Each vault is roofed by 23 x 100 foot clear span cycloid shells of post-tensioned, poured in place, reinforced concrete with an as-cast surface. The vaults are each supported on four 2 x 2 foot corner columns. Calcium lead sheets sheath the shells. Vaults covering interior spaces have a longitudinal 2-1/2 foot slit at the apex braced by concrete struts every ten feet. Lower edges of the shell support seven foot reinforced concrete channels with soffits which house the air and electrical distribution systems. Two way post-tensioning is used in the upper level floor slabs. The lower level is simply poured in place concrete slabs with joist support construction.
On the exterior Kahn used diamond-sawn, travertine infill walls with a reinforced concrete core between the columns. He also used travertine veneer for court paving, steps, and wall copings. Double insulating glass is used on the gallery level; Plexiglass covers the large slits. Doors and frames, windows and bollards are of mill-finish stainless steel. On the interior travertine is again used for infill walls, stairs, balustrades and portions of the floor. The remaining gallery flooring, the cabinet work and interior doors and frames are of quarter sawn white oak. Mill finished stainless steel is also used for the elevators, kitchen and handrails.
The emphasis of this building is the manipulation of natural light for the purpose of creating a dynamic environment.
"We knew that the museum would always be full of surprises. The blues would be one thing one day; the blues would be another thing another day, depending on the character of the light. Nothing static, nothing static as an electric bulb, which can only give you one iota of the character of light. so the museum has as many moods as there are moments in time, and never as long as the museum remains as a building will there be a single day like the other." (2)Kahn cut the three courts on the top floor at right angles to the vaults to open up to the sky and celebrate the different qualities of light. the separate courts, the Green Court, Yellow Court and Blue Court were named such in anticipation of the kind of light that their proportions, foliation and reflective surfaces would enhance. Of course the vaults each have slits at the apex that work as a natural light fixture, letting in light to be reflected onto the sides of the vaults and down the walls, giving the room a glow of silver, and the end walls fall just short of the vault revealing narrow slices of the sun.
"In a 1987 analysis focusing on the building's structure and expression, Peter McCleary described the vaults as a structural hybrid, "neither pure vault nor pure shell", basing his evaluation on the use of both stiff edge-beams and cables within the concrete. The skylight at the apex removes material at the point of maximum compressive stress. "The structural behavior of the roof [is] beyond the intellectual and visual comprehension of most architects and engineers," said Mc Cleary, rejecting published explanations. But he also reported Kahn's own priorities, conveyed to him in conversation between the two during construction. Kahn told him that "the quality of light and place in the then partially completed museum was sufficiently beautiful that, for the moment, he was willing to sacrifice the truth of the structural principle." Most visitors are convinced by the beauty of these architectural spaces in light and accept their structural means unquestioningly as logical."(3)
The Kimbell Art Museum has a fairly simple yet deceptive structural system as far as vertical loading is concerned, especially concerning the corner placement of the columns. Since they are placed 100 feet apart in the longitudinal dimension it would seem that there would need to be more support than just the four corner columns. The rinforced concrete system, however, transfers the loads so well along the vault that the vault can be 100 feet long and only have the four corner columns.
The dead load from the vault is not the only load that is applied to the barrel vault. Along the lower edges of the shells the vault supports a seven foot reinforced concrete channel. This channel houses the air and electrical distribution systems.
Another reason that the columns can be so few and far between are that no additional loads will be added to the system. The system is designed to carry the dead loads of the roof and chases, and the live loads of rain and perhaps a little snow. No further live loads need to be accounted for, thus the great distance between columns can be possible.
Along the apex of each vault there is a two and a half foot slit. This slit seems to break the continuity of the barrel vault. However, along this slit at twn foot intervals there are concrete cross struts. These struts maintain the structural integrity demanded by the barrel vault. A vertical load applied to the apex of the vault would go through the following steps before the forces would be dispersed through the foundation. The load for this hypothetical situation will begin at the apex of the roof and will be transferred along the vault longitudinally and vertically until the load reaches the lower corner of the vault. The load will be combined with the loads of the chases and all the loads will be focused on one of the four corner columns. This load will be directed down the column to the floor. Supporting the upper floor are the four main columns in addition to more columns and shear walls. The spacing of the columns and shear walls on the lower level is about forth feet. The forces of these columns and shear walls continue down to the floor slab where they will then be dispersed in the foundation.
The Kimbell Art Museum uses its shear walls and arched roof forms to create a strong skin that resists lateral loads in both the east-west and north-south directions. The building gains its strength from its post-tensioned reinforced roof shells. These arches rest on exterior travertine infill walls with reinforced concrete cores which connect to the poured in place concrete slab. Loads applied to the east-west axis of the museum strike a concrete facade, where loads are both transferred down to the foundation (fixed connection) and up into the arch and directly down the east-west facade. From these points the remaining forces are transferred into the next bay and the process of transmitting forces into the earth is begun again. This process is repeated through the bays of the building until all the forces have been resolved.
Lateral forces which strike the north or south elevations of the Kimbell Art Museum are also resolved through the building, but differently from the loads of the east-west forces. These forces strike the facade and are again transferred directly into the rigid connection with the foundation. These horizontal forces run parallel with the pre-stressed arch and are transferred along it and down the walls into the earth. The structural theory about how this building deals with lateral loads is that the loads are brought down into the earth by the concrete walls and are distributed along the arches so that the walls are loaded equally so that they do not fail. Building elements such as steel and concrete assure that the form of the building is rigid and will stand a good chance of avoiding failure by wind and earth quake loads. the other type of loading axis on the building are loads that fall at angles to the facades (such as wind coming from the northeast). These types of loads are resolved by a combination of transferring loads across the arch and down the arch in order for them to be resolved by passing down the walls into the earth.
Curt Trolan, Matt Stauber and Lydia Jesse
ARCH 461/561 Spring 1995
I'm writing you from Austin, TX from the UT-School of Architecture. I was browsing the net and came across your case study of the Kimbell Museum. Needless to say, because of our particular location, the Kimbell Museum is one of the most cited buildings (ad nauseum) through the course of our studies. Everyoneâs been there and at some point in time have probably ãanalyzedä it in some way, shape or form.
I just wanted to bring up a point regarding the structure of the building. As far as I know the barrel vault of the roof is not a true barrel vault, i.e. load is not carried longitudinally in the same way as a true barrel vault.
In actuality, the concrete load bearing structures along the curve of the roof are in fact curved beams and should be treated as such. Consequently the "slits" at the top of the barrel shape should not be understood as a break in the integrity of a true barrel vault (this would compromise the force distribution of this arch shape). Rather they might be understood as breaks in the infill between the primary load bearing curved beams; thus the structural integrity is not compromised. This fact might slightly alter your discussion of the structure and in the face of my inability to expound upon the difference between true barrel vault and curvilinear beam, you may want to check with your structures professor.
Thanks nevertheless for your work. If I may be of service in providing you with the titles of texts that may explain the Kimbell structure better, don't hesitate to write.
Respectfully yours,
Rommel Sulit
M.Arch Candidate
UT-Austin
September 1996