For all analyses, at least two vertical distributions of lateral load shall be applied.  One pattern shall be selected from each of the following two groups. Therefore, two different input files are to be generated. One analysis is to be performed by selecting any one method from Group 1. Another separate analysis is to be performed by selecting Method 3 from Group 2.

Group 1

Method 1

A vertical distribution proportional to the value of C_vx given in Equation (3-12) of FEMA 356 : 2000 is performed. Use of this distribution shall be permitted only when more than 75% of the total mass participates in the fundamental mode in the direction under consideration, and the uniform distribution is also used.

Method 2

A vertical distribution proportional to the shape of the fundamental mode in the direction under consideration is performed. Use of this distribution shall be permitted only when more than 75% of the total mass participates in the fundamental mode in the direction under consideration, and the uniform distribution is also used.

Group 2

Method 3

A vertical distribution is performed consisting of lateral forces at each level proportional to the total mass at each level.