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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

The House that LEGO Built

By Robert L. Reid (Editor)

Designed to resemble giant LEGO bricks stacked on top of one another, the LEGO House is an instantly iconic new building in Billund, Denmark. The 12,300 sq m facility houses multiple attractions and features 25 million LEGO bricks that were used to create numerous displays, including a towering tree that is considered one of the largest LEGO structures ever built.

DUBBED THE "Home of the Brick," the LEGO House is a so-called "experience house" in Billund, Denmark, that combines museum like spaces with indoor and outdoor play areas for fans of the brightly colored LEGO building pieces known as bricks. The building is a gift from the LEGO Group to the city of Billund, which is also home to the LEGO Group head office. Open since September 2017, the attraction expects to welcome more than 250,000 visitors per year.

The architect, Bjarke Ingels, the founder of Bjarke Ingels Group (BIG)—which has offices in Copenhagen, Denmark; and New York City—is a self-declared AFOL (adult fan of LEGO). In 2012, BIG won an architectural competition to design the LEGO House, and Ingels and Kjeld Kirk Kristiansen—the third-generation owner of the privately held LEGO Group—were determined to create something extraordinary. Located in the city center, just a 10-minute drive from Billund Airport (which the LEGO Group funded in the 1960s), the new building has become an instant landmark. At night, the site even welcomes visitors arriving by air with eight light beams that emanate from a gigantic keystone LEGO brick on top of the building.

The structure contains four color-coded "experience zones," exhibition areas, restaurants, a LEGO store, a cinema, an auditorium, and supporting facilities. There is also a large gallery of LEGO creations built by fans and an exhibition about the history of the brand—including 200 of the most iconic LEGO boxed sets. The showpiece is the 15 m tall "Tree of Creativity," considered one of the largest LEGO structures ever built. The majestic brick tree rises to the top floor of the 23 m tall structure. On the exterior, the facade creates the illusion that the whole building is made of LEGO bricks, but that appearance actually results from ceramic tiles clipped to a steel frame (for more on BIG's design, see "Embracing the Bricks").

The LEGO House is formed from a series of 21 large overlapping blocks, or boxes, that can each be considered an individual building. On the ground floor, the blocks frame a 2,000 sq m space known as the Square, which is open to the public and illuminated with daylight from the overhead windows between the blocks. The Square was designed to appear like "an urban cave without any visible columns," according to BIG. It allows visitors to take a shortcut through the building on their way to someplace else—though many of them will still spend their day surrounded by LEGOs in some fashion. Approximately 4,500 of Billund's roughly 6,200 citizens work for the LEGO Group.

COWI, based in Kongens Lyngby, Denmark, a suburb of Copenhagen, was selected as the project's consulting engineer early in the planning of the LEGO House and was responsible for the structural and geotechnical engineering, mechanical and electrical systems, and environmental impact analysis. The firm also assisted on a new local plan, assessed the design proposals, created a framework for the construction design, and supervised such key areas as sustainability, energy, acoustics, and fire and security engineering. In an exclusive interview, Civil Engineering asked Jan Bro Nielsen, a senior project manager in the Esbjerg, Denmark, office of COWI, to discuss the details of this remarkable project.

Civil Engineering of the LEGO House

Please describe the LEGO House—what is it like and how are the spaces used?

JAN BRO NIELSEN: Of the building's 21 blocks, or boxes, eight of them are on the ground-floor level, placed around the central plaza—the Square. Within these ground-floor blocks are the administration offices, workshops, wardrobes and toilets, an auditorium-like forum, several restaurants, a production kitchen, building facilities, and a LEGO store.

There are 12 boxes on the first elevated level, which is divided into four colored zones, each representing different aspects of learning. The yellow zone, for instance, is focused on expressing and regulating emotions to help build confidence and make reasoned choices in life. The blue zone stresses how to use logic and cognitive competencies to understand the world and solve complex problems. The red zone strives to stimulate creativity, while the green zone teaches communication skills, especially how to listen and respond to the needs and feelings of others.

There are mezzanine levels within four of the boxes at ground level and one box on the first elevated level. On the second elevated level is a box named the "Masterpiece Gallery," which features a rotating collection of works by artists from around the world whose artwork is made from LEGO bricks.

