Digital Fabrication of a Timber Bridge
Design, optimisation, fabrication and testing at global and connection level
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Abstract
Rapid developments of both new (digital) fabrication techniques and innovative software facilitate the possibility to design, check and construct objects with great complexity and uniqueness without a large price tag. After new techniques slowly entered the field of architecture, the next step is to apply them in civil engineering to design load-bearing structures, dealing with a large number of load cases, outdoor conditions and strict safety requirements.
The application of digital fabrication in civil engineering is examined through a case study: the design of a pedestrian frame bridge made of timber using CNC-milling techniques. In this research a strong focus is on the design, optimisation, detailing and testing of the connections.
This research demonstrates that the combination of a reciprocal gridshell structure in combination with interlocking joints (lap joints) is particularly suitable for digital timber fabrication since a stable system can be obtained without the use of fasteners. The uniqueness of all connections and the strong relation between them makes the design process complex. Nevertheless, with the help of digital design tools like Grasshopper and evolutionary it is possible to deal with a large number of parameters with a complex relation between them.
Additionally lab tests were carried out to get insight in the shear capacity of notched members. The tests show that the verification method for notched members in Eurocode 5 does not accurately predict the shear strength when hardwood is applied. Additional research on the fracture energy of hardwood is required to propose an improved calculation method. Furthermore, the tests have shown that the application of rounded edges and screws as reinforcement significantly improve the shear capacity of notched members. It is therefore always advised to apply rounded edges, if possible in combination with screws.
All in all, the case study has shown that it is possible to design a load bearing free-form gridshell timber structure on both global and connection level, using the advantages of digital design and fabrication techniques.