Sumit Singhal loves modern architecture. He comes from a family of builders who have built more than 20 projects in the last ten years near Delhi in India. He has recently started writing about the architectural projects that catch his imagination.
BMW Welt in Munich, Germany by Coop Himmelb(l)au
September 3rd, 2013 by Sumit Singhal
Article source: Coop Himmelb(l)au
The realization of the technical building facilities within the scope of the architecture led to a planning model with five thematic blocks: Hall, Premiere, Forum, Gastronomy and Double Cone.
A low-tech concept optimized ecologically using high-tech methods
The technical solution here is based on previous experience with large halls. All of the necessary features were realized successfully according to a low-tech concept. The interrelations of daylight and artificial light with ambient climate and acoustics influence people’s feeling of well-being in the Hall. The concept for the technological building systems takes up these relationships and integrates them in an interdependent manner, adapting their range of influence by modifying their dimensions or building in appropriate control mechanisms. A major goal in designing the systems was to save energy.
This aim is achieved by minimizing the mechanical apparatus for ventilation, heating and cooling. The gigantic Hall is thus conceived as a solar-heated, naturally ventilated sub-climatic area, a multifunctional space that does not follow the otherwise customary requirements for heating and ventilation.
A natural air supply is generated by thermal currents, wind pressure and turbulences when air accumulates in the area of the façade and roof projection. Air intake and outflow take place through automatically controlled vents. The “natural aeration” system provides sufficient fresh air to the Hall.
The Hall’s roof system has special significance for the complex made up of heat, cold and air. A 3D simulation of thermal currents and air streams was conducted in order to investigate the spread of exhaust fumes from the cars driven on the Premiere level. Iterative calculations were then carried out to optimize the arrangement of air intake and outflow vents for natural air exchange in such a way that it was possible to remain below the permitted threshold value of around ten percent.
Exhaust gas diffusion prevented through negative pressure
The key task of the new BMW Welt is to deliver cars – in the Premiere section – with all concepts geared toward enhancing the experience of delivery. Because of the exhaust gases that this task involves, special considerations and calculations had to be made in terms of the ventilation plan, since the Premiere is open to the Hall – the major space in this world of experience. Beyond merely fine-tuning the volume of air intake and outflow currents, it was also important to extract the exhaust fumes directly and pump in fresh air. Planning here was based on an assumed turnover of 40 cars per hour, or 250 cars per day.
A room-in-a-room for maximum flexibility
The Forum is a separate event area for up to 1.200 persons, equipped to meet all the specifications for a full-fledged theater or conference room.
The ventilation technology fulfills the high demands on comfort and soundproofing placed on such a sensitive area when it is situated in the middle of other function areas. The technical facilities for this special area were conceived independently, including a plan for integrating them into the architecture. Air is supplied laterally via air jets and is extracted through the ceiling as exhaust air. Based on the number of people in the room, infinite adjustment of the required air volume is possible.
Island solutions place high demands on building systems to ensure well-being
The technical equipment discreetly supports the gastronomic functions. In places where guests spend longer periods of time, air sources are placed near the floor. In order to ensure pleasant air quality even near the glass façades, the vertical façade support profiles are heated to prevent the cold downdrafts typical for this kind of construction.
An event space offering all the options of a public assembly place
The Double Cone is used as an exhibition space and for special events. Air is brought in by means of a low-induction system along the base of the façade and streams into the roof through the opening at the top of the cone. Floor air conditioning and air circulation coolers in the wall and floor areas ensure the necessary comfort level. In the in-between seasons, natural ventilation via façade shutters is used. The structural design of BMW Welt represents a special challenge when determining how to conduct supply lines. Because of the vast support-free space, which is borne by only 11 columns plus the elevator shafts, the supply cross-sections for the Lounge floors and the Tower had to be integrated into the few supporting core cross-sections. This situation necessitated close coordination at a very early project phase between those responsible for structural engineering, the routing of facility services and building technology.
The system of the roof construction consists of an upper and a lower grid layer with a basic grid of 5.0m x 5.0m.
The upper girder grid was cambered upward like a cushion through its own negative weight, and forces were exerted on the lower one conducted from the surfaces and building structures underneath it.
The resulting forms were monitored and optimized in respect of the meaningfulness of the load transfer. The various heights of the support structure elements are adapted to the stresses they must withstand. The interplay of the two girder layers as spatial support structure emerged from the addition of diagonal truss braces. To equalize the stress on the nodes and reduce the free lengths of the top and bottom chords, the points connecting the diagonals of the crossing truss braces are arranged in a staggered pattern.
