The new Broad Museum, in Los Angeles, Calif., looks like a white wedding veil sparkling against the blue California sky. Indeed, the structure has been dubbed “the veil and the vault” by designers who created the unique facade to wrap around the museum’s two key spaces: the public exhibition space and the archive/storage space that will support the foundation’s extensive lending activities.
The vault is enveloped on all sides by an airy, cellular exoskeleton structure made up of 2500 glass-fiber-reinforced concrete (GFRC) panels and 650 tons of steel lifts that span across the block-long gallery; it provides filtered natural daylight. “The process of making the formwork for the uniquely shaped panels was a key factor in the success of this GFRC application,” says David Pakshong of Gensler, the executive architect on the project. Choosing a product with the demands for hundreds of different unique curved shapes for the exterior skin was a big challenge for the design team. Creating hundreds of conical light openings for the building and replicating the front oculus from a parabolic curve would need a product that was flexible and versatile to adapt to this design shape.
The designers created complete geometric information for each panel in three-dimensional (3-D) computer models first. The precast concrete producer imported this data directly into the tool path software to create instructions for the five-axis, computerized-numerical control machine to carve molds out of high-density foam. Before skinning in fiberglass, the foam molds were sanded and sealed to create the negative formwork for the GFRC panels. “The versatility of this rapid prototyping supported the timely resolution of many complex geometric conditions,” Pakshong says.
The high strength of the GFRC skin ensured the additional strength required for the structurally unique shapes. The skin strength and durability allowed for smaller tube framing for the skins, which helped accommodate tight tolerances for panel placement to the structural steel. The panel strength also meets the long life and durability requirements needed at the ground floor where the public has access. “GFRC proved to be the most cost-effective of all the materials analyzed, while meeting the schedule and durability requirements,” Pakshong says.
The frames had to be fabricated to tight tolerances so the locations of the components and connection points were checked with a total station survey before and after welding. The survey data was imported back into the 3-D model of the frame to verify accuracy. Before spraying the skin, the frames were positioned on the mold, surveyed, and verified against the model. Then the setting jigs were locked into position, and the frames were removed. This step in the process was never required before. The skins were sprayed, and then the frames were replaced into the jigs and resurveyed. Finally, they did a full 3-D scan of the finished product to ensure compliance with the model.
Pakshong sees this building as one of the more innovative projects he has ever been a part of. He says, “After four years of working on the building, I am still surprised by the ability of the architecture to challenge the way we understand space.”