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4.8.4. Amplification of Reduced Internal Forces and Displacements According to Equivalent Base Shear Force

4.8.4.1 - In case V _tx ^(X) <E * V _tE ^(X) for any earthquake direction ^(X) , all reduced internal force obtained by the modal calculation method applied according to 4.8.2 or 4.8.3 and The displacement magnitudes will be enlarged by multiplying the equivalent base shear amplification coefficient β _tE ^(X) given by Eq (4.31) .

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Wherein V _t ^(X) to the lateral force Method according to Eq. (4.21) calculated by the total equivalent seismic load (base shear force), V _tx ^(X) is 4.8.2 or 4.8.3 according x direction 'in It shows the total earthquake load obtained . γ _The factor of _E will be taken as follows:

(a) If at least one of the A1 , B2 or B3 type irregularities defined in Table 3.6 is present in the building, γ _E = 0.90 shall be taken.

(b) If none of the irregularities defined in Table 3.6 are present in the building, γ _E = 0.80 shall be taken.

According to the definition given in 4.8.4.2 - 3.3.1 , in buildings with externally rigid walls surrounded by basements, the equivalent base shear force amplification coefficient shall be calculated only for the upper part above the basement floors of the building .

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Page Treeroot@SELFHow does ideCAD scale design values of combined response according to ASCE 7-16?

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Symbols

V = The equivalent lateral force procedure base shear
V_t = The base shear from the required modal combination
C_s = The seismic response coefficient
W = The effective seismic weight
R = The response modification factor in Table 12.2-1
I_e = The Importance Factor
S_D1 = the design spectral response acceleration parameter at a period of 1.0 s
T = The fundamental period of the structure(s)

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A base shear (V) is calculated in each of the two orthogonal horizontal directions using the calculated fundamental period of the structure T in each direction and the procedures of Section 12.8.

The seismic base shear, V, in the earthquake direction considered, is determined by the following equation.

Scaling of Forces per ASCE 12.9.1.4.1

If the calculated fundamental period exceeds C_uT_a in a given direction, C_uT_a is used in lieu of T in that direction. Where the combined response for the modal base shear (V_t) is less than 100% of the calculated base shear (V) using the equivalent lateral force procedure, the forces is multiplied by V∕V_t.

Scaling of Drifts per ASCE 12.9.1.4.2

If the combined response for the modal base shear (V_t) is less than C_sW, and where C_s is determined with Eq. (12.8-6), drifts are multiplied by C_sW∕V_t.

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