Steel Structures III - Advanced Steel and Composite Construction

• Tensioning of cables against each other
  • Prestress does not reduce forces!
    --> but increases the system stiffness
     
• Cable Girder - plane system with prestress
• Jawerth-Girder - La Vilette, Paris
• Fischbauchträger
• Stabilization of arches
  • stays above and below the main beam
  • plane "spoke wheel"
• Spatial spoke wheel - used in very large roofs, such as stadiums
• Cable-stayed facades and cable nets
  • Design criterion for cables is usually deformations --> prestressing level is selected
  • Temperature fluctuations critical for pretension

Free-form surfaces

• Can be generated, for example, using NURBS (non-uniform rational B-splines)
  in CAD programs (e.g. Rhinoceros 3D)
   
• The freeform surfaces are approximated with triangular meshes or a combination of
  triangular and quadrilateral meshes
   
• As a rule, bars and nodes must be able to transmit bending moments
   
• Complex logistics due to many different rods, nodes, and glass panes

Steel tends to corrode in the presence of water

• exposed surfaces --> atmospheric corrosion
• confined areas --> crevice corrosion
• coupling of different metals --> galvanic corrosion

• protective paints (organic coatings)
  • primarily "barrier effect"
     
• protective metallic coatings (e.g. zinc)
  • "active corrosion protection" through galvanic action (sacrificial dissolution of zinc)
  • and "barrier effect"
     
• duplex coatings
  • various layers including metallic and organic coats
    (each layer has a different function)

Appropriate design measures & detailing...

• ... to avoid premature corrosion and degradation of the coating and the steel structure
   
• ... to facilitate inspection and maintenance

Key areas:

• prevention of retention and deposits of water and dirt
• connections & joints
• prevention of galvanic corrosion