Abstract

The technology of reinforcing and repairing concrete structures with carbon fiber reinforced polymer is to paste the carbon fiber on the surface of the concrete with a supporting adhesive to play the role of structural strengthening and seismic strengthening. It is widely used for the strengthening of building beams, slabs, columns and walls, and can be used for the strengthening of bridges, tunnels and other civil engineering. Crack treatment and grouting, combined with steel bonding method strengthening treatment, enhance the stiffness of the roof truss upper chord, has been widely used in the strengthening and reconstruction of existing buildings. In addition to the similar advantages of pasting steel plates, it also has the advantages of corrosion resistance, moisture resistance, almost no increase in structural weight, durability, and low maintenance costs. However, special fire prevention treatment is required, which is suitable for concrete structural members and general structures with various stress properties.

Keywords: carbon fiber strengthening, beam strengthening, slab strengthening, concrete repair

Common problems of beam-slab bearing structure

The main reason for the lack of bearing capacity of beams, slabs and other flexural members in design is the inconsistent calculation of the force, or the calculation of load surge or miscalculation. Severe overloading may also lead to insufficient bearing capacity of beams and slabs, due to insufficient concrete strength during construction, or insufficient bending resistance of beams and slabs due to improper strengthening. In addition, the settlement of the foundation caused some additional stress due to other reasons. When dealing with this stress, some inappropriate devices were used, which adversely affected the beams and plates. For example, adding thin web beams to the beam and plate when dealing with stress, although the effect of the stress can be balanced, and the dead weight is not increased much, but some thin web beams will appear oblique cracks, causing the beam and plate components to rust and the durability is greatly affected. In severe cases, the beams and slabs may break and affect the bearing capacity of the beams and slabs. Some of the reasons for the above situation are the insufficient length of uranium lap joints or the influence of load changes. The main purpose of load-bearing strengthening of beams and slabs is to strengthen the strength, stability, rigidity and durability of components.

strengthening of beam-slab structure

The beam-slab structure that has been built is treated and strengthened, and it is quite different from the unreinforced general structural beam-slab in terms of force. One is that the reinforced structure is equivalent to secondary treatment and secondary stress, and the structure has to be subjected to secondary stress on the basis of the original stress, and the original structure may be deformed and bent. In addition, the original load is not removed during strengthening, which is equivalent to secondary compression. There is a difference between the newly added part of the stress and the original structural load stress. When the two stresses reach their peaks at the same time, the destructive force has reached the limit state. Therefore, the above main problems must be faced when strengthening the beams and slabs, and the new and old parts of the strengthening are different in their work, and there are big differences in the calculation of stress and structural treatment. Therefore, the strengthening of beams and slabs is different from ordinary concrete structural engineering, so carbon fiber strengthening technology should be introduced in the strengthening to improve the strengthening of concrete beams and slabs.

The scope of application of carbon fiber strengthening

It is suitable for the strengthening and repair of various structure types and various structural parts, such as beams, slabs, columns, roof trusses, piers, bridges, cylinders, shells and other structures. The strength grade of the base concrete is not lower than C15, and the carbon fiber cloth strengthening technology has been successfully applied to various beam and slab strengthening and maintenance in China.

In 2014, after Haimen Daxin Bridge tried to use glued steel plates to strengthen the bridge in Haimen. In the Haimen Linjiang Gate Bridge repair, the first attempt to use the method of pasting and wrapping carbon fiber cloth to strengthen the bridge is the first time in the Haimen repair and strengthening bridge construction process. Carbon fiber strengthening can quickly reinforce the bridge, prevent external moisture from entering the concrete cracks and cause corrosion to the steel bars, ensure the durability of the components, help improve the load-bearing capacity of the bridge, and will not affect the normal operation of the bridge during the strengthening. The Linjiang Gate Bridge invested 350,000. The highway department carried out a comprehensive repair of the existing diseases of the Linjiang Gate Bridge, adding 4000kg of expansion joints to tie up the steel bars, pasting 500 square meters of carbon fiber cloth to the bridge arch foot, and 500 square meters of polymer grouting. Through the maintenance of trunk roads and bridges, various hidden safety hazards were eliminated in time, which effectively improved the technical status of trunk roads and bridges in Haimen, and effectively guaranteed the safety and smooth flow of trunk roads.

Carbon fiber strengthening features

Carbon fiber strengthening is the use of carbon fiber cloth and structural glue to reinforce the components. The strengthening damage morphology is bonded with carbon fiber sheets as follows:

(1) The tensile steel bar yields, and then the concrete is crushed under pressure, and the carbon fiber sheet has not yet reached the allowable tensile stress change requirement;

(2) The stress of the steel bar reaches yield, the carbon fiber has exceeded the allowable tensile strain, and has not exceeded the required strain value of the construction project, the tensile reaches the ultimate tensile stress, and the concrete in the compression zone is not crushed;

(3) The strengthening of carbon fiber cloth is too large, the steel bar yields, and the concrete in the compression zone is crushed;

(4) In the normal part of the bearing capacity, the carbon fiber cloth and the concrete foundation surface will peel off.

Construction safety and precautions for carbon fiber strengthening

(1) Carbon fiber sheets are conductive materials. When using carbon fiber sheets, keep them away from electrical equipment and power sources.

(2) The bending of the carbon fiber sheet should be avoided during use.

(3) The raw materials of carbon fiber sheet supporting resin should be sealed and stored away from fire sources and avoid direct sunlight.

(4) The preparation and use place of resin should be well ventilated.

(5) On-site construction personnel should take corresponding labor protection measures based on the use of resin materials.

Concluding remarks

The technology of reinforcing concrete structures with carbon fiber sheets is a hot application in modern civil engineering circles. Therefore, it is necessary to continuously improve all aspects of construction and pay enough attention to the acceptance after construction. On the whole, the comprehensive economic and social benefits of carbon fiber strengthening have achieved a double harvest, and it has a broad market prospect. In addition, there is a large room for improvement in technology.