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Type 1 - Vertical Stiffness
Design code references: NBC 4.1.8.7.(1)(c), 4.1.8.10.(2)(a), NBC Commentaries J-126.
Occurs when the lateral stiffness of a storey’s SFRS less than 70% of that of an adjacent storey, or 80% of the average of the three storeys above and below.
The program determines the stiffness of all wall segments on the level using the same procedure by which it determines the stiffness for Irregularity 4 – In Plane Discontinuity. It then sums all those stiffness values.
If the stiffness on any level is less than 70% of the stiffness on the level above or below, than the irregularity exists.
For those levels with 3 storeys either above or below, the program determines average of the 3 storeys either above or below the level, and if stiffness on the level under consideration is less than 80% of that value, the irregularity exists
Type 2 - Weight (mass)
Design code references: NBC 4.1.8.7.(1)(c).
Occurs when a level is 1.5 x more massive than an adjacent non-roof level, or a roof is 1.5 x as massive as its adjacent level
Table 4.1.8.6 refers to a storey, which is defined in NBC Division A, 1.4.1.2 as the distance from the top of one floor to the top of the floor above it. The roof is considered a separate storey. On the other hand the levels that are defined for apportioning seismic load are defined from the middle of the wall on one level to the middle of the walls on the level above. A roof is considered part of the upper level.
For irregularity detection, the program collects all the masses that are tagged as being on level 2, for example, but come from the lower portion of level 3, and includes them as storey 3 weight. It excludes masses from the roof and gable ends, from the upper storey, and creates a separate storey for these.
For multi-block structures, for mass from roofs on blocks with fewer levels than the highest block, the roof is added to the mass of the level above the highest storey on the block. For example, if Block 1 has 2 storeys and block 2 has 4 storeys, a roof on block 1 will is part of level 3.
Flat roofs and ceilings are part of the uppermost storey of the block they are on, not the roof level.
Type 3 - Vertical Geometry
Design code references: NBC 4.1.8.7.(1)(c), 4.1.8.10.(2)(a), 4.1.8.15.(5), Commentaries J-126,156.
Occurs when the horizontal dimension of the SRFS is more than 30% longer than that of an adjacent storey.
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 Discontinuity of Vertical Lateral Force Resisting Elements - Offset
Design code references: NBC 4.1.8.7.(1)(c), 4.1.8.10.(2)(a), 4.1.8.15.(5), Commentaries J-126,156, 207.
Shearwalls detects whenever the ends of 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 shear lines affected.
Type 4 - In-Plane Discontinuity of Vertical Lateral Force Resisting Elements - Stiffness
Design code references: NBC 4.1.8.7.(1)(c),10.(2)(a), 4.1.8.15.(5), Commentaries J-126,156, 207.
Occurs when there is a reduction of the stiffness of an element on the level below.
Shearwalls compares the rigidity of collinear shear wall segments on adjacent storeys. In doing so, it always uses the linear, 3-term deflection equation because use of the non-linear 4-term equation would create a discontinuity in a structure where both levels were made with the same materials. Furthermore a 1% tolerance has been added because the complexities of calculating stiffness using deflection that includes constant components can create small discrepancies.
It shows both upper and lower storey in table, e.g. 4,3, and shear lines affected. Shearwalls does not implement 4.1.8.15.(5)
Type 5 - Out-of-plane Offsets
Design code references: NBC 4.1.8.7.(1)(c) 4.1.8.10.(2)(a), 4.1.8.15.(5), Commentaries J-126,156.
Shearwalls detects wherever shear walls do not exist on a shear line for particular level, and the program has transferred the force from the shear line 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.(1)(c), 4.1.8.10.(1),(2)(b), Commentaries J-126, 156.
Shearwalls determines the total capacity of all shear walls for each direction on each level, and reports weaker lower levels in the table.
Type 7 - Torsional Sensitivity
Design code references: NBC 4.1.8.10.(2)(a), 4.1.8.11.(10),(11), Commentaries J-127, J177-9.
Occurs when ratio B of maximum to average storey displacements from 4.1.8.11.(10) is greater than 1.7. For buildings with rigid diaphragms with deflection analysis enabled, Shearwalls calculates these displacements and determines Type 7 Irregularities. It outputs a table of intermediate calculations in the Detailed Torsional Analysis Output. refer to Torsional Sensitivity for more details.
Type 8 - Non-orthogonal
Design code references: NBC 4.1.8.7.(1)(c), 4.1.8.8(1), Commentaries J-127.
Shearwalls does not currently allow input of skewed shear walls, so this irregularity does not apply.
Type 9 - Gravity-induced Lateral Demand
Design code references: 4.1.8.10.(5)-(7). Note A-4.1.8.10.(5)
Note A-4.1.8.10.(5) explains that this corresponds to such elements as inclined columns and floor cantilevers. These are outside the Shearwalls building model, and any demand from such elements would affect hold-downs, which are not the primary yielding mechanism. We do not believe this irregularity is relevant to the shearwalls model and no attempt is made to detect it.