Design Principles For Glass Used Structurally - LTH

1 Design PrinciplesFor Glass UsedStructurally Naimeh KhorasaniRapport TABK 04/1025 Lund 2004 Department of Building ScienceBuilding Science DepartmentLund UniversityBox 118221 00 LundSwedenISRN LUTADL/TABK 1025 SEISSN 1103-4467 ISBN2004 Naimeh KhorasaniTABLE OF OF ARCHITECTURAL Glass as a load bearing Glass Glass production on heat strengthened FRACTURE historical fracture mechanics of Glass of STOCHASTIC AAPPENDIX BDesign ..12 Reliability historical 43 Failure prediction for Glass mechanics for of trends Mine is the first step and therefore a small one, though worked out with much thought and hard labour.

2 You my readers or hearers of my lectures, if you think I have done as much as can fairly be expected of an initial acknowledge what I have achieved and will pardon what I have left for others to accomplish. Aristotle ( 384-322 BC) At the start of this research project I thought that finding out the strength of Glass and describing its behaviour during loading would be a very interesting and quiet easy challenge, regarding my background as a Civil Engineer. It would also give me the possibility of developing my skills as a Design engineer and increase my self confidence.

3 I must confess as the project has evolved I have had to question my knowledge and skills and what used to seem easy and understandable was now getting very complex and difficult to describe in one simple and easy way. There were many times when I could not see where all these new influences could be headed. The end of this project seemed VERY far away! So now when I am writing the last sentences of this report, I feel there are some people that I need to express my gratitude towards. These people have been backing me up and guided me through this journey.

4 Their help and devotion have given me motivation to keep on going and enjoying my work meanwhile. Professor Lars Sentler, my supervisor, who has been exposed to my up and down moods and believed in me when I did not. Lars this journey would certainly have not been as interesting and challenging without your motivations and high demands! I would also want to thank Professor Bertil Fredlund for listening to me and guiding me through this sometimes complex academic world. In addition, the following people have contributed through discussions of the application of Glass : Mr Anders Jacobsson, Pilkington, Mr Thomas Grange, MTK, who has also read through and given me comments on this thesis, Mr Tim MacFarlane, Dewhurst & Macfarlane, Mr Andrea Compagno, who has held very interesting courses and workshops about Glass , Mr Anthony Smith Ove Arup and finally Mrs Saga Hellberg and Mr Mikael desj , Glasbranschf reningen, for being my face towards the industry and promoting my project.

5 As a researcher it is very difficult to set work limits and leave work at work. I am glad that my family and my friends have been around and at times forced me to take time off and focus on other matters of life. The joy which this thesis means to me I want to share with all of you! 12 AbstractGlass is a material which is used in increasing demanding applications. This is notonly as structural glazing in facades but also as structural elements like beams andcolumns. In all these applications there is a need for a good understanding of thematerial Glass .

6 This concerns the strength properties which need to be characterizedappropriately to reflect the actual behaviour. Design Principles should provide thenecessary reliability. The response of Glass is considered to be linearly elastic. This means that thetheory of elasticity is directly applicable to analyse the response of Glass . But typicalfor structural units of Glass plates is that the thickness is small compared to the inplane dimensions. This may result in structural complications. When a Glass plate isloaded perpendicular to its plane there will be both bending and membrane rupture strength of Glass is complex.

7 This reflects the influence of flaws,mainly in the surface regions, which will reduce the rupture strength to a fraction ofthe theoretical strength. In addition the rupture stress will exhibit dependencies wherein particular a size and a time dependence need to be addressed. This will furtherreduce the long term rupture stress of analysis of the rupture behaviour of Glass can be done based on fracturemechanics or the stochastic mechanics. This report summarizes and presents availableknowledge based on these add on theories to the theory of AreaB Risk functionD0 reference durationEtot Total energyF Failure probability functionG Energy release rateKt Stress concentration factorKI Stress intensity factorKIC Critical stress intensity factorL Length of the beamM MomentP Load acting on the bodyPf Probability of failureTmin Time to failureTABLE OF SYMBOLS334U Internal elastic strain energyV VolumeV0 reference volumeW Work doneWs Energy

8 Required to create a new crack surfaceY Dimensionless parameter dependent on crack geometrya Crack lengthb Half crack widthb Thickness of the beamc0 Normalization constante Distance between loads acting on the beamh Weibull parameter, time dependenceh Height of the beamm Weibull parameter, size dependencen Number of elements>@EV Mean value of the stress45Vm Stress at the flaw tip>@VarV Variance of the stress' DisplacementU Radius of the curvature of the flawu Elastic strain energy densityV0 Stress far away from the flaw tipV0 minimum strength of a defective elementQ Poisson' s ratioP Shear modulus of the material3 Potential of the body556671 ARCHITECTURAL IntroductionGlass is a material which has been favoured by architects from the time it wasintroduced in buildings.

9 There are several reasons to this but the transparency ofglass is often presented as an important characteristic. Glass could not be producedin larger sizes of reasonable quality until the beginning of the 20th century. A newproduction technique was introduced at the turn of the century which was soonimproved to a continous production of drawn Glass . This opened up new potentialswhich was soon realized by many architects. One of the first examples is the Fagusfactory by Walter Gropius of the Bauhaus group from 1911. In this building largeportions of the facade was completely covered by Glass , something which was latertermed Glass skin facades.

10 This new architectural style opened up a building andgave it a new Glass of high quality known as float Glass from its production techniquewas introduced in the 1960th. This Glass can be produced in very large sizes with anextremely high flatness. Within the production technique the surface finish isimproved and Glass sections with visible internal defects are removed. Theproduction technique requires that residual stresses are introduced. This createscompressive stresses in surface regions which is an advantage in practical use.