FORCE – DEFLECTION MODEL FOR I BEAMS MADE OF POLYESTER RESIN AND RICE HUSK AND UNDER VERTICAL JOINT LOADS

Abstract

The polyester resin reinforced with rice husk has been proposed as a composite material with potential applications on structural elements. To date, experimental and numerical validations of structural elements with this composite material are scarce. This paper describes the force-deflection behaviour for I beams made of polyester resin and rice husk, and under vertical joint loads. 13 I beams were tested under joint loads at the thirds of the beam span, and 3 prismatic coupons of the beam material were tested in compression. Results show the force – deflection curve for the I beams is trilinear, and the three zones of the curve correspond to the cases: beam with first cracks, beam with stabilized cracks, and beam at the failure. The collapse mechanism for the I beams is attributed to bending moment or a combination between bending moment and shear. The collapse mechanism of the beams starts with cracks on the beam bottom flange in tension, and these cracks spread through the beam web until reaching the beam top flange in compression, thus producing the beam failure. This collapse mechanism is considered as semi-ductile since the deflections can be easily observed before the beam failure. The semi-ductility of this mechanism is attributed to the addition of rice husk to the polyester resin, which reduced the fragility of the polyester resin.  Results also show the elastic modulus of the polyester resin with rice husk can be considered of 7.250 MPa for compressive stresses less than 200 MPa, and of 18.205 MPa for compressive stresses of 200 MPa – 1000 MPa. A model for predicting the I beam force – deflection curve based on the 3 zones experimentally observed was proposed. By the variation of the parameters in the model, two theoretical curves that envelope 70 % of the force – deflection curves experimentally obtained, were proposed.