TITLE: Arch Bridge

NAME: Dave Merchant
COUNTRY: USA

EMAIL: kosh@nesys.com
WEBPAGE: www.nesys.com

TOPIC: Great Engineering Achievements
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
JPGFILE: arch_dm.jpg
RENDERER USED: 


        POV-Ray 3.01 - Watcom Win32


TOOLS USED: 


        Adobe Photoshop to create image map textures
        Adobe Photoshop to add copyright and convert to JPEG


RENDER TIME: 


        37 minutes 15 seconds


HARDWARE USED: 


        P-120
        16mb RAM
        Windows 95


IMAGE DESCRIPTION: 


The year is 1912, the year the Titanic sank.

Horses are still a big part of the economy.

There had recently been a catastrophic collapse of a big bridge being built
in Quebec.

Events in Europe were starting to be a concern...

...And two of the most conservative railroads in the world decided to build
a 1017 foot long free span bridge over a busy shipping channel, which had been
named by early sailors for its treacherous tidal flows.

Oh, by the way, make it four tracks wide, strong enough for trains much heavier
than imagined in 1912, and high enough that large ships can pass under it.

And, oh yes, no way to put supports in the middle while you're building it,
so suspend it out from the banks while it's being built, with huge cranes
perched on the uncompleted ends.

*** No Problem! ***


This scene represents Hell Gate Bridge in New York City, just before the final
gap is closed, in approximately 1915.

At the time, it was the longest arch in the world.

The work is proceeding amid the normal traffic in this busy waterway, aided by
the ability to build the bridge without center supports. Beams are
prefabricated
in the yard at the extreme left of the image, and lifted directly from barges
to the ironworkers above. The halves of the bridge are suspended out from the
banks by temporary strongbacks, the brown girders visible at upper right.

The beams are assembled in orange rustproof primer, and painted black after
assembly. The red-brown color of the strongback beams is the result of
weathering of the orange-red primer.

Once the arch has been topped out, the 4 track wide deck will be suspended from
slender beams, leaving plenty of clearance below for ocean going ships.

This bridge was designed to have the same effect on north-south railroad
traffic in the eastern US as the recent Panama Canal had on shipping.
It cut out a several hundred mile roundabout journey, or transfer via car
floats and ferries. It was featured heavily in the railroads' publicity,
and Lionel sold a high-end model of it for rich kids to play with.

Although the main bridge is impressive, from the air it can be seen as a
small part of several miles of bridges leading up to it.

The engineer who designed it, Gustav Lindenthal, is a legend among civil
engineers. An essential design feature was the lightness of the members, which
made it feasible to cantilever it out from the banks, and the relatively small
number of members, which meant fewer pieces to put together.

From a stress analysis standpoint, it's a pretty interesting problem, as the
stresses were reversed at the time the center was joined, and changed further
as the heavy deck was hung. Prior to joining, the overhung ends would be
subject to considerable sway due to wind, and the final connection process was
quite delicate. The strongbacks contained hydraulic jacks for fine adjustment
of the connection, but acceptable error between the ends would still be only
a couple of inches, to avoid accumulating distortion stresses in the arch.

The date is an estimate - groundbreaking was in 1912, completion in 1917, while
the actual steel work was reported to have only taken 2 years, 1914-1916.
The pier foundations at the ends would have been very deep and extensive.
Anchors for the temporary strongbacks also needed to be provided.

Along the far bank are the houses built for the bridge workers, rows of drab,
identical gray houses, intended to be temporary, but which probably remained
as housing for the factory workers streaming into the city.

Four brand new US Army Curtiss R-2's - one third of the Army's inventory -
celebrate the arrival of a new bridge to fly under - a favorite biplane sport
of the era. The shadows in the water show that the leaders have already passed
under the bridge, showing its size. These planes would be worthy of a scene
of their own, as they represent the first real break with the Wright Flyer
paradigm, and began the rapid development of practical aviation.

The B-17 was only 20 years in the future, space travel was 50 years away...


DESCRIPTION OF HOW THIS IMAGE WAS CREATED: 


This image is entirely CSG, done in POV-Ray.
A blob was used for the rope bow fender of the tugboats.

I used several published photos for approximate dimensions.

I had one construction photo, taken from about the same angle as my image,
which was taken just as the final connection was being made. This photo
clearly shows that the girders were painted after assembly, with the
demarcation line as shown here.

Lacking other evidence, black was chosen as the most likely original finish
color, as it hides the stains from coal smoke, and was used on the majority
of steel bridges at the time. There was variation in the red/orange primer
color, so I chose a typical one.

The scene was difficult to compose, as the size of the bridge required a
distant camera location, which caused many small details to be too small to
see.
Antialiasing of the smaller details and hoist cables was also a problem.
I compromised on an angle which showed most of the span, while allowing the
laced girders to be at least minimally visible. I also wanted to clearly
show the gap between the two halves of the arch.

Rather than place each bridge member individually, I wrote an algorithm in
POV-Ray's programming language to produce segments of a parabola,
using vector math to find the length and angles of the diagonals.
The girders are not curved, but are straight segments.
The cross members are incorrect, as they should be diagonal rather than
straight across, but the math started getting too messy.

The lacing of the girders is done with transparent GIF textures,
which cuts down on the potential number of objects enormously.
The final object count is 2479.

All dimensions are parameterized for easy adjustment, and the degree of
completion of the girders, and amount of orange primer waiting to be painted
over with black paint can be adjusted.

I made the biplanes, boats, and buildings with CSG, and developed image map
textures in Photoshop.

The ships are small by modern standards. The freighters are under 300 feet,
and the tugboats are 70 feet. Note that the tugs have timber fenders, as tires
big enough to use as fenders did not exist in 1915.

The biplanes are not quite right, as the first Curtiss Army R-2's had shorter
wing spans, while these represent slightly later versions. I had already
finished the model before I discovered this, and decided not to change it.

The steam cranes on the barges were done for a previous IRTC - Childhood.

The water is a normal bumps pattern, to simulate the random chop found in
a tidal channel. I tried ripples and waves patterns, but bumps looked better.
I just kept cranking up the scaling until it looked unpleasant to be out on.
The water color is open to question - it seems to be very sensitive to the
gamma of individual monitors. At that time, the water was probably quite
polluted, with frequent oil slicks from ships and industrial dumping.

The smoke is halos, the sky is a standard POV-Ray sky-sphere.

The traveler cranes on the bridge were apparently powered by electricity.
They had 4 booms - a main hoist boom, 2 smaller booms to support the girders
during assembly, and one at the back for hoisting men and supplies, and to
work on the strongback girders.

The trees are a hollow shell, with a transparent leaf GIF texture, developed in
Photoshop, of course. Tree size and placement are done with a random function.
They aren't suitable for foreground use, but they render very fast - there are
90 trees in that row.

The ship names came out too small to read in the final image.
The ship names and home ports are:

   Frank N. Stein
    Transylvania

...and...

    Aardvark
   Zelienople

The tugs are not really named, but the names would be of the form: Mary Moran,
Molly Moran, Peggy Moran...

I have not included a ZIP file, but closeup images of the scene and the
individual models can be viewed on my web site, www.nesys.com.


