Analysis of rammed earth arches strengthened with natural fibers

Starting from the awareness that the mechanical characteristics of raw earth are sufficient for use in masonry constructions, two arches models of scale 1:3 in rammed earth were prepared. The two arches, one with only earth and one with earth mixed with gypsum powder were subjected to mechanical tests. Preliminarily tests were performed in order to assess mineralogical geotechnical and mechanical characteristics of the earth and even with the use of an eco-friendly additive. The two arches were subjected to asymmetric load conditions increasing up to incipient collapse characterized by the opening of four hinges. To verify the results obtained from the experimental tests the ultimate loads of the arches were calculated by limit analysis. Subsequently the two arches were strengthened with jute fabric and tested again in order to verify the reinforcing ability of the fabric. The strengthened arches showed a load-bearing capacity three times higher than that of unreinforced structures. In order to set up a numerical method for the prediction of the mechanical response of such structures a finite element analysis was performed using the code Adina. The mechanical parameters adopted in the numerical simulation were obtained by the mechanical tests on earthen specimens. The predictions provided by the numerical results are in good agreement with the experimental ones. The biocompatible reinforcement made with vegetable fiber and earthen matrix showed that it is possible to significantly increase the bearing capacity and the kinematical ductility of structural elements made with rammed earth. This type of reinforcement can therefore also be used for seismic retrofitting.