Cyrco's FRP Bushings Maximizes Strength in Fiber-Reinforced Plastic Composites Tube Structural Framing

Generates More than a 6.0 Shear Service Factor, Doubling the Cooling Tower Institute (CTI) 3.0 Minimum Standard. In Tensile Strength Testing, Cyrco's FRP Bushings Outperforms All Others Commonly Used.

Cyrco FRP Square Tube Shear Bushing in Fiberglass Tubing

Cyrco's FRP Fiberglass Tube Shear Bushings prevents hole wear, cracked tubing, and guides bolts

Cyrco's FRP Fiberglass Tube Shear Bushings All Three Sizes

  • Maximizes load-bearing strength in fiberglass reinforced plastic (FRP) composites, structural tubed framing.
  • In tensile strength testing, Cyrco's FRP Shear Bushings out-performed all other commonly used.*
  • Generates more than a 6.0 Shear Service Factor, doubling the minimum 3.0 Cooling Tower Institute (CTI) standard.* Cooling towers structural framing becomes capable of withstanding the most intense of Category 5 hurricanes.
  • Mating bushings as the two ends meet in the middle (mates) which doubles the torque safety factor, immensely reducing FRP cracked tubing from over torqued bolts.
  • Encases the bolt’s file-like threads, protecting the FRP tube and preventing hole wear that occurs when induced (pumps, motors, fans, foot traffic, etc.) or natural (wind, seismic activity, flowing water, etc.) vibrations are present. Over time, as the hole size increases, the deformation accelerates at a more rapid pace, weakening the structural integrity.
  • Guides bolts quickly from entrance to exit holes therefore greatly reducing build times.
  • Bushings are self-locking into place allowing for pre-assembly.
  • Available in four commonly used sizes: 3/8" bolt 3" tube, 3/8” bolt 3.5” tube, 1/2" bolt 3" tube, and 1/2" bolt 3.5" tube. (09.5mm bolt 76.2mm tube, 09.5mm bolt 88.9mm tube, 12.7mm bolt 76.2mm tube, and 12.7mm bolt 88.9mm tube).
  • Designed, developed, and manufactured by Cyrco, inc.; patented.
  • Buy manufacturer-direct; pricing also available for retailers and wholesalers.
  • Made of chemical and thermal resistant, industrial-grade, quality polymer; Made in the U.S.A.
  • Pre-installation available through major FRP cooling tower retailers.
  • Beneficial to any industry utilizing fiberglass reinforced plastic (FRP) composite tubing for structural framing applications including aerospace, marine, and transportation.


*Joint School of Nanoscience and Nanoengineering of North Carolina A&T State University


Tensile Strength Tests Results of FRP Fiberglass Square Tube Connections Conducted by the Joint School of Nanoscience and Nanoengineering of North Carolina A&T State University

Tensile Test Results FRP Square Tube Cyrco's FRP Mating Square Tube Shear Bushing


Tensile Test Results FRP Square Tube Partial Length Plastic Shear Bushing


Tensile Test Results FRP Square Tube Stainless Steel Bushing


Tensile Test Results FRP Square Tube No Shear Bushing


Tensile Strength Testing Methodology of FRP Fiberglass Square Tube Bolted Connections Conducted by the Joint School of Nanoscience and Nanoengineering of North Carolina A&T State University


FRP Tube Tensile Tester at Joint School of Nanoscience and Nanoengineering of NC A&T State University

This thorough and comprehensive testing targeted the more severe tensile loading rather than compression loading in composite joints. Composite joints subjected to compression loading are less sensitive to joint geometry and are generally stronger than joints subjected to tensile forces. Members are loaded in the lengthwise orientation according to the direction of the pultrusion to utilize the maximum tensile strength available from the FRP. All edge distances exceed the minimum recommendations relative to bolt diameter. As such, the predicted failure mode is bearing failure, rather than failure by tension or shear out. Bearing failure is caused by the bearing pressure forces from the bolt applied to the hole boundary producing delamination of the composite. Historically, bearing failure has been defined as 4% elongation of the bolt-hole diameter. No appreciable load capacity can be expected after the 4% diameter elongation is met. Any further elongation of the holes only allows the structure to become loose and unstable.

