The Web Spinner
Spider Web: 110 Million-Year-Old Structural Design
About 2 months ago I read that scientists discovered a fossilized spider web complete with its entrapped prey in a chunck of amber in Spain. Here is the article from BBC News, Science/Nature section. The fossil dates back to 110 million years ago.
I also found out from an older article that 3 years ago a strand of spider silk was discovered in Lebanese amber. It is about 120 million year-old. Because it is only a single strand, it doesn’t give any information about how the ancient spider web looks like.
Fig. 1. 110 million-year-old fossilized spider web with entrapped prey.
Scientists had been arguing about how ancient spider web configuration looks like. The latest discovery, in which part of the web is well preserved, gives the answer to the question. The latest article said: “The fossil web appears to have been designed along the same lines as the round nets woven by modern spiders.” That means today spider web design has not changed for 110 million years. Why is this so special? Here I am trying to relate spider web to lightweight design and construction.
Figure 2 shows a modern spider web. Spider web structure consists of only tension members. In this way, it achieves the maximum strength-to-weight ratio. It is already very efficient that it passes the natural selection of 110 million years without significant change.
Fig. 2. Modern spider web.
Bridge Design Evolution: From Compression to Tension
One important infrastructure and large scale construction is bridge. Its design has been evolved through many stages and changes. Figure 3 shows the famous Pont du Gard, an ancient arch bridge in France, designed by ingenious roman civil engineer circa first century A.D. The arch is the classic shape of compressive structural design in which any load along the structure will be transferred down compressively to a series of supporting piers. Arch bridge is very tough but has poor strength-to-weight ratio. It also has limitation due to its short span interval.
Fig. 3. Ancient arch bridge: Pont du Gard in France.
As design and material engineering advances, bridge designer favours suspension bridge to achieve optimal strength-to-weight ratio and to accomodate long span requirement. Long span, and thus minimum number of supporting piers, is highly preferred in modern large scale bridge because underwater construction for the piers is expensive and time-consuming. Lightweight design using high-strength steel cables as primary structural members also cuts down cost of material and construction time. Figure 4 shows the slender Severn Bridge in United Kingdom, an example of conventional suspension bridge.
Fig. 4. Modern suspension bridge: Severn Bridge connecting England and Wales.
Spider Web and Suspension Bridge Design Comparison
Notice that as bridge structural design and material advance, they also get closer to the shape of 110 million-year-old spider web design. Construction method of suspension bridge is also very similar to construction process of a spider web. First, the spider will look for at least 2 supports for foundation. In Severn Bridge’s case, those 2 supports are the twin towers and piers. Then it will tie down its primary strand and jump to the other side, stretching the primary strand. After spanning several primary strands, it will weave larger quantity of secondary strands, crossing and connecting all primary strands, to strengthen and stiffen the structure. Just like a suspension bridge.
Trivia: Severn Bridge and Star Wars
Star Wars (1977): “The sounds of the lasers were made by striking one of the suspension wires of the original Severn Bridge. The longer ones were used for the ships while the shorter ones were used for the hand guns.” Source: IMDB Trivia for Star Wars. 😀
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Entry filed under: Interludes.