PSI - Issue 64

Yuan Xu et al. / Procedia Structural Integrity 64 (2024) 1865–1872 Author name / Structural Integrity Procedia 00 (2019) 000–000

1869

5

where σ 0.4T and σ 1.4T are the max principal stresses at the first and second extrapolation points, respectively; σ h,s is the hot spot stress. The SCFs could be calculated by the following equation: (2) where σ n is the nominal stress in brace. For a tubular connection under brace axial load (F), σ n can be theoretically calculated as: (3) where r and t are the brace radius and thickness, respectively. The finite element model was validated by the monotonic test results of the tubular T-joint without CFRP strengthening as well as Lloyd’s Register equations (1998). Table 4 summarizes the verification results at the saddle and crown points. It was demonstrated that the SCFs obtained by the finite element model were in good agreement with the test results and Lloyd’s Register equations. Table 4. Comparison of SCFs among the numerical, experimental data and predictions of Lloyd’s Register (LR) equations (unstrengthened T-joints) Position FEM Test LR Eq. e 1 (%) e 2 (%)

Saddle

9.79

9.76

9.72

0.31

0.77

Crown 16.03 where e 1 and e 2 are the percentage of relative difference of the experimental data and LR equations, respectively. 7.48 8.06 6.45 -7.20

3. Results and discussion 3.1. Hot spot stress and nominal stress Fig. 5. illustrates a typical example of hot spot stress variation at the saddle and crown points and nominal stress variation in the prestressed CFRP strengthened T-joint during the two analytical steps.

a

b

Fig. 5. Variation of σh,s and σn during CFRP prestressing and axial loading. (a) Step 1: CFRP prestressing; (b) Step 2: axial loading.

In Step 1 (CFRP prestressing), the hot spot stress was negative and the absolute value increased linearly with increase of prestress, indicating that the weld toe was under compression when CFRP prestress was applied. In Step 2 (axial loading), the absolute value of the hot spot stress decreased first to offset the effect of prestressing then increased with the axial load, and the compressive stress at the weld toe transformed into tensile stress. Therefore, the SCFs (ratio of hot spot stress to nominal stress) of the prestressed CFRP strengthening joint were not constant with the change of external load as the unstrengthened joint. To compare the efficiency of strengthening parameters, SCFs under 75kN axial load were selected to evaluate the effect of CFRP prestressing. At this specified load level, the pressure effects of CFRP prestress had been consistently counteracted in all the models.