Strongwell, manufacturer of pultruded fibre reinforced polymer composites structures was recently recognized with two prestigious awards for its innovation in the design and manufacture of the world’s tallest freestanding pultruded fiberglass structure- a nearly 200′ tall tower erected in Central Texas.
The tower is designed to launch surface type electromagnetic waves for energy transmission as is part of a decades-long R&D initiative. The use of fiberglass, which is virtually transparent to radio frequencies, minimized signal losses. Along with the other requirements specified by Strongwell’s customer, there is simply no other capable structural material. “Pultruded FRP is an ideal structural material in many applications, but especially this one. The requirements for light weight, high strength, RF-transparency, field fabrication/assembly, and long-term durability made the selection of our materials a perfect choice,” said David Gibbs, Strongwell’s vice president of Sales and Engineering.
The project used over 28,000 FRP hex nuts, 13,400 linear feet of threaded fiberglass rods, and almost 30,000 linear feet of pultruded exterior cladding. The entire structure was manufactured and pre-fabricated at Strongwell’s Bristol, Virginia, location, shipped to the job site, then assembled in sections which were lifted and bolted into place.
Barry Myers, Strongwell’s corporate director of marketing and communications, stated in a presentation about the project: “Strongwell boasts the world’s largest pultrusion machine, top-tier in-house machine and fabrication shops, and R&D and engineering capabilities simply not present with most other pultruders. There’s a reason Strongwell was approached for this project – we were quite possibly the only ones who could actually do it!”
In recognition of the project, Strongwell was recognized by the Southwest Virginia Alliance for Manufacturing (SVAM) with its Innovations in Manufacturing Award. The project was also awarded the Unsurpassed Innovation Award at the Composites and Advanced Materials Expo in Atlanta, Georgia, beating out twelve other finalists.
The idea for transmitting energy wirelessly is not new – Nikola Tesla originally sought to make this technology possible, even commissioning the construction of the Wardenclyffe Tower, a wooden structure built in 1901-1902 for his research. That project was never completed, but the idea remained. Modern materials and technologies may just make this idea one day a reality.
Measuring almost 200 feet (61 meters) in height, the world’s largest freestanding FRP tower was part of a 40-year R&D utility initiative in transmitting wireless energy. The structure meets ASCE 7-10 design specifications and is capable of withstanding wind speeds of up to 115 mph (185 kph).
With the exception of the clevis plates and a few stainless-steel braces, the tower was fabricated and constructed entirely with pultruded fiberglass products made by Strongwell. The majority of structural components were custom designed shapes with high strength reinforcements. Bespoke tooling was designed to pultrude each of the shapes using a vinyl ester resin. In areas where pultrusion would not suffice, hand-layup processes were used.
The complex, lattice-style vertical structure measures almost 20 stories. On the account of strength, the 1/2″ (12.7 mm) thick plates possess a lengthwise pin bearing strength of 30,000 psi (206,843 kPa). The 3/4″ (19 mm) and thicker plates possesses a lengthwise and crosswise pin bearing strength of 20,000 psi (137,895 kPa). Each of the column section’s planar shear strength was measured at 7,250 psi (49,987 kPa).
The interior supports are comprised of wide flange beams, intermediate columns, and corner columns. Individual corner columns in this structure are attached with about 40 threaded FRP hex nuts. Intermediate columns contain about 70.
Over 28,000 FRP threaded hex nuts, 13,400 linear feet (4,084 linear meters) of threaded rods, and almost 30,000 linear feet (9,144 linear meters) of DURASHIELD® was used for exterior cladding. The weight of those three items totalled almost 260,000 lbs. (117,934 kg) of composites.
The use of RF-transparent FRP minimized signal losses. Being outdoors, ultraviolet degradation and corrosion resistance were also factors in material choice selection. In fact, no other structural material was capable of meeting the structural loads and transparency requirements.
The end user reported that they were pleased with the project timeline and material performance. The structure was erected onsite in phases due to internal access and safety structures (handrail, ladders, cages, and landings) being simultaneously installed. Weight reduction played a major role as each fabricated section had to be hoisted, stacked, and fastened to one another.