Irregularity Analysis

Irregularity Table

The program now analysis the structure for irregularities according to NBC Table 4.1.8.6 and the references to these irregularities throughout the NBC 4.1.8. For each irregularity, the table contains

• Irregularity Number
• Type of Irregularity from 4.1.8.6
• References
• Whether the irregularity is detected by the program or must be checked manually by the user of the program
• The level, shearline, and force direction for which the program is irregular. The words “Must check” are placed in this column if other parameters are such that the user must check for the existence of the irregularity.
• The level, shearline, and direction for which the program fails design due to the existence of the irregularity and other parameters making design illegal.
• The numbers of the notes below the table that apply to the irregularity

  Warnings

The program issues bold warnings in advance of the table of two circumstances:

• If design fails because the program detects and irregularity and illegal seismic design parameters for that irregularity
• If the program detects design parameters such that the user must check for an irregularity that the program cannot detect.
• Warnings

  Key Parameters

In advance of the table, the program outputs

• the value of I_EF_aS_a(0.2), upon which many of the rules for irregularities are based
• a note saying that only the provisions based on Ta less than 0.5s and height less than 20 m are considered, as the program restricts seismic design to heights less than that

  Notes

• Notes are output below the table giving
• reasons for failure or that seismic design is not permitted
• reasons that the user must check for an irregularity or other parameters
• reasons that a check is not required or that an irregularity does not apply
• other explanatory information

There are a total of 21 possible notes. The notes are presented as a, b, c, d.. to avoid confusion with the irregularity numbers. The letter(s) for the note(s) applicable to the irregularity are given in the table for that irregularity.

Irregularity list

After the table and notes, the program lists the irregularities, giving a description of the irregularity and an explanation of how Shearwalls treats the irregularity. .

Screen messages

When a discontinuity is found that causes design to fail, or the program detects when the user must check for a discontinuity, following shearwall design a total of 7 possible explanatory warning messages are sent to the screen. These messages are for

• Post-Disaster and Types 1 or 7
• Post disaster and Type 3, 4, or 5
• Type 3, 4, 5 - And there is a weak storey, so no design.
• Type 3, 4, 5 - No weak storey, but program uses shearwall capacity in place of design shear for hold-down calculations
• Type 6, and seismic design not permitted unless design forces factored by RoRd
• Type 6, Seismic design not permitted
• User must check for Type 7.

  Type 1 - Vertical stiffness

Design code references: NBC 4.1.8.7-1c, 4.1.8.10-2a, NBC Commentaries J-126.

If applicable, must be checked by user, who can use relative rigidities of shearlines in Shearwalls

Type 2 - Weight (mass)

Design code references: NBC 4.1.8.7-1c.

No effect for buildings less than 20 m height and Ta < 0.5, or all buildings in Shearwalls.

Type 3 - Vertical Geometry

Design code references: NBC 4.1.8.7-1c, 4.1.8.10-2a, 4.1.8.15-2, Commentaries J-126,156.

Shearwalls checks using the nearest and farthest points from all walls in a storey for each direction. It shows the storey with a long SRFS in the table, and the affected direction(s)

Type 4 - In-Plane Offset

Design code references: NBC 4.1. 8.7-1c, 4.1.8.10-2a, 4.1.8.15-2, Commentaries J-126,156, 207.

Shearwalls detects whenever the ends wall segments on adjacent storeys do not line up to within 3”. It shows both upper and lower storey in table, e.g. 4,3, and shearlines affected.

Type 4 - In-plane stiffness

Design code references: NBC 4.1.8.7-1c,10-2a, 4.1.8.15-2, Commentaries J-126,156, 207.

Shearwalls compares the rigidity of collinear shearwall segments on adjacent storeys. It shows both upper and lower storey in table, e.g. 4,3, and shearlines affected.

Type 5 - Out-of-plane

Design code references: NBC 4.1.8.7-1c, 4.1.10-2a, 4.18.15-2, Commentaries J-126,156.

Shearwalls detects wherever shearwalls do not exist on a shearline for particular level, and the program has transferred the force from the shearline on the floor above directly into the diaphragm. It shows the storey without shear-resisting elements in the table, and the directions(s) affected

Type 6 - Weak Storey

Design code references: NBC 4.1.8.7-1c, 4.1.8.10-1,2b, Commentaries J-126, 156.

Shearwalls determines the total capacity of all shearwalls for each direction on each level, and reports weaker lower levels in the table

Type 7 - Torsional Sensitivity

Design code references: NBC 4.1.10-2a, 4.1.8.11-9,10, Commentaries J-127, J177-9 .

Ratio B of maximum to average storey displacements is greater than 1.7. Shearwalls does not at this time perform deflection analysis, so this must be calculated by the user

Type 8 - Non-orthogonal

Design code references: NBC 4.1.8.7-1c, Commentaries J-127.

Shearwalls does not currently allow input of skewed shearwalls, so this irregularity does not apply.