General Information
Figure 1 shows a covered sports field.
![Covered sports field structure](buildings/sport-buildings/structure-2/1-covered-sport-field.jpg)
Trusses
Figure 2 shows a covered sports field sector.
![Covered sports field structure with main measures](buildings/sport-buildings/structure-2/2-covered-sport-field.jpg)
The span s ≅ 30 m, the span b ≅ 15 m, and the arc rise h ≅ 5 m. Figure 3 shows the structure viewed from below.
![Covered sports field structure with arch trusses](buildings/sport-buildings/structure-2/3-covered-sport-field.jpg)
The steel structure consists mainly of not-braced steel columns, arch trusses, five longitudinal trusses (marked by the numbers), purlins, and metal roofing sheets. Figure 3 shows a schematic partial three-dimensional view of a structure sector.
![Three-dimensional drawing of the steel structure of a covered sports field](buildings/sport-buildings/structure-2/4-3d-view.jpg)
Longitudinal truss 3 has diagonal members, while the remaining longitudinal trusses (1, 2, 4 and 5) do not.
What is the structural purpose of each longitudinal truss?