Prof Patrick de Wilde from the Free University of Brussels gave a lecture at the Lodge on the topic of The Use of Morphological Indicators in Design Decisions for Architectural Structures.
Patrick is a Member of the Board of Directors of WIT and a well-known researcher in structures and materials. He has collaborated with the Institute in several international conferences and participated in other projects. His lectures are always of great interest as they reflect a series of new topics and advanced applications in the field.
The morphological indicators proposed can produce meshes with relation to the morphology of the structures such as buckling indicators, volume or displacement indicators, etc. A volume indicator, for instance, gives an idea of the weight of a structure to bridge a given span.
Previous work was carried out by a few researchers in the past, such as Zaloski (1975) who compared weights and stiffness of different trusses with the flow of forces in beams. Rippol (1989) compared the weight of single trusses and arches and demonstrates the link between volume and geometric slenderness. This work was continued by Samyn (1999) who proposed an analytical expression for many different types of structures, using the concepts of displacement and volume indicators, but without taking buckling into account. Latten (2000), however introduced these new indicators taking buckling, self-weight and second order effects into consideration.
Patrick then presented some interesting examples encompassing different types of structures. One example involves the same structures, but two different materials, ie aluminium and steel, for which case a node rotation can be used as an indicator. Other interesting applications were shown for complex new structural forms, consisting of arches, as with the case of the Levven structures, taking into account buckling, which proved to be a major source of extra weight for the structure. This led to a different solution which offers the designer double the weight of steel rather than seven times as the original design! In this research, the building indicators clearly show how the phenomenon influences the weight of the structure.
Further studies relate to the consideration of parasitic stress, due to non perfect hinges and other second order effects.
Is an arch always better as a structural shape than a beam? This problem can be studies by using structural indicators which show that the use of one or other structural shape is dependent on the possibility of buckling taking place for instance.
Current extension of this study is to involve dynamic effects and analyse tensegrity structures which are defined as "an island of compression in an ocean of tension".
The lecture was followed with a great deal of interest and a lively discussion ensued.
Wessex Institute