Keywords: finite element analysis, nonlinear analysis, nonlinear buckling, plasticity, large displacements.

The process of hot-dip galvanizing of trusses requires some holes in brace members in order to allow the immersion of the structure into the zinc bath. These holes are usually executed near connections for the recovery of the higher amount of liquid, and this practice could have an influence on the ultimate strength of the joint and this point must be evaluated to avoid any non-conservative result that could be obtained by simply applying the formulae from the design codes [1]. In another previous research project [2] the structural assessment was not considered, therefore, this important subject was left for further research using numerical and experimental methods. In this way, the joint behaviour of hot-dip galvanized tubular trusses is an interesting issue to be studied due to the uncertainty caused by the holes required for the galvanizing process.

In this work, a new and innovative procedure, based on the design of experiments (DOE) using the finite element method, is used in order to study the ultimate resistance of a wide steel K-joint' types [3,4], evaluating the effect on the performance of the hollow section joints with and without holes.

The validation of the finite element model was also carried out using twenty-two experimental tests, and a good agreement has been obtained. From the numerical and experimental results, the following facts can be addressed:

• The most important design variables from the ultimate load point of view are the brace size and the brace angle. A higher brace depth and a lower brace angle increases the ultimate load of the joint.
• When the brace size and brace thickness increases the failure mode changes from brace local buckling to chord plasticization, the maximum load decreases. The maximum loads are obtained with small brace angles and intermediate brace thickness.
• Maximum differences between the joint with and without holes are less than 5%, so the structural behaviour of the joint is basically the same.
• It is possible to see the agreement in the failure mode between experimental and numerical results for the joints tested.

Finally, from this research work it will be possible to design these types of joints in a safe way, and with this basis it is possible to include as a design standard the size and location of the galvanizing holes, as stated in the Project CIDET [2].

1

CEN, "Eurocode 3: Design of steel structures. Part 1-8: Design of joints", EN-1993-1-8:2005, European Committee for Standardization, 2005.

2

G. Iglesias, P. Landa, "Recommendations for holes needed due to galvanization process", Final report project 14B, UPV-EHU, ICT, CIDECT, 2007.

3

J.J. del Coz Díaz, P.J. García Nieto, J.A. Vilán Vilán, J.L. Suárez Sierra, "Non-linear buckling analysis of a self-weighted metallic roof by FEM", Mathematical and Computer Modelling, 51(3-4), 216-228, 2010. doi:10.1016/j.mcm.2009.08.032

4

C. López-Colina, M.A. Serrano-López, F.L. Gayarre, F.J. Suárez, "Resistance of the component 'lateral faces of RHS' at high temperature", Engineering Structures, 32(4), 1133-1139, 2010. doi:10.1016/j.engstruct.2009.12.039

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