Project with unidirectional carbon fiber sheet

In 2001, the Yijing Bridge on the Tangtong Line of Hebei Province was repaired and reinforced. Increase the load standard from steam one 13 and drag 60 to steam one 20 and hang one 100. The bridge has a total length of 470m, 33 holes, and the upper structure is a T-shaped simply supported beam. Among them, the reinforcement of the 5-hole T-beam adopts unidirectional carbon fiber sheet, and the effect is very good. The new material carbon fiber sheet will have broad prospects in bridge reinforcement.

Carbon fiber is an ideal material for bridge reinforcement

Carbon fiber is a high-tech material with excellent mechanical properties and is very suitable for bridge reinforcement. Carbon fiber is a fibrous carbon material, a high-tech product manufactured through a special process at a high temperature of several thousand degrees. It has many advantages such as high strength, light weight, corrosion resistance, aging resistance, and stable physical properties. Its tensile strength is 7 to 10 times that of steel. The proportion is only a quarter of steel. The carbon fiber sheet used by Yijing Bridge to reinforce the bridge is precisely because of this.

The advantages of carbon fiber sheet are as follows

Good resistance to acid, alkali and salt. The strength of the carbon fiber reinforced specimens does not decrease after being immersed in 10% sulfuric acid for 3 months, and after being immersed in a saturated solution of 40C calcium hydroxide for 300 hours. Strength does not decrease: at 35. After soaking in salt water for one year, the strength does not decrease.

Good temperature stability. The carbon fiber sheet can be used under the condition of -54-83 degrees Celsius for a long time without changing the strength.

Good water resistance. Immersion in 70 degrees Celsius water for 30 days, the strength does not decrease.

Anti-ultraviolet and anti-aging. After natural exposure test and accelerated exposure test, the infrared spectrometer was used to evaluate the performance of the specimen after the enhanced exposure. It was confirmed that the strength and bonding performance of the carbon fiber sheet could not be deteriorated within 50 years, and no loss of tensile strength was found. .

Reinforcement method with unidirectional carbon fiber sheet

Flexural reinforcement: One-way carbon fiber sheet is attached to the side under tension.

Shear reinforcement: Paste vertically on both sides of the beam or form a U-shaped loop with the ground. It is equivalent to adding shear stirrups.

Anti-crack reinforcement: paste along the vertical direction of the crack.

Reinforcement of the columnar center compression member: the column center ring wraps and pastes.

Shear wall reinforcement: Paste unidirectional carbon fiber sheets along the direction of shear reinforcement on one or both sides of the shear wall.

The carbon fiber sheet reinforcement construction process is as follows. Component surface treatment-base layer treatment-coating of primer coating-putty leveling-coating the lower layer of epoxy resin-pasting unidirectional carbon fiber sheet-coating the upper layer of epoxy resin-curing-protective coating.

Reinforcement design suggestions for unidirectional carbon fiber sheets

It is a new technology to reinforce concrete members with carbon fiber sheets. The strength of the carbon fiber sheet is multiplied by a reduction factor of 0.5 to 0.8 on the basis of the design value provided by the manufacturer.

In actual engineering, reinforcement members are secondary forces. If the original structure is stressed, the stress of the concrete steel bars on the section of the member before reinforcement should be calculated first and then analyzed and calculated based on the assumption of a flat section. If the force of the original structure is small, a common working coefficient is generally 0.8-1.0 for the convenience of design.

In order to ensure the full use of the strength of the carbon fiber sheet, the occurrence of bonding failure should be avoided as much as possible. Adhesives with reliable performance should be selected. The concrete strength of the reinforced components shall not be less than C15. The ends should have reliable anchoring measures, and the anchoring length should be as large as possible.

The test table shows that the rigidity of the reinforced concrete beam is little improved when the carbon fiber sheet with a smaller thickness is used to strengthen the reinforced concrete beam. Therefore, the stiffness must be checked.

The construction quality is particularly important when the carbon fiber sheet is used to reinforce the structure, otherwise the reinforcement effect will be greatly reduced; the end of the carbon fiber sheet should be anchored.