Most of us geocachers know guardrails as hiding spots. Wheather you as a cacher think a guardrail is a good, bad, easy, or hard cache I thought it was time to know a little more about them for what they really are.
What is Guardrail?
A piece of guardrail has two basic shapes. W-Beam guardrail has two "humps" and one "valley". Humps are rises that face towards the traffic (convex surface), while the valley (concave surface) points away from the traffic lane. The other type is Thrie-beam, or T-Beam. This has three humps and two valleys.
There are two basic thicknesses of the metal used in guardrail, as well. 12 guage is the most common, roughly 1/8" thick. 10 guage guardrail, on the other hand, is about 3/16" thick. This added thickness creates a stronger guardrail, but also greatly increases it's weight. Guardrail can also come shop-bent, or curved for certain roadside applications. The two curves are concave and convex, which are shown in the diagram below:
A fourth characteristic of guardrail is the length of each piece, or panel. This size ranges from 25' 0" down to 6' 3". This length is not the overall length of the panel, however, it represents the distance between the outermost post holes. Thus a 12' 6" x 6' 3" panel is actually 13' 6 1/2" long, with post holes centered at 6' 3" apart. These hole distances can vary, as well, from being punched only at the ends, every 6' 3" or 3' 1 1/2", even at custom dimensions.
This brings us into the next topic...
How is guardrail manufactured?
There are a number of fabrication techniques, but we present here a very generic overview of the forming and galvanization of guardrail items.
First a large roll, or coil, of flat metal sheet is slit into the necessary width. W-Beam is cut into 18" wide pieces, while T-Beam is 25" wide. This is done by unrolling the coil and sending the flat sheet through a slitter. This flat rectangular piece is punched by a large press with bits placed at the appropriate dimensions. The punched sheet is slid down the line into the roll-former, where the "humps" and "valleys" are made. The rail shape is then cut at the appropriate length.
This rolled panel of black guardrail, as it is called due to its color, is then sent to be galvanized. The galvanizing procedure includes dipping the panels into prewash solutions of water, acid, and finally into zinc, which is kept molten at a temperature of over 800 degrees C. This turns the panel into a shiny silver color, as it is now coated in zinc.
Galvanization helps prevents rusting from occuring. Rust occurs when a metal is oxidized (loses electrons) to the environment. Zinc is more willing to lose its electrons than steel, so it oxidizes first, leaving "healthy" steel underneath for a much longer period of time. Guardrail beams may be galvanized before or after fabrication.
What is an end treatment?
Guardrail is an effective barrier, as it can contain and redirect a vehicle. However, it is an extremely stiff object to impact directly at the end. Wherever guardrail stops, there needs to be something that not only provides sufficient anchorage for the rest of the "run" - but is also safe for vehicles impacting end-on.
This anchor can range from a simple buffer when the guardrail is installed in a low-speed application, such as a parking facility or warehouse, or can be a full scale terminal system for high-speed roadways.
The purpose of the terminal is to anchor the barrier, yet also protect anyone that happens to hit the guardrail at this point. If no end treatment were used, the stiff panel of guardrail could either enter the vehicle injuring the occupants and/or cause the vehicle to roll-over also injuring anyone inside. Therefore, a large focus of designers and researchers relates to providing more effective and safer end terminals.
Now, where do you think the cache is?