This yielded a lightweight and efficient support structure which, despite the vast expanses to be spanned, could be realized with relatively low material requirements. The vertical support of the roof was effected in the competition design by a series of circulating A-shaped supports, arranged eight meters from the outer edge of the roof and set toward the inside. Further support was provided by the Double Cone and the Lounge, which is conceived as an independent structure. In order to enhance the impression of floating, these circulating supports were then omitted when the program was consolidated in the subsequent design process. Instead, the structural components that were part of the design anyway were utilized as load-bearing elements without effecting the efficiency of the support structure, with just a few additional columns required.
The Double Cone takes the form of two leaning truncated cones with a rounded transition between them. In structural engineering terms, it is conceived as a framework shell made of horizontal rings and two ascending diagonal bands. Both bands are spiral-shaped and turn in the same direction in order to further enhance the impression of dynamism. The mesh size of the Double Cone was originally oriented to that of the roof grid. The glazing was done by means of a secondary structure. The Double Cone is a main roof support element and also plays an essential role in horizontal reinforcement since the horizontal loads in the solid building structure below the Double Cone are discharged via its base points.
Due to the special proposal mentioned at the beginning, the mesh size was halved in order to match that of the glass panes and slide the triangular panes directly into the rectangular hollow profiles measuring 300 x 100 millimeters or 250 x 100 millimeters. In order to ensure the necessary support, all joints were welded into an unbending skeleton shell. The Double Cone is closed on top by a suspended roof with radial and tangential girders, which is hung in a bend-resistant ring-shaped three-chord support.
The façade was conceived as a modified post-and-beam system. Leaning ten degrees out of the vertical, the posts are bent at a height of 7.50 meters. The advantage of the bent construction is that vertical warping of the roof can be taken up by the elastic bending of the posts. This eliminated the need for movement joints in the roof. The posts are coupled with the roof structure at both the top and bottom chord levels. Where the variably running roof edge is higher, the façade is in addition braced against the roof at a height of 15 meters. This reduces the free span widths to the extent that only minimal post cross-sections are required in relation to the height of the façade. The façade posts are placed at intervals of 5 meters. The façade cross-sections consist of two coupled flat steel plates in order to afford hidden routing and easy accessibility in the posts for the building services supply lines.
The glazing is clamped directly to the beams and glued in the butt joints. It was slogged as closely to the edge as possible in order to minimize bending loads from the beams.
The Lounge section of the building is found directly above the Premiere platforms, the heart of BMW Welt, at the height of the top levels E2 to E4, so that it is positively encased in the roof cloud. Due to the larger roof volume at Level E4, this level has a larger floor plan and juts about 6 meters over the floor below. The entire structure, which measures 70 x 34 meters on Level E3 and 70 x 40 meters on Level E4, was planned to rest on only five points so as not to interfere with the Premiere area on Level E1. Based on these limiting conditions, a “load-bearing box” was developed with load-bearing panels and walls in the form of the floor slabs and the surrounding story-high lattice girders. Four of the five load transfer points are found on the longitudinal sides in the vicinity of the surrounding lattice girders. The fifth load transfer point is the internal core with its torsion-resistant cross-section, which at the same time also ensures the necessary bracing.
The roof of the Lounge and the ceiling over Level E3 are executed using composite beams, adjusted to a grid size of 5.0 x10.0 meters. These rest on the composite columns, the surrounding lattice girders and directly on the core. The loads borne by the composite columns are taken up by the lattice grid of the fish-bellied girder, the top chord level of which is likewise bonded to the steel-reinforced concrete ceiling panel above. The encircling, in some parts glazed lattice and the internal core rest in the north on two large steel-reinforced columns and in the south on inclined console-like steel composite structures in the elevator panels. Through these “oblique” intersections at the load transfer points and the great load forces exerted (up to 12,000 KN), high horizontal forces arose that had to be borne through the concrete ceiling panel via the fish-bellied girder level and on into the core.
Furthermore, the horizontal and vertical loads had to be conducted from the adjacent roof to the cantilevered lattice girders on the north side of the Lounge. Through this load and the eccentric load discharge, additional large horizontal stresses were conducted into the floor slab panels. These horizontal loads are conducted by the steel construction into the concrete floor slabs and from these on into the core. With this complex stress on the floor slabs, as well as on the composite beams, it is necessary to design the above-mentioned components to withstand this unusual sequence of forces (large panel strain, bending with normal force for the composite beams).
Due to the geometry, the stresses and the construction of the Lounge, it was necessary to support the Lounge on assembly towers and then to subject it to its load only when complete. In order to carry out the ceiling lowering process in this highly complex support system with as few restraints as possible and to ensure optimal assembly, the bearing points for the composite beams were executed on the core as freely rotating bearing pockets.
Moreover, a ceiling strip between the core and the southern lattice girder, which runs through the middle of the field approx. three meters from the core, was covered in concrete only after the lowering procedure.
