Optimization of gusseted rigid frames by their geometry

Rigid frames has finally established as a widely used structure in buildings for agricultural use. It has an irregular efforts distribution, with a significant concentration of bending moments at its nodes and a big tendency to deformation. The use of gussets at the nodes of the frame allows a variable sizing, achieving, as a consequence, the optimization in the sizing. The susceptible areas to need reinforcement gussets are: base of the pillar and its head, the starting point of the rafter and ridge beam, demonstrating in practice that the effectiveness of these gussets varies depending on the geometry of the frame. It is therefore of great interest to have clear design criteria so that a selection of the truly effective gussets can be made because the indiscriminate use of all of them can be even uneconomic. To tackle the issue, we evaluated the influence of three variables: spans between 10 and 30 m, pillar's height between 4 and 7 m and roof steepness between 5% and 30 degrees, coming to a final amount of 480 cases. The calculation of the structures was made in accordance with the current regulations CTE and EAE and, for each of the cases is obtained the gusseted structure design and optimum sizing. The analysis of the results shows a progression in the optimum positions of the gussets as the geometry of the frames changes. The most important variable is the roof angle, which reduces the need for gussets at the nodes as the slope increases in the beam. In addition, higher frame span requires a higher number of gussets. The pillar height is the variable that affects the least these structures. Therefore, very flat frames with large spans and high height require more gussets than the other cases. As a result, we propose a series of abacuses that allow knowing beforehand the best gussets of a frame depending on their geometry, a useful tool when designing a structure of this type.