Seismic Design Criteria¶

The Seismic Design Criteria tab establishes the Chapter 11 values the building design needs: the MCER spectral accelerations for the site, the site class, the design spectral accelerations SDS and SD1, the seismic design category, and the design response spectrum. Chapter 11 also covers topics the tab does not, such as near-fault sites, geotechnical investigation, vertical ground motion, and site-specific procedures.

Section numbers in the text are ASCE 7-22 unless another edition is named. ASCE 7-16 added Section 11.4.1, Near-Fault Sites, so its later Section 11.4 numbers are one higher. The Code Reference table gives the numbers for each edition.

Key Features¶

• USGS lookup of the site parameters from the project latitude and longitude
• Manual entry of Ss, S1, SMS, SM1, and TL when the values come from elsewhere
• Site classes A through F, including the BC, CD, and DE classes of ASCE 7-22
• Design parameters table with the code reference or source beside each value
• Seismic design category per Section 11.6
• The design response spectrum, drawn for the site

Site Parameters¶

USGS Lookup¶

With Calculate site parameters from USGS switched on:

1. Enter the Latitude and Longitude of the site, in decimal degrees
2. Press Tab. Prose queries USGS for the project's edition, risk category, and site class
3. The Design Parameters table fills in, with "USGS Seismic Design Geodatabase" as the source of each mapped value

The USGS Seismic Design Geodatabase is defined in ASCE 7-22, which takes its values directly (Section 11.4.3). In ASCE 7-10 and 7-16 the values come from the Chapter 22 maps, and the USGS electronic values are mentioned only in a User Note.

The lookup runs again whenever the coordinates, the site class, or the risk category change. The ASCE Hazard Tool button opens ascehazardtool.org in a second window for checking the values.

Manual Values¶

Switch the USGS lookup off to type the values yourself:

Values entered by hand show "User Defined" as their source in the table and the report. With manual values, Use two-period design response spectrum is switched on and locked, because the multi-period spectrum needs the USGS data. ASCE 7-22 permits the two-period spectrum only where multi-period values are not available from the geodatabase (Section 11.4.5). Where the values come from a site-specific ground motion analysis, the design spectrum is the site-specific spectrum of Section 21.3, which Prose does not draw.

Risk Category and Importance Factor¶

Risk Category is read from the structure and cannot be changed here; edit the structure to change it. The Seismic Importance Factor, Ie follows from it per Table 1.5-2.

Site Class¶

Choose the Site Class from the geotechnical report. The list holds A, B, BC, C, CD, D, DE, E, and F. Site Classes BC, CD, and DE exist only in ASCE 7-22 (Table 20.2-1); ASCE 7-10 and 7-16 use A through F. Changing the class reruns the lookup, and SMS, SM1, SDS, SD1, and the seismic design category update with it.

DEFAULT selects the default site class, used where the soil properties are not known in sufficient detail to determine the site class:

• ASCE 7-22 (Section 11.4.2.1): the most critical of Site Classes C, CD, and D
• ASCE 7-16 (Section 11.4.3): Site Class D, with Fa not less than 1.2
• ASCE 7-10 (Section 11.4.2): Site Class D

The default does not apply where the Authority Having Jurisdiction or geotechnical data determine that Site Class E or F soils are present (DE, E, or F in ASCE 7-22).

Design Parameters¶

The table lists every value with its source or code reference:

Response Spectrum¶

The Design Horizontal Response Spectrum chart draws the spectrum for the site. With the USGS lookup on, it is the multi-period design spectrum of ASCE 7-22 Section 11.4.5.1. With Use two-period design response spectrum on, it is the two-period spectrum built from SDS, SD1, and TL: Section 11.4.5.2 in ASCE 7-22, Section 11.4.5 in ASCE 7-10, and Section 11.4.6 in ASCE 7-16.

Summary View¶

The summary on the right lists the site parameters with their references, the design parameters, and the spectrum type. The outline button at the top jumps to a section.

Next Steps¶

With the design criteria set, describe the building and its systems in Building Design.

Code Reference¶