The FRP materials used for this test are fire retardant polyester, compliant with the Cooling Tower Institute (CTI) industry standards. Cross-sectional dimensions of the tubes are 88.9 mm square x 6.4 mm thick (3.5" square x 0.25" thick). Cross-sectional dimensions of the straps are 76.2 mm wide x 9.6 mm thick (3.0" wide x 0.38" thick). Fastener materials are all of S30400-grade stainless steel, Ø12.7 mm-13 (ؽ"-13) UNC. One flat washer is placed below the head of the bolt. One flat washer and one helical locking washer is placed under the nut. All threads are lubricated with a graphite-petrolatum anti-seize compound.

PDF logo Read the Full Tensile Testing Report:


More About Cyrco's FRP Shear Bushings and FRP Plastic Composite Structural Construction

FRP fiberglass composite square tubed structural framing for cooling tower construction

Cyrco's FRP fiberglass shear bushings in cooling tower structural framing


Like many engineering and structural industries, one of the major advancements in today’s construction of cooling tower framing is the use of polymer composites also known as fiberglass reinforced polymer (FRP) structural tubing. Pultruded FRP fiberglass structure members are lighter and cheaper than steel, especially when factoring in expensive freight shipping. Unlike traditional wooden framed towers, even after decades of direct contact with water, FRP members will not decay like wood in high moisture environments, such as that of inside a cooling tower.

A slight disadvantage of FRP framing is that the FRP tubing is a semi-flexible material and when natural elements or induced vibrations are present (wind, motor vibration, foot traffic, etc.) the intregrity of the structural framing can over time become greatly jeopardized.

Flexing causes movement and bolt friction to the drilled hole in the FRP tubing. With back and forth movement, over time the bolt hole size slowly increases. As the hole size increases, the more rapid the pace becomes. This is especially true where contact is made with the bolt’s "file-like" threading against the softer, plastic composite tubing. Vibrations from running motors or other moving mechanical equipment can also cause bolt hole wear in the FRP tubing. Eventually with continuous movement and flexing the cooling tower becomes more prone to a structural collapse.

Cracked FRP Composite Square Tube From An Over Torqued Bolt Cyrco developed, patented, and manufactures a FRP Shear Bushing that mate in the middle, preventing the installer from over torquing the bolts that can create permanent "weak link" stress cracks in the FRP tubing. The joined mating also prevents under-tightened, loose nuts that often unthread and fall to the ground, as the installer knows when to stop tightening as the nut can not tighten any further. With the use of Cyrco's FRP Shear Bushing the nut and bolt are tightened within an ideal torque range, not over torqued, nor under-threaded. Another advantage of our mating bushings is that the tubular connections act as a pass through guide for the bolts, making for a much faster, rapid assembly.

Results from a series of independent testing performed by the Joint School of Nanoscience and Nanoengeering of North Carolina, outlined that Cyrco’s FRP Shear Bushings clearly outperformed all other commonly used FRP shear bushings. Cyrco’s FRP Shear Bushings generated a shear service factor of more than a 6.0, which is more than twice the Cooling Tower Institute (CTI) 3.0 recommended standard.

In all FRP fiberglass member framing applications, especially in excessive weight-stressed, induced mechanical vibronic applications, or high wind geographic locations such as coastal plains where hurricanes and tropical storms are frequent, Cyrco strongly recommends the use of our FRP Shear Bushings.


Composite World Logo Composites World, an industry-leading source for reliable news and information about fiber-reinforced composites manufacturing, recently featured Cyrco's FRP Bushings in a product spotlight article titled:
"Cyrco, inc. Showcases FRP Bushings for Maximizing Composite Structural Integrity"


With FRP fiberglass composite materials becoming ever so more present in an abundant of everyday engineering and structural industries, from marine to aerospace, Cyrco's FRP Fiberglass Tube Shear Bushings are not just limited or beneficial to the cooling tower industry.


Cyrco FRP Fiberglass Square Tube Shear Bushings

  • Affiliates:
  • CTI
  • ISN
  • NFPA
  • Avetta
  • Mid Atlantic Safety Council