The Use of Thermally Damaged Wood in Laminated Wood Beam Structures

Abstract

This paper deals with the experimental research results of laminated wood beam structures made using lamellas produced from the pine trees, partially damaged in forest plantations. The purpose of the research has been to study the stress-strain state of laminated wood beam structures utilizing the wood damaged by the thermal exposure caused by a forest fire. Previously, the authors have carried out a significant amount of research into the physical, mechanical and strength properties of thermally damaged pine wood. They have established the dependence of the strength properties of the wood on the degree of fire damage and the wood sampling points according to the height of the stem. Prior to the experiment on the large-scale models in the “Lira 10.12” software complex, numerical studies of four series of single beams with a span of 6.0 m and a section of 140×500 mm produced from the 1st grade pine wood in the upper and lower parts of the section and from thermally damaged pine wood in the middle part of the section. A comparative analysis of the beams has been performed with varying percentages of replacement of the healthy pine wood with the one weakened by the fire along the height of the section: 76, 62, 51 and 36 %. As a result of the numerical calculation of the beams under study using the derived safety factor equaling 1.136, their actual load-bearing capacity has been determined. It has been established that a decrease in the load-bearing capacity of the СB-2 beams equals 12.2 kN, which is 16.05 % relative to the reference beam CB-5, made entirely of the 1st grade pine wood. For the CB-4 beams a decrease in the load-bearing capacity equals 7.4 kN, which is 9.74 % relative to the reference beam CB-5. The difference between the calculated and experimental breaking loads is 9.5 to 14.3 %. The introduction of the safety factor equaling 1.136 in the numerical calculation ensures sufficient convergence of the calculated and experimental data (the measurement error is 3 %). The load-bearing capacity of the reference beam СB-5, made entirely of the 1st grade pine wood, is 12.38 kN/m. For beams CB-1 to CB-4 it equals from 8.53 to 12.06 kN/m. The relative decrease in the load-bearing capacity did not exceed 31.1 to 32.5 %. It has been established that the CB-4 beam, made using 34 % of lamellas produced from thermally damaged pine wood, allows for the load-bearing capacity of 97.5 % relative to the beams made entirely of the 1st grade pine wood.