Issue 45

D. Yang et alii, Frattura ed Integrità Strutturale, 45 (2018) 45-52; DOI: 10.3221/IGF-ESIS.45.04 48 (a) full penetration weld (b) partial penetration weld (c) fillet weld Figure 3: Weld configuration Calculation parameters and working condition. A total of six finite-element models (WT1~WT6) were established with b0=200, d1=80, t0=10, t1=5, β=0.4, 2γ=20 and τ=0.5, according to the relevant specifications on weld size of tube joints and the empirical range of influencing parameters of steel tubular joints β=d1/b0, 2γ=b0/t0 and τ=t1/t0. In WT1 and WT2, w0/t1 was set to 0.5 and w1/t1 was set to 1.2~2.0; In WT3 and WT4, w0=w1, and w1/t1 was set to 1.2~1.8; In WT5 and WT6, w1/t1 was set to 1.8 and w0/t1 was set to 0.5~1.0. Fig. 4 and Fig. 5 respectively explain the meanings of β, 2γ and τ, and the calculated SCF positions, where w0 is the chord-side weld size and w1 was the brace-side weld size. d 1 Chord Brace Concrete β = d 1 / b 0 2 γ = b 0 / t 0 τ = t 1 / t 0 C0 C45 C60 C90 C180 B0 B45 B60 B90 Figure 4: Schematic diagram of CHS-CFSHS T-joint. Figure 5: Calculated SCF positions Given the symmetry of joints, a half finite-element model was constructed on the finite-element software Abaqus [20]. The steel tube was meshed into incompatible mode eight-node brick elements (C3D8I) and the concrete into eight-node brick elements with reduced integration (C3D8R). The face-to-face discrete method was employed to simulate the contact between steel tube and concrete. The normal contact was simulated as hard contact, and the tangential bond and slip were modeled with the Kulun friction model whose friction coefficient was set to 0.35. Our purpose is to acquire the SCF of CFST joints under the normal working condition, rather than the bearing capacity of these joints. Thus, the monotonic constitutive relation of concrete is not considered here. The elastic modulus was set to E ＝ 2.05×105MPa (steel tube) and 3.45×104MPa (concrete), and the Poisson’s ratio was set to ν ＝ 0.3 (steel tube) and 0.2 (concrete). To disclose of the effect of the weld size, the two ends of all models were constrained by the same hinged connection; the steel grade was set to Q345; the strength of the filled concrete was set to C50; the friction properties were the same between steel tube and concrete. For accuracy and efficiency, the grid size of finite-element modeling was determined in light of the previous studies (Fig. 6). The braces of all models were subjected to axial tension and in-plane bending moment (Figs. 7 and 8). The joints were in elastic phase throughout the simulation according to the rule of fatigue failure.