Connections

Connections are the biggest challenge of material design.

Sketch of a femur

Sketch of a femur

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.

Sketch of column parts

Sketch of column parts

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.

Sketch of wood joinery

Sketch of wood joinery

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?

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