7.1.1 Description
In this chapter is verified a uniplanar T-joint of the welded rectangular hollow sections in which a RHS brace is welded directly onto a RHS chord without the use of reinforcing plates the component based finite element method (CBFEM) to method of failure modes (FM). The T-joint is loaded by an axial force and in-plane and out-of-plane bending moments. In CBFEM is the design resistance limited by 5 % of strain and in FM generally by plate out of plane deformation 0,03 b0 where b0 is the depth of the RHS chord, see Lu et al. (1994).
7.1.2 Method of failure modes
In the case of the axially loaded T-joint of the welded rectangular hollow sections four failure modes can occur. These are chord plastification (chord face failure), local yielding of brace (brace failure), chord side wall failure and chord punching shear. The failure modes of a T-joint loaded in bending are chord plastification, chord side wall failure and local yielding of brace. The chord plastification, local yielding of brace and punching shear are examined in this study, see Fig. 7.1.1. The welds are designed according to EN 1993-1-8:2005 are not the weakest components in the joint and.
Fig. 7.1.1 Examined failure modes, a) Chord plastification, b) Local yielding of brace c) Punching shear
Chord plastification
The design resistance of a RHS chord face can be determined using the method given by FM model in section 7.5 of EN 1993-1-8:2005. The method is also given in the International standard ISO/FDIS 14346 (CIDECT) and is closely described in Wardenier et al. (2010). The design resistance of the axially loaded T-joint of welded rectangular hollow sections is
Fig. 7.1.2 Dimensions of T-joint
7.1.3 Verification of resistance
Results of the method based on failure modes (FM) are compared with the results of CBFEM. The comparison is focused on the resistance and design failure mode. Results are presented in Tab. 7.1.2. The influence of the brace width and thickness and the chord width and thickness on the design resistance of the T-joint is shown in Fig. 7.1.3 for loading by axial force, in Fig. 7.1.4 for in-plane bending and in Fig. 7.1.5 for out-of-plane bending. The study covers three failure modes, namely the chord plastification, the local yielding of brace and the punching shear.
Tab. 7.1.2 Comparison of results of prediction by CBFEM and FM
Fig. 7.1.3 Sensitivity study of T-joint loaded in tension according to failure modes:
a) chord plastification, b) local yielding of brace, and c) punching shear
Fig. 7.1.4 Sensitivity study of T-joint loaded by in-plane bending according to failure modes:
a) chord plastification and b) local yielding of brace
Fig. 7.1.5 Sensitivity study of T-joint loaded by out-of-plane bending according to failure modes:
a) chord plastification and b) local yielding of brace
The sensitivity study shows a good agreement for the applied load cases. The results are summarized in a diagram comparing CBFEM’s and FM’s design resistances, see Fig. 7.1.6. The results show that the difference of the two calculation methods is in all cases less than 10 %.
Fig. 7.1.6 Verification of CBFEM to FM for the uniplanar T-joint between RHS braces and RHS chord according to failure modes: a) tension/compression b) in-plane and out-of-plane bending
7.1.4 Range of validity
CBFEM was verified for typical T-joints of the welded rectangular hollow sections. Range of validity for these joints is defined in the Table 7.8 of EN 1993-1-8:2005 or in the Table 6 of ISO/FDIS 14346, see Tab 7.1.3. Outside the range of the validity of FM also in application of the CBFEM model should be prepared the validation to experiments or the verification to a validated research model.
Tab. 7.1.3 Range of validity for method of failure modes in ISO/FDIS 14346 in Table 6
7.1.5 Benchmark
Example Inputs
Chord
- Steel S355
- Section RHS 180 x 100 x 6,3 Brace
- Steel S355
- Sections RHS 160 x 80 x 6,3
- Angle between the brace member and the chord 90° Weld
- Fillet weld around the brace with throat thickness aw = 5 mm Loaded
- By force to brace in compression/tension
Outputs
- The design resistance in compression/tension is NRd = 348 kN
- The design failure mode is chord plastification
Fig. 7.1.7 Benchmark example for chord RHS 180x100x6,3 and brace RHS 160x80x6,3