earthquake engineering part4 & 5

Tishk International University

Civil Engineering Department

Third Year (2020-2021)

Earthquake Engineering

Asst. Prof. Dr. Najmadeen Mohammed Saeed

[email protected]

Part 4 & 5Earthquake Engineering

Architectural and Planning Aspects

Parts 4 & 5: Architectural and Planning Aspects

Asst. Prof. Dr. Najmadeen 2

Importance Of Features

The behaviour of a building during earthquakes depends

critically on its overall shape, size and geometry, in addition

to how the earthquake forces are carried to the ground.

Hence, at the planning stage itself, architects and structural

engineers must work together to ensure that the unfavourable

features are avoided and a good building configuration is

chosen.



A desire to create an aesthetic and functionally efficient

structure drives architects to conceive wonderful and

imaginative structures. Sometimes the shape of the building

catches the eye of the visitor, sometimes the structural

system appeals, and in other occasions both shape and

structural system work together to make the structure a

marvel. However, each of these choices of shapes and

structure has significant bearing on the performance of the

building during strong earthquakes. The wide range of

structural damages observed during past earthquakes

across the world is very educative in identifying structuralconfigurations

Architectural Features



Rational studies along with a knowledge regarding the

performance of buildings in previous earthquakes have

shown that:

Poor Building architectural design and planning would

decrease the seismo resistant capacity of the building and

also become the cause of collapse of the building

Performance of Structures During Earthquakes



• The seismic analysis and design alone do not ensure

good performance of the structure during

earthquakes. The building planning should also

conform to the principles of earthquake resistant

configuration.

• A real compatibility between the planning and the

structural design avoids a stepping of the seismo

resistant capacity of the building and also provides a

positive, efficient and integral seismic resistant

system

Performance of Structures During Earthquakes



Montreal’s Expo World’ Fair were 354 individual pre-cast concrete unitswere inter-connected with post-tensioning cables, grouped into 158apartments.

Develop Innovative ideas in creating Architecturally Impressive buildings

What will Architects Do?

Unsymmetrical in Plan and Elevation



CCTV Headquarters, CHINA

Unsymmetrical in Plan and Elevation

What will Architects Do?



Earthquake engineers are concernedwith creating earthquake resistantdesigns and construction techniquesto build all kinds of bridges, roadsand buildings.

Earthquake engineers are faced withmany uncertainties and must besmart in their decisions in developingsafe solutions to challengingproblems. They rely on state-of-the-art technology, materials science,laboratory testing and fieldmonitoring.

What Will Earthquake Engineer Do?



IS 1893 (Part I), 2002, Indian Standard Criteria for EarthquakeResistant Design of Structures (5th Revision).

IS 13920, 1993, Indian Standard Code of Practice for DuctileDetailing of Reinforced Concrete Structures Subjected to SeismicForces.

IS 13935, 1993, Indian Standard Guidelines for Repair andSeismic Strengthening of Buildings.

IS 4326, 1993, Indian Standard Code of Practice for EarthquakeResistant Design and Construction of Buildings (2nd Revision).

SP: 22 –Explanatory Handbook On Codes For EarthquakeEngineering

IS 13827, 1993, Indian Standard Guidelines for ImprovingEarthquake Resistance of Earthen Buildings

IS 13828, 1993, Indian Standard Guidelines for ImprovingEarthquake Resistance of Low Strength Masonry Buildings

Indian Standards For Earthquake Design



Part Description

Part 1 General Provisions and Buildings

Part 2Liquid Retaining Tanks– Elevated and Ground

Supported

Part 3 Bridges and Retaining Walls

Part 4Industrial Structures Including Stack Like

Structures

Part 5 Dams and Embankments

Different Parts of IS:1893-2002



IS 1893 (Part 1): 2002 has recommended buildingconfiguration system in Section 7 for the betterperformance of buildings during earthquakes.

An important feature in building configuration is itsregularity and symmetry in horizontal and vertical plane .

Building Configuration




The Irregularities in building configuration systemare classified into two types.

1. Vertical Irregularities- sudden change in strength,stiffness, geometry and mass Results in Irregulardistribution of forces over the height.

2. Horizontal Irregularities – Refers to asymmetric planshape or discontinuous in the horizontal resistingelements such as openings and re-entrant corner andother changes resulting in torsion.

