Last Friday, I was in a church tower in Troy, NY. There were some shitty ladders from the base up to the belfrey, some shitty ladders from the belfrey to the top, and nothing between except the bell frame. So we climbed up the bell frame to get from the ladders below to the ladders above.
The bottom of the picture is looking straight down. You can’t see out the windows for the glare, but ground is about sixty feet down. And yes, that’s pigeon shit all over everything.
Arkansas, 1908*:
The description in the text calls it – correctly – a camelback through truss, but that’s incomplete. The most important distinguishing characteristic of a bridge is the web layout: the pattern of verticals and diagonals. In this case, the three panels at each end of the bridge are those of a Pratt truss, while the four center panels are double-diagonal, indicating that someone was willing to do the extra work required for a statically-indeterminate truss analysis.
We don’t build short truss bridges anymore, as labor costs now govern rather than material costs, so it’s easy to forget how light and fluffy airy they can be.
We also no longer commonly use pin connections or laced built-up members.
*Also, its name is Nimrod.
Mrs__B was making a new pea soup recipe for Mini__B that included the step of blending the cooked soup to give it a smooth, chunkless consistency.
The lid came off the blender and we had santorum all over the damned kitchen. It took me twenty minutes with a wet towel to clean up.
I made a flippant remark on Sadly, No! in response to a flippant remark by A Journal of the Plague Year; AJofPY responded and here’s my response (in which it’s painfully obvious that we agree) to the response to my flippancy regarding AJotPY’s flippancy:
Gustave Eiffel was one of the most talented structural engineers who has ever lived. Since he worked in the mid- to late-1800s, he used more primitive tools than we do today, but measuring what he accomplished doesn’t even require grading on that past-versus-present curve. His bridges and buildings are still beautiful and efficient structures today, with the Garabit Viaduct being one of the better known examples.
Just before Eiffel built his famous tower for the 1889 World’s Fair in Paris, he designed the skeleton of the Statue of Liberty. At the time of the statue’s construction, there was not a single skeleton-frame building in the world; his design of central pylon (with a cantilevered extension for her arm) carrying the skin on flexible straps prefigures modern curtain-wall design by some fifty years.
The Americans who actually built Eiffel’s design messed up the structural shoulder – the connection of the cantilever to the pylon – and the 1980s repair effectively returned to his original plan.
The spiral stair runs up the center of the pylon:
1866, Charles Clark was inspired by Ellet and Roebling and took it out on New Portland, Maine:
186 feet long by – wait for it – 12 feet wide. Since the stability of a bridge deck increases non-linearly with the deck width, this is asking for trouble, as is the lack of stiffening trusses.
I’m a bridge tower, short and stout…
Having the suspenders cables sloped (i.e., having the deck narrower than the natural spread of the cables) helps a bit with stability, as it means wind pushing the deck sideways is, in part, resisted by increased tension in the windward main cable. The Brooklyn Bridge inner main cables are, similarly, in non-vertical planes.
Overall, a sweet little bridge.
Suspension bridges in the modern sense – with a deck that does not follow the cable/rope curve and that is, at least theoretically, stable rather than moving with every gust of wind – really became popular in the mid-1800s. In the U.S. there were two popular, charismatic suspension bridge builders before the Civil War: John Roebling and Charles Ellet. They subscribed to different theories of bridge design, with Roebling saying that the way to make a suspension bridge safe was to heavily brace the deck using diagonal stay cables (most famously at Cincinnati and Brooklyn) and Ellet preferring a thinner, lighter deck. Roebling’s method proved better in the long run, but Ellet’s produced some beautiful results, such as the Wheeling Bridge.
The diagonal stays were not original and were added after a wind storm took down the original deck. Ooops.
Still pretty, though.
