In reinforced concrete structures, beams as important structural forms often need reinforcement due to various damages. Reinforced concrete beams, as the main flexural members, are strengthened because of the insufficient bearing capacity of the beams themselves. There are many factors that cause the insufficient bearing capacity of the beam, such as unfavorable construction, failure of design, improper use of users，after changing the use it is beyond the original carrying capacity and safety guarantee, durability accident failure or the end of life.

In addition, some other factors also cause structural beam reinforcement, such as:

1. the non - uniform settlement of the foundation makes the beam produce additional force.

2. improper material or inherent defect of the beam itself leads to lack of durability, such as the surface crack of material or component or internal micro crack, which causes the carbonization of the protective layer of commodity concrete, to a certain extent, so that the bottom of the beam is eroded, and the yield strength of the steel bar itself can be reduced to the brittle fracture.

3. unreasonable effects of beam structure, such as 60% ~ 80% design load acting on thin web beam, there is severe diagonal crack near the middle of web.

4. others, such as insufficient steel anchorage, insufficient lap length, inconvenient welding, sudden load or transient overload.

Which reinforcement materials can effectively reinforce various damages of beams?

Beam strengthening material -- carbon fiber fabric

In recent years, the technology of CFRP reinforcement and repair of commercial concrete beams has been developing rapidly. Because of its outstanding advantages, such as high strength, high efficiency, quick construction, good corrosion resistance, light weight and no increase of component section, it has been widely used in practical engineering. In many cases, it has replaced all kinds of reinforcement methods created in the last century, and has achieved remarkable economic and social benefits.

Beam strengthening material - bonded steel plate adhesive

The steel plate is bonded to the surface of the concrete component with high performance epoxy adhesive, which makes the steel plate and concrete form a unified whole, and then the purpose of enhancing the bearing capacity and stiffness of the member is to make use of the good tensile strength of the steel plate.

Beam strengthening material -Increased cross section by epoxy rebar adhesive

Enlarging section method is to increase the cross-sectional area of commercial concrete structure or structure, so as to improve its bearing capacity and satisfy normal use. It has the characteristics of simple construction process and strong adaptability. In the engineering practice, there are many cases of filling in the concrete layer of the beam in the drawing area, which increases the effective height of the cross section of the beam, thus increasing the stiffness and effectively improving the bending and shearing resistance of the beam.

Beam strengthening material -prestressed FRP plate

The CFRP prestressed reinforcement method is variable passive reinforcement for active reinforcement. The high strength properties of CFRP (carbon fiber reinforced composite) can be brought into play in advance, and there is a large strain before the two force, which can effectively reduce and even eliminate the strain lag of CFRP sheet, so as to achieve good reinforcement effect.