Mechanical device for prestressing of carbon fiber reinforced polymer (CFRP) sheets

Abstract

A mechanical device was invented for prestressing of carbon fiber reinforced polymer (CFRP) sheets. Significant features of this device are that the CFRP sheets are directly anchored to the mechanical device itself, the prestressing forces are applied with a manual torque wrench without the need for power operated hydraulic jacks and the prestressing transfer is accomplished under slow strain rates. Experimental investigation clearly indicates that the device was efficient in applying prestressing to the CFRP sheets and prestress losses during stressing were maintained at a minimum.

Description

BACKGROUND OF THE INVENTION [0001]Much research has been conducted to date to study the behavior of reinforced concrete (RC) beams strengthened with prestressed fiber reinforced polymer (FRP) sheets and plates. By inducing prestressing the FRP system can be used more efficiently, leading to an increase in the flexural capacity and serviceability of the strengthened beams (Triantafillou et al., 1992; Char et al., 1994; Quantrill and Hollaway, 1998; El-Hacha et al., 2001a; 2001b; El-Hacha et al., 2003). Literature review shows that strengthening of RC beams with prestressed FRP sheets and plates can be grouped under three installation methods.[0002]The first installation method consists of an indirect method for achieving prestress in the FRP system. Saadatmannesh and Ehsani (1991) have investigated an indirect method for prestressing glass FRP (GFRP) plates. Stressing in the GFRP system was achieved by initially cambering the beam upwards with the use of hydraulic jacks followed by b...

AI Technical Summary

Benefits of technology

[0007]A simple mechanical device was invented for prestressing of carbon fiber reinforced polymer (CFRP) sheets that can overcome on some of the disadvantages of currently used prestressing systems. Significant features of this device are that the CFRP sheets are directly anchored to the mechanical device itself, the prestressing forces are applied with a manual torque wrench without the need for power operated hydraulic jacks, and the prestressing transfer is accomplished under slow strain rates. Experimental investigation clearly corroborates that the device was efficient in applying prestressing to the CFRP sheets and prestress losses during stressing were maintained at a minimum.

Problems solved by technology

Some of the disadvantages associated with this method are that it is labor intensive, only low levels of prestressing can be induced in the plates, not easy to achieve the desired level of prestressing in the plates or sheets, and the reacting floor or foundation must be capable of sustaining the applied vertical loads.

In many instances these anchors serve as a permanent anchorage to the FRP system leading to a costly solution due to the high costs associated with fabricating the specialized prestressing anchors and plates.

If left in place, permanent steel anchors are likely to be exposed to significant weathering or galvanic corrosion due to contact with the carbon fibers.

Also, the anchors may need to be removed for aesthetics reasons, leading to potential debonding of the prestressing sheets or plates.

Other disadvantages that can be associated with this method are that it tends to be laborious, and the beam surface must be properly treated (ACI 546, 1996) prior to drilling for installation of the anchors.

In many of these systems the release method was carried out under high strain rates leading to premature debonding and further accentuating the need for end anchorages.

In addition, many of the systems proposed in the literature require the use of specialized equipment.

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