GFRP concrete reinforcement

Reinforcement composed of fiberglass bars and stirrups, capable of replacing classic cages made of steel elements, either temporarily or permanently. In the construction of tunnels with the use of TBMs, the special mechanical-physical characteristics of these products (high tensile strength and low shear strength) allow reinforcing the concrete of temporary diaphragms while maintaining high performance, not creating obstacles to the milling head. Crossing the diaphragm will be done quickly, without change of equipment and in total safety. The resistance to corrosion and chemical attack of FRP profiles increases their durability, making them ideal for permanent structures built in aggressive conditions.
The reinforcing rebar consists of a multitude of continuous fibers, oriented in the direction of load, bonded by a polyester or vinylester resin matrix. The surface is characterized by a ribbing that increase the resistance to pulling-out. Frp stirrups are made by bending a bundle of resin-impregnated fibers. Subsequently, these raw bars are heat-cured. This procedure allows a high fiber content and near-parallel fiber alignment, thus providing high strength and a modulus of elasticity similar to that of straight bars. Steels can be produced in 2d (e.g., z-shapes, circular and rectangular) and 3d (spiral).
• Corrosion resistant • High tensile strength • Low weight • Easy cutting
• D-Wall • Building foundation • Soft-eye • Waterway Engineering • Exposed Structures
• Design • Assembling

No preparation works are needed for TBM brekthrough

For several decades, TBM’s have been used for the construction of tunnels. Depending on the local situation, the TBM may be placed at the start or at the end of its drive; for example maybe in a precut in the open terrain or maybe by lowering it into an excavation shaft down to the tunnel level. This latter technique is used mostly in congested city areas. A few years ago, starting and receiving a TBM in an excavation shaft required extensive measures such as breaking through the walls of the shaft, which are secured out of steel reinforced concrete. This preparation work needed time and has been expensive. In recent years however the use of Soft-Eyes in these areas are becoming more and more popular. A Soft-Eye may for example be a diaphragm wall or bore piles reinforced with Glass Fiber Reinforced Polymer bars (GFRP) instead of reinforcement out of steel. Also an anchored tunnel face with GFRP anchors will not obstruct the TBM head driving through. The use of GFRP products in tunnelling is getting more and more common in Southeast Asia and is widely applied in Europe and Japan nowadays.

No obstruction of the TBM's cutter head driving through the diaphragm wall

Soft-Eyes consist usually of bore piles or diaphragm walls, which are locally reinforced with GFRP bars. The sections below and above the tunnel are reinforced conventionally. Depending on the designer and contractors preferences, full rectangular sections are built out of GFRP bars and the fiber reinforcement follows more closely the tunnel section resulting in a circular arrangement of the GFRP links or may be a circular sections. Both possibilities have their advantages. While a rectangular arrangement saves time during the design and assembly of the cages, following more closely the tunnel section thus reducing the material costs for the GFRP bars. Often applied as a compromise, where the vertical bars cover a rectangular section, while the shear links follow the circular layout. Experience shows that this approach decreases the material costs for the GFRP material by less than 5% still maintaining the detailed design and managing the assembly of the cage to be efficient. Building the corresponding reinforcement cages out of GFRP bars on site requires the same working procedures as for an equal steel cage. The necessary bars are tailor made and delivered to site where the assembly takes place. The bars are fixed together with binding wire, cable binders or similar products. U-bolts are used for clamping bars together when high loads have to be transferred over a connection. This is a connection between the vertical GFRP bars and the corresponding steel bars, which have to carry the dead load of the reinforcement cage during the lifting process and lowering of the cage into the trench. Welding as is commonly done with steel reinforcement but not possible with GFRP bars.