The design idea behind the bridge, which allows the street to be crossed on foot and connects BMW Welt to the Museum, as well as linking the functional areas within BMW Welt, was to expand the space in BMW Welt. Therefore, the structure and form of the bridge outside of BMW Welt (exterior bridge) followed the form of the bridge inside (interior bridge). The functional and formal concepts were in this way extended over Lerchenauerstrasse, and the BMW areas on the opposite side (company headquarters and museum) were connected to vehicle traffic without an intersection.
Inside BMW Welt, all publicly accessible areas, such as the Forum, the Tower and the Double Cone, are connected by this bridge. In order to avoid columns in the interior, the bridge was suspended from the roof. At defined panorama points, curving bays in the bridge invite guests to pause and take in the scene. The largest span of the exterior bridge is around 60 meters. The material chosen for the outer cladding is glass-bead-blasted stainless steel – the same as the outer skin of BMW Welt.
The Forum is supplemented by a fullservice conference area that is cantilevered out 20 meters from the body of the Forum, dictating its appearance toward the north. The size of the conference rooms can be adapted for various requirements using mobile dividing walls.
Another consequence of the variety of desired uses was that the Forum had to be sound-insulated from the rest of the building. Noise from the loading yard located directly below could not be allowed to permeate into the Forum, nor should there be any mutual disturbance between the Forum and the adjacent rooms. Vibrations from the pressing plant on the opposite side of the street also had to be eliminated as far as possible.
The heart of the Forum is the large Auditorium, which is equipped with variable hydraulic platforms. The Auditorium provides a backdrop for a wide variety of possible events, from banquets to classic theater. The platform topography is made up of one-meter-wide platform strips on guide rails along the longitudinal sides of the Auditorium. These are infinitely adjustable in height using push-pull chains. The theater space thus offers maximum flexibility. Various heights can be created according to event type. The event space itself is supplemented by lateral stages, backstage and under-stage areas.
A mobile wall can be moved aside to open up the Auditorium to the Hall along its entire width. This moveable gate functions like a reversed “iron curtain,” since it is not raised but rather sunk into the floor. The whole Auditorium then becomes a stage, with the boundaries between stage and audience flexibly adjustable to fit the event concerned. Since fire prevention regulations now allow audience members to be on stage, the Auditorium itself can form a vast stage without any need for fire-preventing separation measures between audience and performers.
The mushroom-shaped tower in the southwest part of the Hall houses mixed uses, both publicly accessible ones such as shops, the Junior Campus children’s & youth adventure areas, restaurants on several levels, as well as the private administrative area. Encapsulated interior spaces with walk-through terraces and open galleries form an abstract topography under the roof. In terms of construction, this tower takes on a major role in the reinforcement and load-bearing work for the entire roof. The restaurant core with its rectangular cross-section projects over the Hall approx. 10.5 meters on Levels E3 and E4 on the east side, approx. 4.0 or 6.0 meters on the other sides. In order to minimize the stresses on the cantilevered wall panels, the floor slabs in these areas are executed in a steel composite. The horizontal and vertical roof loads are supported on the south and west sides (cantilever of 6.0 meters). Due to these stresses and the necessary warping limitations for the entire roof system, the cantilevered walls are prestressed. The rectangular core cross-section could not be carried out due to the delivery function on the first lower level. This meant that approx. 50% of the reinforcing core walls had to be taken up on Level E0. This was done by extending one core wall on Level E0 up to a supporting structural component. In order to model this load-bearing effect, the entire Tower was studied in a three-dimensional calculation using the finite elements method.
The stage for handing over new vehicles is called “Premiere.” It is the final and most important station in the sequential process in which customer and vehicle are brought together. This realm is made up of the actual handing-over area with its 20 rotating platforms and 10 additional hand-over sites on the eastern façade, the actual exit ramp, and the Marina, a slightly raised area that cannot be driven on, located within the elliptically arranged rotating platforms and connected to the Lounge Level E3 via a 30-meter-long hanging stairway. The optimal presentation of the vehicles, together with the role played by specially dramatized sight lines in the “stage setting” as well as the uniqueness of the location, are designed to make vehicle delivery an authentic and one-of-a-kind experience for the customer.
The rotating platforms not only ensure that the vehicle is always presented to the customer from its “best side,” but can also be turned for entry and exit to ensure a minimum of maneuvering. The hand-over spots are lit with HMI lamps. These are integrated into the ceiling inside lightproof boxes of approx. 6 meters in length.
Flexible blades on the underside of the light boxes shield the direct view of the lamps and minimize the light reflections on the car paint.
The entire area is equipped with a hollow floor with a high-pressure exhaust function, making it possible to draw off the vehicle emissions as close as possible to the point of origin.
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