Correction factors for stress intensity of CFRP-strengthened wide-flange steel beams with various crack configurations

Abstract

This paper presents the crack-tip behavior of wide-flange W4×13 steel beams strengthened with carbon fiber reinforced polymer (CFRP) sheets. A notch is created at midspan of the beams to represent various levels of initial damage (or crack propagation). Of interest is the correction factor of stress intensity that affects the capacity of the strengthened beams. Three-dimensional finite element models are developed to predict stress singularity at the crack tip, including an adaptive mesh formulation along with isoperimetric quadratic elements. Upon validating the modeling approach with a previously conducted experimental program, an extensive parametric study is conducted to evaluate the effect of the notch-depth-to-height ratio (a0/h), CFRP-to-steel area ratio (ψ), and CFRP-to-steel modular ratio (η) of the strengthened beams. The stress intensity of the damaged (notched) beams is reduced with the presence of the CFRP, which generates a crack-bridging effect. The correction factor of stress intensity for the unstrengthened and strengthened beams noticeably diverges from each other beyond an a0/h of 0.3. CFRP properties such as the number of layers and modulus influence the crack-tip plasticity of the strengthened beams. A correction factor is proposed for the strengthened beams, based on the response surface-regression analysis procedures associated with 75 numerical models.