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The Civic tower, in Pavia, built nine hundred years ago, fell down in 1989. Dr. Gideon van Zijl knows how engineers and architects can prevent this from happening in future.

/strong>The porous, cementitious material used in buildings changes in time, owing to moisture and the constant load from the construction above. If the load on the masonry is too heavy, it may result in excessive shrinking, deforming and cracking. This can lead to the collapse of buildings, like the Civic tower, in Italy. Computational analysis can prevent this in future, according to Dr. Gideon van Zijl, who received his PhD last Monday. He discovered that masonry deformation (creep) continues to occur during a building's life if the load on the masonry exceeds a certain maximum value. Short term, exceeding this maximum is not necessarily problematic; but over time, such a building will eventually collapse. Architects can avoid this and build 'everlasting' constructions by keeping the load below the maximum value given by Van Zijl's computer model.Van Zijl's computer model attempts to bridge the gap between the fundamental scientific knowledge of physical processes and mathematical descriptions, and the daily, practical realities for architects. His computer model can simulate and predict the interaction of shrinkage, creep and cracking in masonary structures of practical relevance and scale.Van Zijl's PhD-project at Civil Engineering was motivated by the wishes of architects to have more information about where movement joints in masonry walls should be made to prevent random cracking of a wall. Movement joints prevent cracking % due to wall shrinkage % when the masonry becomes drier. Van Zijl: 'In practice, the three analytical rules and thumb-rules currently used all give rather different advice on how far apart the movement joints should be situated. Therefore, architects want more accurate predictions. With our model we can predict the crack width in the wall between the movement joints. Small cracks are acceptable. However, if we predict big cracks, they must and can be avoided by making more movement joints.'Computational analysis is a specialist task; however, this does not threaten its viability, according to Van Zijl: 'We do many calculations of different walls and different humidity. From this we extract design codes that are just as easy to interpret as thumb-rules and analytical rules.'Van Zijl chose Delft Technical University for his PhD because, Professor Rene Borst, was an 'upcoming star and led a dynamic group with many PhD-students, offering me the opportunity to discuss my project with others. In South Africa, I'd have been working on my own.' However, having done his PhD in The Netherlands, Van Zijl had to endure a bad night of sleep prior to defending his thesis: 'In South Africa, a hundred people receive their PhDs in a ceremony that only involves shaking hands. You don't have to defend your thesis in public!'Currently, Van Zijl is working at the Faculty of Architecture, bearing constructions and mechanics. His computer model will probably soon be used in a new project: 'We're studying the process of tunnelling beneath historical buildings in Amsterdam, how it influences the buildings and whether there's a way to avoid damaging them.'

The Civic tower, in Pavia, built nine hundred years ago, fell down in 1989. Dr. Gideon van Zijl knows how engineers and architects can prevent this from happening in future.The porous, cementitious material used in buildings changes in time, owing to moisture and the constant load from the construction above. If the load on the masonry is too heavy, it may result in excessive shrinking, deforming and cracking. This can lead to the collapse of buildings, like the Civic tower, in Italy. Computational analysis can prevent this in future, according to Dr. Gideon van Zijl, who received his PhD last Monday. He discovered that masonry deformation (creep) continues to occur during a building's life if the load on the masonry exceeds a certain maximum value. Short term, exceeding this maximum is not necessarily problematic; but over time, such a building will eventually collapse. Architects can avoid this and build 'everlasting' constructions by keeping the load below the maximum value given by Van Zijl's computer model.Van Zijl's computer model attempts to bridge the gap between the fundamental scientific knowledge of physical processes and mathematical descriptions, and the daily, practical realities for architects. His computer model can simulate and predict the interaction of shrinkage, creep and cracking in masonary structures of practical relevance and scale.Van Zijl's PhD-project at Civil Engineering was motivated by the wishes of architects to have more information about where movement joints in masonry walls should be made to prevent random cracking of a wall. Movement joints prevent cracking % due to wall shrinkage % when the masonry becomes drier. Van Zijl: 'In practice, the three analytical rules and thumb-rules currently used all give rather different advice on how far apart the movement joints should be situated. Therefore, architects want more accurate predictions. With our model we can predict the crack width in the wall between the movement joints. Small cracks are acceptable. However, if we predict big cracks, they must and can be avoided by making more movement joints.'Computational analysis is a specialist task; however, this does not threaten its viability, according to Van Zijl: 'We do many calculations of different walls and different humidity. From this we extract design codes that are just as easy to interpret as thumb-rules and analytical rules.'Van Zijl chose Delft Technical University for his PhD because, Professor Rene Borst, was an 'upcoming star and led a dynamic group with many PhD-students, offering me the opportunity to discuss my project with others. In South Africa, I'd have been working on my own.' However, having done his PhD in The Netherlands, Van Zijl had to endure a bad night of sleep prior to defending his thesis: 'In South Africa, a hundred people receive their PhDs in a ceremony that only involves shaking hands. You don't have to defend your thesis in public!'Currently, Van Zijl is working at the Faculty of Architecture, bearing constructions and mechanics. His computer model will probably soon be used in a new project: 'We're studying the process of tunnelling beneath historical buildings in Amsterdam, how it influences the buildings and whether there's a way to avoid damaging them.'

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