The structure organizes and is expressed through the fifth floor. this level is out of contact with the main room and is an entity unto itself. The entire building is load bearing masonry, the exterior walls of brick, the interior floors, walls, columns
and "X" bracing above, of poured in place concrete. Much is made of the upward narrowing of the exterior brick columns, which reduce their width in elevation as they rise upward, supposedly to illustrate the lightening of the loads of the building. How
ever, the real weight of the floors and stacks is carried by a separate system, just behind the tapering brick facade. The real columns are of the same dimension all the way to the ground. The brick does, however, give a feeling of rigidity to the exter
ior box, while the interior appears plastic and layered because of the use of the polished concrete. Fortunately, as this material application was with respect to the movement of light throughout the building, in fact, concrete was used as a result of bu
dget cuts. Kahn had chosen brick for the entire interior, but it turned out to be far more expensive that the Academy could afford.
The horizontal loading upon the structure is limited to forces from wind and earthquake. These loads would travel through the facade and into the floors of the outer ring which are supported by the brick columns and jack arches. This is not the place wh ere the shear forces stop. The poor stringth of a masonry structure acting in tension requires that these forces be transfered into the box. They would move across the stack floors and be partially transferred downward by the concrete service cores. Th e remaining load would be picked up in the columns that are angled at 45 degrees. this core is the strongest place in the building to resist shear. The columns there are braced with the massive concrete "X" above the main room and with the suspended con crete walls which extend from the second to the fifth floors. It is this main reading room box, in conjunction with the concrete ceiling deck, that hold the building together against horizontal loading. All of these actions are transferred down to the c oncrete pan foundation. While we lack construction details for this base of the columns, considering their size, this column/pan joint probably transfers moment, tying the basement slab into the shear structure of the building.
The vertical load bearing elements of the Exeter Library consist of two separate systems serving independent functions. The exterior brick facade is a distinct, self supporting layer, rising directly from its foundation, forming the enclosure to teh buil ding. The rest of the building inside the facade is a concrete structure.
The facade is load bearing, but only bears the weight of the bricks above, the apndrels and windows. The brick piers taper to the top in elevation, emphasizing the load bearing nature of brick and the fact that more material needs to be at the bottom. S ince the brick facade is not supporting the floors behind, this tapering of the brick columns ends up being a referential gesture. The forces acting upon the structure are, gravity, the dead load of the material that composes the facade, wind load and a minor snow load. These will all apply vertical forces except the wind load. this applies a lateral force and needs to be transferred. The piers that form the vertical lines of the facade are in compression, transferring all loads to the concrete slab, from there to be distributed to the earth. The loads of the bricks above the windows are transferred horizontally across the jack arch into the piers. the eroded corners of the building expose the true nature of the exterior walls.
If a live load were applied to the roof of the Exeter Library such as snow, it had a journey of about eighty feet before it reaches the slab and the earth. The roof is supported by two massive concrete beams that span the atrium. These beams which measu re 18 inches wide by 16 feet deep weigh 87 tons. While they contribute to the rigidity of the box, they are mostly superfluous with respect to vertical loads. Their function is mainly architectural, serving to diffuse the light entering through the cler estory and giving the space visual stability. Thses beams are supported at their ends by 2 x 6 foot concrete columns that are turned at 45 degrees to the walls. These columns transfer this compressive force to the slab below. four walls define the spac e of the central atrium. These walls are one foot thick concrete, with large circular holes removed from the middle. They are suspended 17'-4" above the main floor by the four 2 x 6 foot columns which carry the load to the ground.
Each corner has a concrete service core. The side walls of these cores are two foot thick concrete. They support the floors, including the stacks, by acting in compression. The cores contain elevators, stairs, toilets and mechanical systems.
The final vertical load bearing system is the outer ring, shich contains the reading carrels and defines the exterior arcade on the entrance level. the floors are one way concrete slabs supported by brick piers and jack arches. It is interesting to note
that these load bearing piers maintain their dimensions to the top in contrast to the adjacent non-load bearing facade with tapering columns. A load in the middle of one of these floors would travel across the slab, into the arch and down the column to
the slab, rather than through the adjacent brick facade.
Ross Leventhal and Ray Strang
ARCH 461/561 Spring 1995
Do you have questions about adding a case? or a building to suggest??????? send a message to me....... chrisl@aaa.uoregon.edu