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Tue, 15 Oct 2019 00:51:48 GMT

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RAM SS Orthogonal Effect with Redundancy Factor

Jian Xiao — Tue, 15 Oct 2019 15:47:58 GMT

Hi,

I have a building with two orthogonal braced frame intersecting, which makes one of the column forms both lateral system in the orthogonal direction. Per ASCE 7-10, section 12.5.3.a, Orthogonal Combination Procedure shall apply (see figure 1 below)

Figure 1

Also, due to the number of bay of braced frame in each orthogonal direction (2-bay in y-direction and 1-bay in x-direction), per ASCE 7-10, section 12.4.3.2.b, I have used rho of 1.0 and 1.3 in x-direction and y-direction, respectively. (See Figure 2 below)

Figure 2

However, when I output the ASD load combination, I found out that, when RAM detected that the load case contains the force in the direction which requires rho of 1.3, regardless of whether it is in 100% or 30% due to orthogonal effect, the entire load combination gets amplified by rho factor. With that said, since I have applied orthogonal effect per code, basically all the load case will contain the x-direction load, regardless of whether it is in 100% or 30%, the entire load case was multiplied by 1.3. But then the advantage of reducing redundancy with 2-bay will be lost.(See Figure 3 below).

My interpretation of the load comb is that 0.91E_9 = 0.7*1.3*(0.3Ex+Ey) = 0.7*1.3*0.3*Ex+0.7*1.3*Ey. However, I believe the correct load comb shall be 0.7*1.3*0.3*Ex + 0.7*Ey.

It would be great if I can get some ideas how to solve this and take advantage of the rho=1.0 in y-direction.

Thank you!

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RAM SS Orthogonal Effect with Redundancy Factor