# The Resistance of Welded Joints of GAlvanized RHS Trusses with Different Vent Hole Geometries
## 1 Introduction  
There are several techniques for protecting steel structures against corrosion. However, when the structure to be protected is a steel lattice girder in which the chords and braces are hollow sections, the most cost-effective protection technique is probably the hot-dip galvanizing process. Although the term 'galvanizing' has been widely used to describe the coating of steel with zinc, it is necessary to clear up some misconceptions, as discussed in [1]. The process of hot-dip galvanizing (HDG) requires the immersion of the structure, which has been cleaned previously, in a big kettle containing a bath of molten zinc at a temperature of 450 \({}^{\circ}\)C [2]. The structure is introduced into the kettle at an angle, which allows the air to move inside the hollow sections and to escape at the same time as the zinc is flowing into those sections. A reaction between the iron in the steel and the zinc produces some intermetallic layers, which create a barrier with the environment and cathodically protect the steel. A coating is formed that provides protection for both the inside and outside of the pieces, not onlyfor the flat surfaces, but also for the corners and edges of the tube, ensuring a long maintenance-free service life that can be extended for 75 years in most environments [3]. As a result, the Life-Cycle Cost (LCC) of these structures remains the same as its initial cost. This is an advantage of the HDG when compared with other systems of protection when considering the Life-Cycle Cost. In the case of a lattice girder, an alternative could be to separately galvanize the brace members and to weld them onto the chords later. Nevertheless, the welding process for galvanized pieces requires them first to be brushed in order to remove the coat, then to be welded, and finally to be sprayed with a coat or a paint with a high zinc content. This results in a lower-quality coating when compared with the results obtained by immersion of the whole structure in a kettle. Furthermore, the increasing capabilities of galvanizing plants make the immersion of a full structure or a part thereof the best options in the specific case of lattice girders. Then, if a lattice girder with hollow chords and braces needs to be galvanized, their braces have to have been machined previously in order to produce ventilation holes in the proximity of the welded connection, or even interrupting the welds. Vent holes are required to fill the inner part of the brace members to protect them from corrosion. They are also necessary to allow the immersion of the structure in the zinc bath and to recover excess fluid after the bath so that it can be reused. In this situation, the holes should be big enough to efficiently fulfil the requirements described, but it is important to be aware of the potential reduction in joint strength in the case of excessive hole size. There are no prescriptions or practical recommendations in the design codes [4; 5; 6], standards [7; 8], or design guides for hollow structural sections [9; 10; 11; 12]. So inevitably, there are some doubts among structural steel designers with respect to the effect of vent holes on joint resistance, and this lack of knowledge may reduce the use of galvanized lattice girders, despite their high efficiency. The range of applications for hollow steel sections (HSS) in general, and rectangular hollow sections (RHS) more specifically, has increased noticeably in recent decades, and covers many types of construction--particularly trusses--due to certain advantages [13], not only with respect to member design, but also associated with joint design [14]. With regard to the selection of hot-finished or cold-formed manufacturing methods for hollow sections, [PERSON] and [PERSON] [15] concluded that as long as the products are in accordance with European standards [7; 8] and the design is carried out sensibly, cold-formed products perform efficiently in all structural applications.