement accuracy.
The BMW Welt construction site is continually undergoing changes. "Sometimes a point due to be set out has disappeared [or] has been hidden by new construction elements," Vokal says. "In other cases, unforeseen control measurements are suddenly required." Even under these time-critical circumstances, the control unit's high functionality as well as its seamless data flow between the total station and the software make in-house processing of measured coordinates possible. This prevents the surveying work from becoming a never-ending task. Field data captured daily is directly transferred to computer-aided 3D construction plans the same evening, in order to assess current construction conditions and compare them to the original design data. This way, constructional defects and errors can be detected rapidly and rectified immediately. With their precise and accurate surveying data, Vokal + Partner surveyors provide critical support and assistance to the different trades engaged in the construction work on the BMW Welt project.
Today, the innovative architectural designs such as those displayed by BMW Welt are part of many construction projects worldwide. They represent visionary ideas and launch future concepts. But without the contribution of surveyors and their advanced technology, such dreams could never come true. The supporting efforts of the surveyors enable companies like BMW to symbolically represent their renowned names and reputations through innovative architecture.