An important feature in building configuration is itsregularity and symmetry in horizontal and vertical plane .



Example of Plan Irregularity

Example of Vertical Irregularity

Building Configuration Problems



Building Configuration Problems

(a) Setbacks (b) Weak or Flexible Storey

(c) Slopy Ground(d) Handing or

Floating Columns

(e) Discontinuing

Structural Members

Reinforced Concrete Wall Discontinued in Ground Storey



Choice Of Method For Multistoried Building



Map of Iraq with four regions.

Map Of Iraq With Four Regions

Zone-II (Low-Intensity Zone) 6 (or less)

Zone-III (Moderate Intensity Zone) 7

Zone-IV (Severe Intensity Zone) 8

Zone-V (Very Severe Intensity Zone) 9



Map Of Iraq With Four Regions



Four Virtues Of Earthquake Resistant

Bui ld ings are:

1) Strength

2) Stiffness

3) Ductility

4) Configuration

Four Virtues Of Earthquake Resistant Buildings



Good Structural Configuration: Its size, shape and structuralsystem carrying loads are such that they ensure a direct andsmooth flow of inertia forces to the ground.

Lateral Strength: The maximum lateral (horizontal) force thatit can resist is such that the damage induced in it does notresult in collapse.

Adequate Stiffness: Its lateral load resisting system is suchthat the earthquake-induced deformations in it do notdamage its contents under low-to moderate shaking.

Good Ductility: Its capacity to undergo large deformationsunder severe earthquake shaking even after yielding, isimproved by favourable design and detailing strategies.

Importance



VERTICAL IRREGULARITIES

Vertical Irregularities



1a - Stiffness Irregularity -Soft Story

1b - Stiffness Irregularity - Extreme Soft Story

2 - Weight (Mass) Irregularity

3 - Vertical Geometry Irregularity

4 - In-plane Discontinuity in Vertical Lateral Force Resisting Elements

5 - Discontinuity in Capacity - Weak Story




Type 1: Stiffness Irregularities

Soft story

◦ Architectural considerations

Taller first story

Unreinforced infill in upper stories

Completely open ground story

◦ Soft StoryStiffness related

Lateral stiffness of adjacent stories

RC beamsRC columns

Infill




Example◦ Stilts (open ground storey)Used as parking lots, garages

Apartments & commercial buildings

Prevalent in many countries like India, Iran

Turkey,etc.

◦ Intermediate open storeyMachinery, recreations,etc.




Soft Story RC Frames…

Seismic performance

◦ Under lateral loads

Excessive story deformation

Shear failure of columns

Excessive

deformation




Type 1: Stiffness Irregularities

1a - Soft Story

◦ the lateral stiffness is less than

70% of that in the story above

or less than 80% of the average

stiffness of the three stories

above.

1b - Extreme Soft Story

◦ the lateral stiffness is less than

60% of that in the story above

or less than 70% of the average

stiffness of the three stories

above.




Soft Storey Collapse




Soft Storey




Where is ground storey? (BHUJ,2001)




Ground Storey Collapse of a 4-Storey

Building with Open Ground Storey at

Bhuj

Olive View Hospital, which nearly

Collapsed due to Excessive

Deformation in the First Two Storeys

during the 1972 San Fernando

Earthquake




AVOID SOFT STOREY GROUND FLOORS

Often the columns

are damaged by the

cyclic displacements

between the moving

soil and the upper

part of the building





AVOID SOFT STOREY GROUND FLOORS



Soft mid storey failure




What happened to the upper floors (Turkey 1999)

Did they not know column of building should be stronger than beam?




Type 2: Weight (Mass) Irregularity

Mass irregularity shall beconsidered to exist wherethe effective mass of anystory is more than TWOtimes the mass of anadjacent story.


Equipment



Heavy load at Top




Short column failure due to

insufficient transverse reinforcement

Krishna Apartments, Airport Road,

Bhuj




Type 3:Vertical Geometry Irregularity

Vertical geometry irregularity shall be considered to exist when the

Maximum horizontal projection exceeds 15 to 20% of the Base width.




• Vertical geometryirregularity shall beconsidered to existwhere the horizontaldimension of thelateral force-resistingsystem in any story ismore than 130% ofthat in an adjacentstory.




