Reinforcement of frame beam-column joints by fiber reinforced polymer(FRP) wrap

After carbon fiber reinfroced polymer(CFRP) wrap used in beam and column joints, the height of beam end section increases, and its shear and flexural bearing capacity also increases.

Project overview

When detecting the structural entity, it is found that there is a serious honeycomb surface phenomenon at the beam column joints, and the concrete strength grade is not satisfied with the design requirements. After checking, the bearing capacity does not meet the design requirements and needs do structural strengthening.


Basis for rehabilitation

The reinforced concrete cast-in-place frame structure is one of the most widely used structural forms in China's seismic area. The principles of its seismic design are "strong column and weak beam, strong shear weak bend, strong joint and strong anchorage."


Beam column joint is an important part of reinforced concrete frame structure, including the core area where the beam column intersects, and the beam end and column end connected with it. The strong nodes can maintain the integrity of the frame, so that the internal force can be transferred and distributed in the beam and column members, and the joints should be coordinated to resist external forces.


Reinforcement scheme

If there are serious honeycomb in the beam column joints and the concrete strength grade is not satisfied, the concrete grouting treatment is carried out by using the buried grouting pipe, the exhaust pipe, the surface of the mortar or the filling concrete closed, and then the carbon fiber reinfroced polymer wrap is attached to the joint.


When the beam column joint is strengthened, the carbon fiber fabric should meet the following requirements: the unit area mass is 300 g/ M 2, the tensile strength standard value is more than 3000 MPa, the modulus of elasticity is more than 210000 MPa, and the elongation is more than 1.5%.


In strengthening construction, we should pay attention to the following two matters:

  • Before the reinforcement is started, all floor loads must be removed to avoid excessive deformation at the beam ends of the beam column joints, and the armpit should not be fully utilized.

  • Scavenging, loosening, honeycombed, corrosion and other deteriorated concrete surface of the reinforced component, exposing the concrete structure layer, and using the repair material to smooth the surface. The surface of the pasted concrete should be polished and removed from the surface, such as floating slurry and oil dirt, until the new surface of the concrete structure is exposed. When bonding carbon fiber cloth, the concrete surface should be cleaned and kept dry.


After CFRP used in beam and column joints and the method of combining the end of the concrete beam with the armpit,  the height of beam end section increases, and its shear and flexural bearing capacity also increases. The shear deformation of the beam column joints is restrained by the effect of the CFRP ring to the wrapping. The shear deformation of the core area is greatly reduced, and the shear strength and stiffness of the core area are improved.





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