The Direction attribute is intended to identify two principal horizontal directions of the building plan. It is possible to specify different (LLRS) and the corresponding Material of the Lateral Load-Resisting System in two directions called Direction X and Direction Y; these systems are often referred to as Hybrid Systems or Mixed Systems. Where it is possible to specify directions, Direction X is parallel to street, and Direction Y is perpendicular (orthogonal) to street. In some cases, it is not possible to identify Direction X and Direction Y - thus the user can select Unspecified Direction.
Note that other types of hybrid systems can be described by the Hybrid Lateral Load-Resisting System attribute, which should be applied in one of the following cases: a) there is more than one LLRS in the building, but there is no clear distinction between LLRSs in directions X and Y, or b) there is only one LLRS, but two or more materials of the LLRS are used in different portions of the building.
A building showing possible orientation for Directions X and Y
EXAMPLE 1: A building has two different LLRSs: reinforced concrete flat plate (slab and column system) parallel to street, and reinforced concrete wall system perpendicular to street, as shown below. In this case, Direction X (parallel to street) is associated with a flat plate system (LFLS) (see Section 2), and Direction Y (perpendicular to street) is associated with a wall system (LWAL) (see Section 1).
EXAMPLE 2: The Direction attribute can be used to describe a hybrid LLRS from Chile, with reinforced concrete frames in longitudinal direction (Direction X) and confined masonry in transverse direction (Direction Y). It is assumed that Direction X (parellel to street) is longitudinal direction because entrance to individual housing units is in that direction (M. O. Moroni Yadlin).
EXAMPLE 3: The Direction attribute can be used to describe a hybrid system from Chile, where confined masonry is used in one direction and reinforced concrete shear walls in other direction (Moroni, Gomez, and Astroza, Chile,). The photo shows an earthquake-damaged building, and the drawing shows a typical building plan (not related to the building shown on the photo).