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Structural Concrete - Hassoun

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20.3 Analysis Procedures 807<br />

The lateral force that will be applied to level x of the structure, F x , can be determined from<br />

the following equation:<br />

F x = C vx V (20.17)<br />

C vx =<br />

w xh k x<br />

n∑<br />

(20.18)<br />

i=1<br />

where<br />

C vx = vertical distribution factor<br />

k = distribution exponent related to building period<br />

k = 1 for building having a period of T ≤ 0.5 s<br />

k = 2 for building having a period of T ≥ 2.5 s<br />

k = 2, or linear interpolation between 1 and 2, for buildings having a period of 0.5 s ≤ T ≤ 2.5 s<br />

h i , h x = height from base to level i and x<br />

w i , w x = portion of total effective seismic weight of the structure, W, located or assigned to level i or x<br />

n = number of stories<br />

V = total design lateral force or shear at base of the structure<br />

w i h k j<br />

20.3.2 Summary: Equivalent Lateral Procedure<br />

Step 1. Determine seismic design category according to Section 20.2 and choose an appropriate<br />

I e value from Table 20.1.<br />

Step 2. Choose R value from Table 20.7.<br />

Step 3. Determine T using Eq. 20.15 or 20.16, as applicable.<br />

Step 4. Calculate C s using Eq. 20.11 and check for C s,max (Eq. 20.12a or Eq. 20.12b) and C s,min<br />

(Eq. 20.13 or 20.14, whichever is applicable). Ensure that C s,min ≤ C s ≤ C s,max and<br />

if C s > C s,max , then choose C s = C s,max ⋅<br />

if C s > C s,min , then choose C s = C s,min ⋅<br />

Step 5. Calculate effective seismic weight, W, as described in Section 20.3.1.<br />

Step 6. Calculate seismic base shear using Eq. 20.10.<br />

Step 7. Using Eq. 20.17, calculate seismic lateral load, F x , for every level of the structure.<br />

20.3.3 Simplified Analysis<br />

The simplified analysis procedure for seismic design described in Section ASCE 7-10, Section<br />

12.14.8.1, is applicable to any structure that satisfies the following limitations and conditions:<br />

The seismic base shear and lateral seismic forces are calculated as follows:<br />

• The structure shall qualify for risk category I and II.<br />

• The site class shall not be class E or F.<br />

• The structure shall not exceed three stories in height above grade.<br />

• The seismic force resisting system shall be either a bearing wall system, or building frame<br />

system.

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