Finite element simulation the mechanical behaviour of prestressed glulam beams

Abstract

For many years, prestressed glued beams have been successfully used, for example, in construction as supporting structures. Based on the analysis of recent studies of prestressed wooden beams, the aim of the research was to develop a design with a reduced consumption of materials. The technical result is achieved in that the method of manufacturing a prestressed straight wooden beam consists in gluing thin pre-curved lamellas to the required height, after which the glued lamella block is cut in height along the longitudinal axis and then the cut parts are glued together with each other by their curved sides (surfaces). The purpose of the experiment was to investigate the bending stiffness of a rectilinear beam glued from curved lamellae in the case when there are no preliminary stresses in the lamellae, with the case of the presence of such stresses. The first load option was to create a pre-stressed state of the beam and determine the maximum normal stresses. The prestressed state of the lamellae in the bent and fixed (glued) position was simulated by stretching the upper layers of each of the lamellae during their global contact. When bent, it was found that each of the lamellae has stretched areas in the upper part with tensile stress from SX = +25 MPa to SX = +35 MPa and compressed regions in the lower part with compression stress from SX =-30 MPa to SX =-60 MPa. The second variant of the load was to create a workload on the top plane of the beam in the absence of prestressing. The maximum deflection in the middle of the beam was URES = 1,535 mm. The values of internal stresses in this case are in the range from SX =-57 MPa in the compressed zone to SX = + 82 MPa in the tension one. The third variant of the load consisted in the presence of both prestressing and working load. The maximum deflection in the middle of the beam was URES = 0,466 mm. The values of the internal pressure with the range from SX =-10 MPa to SX =-100 MPa in the compressed area to SX = + 20 MPa to SX = + 60 MPa in tension one. The results of computational experiments show that by applying prestressed, in the direction opposite to the bending of the workload, we can compensate for the influence of the workload. It has been established that the application of the prestressing phenomenon makes it possible to create structures of rectilinear glued wooden beams of reduced material consumption, while the effect of increasing the carrying capacity of a wooden beam will be limited by the compressive strength of the material from which it is made. In order to obtain more accurate values of the increase in the coefficient of increasing the bearing capacity of the proposed construction of a wooden beams, it is planned to conduct in-vito experiments on a special software and hardware complex of the laboratory of mechanical tests of the Department of Forest Resources exploitation of the ZhNAU.