Structure

“The room is the beginning of architecture.”

—   Louis I. Kahn

One of the architect’s fundamental tasks is formulating the structure, or arrangement of forms, that the building will assume. Each architect has an individual approach to developing that initial concept. Kahn is often quoted as first asking, “What does this building want to be?” He believed that the essence of the structure started with the room, and thinking about how that space would be used and how it should feel. From that point, the building evolved as a “family of rooms” with a simple plan based on classical proportion, repetition, and variation.

In the case of the Kimbell, director Richard Brown provided an initial list of important considerations for generating ideas for the structure. In that “Pre-Architectural Program,” Brown specifically stated that “natural light should play a vital part in illumination.” This stipulation, along with Kahn’s own strong interest in the use of natural light, resulted in Kahn’s early concept of a room with a vaulted ceiling that would allow natural light to enter the space from above. The vault also appealed to Kahn’s admiration for ancient structures—from Roman arches and storage warehouses to Egyptian granaries.

Kahn determined the exact shape of the vault through his collaboration with a structural engineer, Dr. August E. Komendant. As opposed to semicircular vaults, the cycloid vault has gently rising sides that give the impression of monumentality without overpowering the visitor. By mathematical definition, the cycloid is the curve traced by a point on the circumference of a circle that rolls on a straight line without slipping. This geometric form is capable of supporting its own weight and has been likened to an eggshell for its ability to withstand heavy pressure. At the Kimbell, the weight for each vault is directed through four corner columns measuring two square feet. Unlike classical precedents, Kahn’s vaults are interrupted at the top by skylights and require concrete struts that connect the shells at ten-foot intervals. Additionally, Kahn and his engineers placed long steel cables inside along the length of each vault. After the concrete had hardened for a week, hydraulic jacks were used tighten the cables to create a system of post-tensioning that distributes and supports the weight of the roof—similar to a suspension bridge.

Like classical buildings (such as the Parthenon), the Kimbell’s structure is based on a consistent mathematical model. The basic plan is composed of sixteen cycloid vaults (100 x 20 feet) that are arranged in three parallel units of six, four, and six in the Kimbell. Other elements are based on a ratio of 20 to 10. For example, on the floor, wood sections measure 20 feet and travertine sections are 10 feet. The building is based on these “rules” of logic, enabling the visitor to easily follow and “read” the structure.

Although the structure is based on a simple plan of unadorned, repeated forms, Kahn also introduced variations on those basic forms and “themes.” The porticos at the Kimbell’s entrance on the west side of the building first introduce the vault to the approaching visitor and demonstrate the form’s versatility. Within the Museum, visitors see that vaults cover the galleries, an auditorium, and the Buffet Restaurant. Kahn also varied the size of the courtyards. The North courtyard is 40 square feet, while the South courtyard is 20 square feet.

The “rooms” were designed to relate to the visitor on an intimate level to enhance their experience of the artworks on view. The space, in fact, was designed to be as flexible as possible within the confines of the vaulted spaces. Moveable walls can be attached to the soffits (the underside joint between arches) in various configurations to best suit the Museum’s display needs.