What it checks
The module calculates the Equivalent Lateral Force (ELF) base shear for nonbuilding structures, including racks, tanks, vessels, stacks, and towers. It determines the governing design section for supported items by evaluating the relationship between the supported structure and its support.
The design method follows ASCE 7-22 Chapter 15, utilizing the ELF procedure with specific coefficients for Response Modification Factor (R), Overstrength Factor (Omega0), and Deflection Amplification Factor (Cd). The module enforces structural height limits per Seismic Design Category (SDC) and applies specific minimum values for the Seismic Response Coefficient (Cs) based on the system type and reference documents.
The sequence of checks begins with selecting the appropriate system row from Table 15.4-1 or Table 15.4-2. It then verifies the structural height against SDC-specific limits, calculates the importance factor (Ie), and determines the governing Cs value by comparing the calculated period-based value against minimum floors and the rigid branch threshold. Finally, it evaluates the Sec. 15.3 criteria to determine whether Chapter 13 or Chapter 15 governs the design of the supported item.
Inputs
- System Selection - The nonbuilding structure type selected from Table 15.4-1 (similar to buildings) or Table 15.4-2 (not similar to buildings).
- Seismic Parameters - Seismic Design Category (SDC), Site Class, and spectral accelerations (SDS, S1) in g.
- Structural Properties - Structural height (hn) in feet, fundamental period (T) in seconds, and weight (W) in kips.
- Importance - Risk Category for the importance factor (Ie) or a direct override value.
- Reference Documents - Specification for tanks or vessels (e.g., AWWA D100, API 650) to determine the applicable Cs minimum path.
- Support Conditions - Weight ratio and period ratio for the supported structure to evaluate Sec. 15.3 governing criteria.
What it reports
- Base Shear (V) - The calculated ELF base shear in kips, derived from the product of Cs and W.
- Seismic Response Coefficient (Cs) - The final Cs value, compared against the Eq. 12.8-4 cap, the Eq. 15.4-1 or 15.4-3 minimum floors, and the rigid branch threshold.
- System Coefficients - The R, Omega0, and Cd values retrieved from the selected table row.
- Height Limit Verdict - A pass/fail status for the structural height against the SDC-specific limit, including NL (no limit) or NP (not permitted) designations.
- Importance Factor (Ie) - The value determined from Table 1.5-2 or the user override.
- Governing Section - The verdict from Sec. 15.3 indicating whether Chapter 13 or Chapter 15 governs the supported item design.
- Rigid Branch Status - An indication if the period is less than 0.06 seconds, triggering the rigid branch calculation V = 0.30*SDS*W*Ie.
- Alternative Row Hint - A suggestion for a sibling row with a higher height limit if the current row is refused for height.
Code references
The engine cites ASCE 7-22 Chapter 15, specifically Tables 15.4-1 and 15.4-2, Equation 15.4-5, and Section 15.3. It also references Section 15.4.1.1 for the importance factor, Section 15.4.2 for the rigid branch, and Equations 12.8-4, 12.8-7, 15.4-1, 15.4-2, and 15.4-3 for Cs calculations. For steel storage racks, the module references AISI S100.
Limits
The module refuses inputs for Seismic Design Category A, as Chapter 15 tables do not print an A column and Section 11.7 covers SDC A separately. It does not default unknown keys, bad SDCs, or zero weights; these inputs are refused. The module assumes the structural system is selected from the predefined rows in Tables 15.4-1 or 15.4-2. It does not design the supporting structure itself but only determines the governing section for the supported item. Results are engineering aids; the engineer of record is responsible for the design.