Staking day on site, laying out and adjusting 22 corners of a 5,100 SF footprint to see how the placement feels... with just a string and a 300' tape.Share: Follow:
(continuing the 2,500 page, unabridged dictionary exploration)
Clerk of the works, n. - An architect or other client representative working on a construction site to ensure the quality of materials and workmanship in accordance with the contract drawings and specifications.Share: Follow:
More fun with the 2,500 page, unabridged dictionary, without which our literature would be as lost as our architecture...
Blazing in gold, and quenching in purple,
Leaping like leopards in the sky,
Then at the feet of the old horizon
Laying her spotted face to die;
Stooping as low as the oriel window,
Touching the roof, and tinting the barn,
Kissing her bonnet to the meadow-
And the Juggler of Day is gone!
-- Emily Dickinson, 1864
I recently aquired a 2,500 page, five inch thick, 1975 unabridged Webster's Dictionary. But the massive heft and bulk bely its paucity of architectural information.
This dictionary has five entries for kern, but no definitions for the critical structural idea that spanned 1,000 years of architecture and responsible for every stone church in the Middle Ages and Renaissance.
The kern is the concept that enabled Dark Ages cathedrals to reach new heights, despite only stone masonry with no ability to resist tensile forces. James Ambrose, in my 1988 structural textbook, Building Structures, defines a kern as "a zone around the centroid of the section within which an eccentric force will not cause tension on the section."
Simply put, a kern is the center third of a foundation. When stacking stone, its foundation will resist rotating, lifting a side off of the ground, or cracking in tension as long as the weight and forces of the structure above are within this center third.
As soon as forces become eccentric beyond that zone, tension happens. The foundation will want to twist in the ground and additional measures must be taken to avoid a failure. This is easily mitigated with steel today, but before the Industrial Age, builders had to design with the kern to ensure stability.Share: Follow:
Connections are the biggest challenge of material design.
I like to use a femur to illustrate this concept. Do you see the straight shaft of the bone? Relative to the rest, it is quite simple. Although you wouldn't want it to happen, a femur broken in the middle can heal, maybe with assistance of pins and plates, back to 100% mobility.
Broken joints, on the other hand, are rarely fully restored. Hip replacements can be pretty successful. But the complexity of interfaces between bone, cartilage, ligaments, tendons, bursa sacs and muscles at the other end make full recovery unlikely.
Architectural materials are no different.
A femur is much like a column. Designing a column size is relatively simple work. There are common tables to set the basic sectional dimensions capable of managing a given vertical load.
The real work in structural design is determining how the column's base and capital are connections at its base and the beams it supports. Are they welded or bolted? Are there lateral forces being managed by those connections? How do we manage cracking and settling at the footing? Are the beams resting on top of the column or are they bolted on to its side? Are vertical columns continuing above? Countless more decisions are resolved. Just like in animal structures, failures in building structures are most likely at the connections, too. So designers spend most of their time working out connection details.
The same principle can be seen in materials. Take for example, wood. It is beautiful, but challenging to work because it is unstable. Wood warps and moves even with minor temperature or humidity changes. Much of wood design and craftsmanship involves designing around this temperamental nature.
The slab in the sketch below is a piece of wood that will move a great deal in the vertical direction. Wood is more stable along its length, but perpendicular to the grain movement can be up to a half a percent. You won't notice this... until it cracks.
Traditionally, wood movement was managed by floating a panel assembly of wood in a frame. The panel, itself a series of pieces sometimes joined by tongue-and-groove joints, floated in grooves carved into the sides of the styles and rails of the frame that held it. The subtle offsets, grooves, mortises, and tenons all do their job to avoid cracking and maintain a well-formed rectangle for the life of the piece.
In fact, the historical name for a woodworker, prior to these engineered wood products, was a joiner. The skill of the craft was artfully assembling solid wood without it coming apart.
Today, we are spoiled by engineered wood products: plywood, particle board, high density fiberboard (hardboard, such as Masonite), medium density fiberboard (MDF), oriented strand board (OSB), melamine (plastic coating), laminates (phenolic-impregnated paper), thin wood veneers, laminated timber (glue-lam, cross-laminated, laminated strand), etc. Modern glues and resins, in combination with the re-orientation of wood fibers, make it more stable.
I venture that all these engineered products have completely spoiled our sensibilities to natural materials. Before engineered wood products, wood was used only in solid form. Thus the qualitative term solid wood, although I'm not sure anybody really comprehends that term these days. Imagine the challenge of putting together cathedral paneling in solid wood with only weak animal hide glues. Outside of the rare craftsman, all the products we see and use today from big box stores, retail furnishing centers, internet merchants, and mass flat pack channels are created from engineered woods.
So, now that all of our wood products are stable, has our understanding of materials warped?Share: Follow: