Prolyte Campus blog: Stick to the nodes – Part 2

Rigging and such
In a previous Prolyte rigging blog it was explained that the node points are the positions in a truss structure where the truss must be supported and application of (serious) loads must take place. Resulting in the quest to define the useable area around the theoretical scientific node point.

Node point discussion
There are some different points of view on node points in our business. This is caused by the fact that welding in aluminium alloys causes a weakened area in the material in and around that weld, known as the HAZ (heat affected zone).  We know that almost all trusses do have a multitude of welding positions that will meet in node points and can be heavily present in the connection part areas. Obviously there are several types of joining aluminium, and each of them has its pro’s and con’s. We see all different kinds of noding, in truss design, depending on the truss type; from 2-point noding to 5-point noding.
One argument is that the pattern of diagonals and braces should be arranged in such a way that the HAZ in the chords remains as small as possible (e.g. 2-point noding). True in a sense, but all too often that particular point comes from manufacturers that don’t know (or care) much about how arrangement of braces can affect the safety of slinging. A combination of many details, beyond the drawing board, lead to a safe and sound truss. Calculating with several strengths inside one cross section of the material, ignores the fact that the weak area can initiate a failure as well. After all: a chain is no stronger than its weakest link.

Structural Calculations
Any structural report is to be based on safe and sound engineering principles. Where the weakening by the fusion welding process is present, it is to be included in the loading data resulting from it. However, it’s easy to find a way to cheat on data, and move into competition politics. Welded nodes are a normal thing in a truss module, and they are the points where the forces of supporting it, or the load application to it must be transferred into that module, being either 4- or 2-point noding.
Therefore, it’s good practice to really try to understand the basics behind what is presented – if it’s too complicated, let someone explain it to you.

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Hendrik Deitert HVMC Show- & Veranstaltungstechnik, Germany