The roofs of many of the boxes are accessible to visitors and offer space for exhibitions and play areas. Eight of the boxes are restricted areas.

The basement is built in two levels. The deepest part has a floor level 6 m below the ground-floor level and houses the "History Collection," which is the official history museum of LEGOs and features hundreds of the most iconic LEGO sets, as well as a "digital vault" that enables visitors to see every LEGO set ever made. There are also a theater, a vestibule, and storage areas in the lower part of the basement. The upper part, which is 4.5 m below the ground-floor level, consists of underground parking, technical areas, and employee restrooms.

What about this project was especially interesting or challenging from a structural point of view?

The buildup of a complete three-dimensional finite element model using ETABS [software manufactured by Computers and Structures Inc., based in Walnut Creek, California], including both steel and concrete, was challenging, in particular because of the sensitivity of the model. Changes made locally on one side of the model caused changes in the stress results on the other side of the model. According to the European building codes, known collectively as Eurocodes, two independent finite element models had to be made for dealing with the large spans in the LEGO House, which reach 45 m, combined with the potential number of people in the building. The second finite element model was created in Robot [manufactured by Autodesk Inc., of San Rafael, California]. This is a good safety precaution in general, and it helped us to understand the very complex structural system and to eliminate possible errors.

It was also interesting to work on a building that, in every sense, is unique. You will not find anything similar anywhere else. Working closely with the LEGO Group and BIG, I think there are many unique and important lessons we can take with us from this project.

In dealing with the structural design, what were the major challenges?

The building seems to defy gravity and the other forces acting on its various structures. The main reason is that no columns were allowed in the Square area. Also, the ceiling above the Square was interrupted in a way that made it impossible to add normal tension members in that structure. The four cantilevered corner boxes were also a challenge because it was difficult to find possible support and anchoring positions for these boxes without interfering with the functionality of the rooms. Relatively short wall systems of either steel or concrete were used to create tension-pressure systems to support the cantilevered boxes. As the walls are short, the tension-pressure forces are rather high. These wall systems continue down in the basement.

The building is such a wonderful, whimsical structure—but it is also a building that people must be able to enter and leave safely, work in, and play in. How do you balance the whimsical with the practical?

Safety is an absolute top priority for the LEGO Group, so everything was planned with safety in mind. Elevators and ramps make the building fully accessible for disabled people. It includes an inside/outside elevator, which makes it possible to access the roof. In the beginning of the planning process, COWI developed several concepts to address the building's structural challenges, but the only solutions that were accepted by the LEGO Group and BIG were the ones that made possible the large, column-free space of the Square. COWI had to respect this decision, even though it increased the costs of the project. We had a saying that we had to build it like a bridge, with the so-called keystone box as the top of the bridge. The structural forces in the steel and concrete were, in certain positions, well beyond what you normally see in a relatively low building like this.

It was also a challenge to plan the geometry of the main mechanical and electrical installations because the boxes are displaced both horizontally and vertically. The equipment for the ventilation system was installed in the technical room in the basement, while 300 km of electrical cables were installed throughout the building.

What was on the site of the LEGO House prior to this project?

The old town hall building of Billund had been located where the LEGO House is now, right in the center of the city, surrounded by low residential buildings, shops, offices, and banks. Because of a major national reorganization of public administration, the town hall building was no longer in use at the time this project started. The LEGO Group bought the 30-year-old building and demolished it to make room for the LEGO House.

Tell me about the foundations—what are the details?

The foundations were made from watertight, reinforced-concrete plates with a minimum thickness of 400 mm that, in many locations, increased to a thickness of 1.5 m to accommodate the forces from the superstructure. The reinforcement ranged from 8 to 32 mm in diameter. The bottom level of the lower part of the plate is located approximately 7 m below grade, but the groundwater level is roughly 2 m below grade. This resulted in an uplift pressure caused by the groundwater of 50 kN per sq m. To offset that pressure, the basement is anchored by 240 ground anchors, 40 mm in diameter and ranging in length from 17 to 25 m. Each anchor is designed to accommodate an uplift pressure of 630 kN.

