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Lecture 4

This document discusses several types of irregularities that can occur in building structures according to codes like UBC-97 and ASCE 7-16. It defines stiffness, mass, strength, vertical geometric, torsional, reentrant corner, diaphragm discontinuity, and nonparallel system irregularities. Each type of irregularity is explained, such as stiffness irregularity existing if a soft story is present and mass irregularity existing if a story's mass is more than 150% of the mass of the story above or below.

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Zeeshan
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42 views15 pages

Lecture 4

This document discusses several types of irregularities that can occur in building structures according to codes like UBC-97 and ASCE 7-16. It defines stiffness, mass, strength, vertical geometric, torsional, reentrant corner, diaphragm discontinuity, and nonparallel system irregularities. Each type of irregularity is explained, such as stiffness irregularity existing if a soft story is present and mass irregularity existing if a story's mass is more than 150% of the mass of the story above or below.

Uploaded by

Zeeshan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Lecture # 04

Irregularities in Building Structures

Organized by Dr.Aslam Faqeer Mohammad 49


As per UBC-97

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As per UBC-97

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As per ASCE 7-16

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As per ASCE 7-16

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Permitted Analysis Procedure

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Building Irregularities
The impact of irregularities in estimating seismic force levels, first introduced into the
Uniform Building Code in 1973,
These irregularities are

Stiffness Irregularity

Stiffness irregularity; or presence of soft story


Organized by Dr.Aslam Faqeer Mohammad 56
Building Irregularities
Mass Irregularity

Mass irregularity exists if mass of any story is more than 150% of the
mass of the story below or above. M2 > 1.5M1 or 1.5M3.

Mass irregularity

Organized by Dr.Aslam Faqeer Mohammad 57


Building Irregularities
Strength Irregularity

A weak story is one in which the story strength is less than 80% of that in the story
above. The story strength is the total strength of all seismic-resisting elements sharing
the story shear for the direction
under consideration.

Strength irregularity

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Building Irregularities
Vertical Geometric Irregularity

Vertical geometric irregularity shall be


considered to exist where the horizontal
dimension of the lateral-force-resisting
system in any story is more than 130%
of that in an adjacent story.

Vertical irregularity
Organized by Dr.Aslam Faqeer Mohammad 59
Building Irregularities
Torsional Irregularity

Torsional irregularity exists when dmax, the maximum story drift at a corner including
accidental torsion, is more than 1.2 times the average of the drifts at the
corresponding corners.

Torsion irregularity
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Building Irregularities
Irregularity due to reentrant corners

This irregularity exists when plan configuration of the building and its lateral system
have projections greater than 15% of the plan dimension in the corresponding
direction. b > 0.15B or a > 0.15A.

Presence of Reentrant Corners


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Building Irregularities
Irregularity due to diaphragm discontinuity

This irregularity exists if: 1) the area b × d of the opening is more than 50% of the area
B × D of the diaphragm; or 2) the change in diaphragm stiffness is more than 50%
from one story to the next.

Organized by Dr.Aslam Faqeer Mohammad


diaphragm discontinuity 62
Building Irregularities
Irregularity due to nonparallel system

A nonparallel system irregularity exists when a lateral system is not parallel to or


symmetric about the building’s orthogonal axes.

nonparallel lateral force resisting system

Organized by Dr.Aslam Faqeer Mohammad 63

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