Simplified seismic design
The seismic base shear and level forces of a simple bearing wall or building frame building by the simplified alternative procedure of ASCE/SEI 7-22 12.14: the eligibility conditions of 12.14.1.1, SDS of 12.14.8.1, the seismic design category, R and the system limitations of Table 12.14-1, V = F SDS W / R, the level forces in proportion to the level weights, story shears and overturning. It is an analysis: the result reads Calculated.
Inputs of the simplified seismic design #
- SDS: entered (2/3 SMS from the USGS values by 11.4.4), or 2/3 Fa Ss with Fa = 1.0 for a rock site (not more than 10 ft of soil between the rock and the bottom of the footing or mat) or 1.4 for a soil site (12.14.8.1). Ss need not be taken above 1.5 (permitted; on by default, yours to clear).
- S1: only for the seismic design category: S1 ≥ 0.75 g makes it E (12.14.1.1).
- Risk category and site class: the procedure needs risk category I or II and a site class other than E or F.
- System: a row of Table 12.14-1 (bearing wall systems A.1 to A.18, building frame systems B.1 to B.26) with R and the limitation in SDC B, C and D / E.
- Levels: one row per story above grade plane (at most three): height above the base and the seismic weight (12.14.8.1 items 1 to 5: storage, partitions, permanent equipment, snow over 30 psf, roof gardens).
- Limitations 5 to 12 of 12.14.1.1: lines of resistance, center of weight, diaphragm overhangs, line spacing for diaphragms that are not flexible, orientation, use in both directions, no offsets, no weak story. Each is a check box you confirm; all are on, as the code requires.
Checks performed #
| Check | Basis |
|---|---|
| Eligibility | 12.14.1.1 items 1 to 4 checked (risk category, site class, three stories, Table 12.14-1 system); items 5 to 12 as confirmed; any item not met: NOT FEASIBLE |
| SDS | 12.14.8.1 (Fa 1.0 / 1.4, Ss ≤ 1.5) or 11.4.4 |
| Seismic design category | Table 11.6-1 with the simplified SDS; E where S1 ≥ 0.75 g (12.14.1.1) |
| System limitation | Table 12.14-1: P / NP by SDC, the 40 ft entry of intermediate precast walls (footnote c) and the 35 ft limit in SDC D of light-frame walls of other materials (footnote d) |
| Base shear | V = F SDS W / R, F = 1.0, 1.1, 1.2 for one, two, three stories (Eq. 12.14-12) |
| Vertical distribution | Fx = wx V / W (Eq. 12.14-13), story shears (Eq. 12.14-14), overturning (12.14.8.4; foundations may use 75 %) |
| Load effects | Eh = QE (no redundancy factor), Ev = 0.2 SDS D (zero where SDS ≤ 0.125), Emh = 2.5 QE (12.14.3) |
| Drift | Not calculated; 1 % of hn where a value is needed (12.14.8.5) |
The drawings show the building elevation (story heights to scale, the width schematic) with the level forces, and the story shear and overturning moment diagrams.
Limitations #
- One direction per calculation (12.14.1.1 item 10 requires the procedure in both: run each direction).
- The horizontal distribution (12.14.8.3), diaphragm, collector, wall anchorage and connection forces of 12.14.7 and the design of the elements are not part of the calculation.
- Footnote c of Table 12.14-1 (the 40 ft entry of intermediate precast shear walls) is read from the text copy, where the footnote text does not match the entry (to confirm against the code text).
- No auto-design: nothing is sized.
Verification examples #
Verification status: 32 values compared in 20 examples (17 published, 3 hand calculations from the cited equations): 32 within tolerance, 0 recorded deviations. Code basis: the provisions it uses were read in the target edition.
FEMA P-1051 Example 14.1 designs a three-story wood light-frame building by the simplified procedure (ASCE 7-10; the 12.14 equations are the same in 7-22, renumbered). FEMA P-2192 has no 12.14 example.
| Example | What it checks | Published | ILX Calcs |
|---|---|---|---|
| P-1051 14.1 | SDS 0.89, F 1.2, R 6.5, W 751 kips (pp. 726 to 730) | V 123.4 kips; F roof 30.0, 3rd 46.7, 2nd 46.7 kips | same |
Hand calculations (closed form): SDS with Fa = 1.4 (1.2507 g), the Ss cap on a rock site, a two-story building (F = 1.1, base overturning, 1 % drift, Ev), and the R of Table 12.14-1 rows.