What were the soil conditions like?

At the foundations, approximately 7 m below grade, the soil is mainly glacial sand. But approximately 11 m below grade is a thin layer of clay. Groundwater leveling was necessary during the construction phase until the anchor system was in place and sufficient dead load from the building was present. Sheet piling was installed to create a construction pit, from which 26,000 cu m of soil was excavated. The sheet piling was anchored by 145 pieces of horizontal, sloping ground anchors. Because of the presence of the layer of clay, which is watertight, groundwater had to be pumped from two areas, one below and one above the clay. This was done to avoid a breach of the clay layer caused by the uplift pressure. Approximately 300 cu m per hour of groundwater was pumped to a grass field located 1.5 km from the construction site. The field was surrounded by an embankment to control and filter ocher from the water.

Which materials were used to build the LEGO House?

The superstructure is a large, three-dimensional steel structure shaping the boxes, with the keystone box as the center of the structure. The floors and roof levels of each box are made of precast and prestressed hollow-core concrete elements. The walls surrounding the staircases, elevator shafts, and some walls on the ground floor are made of either precast concrete elements or cast-in-place concrete, depending on the forces that are acting on the walls. The substructure is mainly cast-in-place concrete, heavily reinforced and watertight.

Are any parts of the building, even just decorative features in the walls or floors, made from actual LEGO bricks?

Not really, but everything is made to look like it was. The keystone box is scaled to resemble a giant LEGO piece with the same 2 by 4 width-to-length ratio of the classic plastic brick. The eight studs in the keystone brick are actually skylights, and the roof of the keystone is accessible to visitors, who can stand on the glass above the skylights, which is structurally robust enough to support their weight. Inside the keystone, visitors experience the illusion of being inside a LEGO brick with three tubes. These are actually podiums used for the Masterpiece Gallery exhibition. The space for the History Collection in the basement is also scaled to resemble a 2 by 4 brick, as are the tiles on the facades of all the boxes.

What were the gravity and lateral systems for the structure?

The superstructure is formed from a heavy steel structure located along the building perimeter, behind the facades, and the keystone box. The main supporting system is a so-called megatruss that features three key corbels, designated T, Q, and N [see illustration]. The megatruss is supported and anchored in the outer ground-floor boxes within concrete walls 600 to 900 mm thick and by steel transfer trusses. The total span of the system is 45 m. The keystone box is 26 m long and the Q, N, and T corbels each cantilever 10 m.

The loads in these structures are exceedingly high because the keystone box supports half of the loads from the surrounding exhibition boxes; the other half are supported on top of the ground-level boxes. The horizontal forces in the megatruss and the corbels are also very high. The lateral forces are fixed in the concrete walls located around staircases and in certain concrete walls on the ground floor.

A section of the concrete floor above the basement, underneath and along the keystone box, is made from prestressed cast-in-place concrete and contains the tensioned member, which could not be installed at the ceiling level of the Square.

Can you discuss the roof design, especially how it supports public access?

All of the roof surfaces feature a soft, permeable surface normally used for playgrounds. This surface is colored in different tones of red, green, blue, and yellow—corresponding with the different zones inside the building. Just beneath this soft surface is an 80 mm thick secondary concrete layer, reinforced with polyethylene fibers. This concrete layer was used on all the boxes with public access and exhibitions. It allows for random drilling to secure play equipment and exhibition items without damaging the watertight membrane beneath it.

What are the structural aspects of the facade system?

COWI and BIG had discussions regarding possible settlement in the main steel structure, specifically: How might settlement affect the tiled facades and the glass surfaces for the building's large windows? Several ways of securing the facades were discussed, but in the end a simple vertical steel frame at the top of each box and a horizontal steel frame at the bottom was chosen.

In all, 65,406 pieces of standard tiles were mounted to the exterior of the building, and another 17,261 pieces of standard tiles were mounted inside the building, along with 3,348 pieces of special tiles at the corners, top of walls, and other locations. Some 2,000 metric tons of steel, 7,000 cu m of cast-in-place concrete, 300 metric tons of steel reinforcement, 1,531 pieces of hollow core slabs, and 302 pieces of precast concrete wall elements were used for the construction.

