Irregularities

The program allows you to input whether the structure has irregularities defined in ASCE 7 12.3.2 and Tables 12.3-2 and 12.3-3.

These irregularities are used to determine:

• whether the structure is permissible under 12.3.3.1 for each Seismic Design Category,
• the regularity criterion for limiting the value of the design seismic response parameter S_DS as per 12.8.1.3
• the conditions in 12.3.4.2 whereby the redundancy factor ρ is equal to 1.0
• the application of the 25% increase in drag strut forces as per 12.3.3.4.

Refer to Irregularities for more details.

There are checkboxes for the the N-S and E-W force directions for the following single irregularities or groups of irregularities, which should be checked if any one of them is deemed to exist:

Horizontal Irregularities

• 1a Torsional
• 1b Extreme Torsional
• 2 Corner, 3 Diaphragm or 4 Offset

These correspond to the ASCE irregularities as follows:

• Corner = Reentrant Corner
• Diaphragm = Diaphragm Discontinuity,
• Offset = Out-of-Plane Offset.

If 1a Torsional is checked, then 1b Extreme Torsional is unchecked and vice-versa.

Vertical Irregularities

• 1a Soft story, 2 Weight or 3 Geometric
• 1b Extreme Soft or 5a Weak Story
• 4 In-plane Discontinuity
• 5b Extreme Weak Story

These correspond to the ASCE irregularities as follows:

• Soft story = Stiffness – Soft Story
• Weight = Weight (mass)
• Geometric = Vertical Geometric
• Extreme Soft = Stiffness – Extreme Soft Story
• Weak Story = Discontinuity in Lateral Strength – Weak Story
• In-plane Discontinuity = In-plane Discontinuity in Vertical Lateral Force Resisting Element
• Extreme Weak Story = Discontinuity in Lateral Strength – Extreme Weak Story

Use detected torsional irregularity for design

This checkbox is used to indicate that if the program detects a torsional irregularity during the analysis of the structure for design, but one was not selected in the Site Dialog, it applies that irregularity to the determination of whether the structure is permissible, redundancy factor ρ, and the 25% drag strut force increase. Conversely, if no torsional irregularity is detected but one was selected in the Site Dialog, the torsional irregularity is not applied.