Calculated parameters for flexural strengthening of RC beams using carbon fiber reinforced polymer(CFRP) sheet

Beam section: 250x700

The strength grade of concrete is: C25

Steel grade: two grade steel

Thickness of concrete protective layer: 25mm

Number of steel bars: double rows and above

Bending moment value before reinforcement: 50KN.M

Bending moment value after reinforcement: 417KN.M

Tensile reinforcement area: 2280mm

Compressed reinforcement area: 509mm

The ultimate bending moment of the section of the original beam: Mu

the height of the compression zone of the original beam is X'

x'= fy* (As - As') / (fc * b)=178.59mm

x'≤2a ，x'= 2a， x'>ζbho，x'= ζbho

x'=2a ，Mu= fy * As * (h - 2 * a)

x'>ζbho ，Mu = fc * b * x' * (h - x' / 2) + fy * As' * (h - a)

2a<x'≤ζbho ，Mu=fc * b * x' * (h - x' / 2) + fy'* As' * (h - a) - fy'* As *a

Mu=410.44KN.M

If M>1.4Mu can not be reinforced, M<Mu does not need to be strengthened,The rest of the situation is treated as follows:

After the reinforce beam according to the specification of the important components of not more than 0.75 ζbho. Therefore, the following judgment is made: the relative height of the compression zone is x

x≤2a ,x = 2a

2a<x'≤0.75ζbho

x=(fc * b * h - Sqr((fc * b * h) * (fc * b * h) + 2 * fc * b * (fy * As' * (h - a)- fy * As * a - M ))) / (fc * b)

x=182.83mm

Considering the effect of two stress, the lag strain of fiber composites εfo

εfo=αf*Mok/(Es*As*ho)

εfo=1.37*50/(2000000*2280*675)=0.00022

x>2a

CFRP width=(fc * b * X + fy * As' - fy * As) / (wf * ff) / km /(nf * tf)

The results are as follows:

Carbon fiber fabric strength grade: high strength II grade, area quality <=300 and no pre impregnation material

Carbon fiber layer number: 1 layers

Carbon fiber cloth thickness: 0.167mm

Carbon fiber cloth width: 60.6mm

Paste extension length: 857.5mm