The strength of glulam beams with holes - A probabilistic fracture mechanics method and experimental tests

Författare

Henrik Danielsson

Summary, in English

This thesis deals with experimental tests and methods for strength

analysis of glulam beams with holes. Test results and methods for

strength analysis available in literature are compiled and

discussed. The methods considered comprise both code strength design

methods and more general methods for strength analysis.

New strength tests of beams with quadratic holes with rounded

corners are presented. The test programme included investigations of

four important design para\-meters: material strength class, bending

moment to shear force ratio, beam size and hole placement with

respect to beam height. One important finding from these tests is

the strong beam size influence on the strength. This finding is in

line with previous test results found in literature but the beam

size effect is however not accounted for in all European timber

engineering codes.

A probabilistic fracture mechanics method for strength analysis is

presented. The method is based on a combination of Weibull weakest

link theory and the mean stress method which is a generalization of

linear elastic fracture mechanics. Combining these two methods means

that the fracture energy and the stochastic nature of the material

properties are taken into account. The probabilistic fracture

mechanics method is consistent with Weibull weakest link theory in

the sense that the same strength predictions are given by these two

methods for an ideally brittle material. The probabilistic fracture

mechanics method is also consistent with the mean stress method in

the sense that the same strength predictions are given by these two

methods for a material with deterministic material properties.

A parameter study of the influence of bending moment to shear force

ratio, beam size, hole placement with respect to beam height and

relative hole size with respect to beam height is presented for the

probabilistic fracture mechanics method.

Strength predictions according to the probabilistic fracture

mechanics method is also compared to the present and previous test

results found in literature and also to other methods for strength

analysis including code design methods. The probabilistic fracture

mechanics method shows a good ability to predict strength, with the

exception of very small beams.

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