Disaster management

1. DISASTER RESISTANT STRUCTURES
Submitted by-
Khelang jamatia
Biswajeet prasad
Kumar satyam

2. BUILDING FORMS AND ITS IRREGULARITIES

4. BUILDING IRREGULARITIES
 As per IS code 1893:2002, the irregularities are classified in two types:
1. Plan Irregularities
• Torsion Irregularity.
• Re-entrant Corners
• Diaphragm Discontinuity
• Out-of-Plane Offsets
• Non Parallel Systems .
2. Vertical Irregularities
• Stiffness Irregularity – Soft Storey & Extreme Soft Storey.
• Mass Irregularity.
• Vertical Geo-metric Irregularity.
• In-plane Discontinuity

5. TORSIONAL IRREGULARITIES
Before explaining the term torsional irregularity, Lets get acquainted with the terms drift and story drift.
What is drift?
- Drift of a building in simple terms can be defined as the horizontal displacement undergone by the building with respect to its
base when subjected to horizontal forces such as wind and earthquake loads.
What is story drift?
- Thus story drift can be defined as the displacement of one floor level of the building with respect to its adjacent level above or
below the considered floor level.
Fig: drift
Fig: story drift

6. TORSIONAL IRREGULARITIES
 Torsional irregularity is considered to exist when the maximum storey drift,
computed with design eccentricity, at one end of the structure transverse to an axis
is more than 1.2 times the average of the storey drifts at the two ends of the
structure.
 Torsional irregularity in a building occurs when the center of mass of a building and
the center of rigidity does not line up.This creates non-uniform ductility demands in
the structure as well as a twist in a building.
How to avoid torsional irregularity?
 Torsional irregularity can be avoided by increasing the lateral stiffness along the
column line with maximum story drift by increasing the column sizes, adding
retaining wall or bracings.
Fig: torsional irregularities in building

7. RE-ENTRANT CORNER
 Plan configuration of the structure and its lateral force resisting system contain re-entrant
corners, when both projections of the structure beyond the re-entrant corner are greater
than 15% of its plan dimension in given direction.
 Re – entrant corners mainly cause two problems, one is torsion and the other is difference in
the stress induced in different wings of the building causing stress concentration at the
corner.
Solution to avoid re-entrant corner:
 There are two basic alternative approaches to the problem of re-entrant corner forms.
1. Separate the building into simpler shapes.
2. Tie the building together more strongly with element positioned to provide more balanced
resistance.
Fig: damages caused to the roof diaphragm at the re
entrant corner of west anchorage high school, Alaska,
during 1964 earthquake

8. DIAPHRAGM DISCONTINUITY
 Diaphragm with abrupt discontinuities or variations in stiffness, including those having cut-out or open areas greater than
50% of the gross enclosed diaphragm area, or changes in effective diaphragm stiffness of more than 50% from one storey to
the next.

9. OUT-OF PLAN OFFSETS
 Discontinuities in a lateral force resistance path, such as out-of-plane offsets of vertical elements.
Fig: out of plane offset irregularities

10. NON-PARALLEL SYSTEMS
 The vertical elements resisting the lateral force are not parallel to or symmetric about the major orthogonal axes or the lateral
force resisting elements.

11. VERTICAL IRREGULARITIES
Vertical irregularities are characterized by vertical discontinuities in the distribution of mass, stiffness and strength. In set-back
structures there is a sudden change in the vertical distribution of mass, stiffness, and in some cases, strength.

12. WHAT ISVERTICAL SETBACK?
 If the structure is underground, the vertical separation distance represents the distance from the point of infiltration
through the bottom of the system to the structure, while the horizontal separation (often called setback) distance is the
shortest distance from the edge of the system to the structure.

13. WHAT IS STIFFNESS IRREGULARITY?
 Stiffness irregularity (soft storey):A soft storey is one in which the lateral stiffness is less than 70 percent of that in the storey
above, or less than 80 percent of the average stiffness of the three storeys above.

14. WHAT IS PLAN IRREGULARITY?
 Plan or vertical irregularity makes structures vulnerable under seismic loading.Torsional irregularity, overturning
moment can rise abruptly having irregularity in a structure. Hence, effect of irregularity is a very important issue
to be considered during building design.

15. WHAT IS MASS IRREGULARITY?
 Mass irregularity is considered to exist where the seismic weight of any storey is more than 200 percent of that
of its adjacent storey. Mass irregularity is an important factor which affects the response of the structure under
seismic loads.

16. REFRENCE
 https://www.researchgate.net/publication/273447330_Review_of_different_structural_irregularities_in_buildings_Journal_of_Structural_Engineering
 www.google.com
 www.youtube.com
 http://www.ijarse.com/images/fullpdf/1523789300_PG553ijarse.pdf

17. THANKYOU!