The Influence of holes, dowels and notches on the eigenfrequency of timber boards

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School of Engineering | Master's thesis
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Date

2025-11-21

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Mcode

Degree programme

Master's Programme in Building Technology
Rakennustekniikan maisteriohjelma
Magisterprogrammet i byggnadsteknik

Language

en

Pages

52

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Abstract

This thesis investigates the changes in the eigenfrequency of a known grade of timber with defects. The defects investigated are designed to emulate typical defects found in salvaged structural timber, including holes, embedded dowels, and notches. The magnitude of influence of each of these defect parameters, such as sizes and quantities, are considered. Non-destructive impact tests were utilised to measure the longitudinal frequencies responses and analyse the first eigenfrequency of Spruce boards (2700×148×48 mm) when increasing severity of defects are introduced. The investigations found that the longitudinal eigenfrequency of boards reduces as the quantity or size of holes increases, and that the rate of change is consistent regardless of the holes’ orientation. Tests also reveal that the geometry of defects had a strong influence on the reduction of eigenfrequency, with notches exhibiting far greater reductions as compared to holes. In the case of boards with embedded dowels, increasing quantities and sizes of dowels led to reductions in the eigenfrequencies at a faster rate than that of the same unfilled holes.

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Supervisor

Collins, Steven

Thesis advisor

Ranttila, Henri

Keywords

timber, defects, reuse, eigenfrequency, modulus of elasticity, machine grading

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https://urn.fi/URN:NBN:fi:aalto-202512159170

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[dipl] Insinööritieteiden korkeakoulu / ENG