In these times, it is therefore necessary to reintroduce, consciously, the social purposes which columns have, alongside their structural functions. Let us try to define these social purposes exactly.
A column affects a volume of space around it, according to the situation. The space has an area that is roughly circular, perhaps 5 feet in radius.
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The sface around the column.
When the column is too thin, or lacks a top or bottom, this entire volume—an area of perhaps 75 square feet—is lost. It cannot be a satisfactory place in its own right: the column is too thin to lean against, there is no way to build a seat up against it, there is no natural way to place a table or a chair against the column. On the other hand, the column still breaks up the space. It subtly prevents people from walking directly through that area: we notice
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that people tend to give these thin columns a wide berth; and it prevents people from forming groups.
In short, if the column has to be there, it will destroy a considerable area unless it is made to be a place where people feel comfortable to stay, a natural focus, a place to sit down, a place to lean.
Therefore:
When a column is free standing, make it as thick as a man—at least 12 inches, preferably 16 inches: and form places around it where people can sit and lean comfortably: a step, a small seat built up against the column, or a space formed by a pair of columns.
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| thick columns |
You can get the extra thickness quite cheaply if you build the column as a box column (216); complete the “place” the column forms, by giving it a “roof” in the form of a column capital, or vault which springs from the column, or by bracing the column against the beams-—column connection (227). And when it makes sense, make the column base a sitting wall (243), a place for flowers—raised flowers (245), or a place for a chair or table-DIFFERENT CHAIRS (25 1). . . .
227 COLUMN CONNECTIONS**
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. . . the columns are in position, and have been tied together by a perimeter beam—box columns (216), perimeter beams
(217). According to the principles of continuity which govern the basic structure—efficient structure (206), the connections need stiffening to lead the forces smoothly from the beams into the columns, especially when the columns are free standing as they are in an arcade or balcony—arcade ( i i 9), gallery surround (166), SIX-FOOT BALCONY (167), COLUMN PLACE (226). You may also do the same in the upper corners of your door and window frames—frames as thickened edges (225)—making arched openings.
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The strength of a structure depends on the strength of its connections; and these connections are most critical of all at corners, especially at the corners where the columns meet the beams.
There are two entirely different ways of looking at a connection:
1. As a source of rigidity, which can be strengthened by triangulation, to prevent racking of the frame. This is a moment connection: a brace. See the upper picture.
2. As a source of continuity, which helps the forces to flow easily around the corner in the process of transferring loads by changing the direction of the force. This is a continuity connection: a capital. See the lower picture.
x. A column connection as a brace.
As a building is erected, and throughout its life, it settles, creating tiny stresses within the structure. When the settling is uneven, as it most always is, the stresses are out of balance; there is strain in every part of the building, whether or not that part of the building was designed to accept strain and transmit the forces on down to the ground. The parts of the building that are not designed to carry these forces become the weak points of the building subject to fracture and rupture.
Effects of uneven stresses on a frame.
Rectangular frames, especially, have these cracks at the corners because the transmission of the load is discontinuous there. To solve this problem the frame must be braced—made into a rigid frame that transmits the forces around it as a whole without distorting. The bracing is required at any right-angled corner between columns and beams or in the corners of door and window frames.
2. A column connection as a capital.
This happens most effectively in an arch. The arch creates a continuous body of compressive material, which transfers vertical forces from one vertical axis to another. It works effectively because the line of action of a vertical force in a continuous compressive medium spreads out downward at about 45 degrees.
And a column capital is, in this sense, acting as a small, underdeveloped arch. It reduces the length of the beam—and so reduces bending stress. And it begins to provide the path for the forces as they move from one vertical axis to another, through the medium of the beam. The larger the capital, the better.
A capital that acts the same vuay as an arch.
A column connection will work best when it acts both as a column capital and as a column brace. This means that it needs to
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227 COLUMN CONNECTIONS
be thick and solid, like a capital, so that there is a lot of material for the forces to travel through, and stiff and strong and completely continuous with the column and perimeter beam, like the brace, so that it can work against shear and bending.
The bone structure, shown below uses both principles, to transfer compressive stress from one strut to another, continuously, throughout a three-dimensional space frame of struts. The structure is most massive at the connections, where the forces change direction.
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| Connections inside a bone. |
A similar column connection can be made integral with poured hollow columns and beams. The forms for the connection are gussets made of skin materiaclass="underline" then fill the column and the gussets and the beam in a continuous concrete pour.
Of all the patterns in the book, this is one of the most widespread and has taken the greatest variety of outward forms throughout the course of history. A solid wood capital on a wood column, or a continuously poured column top, and arches of stone, brick, or poured concrete are all examples. And, of course, typical column capitals—a larger stone on a stone column or typical gusset plate or brace—even if weak in some ways, also help a great deal. But only relatively few of the historical column connections succeed fully in acting both as braces and as capitals.
Therefore:
Build connections where the columns meet the beams. Any distribution of material which fills the corner up will do: fillets, gussets, column capitals, mushroom column, and
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most general of all, the arch, which connects column and beam in a continuous curve.
The connection is one of the most natural places for ornament (249): there is a wide variety of possible connections, carvings, fretwork, painting, for this critical position. In certain cases, the connection may act as an umbrella for a column place (226). . . .