Ductility and Stiffness of Laminated Veneer Lumber Beams Strengthened with Fibrous Composites

Michał Marcin Bakalarz,Paweł Grzegorz Kossakowski

doi:10.3390/fib10020021

Michał Marcin Bakalarz, Paweł Grzegorz Kossakowski

Open Access

https://doi.org/10.3390/fib10020021

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Journal: Fibers	Publication Date: Feb 15, 2022
Citations: 9	License type: CC BY 4.0

Affiliation: Kielce University of Technology

Abstract

The paper presents the results of experimental research on unstrengthened and strengthened laminated veneer beams subjected to 4-point bending. Aramid, glass and carbon sheets with high tensile strength (HS) and ultra-high modulus of elasticity (UHM) glued to external surfaces with an epoxy resin adhesive were used as reinforcement. Two reinforcement layouts were used: (1) sheets glued along the bottom surface and (2) sheets glued to the bottom and side surfaces. Based on the test results, the flexural strength, flexural ductility and stiffness were estimated. Compared to the reference beams, the maximum bending moment was higher by 15%, 20%, 30% and by 16%, 22% and 35% for the Aramid Fiber Reinforced Polymers (AFRP), Glass Fiber Reinforced Polymers (GFRP) and Carbon Fiber Reinforced Polymers (CFRP) HS sheets, respectively. There was no significant increase in the flexural bending capacity for beams reinforced with UHM CFRP sheets. Similar values of bending ductility indices based on deflection and energy absorption were obtained. Higher increases in ductility were observed for AFRP, GFRP and CFRP HS sheets in “U” reinforcement layout. The average increase in bending stiffness coefficient ranged from 8% for AFRP sheets to 33% for UHM CFRP sheets compared to the reference beams.

Highlights

Bending strengthening of timber beams is required, inter alia, due to increasing load values, compensation for degradation of the mechanical properties of wood or the need to reduce excessive deflections
Four types of polyester matrix composite sheets were used in the research: Aramid Fiber Reinforced Polymer (AFRP), Glass Fiber Reinforced Polymer (GFRP), High Strength Carbon Fiber Reinforced Polymer (HS Carbon Fiber Reinforced Polymers (CFRP)) and Ultra-High Modulus Carbon Fiber Reinforced Polymer (UHM CFRP)
Modulus of Rupture (MOR) determines the maximum normal stress occurring in the outermost fibers subjected to compression or tension, determined for the maximum value of the bending moment recorded in the 4-point bending test

Summary

Introduction

Bending strengthening of timber beams is required, inter alia, due to increasing load values (resulting, for example, from a change in the way of use), compensation for degradation of the mechanical properties of wood (decreasing their strength and stiffness with crack extension [1]) or the need to reduce excessive deflections. In the case of reinforced elements made of glued laminated timber, they can be made of lower-grade timber or with a smaller cross-section and lighter timber. Elements made of solid timber, glued laminated timber or engineering wood products can be strengthened. Conventional reinforcement of such elements is made of steel or aluminum. In addition to design requirements, the choice of reinforcement measurements is constrained by other factors such as aesthetic aspects, cost, access to the reinforced element or fire protection requirements

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Conclusion