Numerical, Theoretical, and Experimental Analysis of LVL-CFRP Sandwich Structure

Abstract

Optimization of structural elements via composition of different components is a significant scientific and practical point-of-view problem aimed at obtaining more economical and environmentally friendly solutions. This paper presents the results of a static work analysis of small-size laminated veneer lumber (LVL) beams reinforced by a Carbon Fiber Reinforced Polymer (CFRP) sheet. The nominal dimensions of LVL beams were 45 × 45 × 850 mm, and 0.333- and 0.666-mm thick reinforcement layers were used. The reinforcement was applied on opposite sides of the cross section obtaining a sandwich-type structure. An epoxy resin was used as a bonding layer. The bending tests were conducted in the so-called four-point bending static scheme in edgewise and flatwise conditions. The results of experimental tests confirmed the validity of this combination of materials. The highest load-bearing capacity was obtained for configuration, where CFRP sheets with a thickness of 0.666 mm were placed on the sides of the core, parallel to the direction of loading and the veneer’s grain in the core. The increase in this case was up to a maximum of 57% compared to the core alone. The highest bending stiffness increase, 182% compared to the core alone, involves placing two layers of sheets perpendicular to the direction of loading, i.e., on the upper and lower surfaces. The presented novel sandwich structure can be competitive against traditional steel and reinforced concrete elements in civil engineering and can be utilized as beams or slabs.

Strengthening of Laminated Veneer Lumber Slabs with Fiber-Reinforced Polymer Sheets—Preliminary Study

“…Curves plotted with the red color were obtained from numerical analysis; curves plotted with the black color were from experimental tests. The obtained results are within the expected deviation when compared to the similar research regarding strengthening timber elements with FRP materials; for example, a 10% relative error was obtained when applying such a model for an LVL CFRP sandwich structure [43]. It should be pointed out that after the initial phase, due to the degradation of bending stiffness, the non-linear behavior of real-life elements occurs faster than in the simulation.…”

“…Raftery et al [10] concluded a 10% enhancement of stiffness for timber beams strengthened with basalt rods with a 1.4% reinforcement ratio. From the point of view of the location of reinforcement, the most effective solution is the configuration wherein the reinforcement is placed on an external compressed and tensile face of the beam [43]; the average increases were 86% and 182% for one and two layers of CFRP, respectively. A slightly less effective solution is positioning the reinforcement on the sides of the beam.…”

“…The tension failure of unreinforced beams made out of timber or engineering wood products with relatively low moisture contents was reported by many scientists [2]. The shear failure mode is typical for slab-like LVL elements strengthened with FRP materials [43]. The rupture of UHM CFRP sheets, due to their low elongation-at-rupture value, was reported in several tests [7] when applied to the tensile face of a beam.…”

“…Similar differences between experimental and theoretical bending stiffness values, up to 7%, were obtained in [46] for full-scale LVL beams strengthened with various CFRP composites. An analogical conclusion can be drawn for LVL CFRP sandwich structures [43]. However, it should not be used to evaluate the load-bearing capacity when the shear failure may occur [43], for using an FRP with low elongation at rupture, or when the reinforcement ratio is high [51].…”

“…An analogical conclusion can be drawn for LVL CFRP sandwich structures [43]. However, it should not be used to evaluate the load-bearing capacity when the shear failure may occur [43], for using an FRP with low elongation at rupture, or when the reinforcement ratio is high [51]. The transformed cross-section method was proven to be an effective solution for the evaluation of bending stiffness in timber beams reinforced with FRP materials.…”