Concrete buildings shall be classified into one of the following structural 6+1 types according to their behaviour under horizontal seismic actions.
Column is the vertical structural element of aspect ratio lw/hw≤4, while wall is the vertical structural element of aspect ratio lw/hw>4. In the building base, VF implies the seismic shear carried by all columns, VW the seismic shear carried by all walls and Vtot= VF + VW the total seismic shear at ground floor level.
1. Frame system
Structural system comprising only columns, or both columns and walls, in which columns are the main resisting elements with VF/Vtot>0.65.
2. Ductile wall system (coupled or uncoupled)
Structural system comprising only walls, or both columns and walls, in which walls are the main resisting elements with VW/Vtot>0.65.
3. Frame-equivalent dual system
Structural system comprising both columns and walls with 0.50<VF/Vtot≤0.65.
4. Wall-equivalent dual system
Structural system comprising both columns and walls with 0.50<VW/Vtot≤0.65.
5. System of large lightly reinforced walls
System comprising at least two walls in the horizontal direction considered satisfying the three following conditions:
- The horizontal dimension is lw≥min(4.0 m, 2hw/3),
- The walls collectively support at least 20% of the total gravity load from above in the seismic design situation.
- The fundamental period of the structure is ≤0.5 sec
If the first of the above conditions is satisfied but either the second or the third is not, then the system is classified as ductile wall system and all of its walls should be designed and detailed as ductile walls.
6. Inverted pendulum system
System in which 50% or more of the mass is in the upper third of the height of the structure.
One-storey frames with column tops connected along both main directions of the building and with the value of the column normalized axial load νd exceeding 0.3 nowhere, do not belong in this category.
7. Torsionally flexible system [EC8, 188.8.131.52(4)P]
Provided that at the characteristic floor either rx<ls, or ry<ls is satisfied, then the system is classified as torsionally flexible. In the floor of the example min(rx, ry)= min(3.91, 3.08)=3.08 m >ls=2.81 m, thus the building is not torsionally flexible.