Onestory buildings with h less than or equal to 30 ft, buildings
two stories or less framed with lightframe construction,
and buildings two stories or less designed with flexible
diaphragms.
Building structures that are regular (as defined in
Section 12.3.2) and conform to the following:
 The eccentricity between the center of mass and the geometric centroid of the building at that level shall not exceed 15 % of the overall building width along each principal axis considered at each level and,
 The design story shear determined for earthquake load as specified in Chapter 12 at each floor level shall be at least 1.5 times the design story shear determined for wind loads as specified herein.
Building structures that are regular (as defined in
Section 12.3.2) and conform to the following:
 The design earthquake shear forces resolved to the vertical elements of the lateralloadresisting system shall be at least 1.5 times the corresponding design wind shear forces resisted by those elements.
Buildings meeting the definition of a torsionally regular buildings
contained in Section 26.2.
EXCEPTION: If a building does not qualify as being torsionally regular under wind load, it is permissible to base the design on the basic wind load Case 1 that is proportionally increased so that the maximum displacement at each level is not less than the maximum displacement for the torsional load Case 2.
EXCEPTION: If a building does not qualify as being torsionally regular under wind load, it is permissible to base the design on the basic wind load Case 1 that is proportionally increased so that the maximum displacement at each level is not less than the maximum displacement for the torsional load Case 2.
The torsional wind load cases need not be considered if the wind
force in each vertical MWFRS element of a building is scaled
to be 1.5 times the wind force calculated in the same element
under the basic wind load.
Square buildings
with L/B = 1.0, where all the following conditions are
satisfied:
 The combined stiffness of the MWFRS in each principal axis direction shall be equal, and
 The individual stiffness of each of the MWFRS in each principal axis direction shall be equal and symmetrically placed about the center of application of the wind load along the principal axis under consideration, and
 The combined stiffness of the two most separated lines of the MWFRS in each principal axis direction shall be 100% of the total stiffness in each principal axis direction, and
 The distance between the two most separated lines of the MWFRS in each principal axis direction shall be at least 45% of the effective building width perpendicular to the axis under consideration.
Square buildings
with L/B = 1.0, where all the following conditions are
satisfied:
 The combined stiffness of the MWFRS in each principal axis direction shall be equal, and
 The individual stiffness of the two most separated lines of the MWFRS in each principal axis direction shall be equal with all lines of the MWFRS symmetrically placed about the center of application of the wind load along the principal axis under consideration, and
 The combined stiffness of the two most separated lines of the MWFRS in each principal axis direction shall be at least 66% of the total stiffness in each principal axis direction, and
 The distance between the two most separated lines of the MWFRS in each principal axis direction shall be at least 66% of the effective building width perpendicular to the axis under consideration.
Rectangular
buildings with L/B equal to 0.5 or 2.0 (L/B = 0.5, L/B = 2.0),
where all the following conditions are satisfied:
 The combined stiffness of the MWFRS in each principal axis direction shall be proportional to the width of the sides perpendicular to the axis under consideration,
 The individual stiffness of each of the MWFRS in each principal axis direction shall be equal and symmetrically placed about the center of application of the wind load along the principal axis under consideration,
 The combined stiffness of the two most separated lines of the MWFRS in each principal axis direction shall be 100% of the total stiffness in each principal axis direction,
 The distance between the two most separated lines of the MWFRS in each principal axis direction shall be at least 80% of the effective building width perpendicular to the axis under consideration.
Rectangular
buildings with L/B equal to 0.5 or 2.0 (L/B = 0.5, L/B = 2.0),
where all the following conditions are satisfied:
 The combined stiffness of the MWFRS in each principal axis direction shall be proportional to the width of the sides perpendicular to the axis under consideration,
 The individual stiffness of the most separated lines of the MWFRS in each principal axis direction shall be equal with all lines of the MWFRS symmetrically placed about the center of application of the wind load along the principal axis under consideration,
 The combined stiffness of the two most separated lines of the MWFRS in each principal axis direction shall be at least 80% of the total stiffness in each principal axis direction, and
 The distance between the two most separated lines of the MWFRS in each principal axis direction shall be 100% of the effective building width perpendicular to the axis under consideration.
Rectangular
buildings having L/B between 0.5 and 1.0 (0.5 < L/B < 1.0) or
between 1.0 and 2.0 (1.0 < L/B < 2.0), the stiffness requirements
and the separation distances between the two most separated
lines of the MWFRS in each direction shall be interpolated
between Case A and Case C and between Case B and Case D,
respectively (see Fig. D1.51).
Main Wind Force Resisting Systems  Appendix D  h ≤ 160 ft.  

Figure D1.51 Case E  MWFRS  Requirements of Case E  Wind Torsion Exclusion See Figure 27.48 
Enclosed Simple Diaphragm Buildings  
Rectangular buildings
having L/B between 0.2 and 0.5 (0.2 ≤ L/B < 0.5) or between 2.0
and 5.0 (2.0 < L/B ≤ 5.0), see Fig. D1.52, where all of the following
conditions are satisfied:
 There shall be at least two lines of resistance in each principal axis direction,
 All lines of the MWFRS shall be symmetrically placed about the center of application of the wind load along the principal axis under consideration,
 The distance between each line of resistance of the MWFRS in the principal axis direction shall not exceed 2 times the least effective building width in a principal axis direction, and
 The individual stiffness of the most separated lines of the MWFRS in each principal axis direction shall be equal and not less than (25 + 50/n) % of the total stiffness where n is the required number of lines of resistance in the principal axis direction as required by conditions 1 and 3 of this section. The value of n shall be 2, 3, or 4.
Main Wind Force Resisting Systems  Appendix D  h ≤ 160 ft.  

Figure D1.52 Case F  MWFRS  Requirements of Case F  Wind Torsion Exclusion See Figure 27.48 
Enclosed Simple Diaphragm Buildings  
