Problem types

Because of the insufficient bearing capacity of the original concrete beams, carbon fiber reinforced polymer(CFRP) fabric is used in the strengthening method.

The parameters of the carbon fiber sheet at the bottom of the beam:

CFRP grade: Grade I

Modulus of elasticity Ecf = 2.30 * 10⁵ MPa

Design value of tensile strength FF = 2300 MPa

Single layer thickness t CFV = 0.167 mm

Weight: 300g/m2

Do not consider the two force

The reinforcement area is 750mm² after the load is increased, and the bond size of carbon fiber cloth is converted by the equal strong substitution principle.

Design value of tensile strength of steel bar: 360N/mm2

Design value of tensile strength of carbon fiber cloth: 2300 N/mm2

The lack of reinforcement area * reinforcement tensile strength design value is less than or equal to the carbon fiber cloth thickness * width * design value of tensile strength of carbon fiber cloth

750*360 = 0.167* width *2300

Width = 702.94

The dimension of beam section is 400*900, and the width of structural beam is 400, which can not meet the width of carbon fiber cloth. Considering the double layer carbon fiber cloth, the carbon fiber cloth multilayer paste reduction factor is calculated.

The reduction coefficient of =1.16- (layers of elastic modulus design value * * thickness) /308000 = 0.9

=1.16-(2*230000*0.167)/308000 

=0.91

=1.16-(2*230000*0.167)/308000 

=0.91

                                              =1.16-(2*230000*0.167)/308000        

                                              =0.91

Reduction coefficient            =0.9

750*360 = 0.167* width *2300*0.9

Width = 781.05

The width of beam is 400mm, CFRP double-layer area: 2*400=800 = 781.05, meet the strength requirements.