The present paper deals with the problem of the identification of the optimum rib thickness in ribbed R/C floors without shear reinforcements, particularly in those floors that are made by using prefabricated or partly precast elements and industrially produced temporary or permanent shutterings. The rib thickness is an important factor both of the floor weight and of its cost, as the ribbed section makes R/C floors lighter by removing a part of the cracked concrete below the neutral axis. Unfortunately, due to the mass production, in this case the rib thickness is chosen by the manufacturer instead of the R/C floor designer, so that the choice of the rib geometry should be made by the manufacturer by optimizing it. In fact it is not possible to make R/C floors too much lighter by exceedingly reducing the rib thickness because, close to the floor ends, the moment of resistance and the shear resistance would become too low. In this way, being the ribbed section stopped off close to the floor ends to increase the moment of resistance and the shear resistance, the floor would become heavier at its ends with a solid cross-section so that, due to an eventually too much reduced rib thickness, this heavier part would become too long and the concrete volume removed in the lighter ribbed part of the floor would be recovered in the heavier part at the floor ends. Consequently, the problem is whether it is better to make R/C floors with thicker ribs to reduce the heavier part of the floor at its ends, or to make the floor lighter in the span with thinner ribs but having a long heavier part at the floor ends. Therefore, by using nonlinear programming, we make an analysis at the ultimate limit state to find out the best way to make R/C floors lighter and with thin ribs. Depending on the type of R/C floors, this approach can be used by the designers as well as by the manufacturers which make permanent or removable moulds, partly prefabricated ribs, burnt clay or concrete hollow blocks, partly precast floor panels and, anyway, every industrialised product for R/C floor construction related to the rib thickness; this allows the industry to choose the size of its industrialized products that will determine the rib thickness in a great number of R/C floors.
On the optimization of rib geometry in the mass-production of ribbed R/C floors
FENU, LUIGI
2003-01-01
Abstract
The present paper deals with the problem of the identification of the optimum rib thickness in ribbed R/C floors without shear reinforcements, particularly in those floors that are made by using prefabricated or partly precast elements and industrially produced temporary or permanent shutterings. The rib thickness is an important factor both of the floor weight and of its cost, as the ribbed section makes R/C floors lighter by removing a part of the cracked concrete below the neutral axis. Unfortunately, due to the mass production, in this case the rib thickness is chosen by the manufacturer instead of the R/C floor designer, so that the choice of the rib geometry should be made by the manufacturer by optimizing it. In fact it is not possible to make R/C floors too much lighter by exceedingly reducing the rib thickness because, close to the floor ends, the moment of resistance and the shear resistance would become too low. In this way, being the ribbed section stopped off close to the floor ends to increase the moment of resistance and the shear resistance, the floor would become heavier at its ends with a solid cross-section so that, due to an eventually too much reduced rib thickness, this heavier part would become too long and the concrete volume removed in the lighter ribbed part of the floor would be recovered in the heavier part at the floor ends. Consequently, the problem is whether it is better to make R/C floors with thicker ribs to reduce the heavier part of the floor at its ends, or to make the floor lighter in the span with thinner ribs but having a long heavier part at the floor ends. Therefore, by using nonlinear programming, we make an analysis at the ultimate limit state to find out the best way to make R/C floors lighter and with thin ribs. Depending on the type of R/C floors, this approach can be used by the designers as well as by the manufacturers which make permanent or removable moulds, partly prefabricated ribs, burnt clay or concrete hollow blocks, partly precast floor panels and, anyway, every industrialised product for R/C floor construction related to the rib thickness; this allows the industry to choose the size of its industrialized products that will determine the rib thickness in a great number of R/C floors.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
