Practical Analysis of Seismic Load Using the ASCE 7-16

This article provides an example of seismic load calculation of the residential building to the ASCE 7-16.

The building is assumed to be located in Bridgeville, California, with a reinforced concrete moment-resisting frame with 3 storeys and a total height of 29.53 ft.

Figure 1: An example of a residential building for seismic load calculation using the ASCE 7-16 procedure

The detailed calculation of the seismic loads is performed according to the specification of ASCE 7-16 (check out the article for detailed outline of the procedures for calculating seismic loads in residential buildings using the linear static approach in Chapters 11 and 12 of the ASCE 7-16).

Step 1: Identifying Site Class and Spectral Parameters

Using the ASCE 7 Hazard Tool, we specified the building's location, a risk category II as default for residential buildings and a site class C to obtain the spectral parameters, Sₛ value of 2.29g, S₁ value of 0.869g, and a long period Tₗ of 8s.

The building has a natural period, T, of 0.187s.

Step 2: Defining the Seismic Ground Motion Values

Once the spectral parameters for the building's site are obtained, the site coefficients (Fₐ and Fᵥ) are defined using the data provided in Table 11.4-1 and Table 11.4-2 in ASCE 7-16.

Thereafter, the design response spectrum is developed using the following equations:

Step 3: Obtaining the Seismic Force Resisting System (SFRS) Properties

Once the design spectrum is established, the response modification coefficient, R based on the type of seismic resisting system and the material used, importance factor (Iℯ), and approximate period parameters Cₜ and Cₓ are obtained from Table 12.2-1, 1.5-2, and 12-.8-2 respectively in ASCE 7-16.

Step 4: Calculating Seismic Response Coefficients

Thereafter, the seismic response coefficient is calculated and checked against the required conditions.

Step 5: Calculating the Effective Seismic Weight on the Building and Seismic Base Shear

Finally, the seismic base shear of the structure in the direction of concern is calculated and distributed to each story.

Once the parameters are obtained and set, the effective seismic weight of each story in the residential building is calculated based on the self-weight of the structural and non-structural elements and the partial contribution of the live load in the building (Figure 2).

Table 1. Vertical distribution of seismic forces calculated using Eqs. 12.8-11 and 12.8-12 in the ASCE 7-16)

Figure 2: Vertical distribution of seismic forces for the given example as per the ASCE 7-16

Conclusion

In order to comply with ASCE 7-16 requirements for analyzing seismic loads in residential buildings, engineers must follow the procedure outlined in Chapters 11 and 12. To find out how ClearCalcs integrates these calculations for seismic load analysis, check out our Seismic Analysis Calculator to ASCE 7-16.

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