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According to EC8 (§5.2.2.1) concrete buildings should be classified to the following structural types:

• Wall system: structural system in which both vertical and lateral loads are mainly resisted by vertical structural walls, either coupled or uncoupled, whose shear resistance at the building base exceeds 65% of the total shear resistance of the whole structural system
• Frame system: structural system in which both the vertical and lateral loads are mainly resisted by spatial frames whose shear resistance at the building base exceeds 65% of the total shear resistance of the whole structural system
• Dual system: structural system in which support for the vertical loads is mainly provided by a spatial frame and resistance to lateral loads is contributed to in part by the frame system and in part by structural walls, coupled or uncoupled Dual system can be:
• a) Wall equivalent dual system .
• b) Frame equivalent dual system.
• Torsionally flexible system: dual or wall system not having a minimum torsional rigidity
• Inverted pendulum system: system in which 50% or more of the mass is in the upper third of the height of the structure, or in which the dissipation of energy takes place mainly at the base of a single building element EC8 does not consider as inverted pendulums one-storey frame systems with beams on both directions, if the axial force v_d =N_d/A_cf_cd is less than 0.3 on all columns.
• Ductile wall system. Ductile wall is fixed at its base so that the relative rotation of this base with respect to the rest of the structural system is prevented, and that is designed and detailed to dissipate energy in a flexural plastic hinge zone free of openings or large perforations, just above its base
• System of large lightly reinforced walls. A lightly reinforced wall is a wall with large cross-sectional dimensions, that is, a horizontal dimension lw at least equal to 4,0 m or two-thirds of the height hw of the wall, whichever is less, which is expected to develop limited cracking and inelastic behaviour under the seismic design situation

The most recent standards for the design of concrete buildings adopt lower behavior factors for the wall systems in comparison with the frame ones. This happens because:

• Long walls l_w have in general lower percentage of longitudinal reinforcement rather than the beams and the columns that consist frames.

The actual behavior of walls and wall systems under cyclic loading is less examined than the one of frame systems, because scientific research in walls is more difficult and analytical. As a result, the standards establish larger security margins (Fardis, 2009 b).