Building Irregularities

1. BUILDING
IRREGULARITY
Engr. Mridul Hasan, PEng.

2. Building irregularity
Buildings with irregularity in plan or elevation suffer much more damage in earthquakes than buildings with regular configuration. A building may
be considered as irregular, if at least one of the conditions given below are applicable:
Plan irregularity: Following are the different types of irregularities
that may exist in the plan of a building.
(i) Torsion irregularity
Mexico City building failure associated with the torsional-translation motion, (Earthquake Engineering ANNEXES, 2007)
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3. (ii) Re-entrant corners
Damages caused to the roof diaphragm at the re-Entrant Corner of West Anchorage High School, Alaska, during 1964 Earthquake.
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4. (iii) Diaphragm Discontinuity
Diaphragms with abrupt discontinuities or variations in stiffness, including those having cut-out [Figure 6.2.27(c)] or open areas greater than 50
percent of the gross enclosed diaphragm area, or changes in effective diaphragm stiffness of more than 50 percent from one story to the next.
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5. (iv) Out- of-Plane Offsets
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6. (v) Non-parallel Systems
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7. A building damaged due to torsion eccentricity.
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8. Vertical Irregularity: Following are different types of irregularities
that may exist along vertical elevations of a building.
(i) Stiffness Irregularity - Soft Storey
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9. Example buildings having first soft story collapse after earthquake (a) China earthquake 2008
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10. Photo shows the Yun Men Tsui Ti building, a large commercial-residential complex, severely rotated in Hualien, Taiwan, on Feb. 10, 2018, in the wake of
a powerful earthquake. Kyodo via AP Images
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11. (ii) Mass Irregularity
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12. (iii) Vertical Geometric Irregularity
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13. (iv) Vertical In-Plane Discontinuity in Vertical Elements Resisting Lateral Force
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(v) Discontinuity in Capacity - Weak Story
A weak storey is one in which the storey lateral strength is less than 80% of that in the storey above. The storey lateral strength is the total
strength of all seismic force resisting elements sharing the storey shear
in the considered direction [Figure 6.2.28(e)]. An extreme weak storey
is one where the storey lateral strength is less than 65% of that in the
storey above.