Nonbuilding structures (seismic)

The seismic base shear of a nonbuilding structure by ASCE/SEI 7-22 Chapter 15: the system of Table 15.4-1 (similar to buildings) or Table 15.4-2 (not similar) with R, Ω0, Cd and the height limits, the importance factor of 15.4.1.1, the period of 15.4.4, rigid structures (15.4.2) and nonrigid ones by 12.8 with the Chapter 15 minimums, the vertical distribution, and the basics of tanks and vessels. It is an analysis: the result reads Calculated.

Inputs of the nonbuilding structure #

• Seismic hazard: SDS, SD1, S1 and TL (the ASCE Hazard Tool); the risk category by the hazard of the contents and the function (Table 1.5-1), and Ie of a reference document or of Chapter 15 where it is larger (15.4.1.1, for example 1.5 for storage racks open to the public). Ie is the largest.
• System: a row of Table 15.4-1 or 15.4-2 (the table is named in the list), or Other with R, Ω0 and Cd entered (a Table 12.2-1 system for a structure similar to buildings, 15.4.1 item 1a). Where the code offers a choice of rows (an ordinary braced frame with its limited height, a permitted height increase or unlimited height), the row is yours.
• Reference document: for tanks and vessels designed to AWWA D100, D103, API 650 Appendix E or API 620 Appendix L, and stacks and chimneys designed to ACI 307, the minimums of Eqs. 15.4-3 and 15.4-4 replace 15.4-1 and 15.4-2.
• Liquid tanks: a ground-supported liquid tank has an impulsive and a convective component (15.7.2, 15.7.6); the calculation gives the impulsive base shear. Confirm that the weight and period entered are the impulsive ones.
• Period: from a substantiated analysis (entered) or Eq. 15.4-6 from level forces fi and the elastic deflections δi they cause. The approximate period formulas of 12.8.2.1 are not used for nonbuilding structures (15.4.4).
• Cs method: Method 2 (SDS, SD1) or Method 1 with Sa at T from the multi-period design spectrum (12.8.1.1).
• Levels: height above the base and the operating weight with normal contents (15.4.3) of each level; for Eq. 15.4-6 also fi and δi.

Checks performed #

The drawings show a schematic elevation (a frame outline for structures similar to buildings, a line for stacks, vessels and towers) with the level forces, and the shear and overturning moment diagrams.

Limitations #

• Nonbuilding structures supported by other structures (15.3: Chapter 13 below 20 % of the combined weight, the combined analysis above), the special provisions of 15.5 and 15.6, and the designs of the reference documents are outside this calculation.
• Liquid tanks: the convective (sloshing) component, freeboard, hydrodynamic pressures and the vertical acceleration of 15.7 and 15.1.4 are not computed.
• Tables 15.4-1 and 15.4-2 are subsets (the cantilever storage rack and reinforced concrete tabletop rows are not listed: use Other). The text copy of ASCE 7-22 loses the R, Ω0, Cd of the distributed mass cantilever row; 3, 2, 2.5 are taken from FEMA P-1051 (to confirm against the code text). The text of 15.4.1 item 2 and 15.4.4 refers to the 12.8 equations by their ASCE 7-16 numbers; the minimums and period formulas meant are applied (to confirm against the code text).
• One direction per calculation. No auto-design: nothing is sized.

Verification examples #

Verification status: 67 values compared in 24 examples (19 published, 5 hand calculations from the cited equations): 67 within tolerance, 0 recorded deviations. Code basis: partial. Only some provisions were read in the target edition; the rest rests on older editions, examples or summaries.

FEMA P-1051 Chapter 17 works nonbuilding structures to ASCE 7-10; the equations used are the same in ASCE 7-22 (renumbered). FEMA prints Cs to three digits.

Hand calculations (closed form): a rigid structure (Eq. 15.4-5), Eq. 15.4-2 and Eq. 15.4-4 for a steel stack with S1 = 0.75 g, the 0.03 minimum of Eq. 15.4-1, the Rayleigh period of Eq. 15.4-6, and Table 15.4-1 / 15.4-2 rows.