PSI - Issue 64

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

1868

4

The CFRP sheet was modelled using the shell element S4R, which is a 4-node doubly curved thin or thick shell with reduced integration. 3D brick element defined by incompatible mode 8 nodes (C3D8I) was used for the modelling of the steel tubular joint and its weld profile. No residual stresses were considered in this finite element model. Fig. 4 illustrated a typical finite element model of the prestressed CFRP strengthened T-joint. One end of the CFRP sheet was attached to one side of the brace, and the other end was bypassed the chord and attached to the opposite side of the brace, so that the CFRP sheet was U-shaped to hang the chord. The mechanical anchorage here was simplified as two reference points which connecting the end of the CFRP sheet and the brace (Fig.2). The translational and rotational motion as well as all other active degrees of freedom were coupled for these two pair of interfaces. Meanwhile, the CFRP shown in red in Fig.4 was tied to the chord bottom to simulate a perfect bond.

Coupling

CFRP

Reference point 2

Reference point 1

T-joint

Tie

Fig. 4. A typical FE model of the prestressed CFRP-CHS T-joint.

An experimental study has been conducted on the tubular T-joint subjected to monotonic loading. Therefore, boundary conditions in the finite element model were consistent with the test. Both ends of the chord were hinged, and the end of brace was subjected to axial loading. The numerical simulation was consisted of two analytical steps, i.e., CFRP prestressing, and the second axial loading on the brace. Properties of steel tubes used in the numerical analysis and experimental study were determined by uniaxial tensile tests for steel coupons of chords and braces in accordance with GB/T228.1-2010, as shown in Table 2. Properties of CFRP are obtained from the literature of Xu et al. (2020), as shown in Table 3.

Table 2. Properties of steel tubes. Member

Yield stress (MPa)

Ultimate tension stress (MPa)

Young’s modulus (GPa)

Chord Brace

380 406

564 563

200 200

Table. 3. Properties of CFRP sheets. Nominal thickness (mm)

Tensile modulus (GPa)

Tensile strength (MPa)

Poisson’s ratio

0.167

250

3789

0.3

In this study, as recommended by IIW-XV-E (1999) and CIDECT (2000), the hot spot stress at the weld toe was calculated by linear extrapolating the stresses at distances of 0.4 T and 1.4 T from the weld toe. Therefore, the hot spot stress along the connection intersection can be extrapolated by the following equation: (1)