1. TRUSS
Support reaction forces from continuous beam structures shall be determined a competent person, as loading from one side of the support, effects the other side of the support. Is shall be noticed that load shifts can easily occur while for example lifting a continuous beam structure by means of lifting machinery. The shorter the span distances in between the supports of a continuous beam, the easier load shifts can occur. For example lifting a truss span on four electric chain hoists (from left to right motor A,B,C,D). And two hoists (B and D) are ¼ of chain link lower. Then it can occur that the complete truss is only support from hoist A and C. Which may result in an overloaded support and even an overloaded truss structure. It is therefore strongly recommended to lift heavy loaded continuous beams structures with a load measurement system. It is obvious that support reaction forces at threedimensional truss structures shall be determined with the loadings which can be directed in worst case scenario from six directions. Special care should be taken with building truss structures at a subsoil, for example ground supported structures. The subsoil shall have sufficient allowable bearing pressure to withstand the occurring support reaction forces coming from the truss structure. In which a distinction shall be made in between bearing pressure and concentrated loads. Allowable floor loading or bearing pressure is generally be given as a loading per square meter, for example 500kg/m². But support reaction forces of a truss structure are mainly concentrated loads (loading a at small area/surface – for example coming from a base plate or spindle), which shall be compared with permissible soil pressure. It the permissible soil pressure of a subsoil is not sufficient for the support reaction of a truss structure, distributing of the concentrated load of the truss structure can be done by using load spreaders, like wood pads or spreader bars. These elements spread the concentrated load at a wider area.
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1.6.4 Stability In a situation where a truss structure is subject to horizontal forces, lateral forces or imperfection, stability of the truss structure shall be evaluated. Also truss structures on sloping or uneven subsoil require an evaluation on stability. Instability is not only a problem with three-dimensional structures, but can also be a problem a twodimensional structures. For example by asymmetrical loading of the truss spans, where a LED wall or lighting fixtures are only support from one bottom main chord of a square truss. For three-dimensional structures, stability shall be checked on uplifting, overturning and sliding. Overturning of a truss structure may also occur by a cantilever load. In every case the stability against overturning needs to be guaranteed. Structural calculation carried out by qualified and competent persons is always highly recommended if it comes to truss structures in which stability is not apparent. 1.7 USE OF TRUSS Information about the safe use of truss and helpful advices for daily practice 1.7.1 Planning and selection In the phase of planning an event where trusses shall be used, one of the first actions is to determine load assumptions and to select the appropriate trusses with regard to load bearing capacity, stability and efficiency. The selection can be based on a check list. A risk assessment for the subsections of truss and rigging for an event shall be self-evident. One of the results of the risk assessment should be the need of structural calculation, use of load cells, etc. 1.7.2 Assembly The assembly of Prolyte truss is widely self-explanatory (intuitive). Prolyte always followed the principle of foolproof assembly but practice has shown that people always will find creative ways to interpret the principles their own way. Irrespective of the easiness of the assembly of Prolyte truss, products placed on