In reading four Ching talks about structural units, structural spans, structural patterns, and lateral stability. Structural units can be capable of defining and enclosing the volume of space for a habitation with the principal structural elements of column, beam, slab, and loadbearing wall. Structural spans explain the relationship between the span and the spacing of elements that influence the dimensions and scale of the space that are defined by the structural system of a building. Structural patterns are basically preparation of principal vertical supports of regulating the selection of a spanning system and also that determines the possibilities for the ordering of spaces and functions in a building. 2.22 “Lateral stability” explains how structural systems must be designed to carry vertical gravity loads and also withstand lateral wind and seismic force from any direction. The mechanisms for ensuring lateral stability are knee bracing, k-brace, and cross bracing. Ching also explains how the torsional effects of lateral forces are determined by the asymmetrical layout of irregular structures generally requires dynamic analysis.