Looking inside the building, can you tell me more about the decisions made here?

The wooden floor in the Square was installed on top of a secondary reinforced-concrete slab 150 mm thick, which itself is located above a 50 mm thick insulation mat designed to avoid and control any problems with noise. The slab was divided in 6 by 6 m sections to avoid cracking.

The main staircase, named the "Epic Staircase," surrounds the Tree of Creativity. The staircase, which weighs 40 metric tons, required additional reinforcement and large prestressed transfer beams to carry its own dead load as well as the dead load of the tree, which weighs 25 metric tons.

What special conditions must the building accommodate?

According to a Danish amendment to the Eurocodes, the building has to accommodate snow and wind loads. Because of the building's irregular shape, the design had to accommodate higher-than-usual snow and wind loads. In the end, though, the relatively heavy live load of 5 kN per sq m on all of the rooftops was also critical in the structural design. The seismic load is calculated as a horizontal force representing 1.5 percent of the total load, including safety factors but excluding wind load.

Are there any other details concerning the structural design that engineers might find interesting?

To assist the contractor [K.G. Hansen & Sønner A/S, of Grindsted, Denmark] with understanding the complexity of the building, and how the building had to be constructed, we generated a four-dimensional model of the structure. The four-dimensional model served as a link between the time schedules and the structural models, allowing us to replay a movie showing the construction process generally or in specific details. The four-dimensional model was highly appreciated by the contractor.

How has the building been received by the client and the public?

With a big smile! The LEGO House is said to be everything the client dreamed of—and for that I feel BIG deserves full credit. Beginning with the competition that BIG won in 2012, the design phase took place during 2013 and 2014. The old Billund town hall was demolished during spring 2014, and the excavation for the underground portions began during summer 2014. The building was ready for the installation of exhibits by spring 2017, and the grand opening was held September 28, 2017.

The feedback from visitors has been both overwhelming and highly positive. Last December, the LEGO House was named Denmark's "Building of the Year" by a committee that included the Danish Construction Association and the Confederation of Danish Industry for 2017—an award that salutes the technical skills that went into this structure and the positive impact it has already had on society, both locally and internationally.

PROJECT CREDITS

Owner: The LEGO Group, Billund, Denmark 
Architect: BIG, Copenhagen, Denmark; and New York City 
Structural and geotechnical engineer, mechanical and electrical systems engineer, environmental engineer, sustainability consultant, energy, acoustics, and fire and security engineer: COWI, Kongens Lyngby, Denmark 
General contractor: K.G. Hansen & Sønner A/S, Grindsted, Denmark 
Facade consultant: Skandinaviska Glassystem AB, Göteborg, Sweden

Turning Imagination Into Reality

JAN BRO NIELSEN, a senior project manager at COWI, and Brian Yang, a partner with Bjarke Ingels Group, were key figures in making the LEGO House a reality. Both shared childhood memories of the iconic building blocks with Civil Engineering.

CIVIL ENGINEERING: Did you play with LEGO bricks as a child? What role can the bricks play in encouraging children to become engineers and designers as adults?

NIELSEN: The LEGO brick is 60 years old now, and I suspect every child in Denmark plays with either LEGO or DUPLO bricks at some time. I did as a child, and I remember that my LEGO toys were my favorites. I passed this interest on to my two daughters, now adults. I also remember that I tended to take charge when new LEGO sets were given as presents for Christmas or birthdays, but I hope I also gave my daughters the space for them to enjoy building with LEGOs. I have no doubt that playing with three-dimensional colored bricks can develop creative skills and spatial understanding for children—and you never know what that can lead to in later life.

YANG: It's almost a cliché that half the people who apply to architecture school put in their application essay that they played with LEGO bricks as kids, and that's what inspired them to become an architect. But I absolutely played with LEGO bricks—I had a big red tub full of bricks that I still remember quite well. That's the great thing about the bricks: this idea of creativity through play and learning! It's such a simple, standardized system, and the brick in a way represents a kind of intersection between something abstract you can imagine in your mind and the kind of physical reality of the world around you. So it's an element that allows you to easily translate imagination into reality, and I think that's kind of the genius thing about it!

