Superbridge over Gibraltar

Carbon nanotube bundles are becoming a feasible and economically convenient solution for the realization in our time of super bridges, such as those required across the Straits of Bab al Mandab, Messina or Gibraltar (main spans ∼2.7, 3.3 or 3.5 km, respectively). The Straits of Bab al Mandab bridge would be intercontinental bridges between the Arabian Peninsula and the Horn of Africa and would cross the Red Sea. A Gibraltar bridge would be between Spain and Morocco would connecting the Atlantic Ocean to the Mediterranean Sea.

Several engineers have advanced designs for the Gibraltar Bridge on various alignments and with differing structural configurations. Professor T.Y. Lin’s proposal for a crossing between Point Oliveros and Point Cires was designed with 14,000 meter length, deep piers, and 5000-meter spans.

10 GPa-strong carbon nanotube fibers are today available (Koziol et al 2007), suggesting that long cables with a similar strength could be realized in the near future. Those new materials could make super-bridges more feasible.

OPAC Engineers ere engaged by Professor Lin to study structural configurations, stiffening systems, and aerodynamic performance issues for the Oliveros-Cires crossing’s 5000 m spans. Professor Lin’s proposed a hybrid stayed-suspension bridge concept. The hybrid stayed-suspension bridge was developed into the most suitable alternative, with greater rigidity and better aerodynamic characteristics than competing systems with much smaller spans. They estimated a $15 billion cost.

Stronger carbon nanotube tethers

Drum-rolled carbon nanotube tethers have been made with a strength of 9.6 GPa.

In 2016, Jian Nong Wang and his colleagues made nanotubes with a process akin to glass blowing: Using a stream of nitrogen gas, they injected ethanol, with a small amount of ferrocene and thiophene added as catalysts, into a 50-mm-wide horizontal tube placed in furnace at 1,150–1,130 °C.

They packed the nanotubes even more densely by pressing the film repeatedly between two rollers.

The resulting films had an average strength of 9.6 gigapascals. By comparison, the strength of nanotube films made so far has been around 2 GPa, while that for Kevlar fibers and commercially used carbon fibers is around 3.7 and 7 GPa, respectively. The films are four times as pliable as conventional carbon fibers, and can elongate by 8% on average as opposed to 2% for carbon fibers.

DRUM ROLL Spooling a cylinder of blown carbon nanotubes onto a rolling drum, researchers create a black film containing aligned, densely packed nanotubes (left). After being passed through a roller several times, the film becomes flatter and the nanotubes more densely packed (right). The film is exceptionally strong and ductile.
Credit: Nano Lett

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