Preservation ABCs: X is X-ray

Preservation ABCs is a series that will work its way from A to Z, bringing words into conversation that are relevant to historic preservation, whether it’s an idea, feature or vocabulary term. The idea is to help you see preservation everywhere you look and wherever you go. Enjoy! See previous letters.

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X is for X-ray 

X-rays are not just for people in hospitals or luggage in airport security; x-ray technology provides non-destructive testing techniques to aid in building forensics as well as art and object conservation. Non-destructive testing allows for greater exploration without unnecessarily harming historic fabric. X-rays can detect voids in building materials as well as leaks, cracks, and other signs of deterioration. Part of this is to understand the structure and ensure the safety of the researchers/contractors. X-ray fluoroscopy is used to identify materials such as lead, which you know is a common question about buildings today. (See NPS Brief 35: Understanding Old Buildings.)

If you’re involved in the preservation technology field and the building sciences, you know how in depth this topic can go (books, courses, careers). Check out this NCPTT report for more information about x-rays and other digital technologies in historic preservation. It is important to remember that science and historic preservation are connected, just as engineering and preservation are linked.

Preservation ABCs: B is for Bridge

Preservation ABCs is a series that will work its way from A to Z, bringing words into conversation that are relevant to historic preservation, whether it’s an idea, feature or vocabulary term. The idea is to help you see preservation everywhere you look and wherever you go. Enjoy! See previous letters.

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B is for Bridge

A historic plate girder bridge on an active rail line in Richford, VT. Historic bridges come in all shapes, sizes and structures.

A bridge carries a road, rail line or other traveled way over a watercourse, landform or even other thoroughfares. Most will think of our great bridges such as the Brooklyn Bridge, the San Francisco Bay Bridge, the Verazzano Bridge, the Lake Champlain Bridge, Scotland’s Fourth Rail Bridge, the London Bridge and other engineering marvels. But like that photograph above, a simple plate girder bridge on the rail line, small bridges play an important role in our history and landscape as well.

Bridges are constructed of wood, iron, steel, concrete or stone. The technology of bridge engineering is endless but a list of common types includes covered, wood truss, metal truss, concrete arch, masonry arch, girder, suspension, cable stay — you have probably heard many of these terms.

Although we could discuss bridge engineering and delve into types of trusses and structural systems, the better lesson of these Preservation ABCs is to understand why bridges are important on the landscape. If you’re not an engineer or a preservationist working in the transportation world, why do bridges matter to you? There are a few simple reasons to share.

First, bridges are part of our collective settlement patterns and how we move throughout the landscape, where we go, how we cross uneven landforms or waterbodies. Many bridges we can see on the landscape as we travel up hills, down hills or approach from the distance. Bridges signal a change in the ground beneath our feet and our vehicles. They allow us to read our environment.

Second, bridges are integral parts of our communities. While more than indications of a change in landscape, bridges serve as the gateways to communities, large or small. Bridges are visual structures just as buildings, which hold stories, memories, history and contribute to historic districts and settings. Even without understanding the engineering, it is feasible to read a bridge by its materials, design and railing ornamentation. This will place the bridge in a certain time period. For example, many truss bridges in Vermont were constructed following the 1927 flood, which destroyed hundreds of bridges. These are standing reminders of that period in history.

Third, the construction and engineering of bridges represents advances and lessons in our technology and the reach of our resources. Many early bridges, such as wood truss bridges in Vermont, were constructed by hand with local materials, based on the know-how of locals. Why? Because that is what was available. Iron could not be forged and shipped across colonial America. As technology changed, the industrial plants developed, the population and knowledge base grew, roads improved, ideas shared more easily, etc. every community had greater access to materials, experts, plans and technology.

There you have it: reading the environment, being an integral part of history and current communities, and telling the story of technology and innovation. The list could go on. Maybe you just like the aesthetics of bridges. That’s a good place to start, too.

These ideas and reasons for the importance of bridges are intertwined, but hopefully aid in appreciation as to why our historic bridges matter.