What is a double-skeleton structure?
A double-skeleton structure is a load-bearing system in which two independent frames are placed alongside or within each other and together carry the building. It is used in high-rise buildings, double facades and projects that require maximum floorplan flexibility.
How does a double-skeleton structure work?
A standard skeleton consists of a grid of columns and beams. In a double skeleton, two frames work in parallel:
- Inner skeleton — often around a stable core (stair and lift shaft)
- Outer skeleton — along the facade, supporting the floors directly or carrying a second facade layer
- Connections — links between the two skeletons provide stability
Variants include:
- Tube-in-tube — a closed core surrounded by a second ring of columns (high-rise)
- Mega-frame — large outer frame with internal storey structures
- Double facade — two facades a short distance apart, each with its own frame
- Timber frame inside concrete frame — material combination for insulation and circularity
Application
- High-rise — stiffness against wind and seismic loads
- Flexible offices — column-free workspace
- Double facades — energy and acoustic benefits
- Renovation — new skeleton around an existing one
- Circular construction — demountable outer skeleton around a durable inner one
Points of attention
- A double skeleton uses more material and costs more
- Stiffness balance between the two frames must be tuned carefully
- Movement joints prevent unintended load transfer
- Fire and building physics must be considered per facade layer
- Connections between the skeletons are usually the critical detail
Related terms
- Skeleton construction
- Structure
- Box construction
- Composite beam
- Concrete skeleton
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