Embracing the Bricks

WHEN BJARKE INGELS GROUP (BIG) submitted its proposed design for the LEGO House as part of an invited competition in 2012, the architecture firm decided "to completely embrace the spirit of the bricks," says Brian Yang, a partner in BIG's Copenhagen, Denmark, office. This meant not only creating a physical scale model of the design made almost entirely from white LEGO bricks, but also creating a box with printed images of the model on the sides, as though it had been purchased at a toy store. "We even submitted the design report as a kind of facsimile of a LEGO brick manual," Yang adds.

Moreover, the winning design, which features giant overlapping blocks, each resembling an enormous LEGO brick, "embraced the idea of the LEGO proportion," Yang says. That proportion follows the familiar 2 by 4 ratio of two studs across the width of a standard LEGO brick and four studs in the long direction. This is best seen in the so-called keystone segment that tops the LEGO House building in Billund, Denmark, and features eight raised, round skylights in that classic 2 by 4 arrangement. In fact, the proportion was so important to the design that Kjeld Kirk Kristiansen, the owner of the privately held LEGO Group that manufactures the famous toy bricks, reportedly brought a tape measure to the building site as the facades were being mounted "to ensure that we really stuck to what we had told him we would do," says Yang, who adds that he heard about Kristiansen's visit but did not witness it.

To match the world of LEGO brick construction—in which the bricks interlock to create structures—the LEGO House was designed without any visible supports, Yang adds. This required close integration with the engineers at COWI, based in Kongens Lyngby, Denmark, a suburb of Copenhagen, to create column-free spaces and enclose the structure and the mechanical and electrical services within the building's walls. That represented both "an extensive challenge and an opportunity to integrate architecture and engineering," Yang says, so that "the building itself could be a kind of visual and living representation of the effortlessness of how you combine bricks." Not everything in the building is scaled exactly to LEGO brick dimensions or styles, however. For example, if the building had to accommodate the typical LEGO figure it would have meant designing the structure for people who are "four times as wide as a normal human being," Yang notes. So the designers had to "balance for elements that need to meet functional purposes for occupation [by real people]," he explains. "The challenge has been to integrate everything as effortlessly as possible, to find solutions that make everything blend in a seamless manner."

No actual LEGO bricks were used in the construction of the building, although certain parts of the foundations were cast in concrete in the shape of large LEGO bricks, Yang says. The attraction is filled with sculptures made from LEGO bricks, however, including people sitting on benches, dinosaurs in a special gallery that will feature ever-changing displays, and even "a huge, multicolored waterfall that spills out of one of the walls," Yang says.

Viewed from the ground, the exterior of the LEGO House still follows the mostly white color scheme from BIG's design model; in fact, when examined closely the facades appear to be made from layer upon layer of large, white LEGO bricks. But that is an illusion created by glazed tiles, Yang explains. From the air, the roofs of the overlapping blocks, many of them accessible to the public, present large swathes of bright red, green, yellow, and blue, with the keystone block in white. This aesthetic was adopted when it became clear that the flight path to Billund's airport would bring planes directly over the LEGO House, making the building "an incredible landmark and a great opportunity to express the kind of color and life of LEGO bricks," Yang says.

Although the LEGO Group initially considered potential sites around the world, from New York City to Tokyo, for the LEGO House, the company's leadership ultimately decided on Billund because "they felt very strongly that they should give back to and affirm the importance of the city of their birth," Yang says. They knew this decision would likely mean fewer potential visitors than if they had built the attraction in a major metropolitan area, Yang adds, but "a strong feeling of allegiance guided where to locate it."

To construct the LEGO House on the site of the former Billund city hall involved the relocation of a stream that runs through the center of the city. Years earlier, as the city of Billund grew, the stream was enclosed in concrete, Yang notes, but as a separate project the stream was diverted to the south of the LEGO House and reopened. Now, visitors can sit in the LEGO House cafe and enjoy the view over the water.

"One of the broader goals of the [LEGO House] project was to look at how the city center could be improved," Yang explains. "So, for example, opening the stream back up and bringing nature back into the very center of the city was something people felt would be a strong, positive outcome."—ROBERT L. REID

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