Stress concentration & change in the stiffness




Crushing of corner column Building

Insufficient reinforcement :Tera Nam

Mandir, Main Road, Bhuj




Type 4: In-Plane Discontinuity in Vertical Lateral Force Resisting Elements

An in-plane offset of the lateral force-resisting elements greater than the length ofthose elements or areduction in stiffness in the resisting element in the story below.

Design forces for lateral force connections to be increased




Type 5:Discontinuity in Capacity - Weak Story

A weak story is one in which the story lateral 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.

Do not confuse STIFFNESS withSTRENGTH.




Weak & soft story

◦Weak storyStrength related

Lateral strengths of adjacent stories

◦Soft StoryStiffness related

Lateral stiffness of adjacent stories




PLAN STRUCTURAL IRREGULARITIES

Plan Structural Irregularities




The Irregularities in building configuration system are classified into two types.

1. Vertical Irregularities- suddenchange in strength,stiffness, geometry and mass results in irregulardistribution of forces over the height.

2. Horizontal Irregularities – Refers to asymmetric planshape or discontinuous in the horizontal resistingelements such as openings and re-entrant corner andother changes resulting in torsion.




L shaped Building




L – Shape in Plan/ Elevation?




Seismic behaviour of irregular shaped plans differs fromregular shapes because the first can be subjected to theirasymmetry and/or can present local deformations due tothe presence of re-entrant corners or excessive openings.Both effects give origin to undesired stressconcentrations in some resisting members of thebuilding





Plan Structural IrregularitiesOn the contrary, the ideal rectangular or square plane,

structurally symmetric, with enough in-plane stiffness inits diaphragm, presents an ideal behaviour. Buildingshaped like a box, such as rectangular, both in plan andelevation, is inherently stronger than one that is L-shaped or U-shaped, that is a building with wings




Plan Structural Irregularities1a - Torsional Irregularity

1b - Extreme Torsional Irregularity

2 - Re-entrant Corners

3 - Diaphragm Discontinuity

4 - Out-of-plane Offsets

5 - Nonparallel Systems




Plan Irregularities

Torsion Irregularities with

Stiff Diaphragm

If max drift is more than 1.2

times the average

Building with Re-entrant Corners

Non-parallel SystemsDiaphragm Discontinuity




Type 1:Torsional Irregularities1a - Torsional Irregularity

◦ larger story drift more than 1.2

times average story drift

1b - Extreme Torsional Irregularity

◦ larger story drift more than 1.4

times average story drift

Design forces for lateral force

connections to be increased




Torsion of unsymmetrical Plans

Direction of Ground Motion

CG. Of Building mass

Applied force

Center of lateral resistant /stiffness center

Resisting force




Proper Improper




Torsion of Buildings on Sloping Ground




TorsionAnalysis

The analysis must take into account any torsional

effects resulting from the location of the masses

relative to the centers of resistance.

In addition to the predicted torsion, accidental

torsion must be applied for structures with rigid

diaphragms by assuming the center of mass at each

level is moved from its actual location a distance

equal to 5% the building dimension perpendicular to

the direction of motion.




Type 2: Re-entrant Corners

Both projections beyond the corner are more than15% of the plan dimension of the structure in the samedirection

Un-symmetrical Plans




Guidelines for Planning

Desirable geometry of buildings

Separation

L< 3B

B

B

< 0.2B

PLANS




A should be small

If L =100 m , A can be max of 15 m

Definition of Irregularity as per IS 1893




ROLE OF FLOORWhen beams bend in vert

direction during earthquake the

thin slabs move along with them

(fig) & when beams move with

columns in horizontal direction

the slab forces the beams to

move together with it.

In most buildings the geometric

distortion of slab is negligible in

the horizontal plane; this

behavior is known as rigid

diaphragm action.




Type 3: Diaphragm Discontinuities

Diaphragms with abrupt discontinuities or variations in stiffness,

including those having cutout or open areas greater than 50% of

the gross enclosed diaphragm area, or changes in effective

diaphragm stiffness of more than 50% from one story to the next.




Type 4: Out-of-Plane Offsets Discontinuities in a lateral

force resistance path, such as

out-of-plane offsets of the

vertical elements.

Design forces for lateral

force connections to be

increased




Type 5: Nonparallel Systems The vertical lateral force-resisting

elements are not parallel to or symmetric

about the major orthogonal axes of the

lateral force resisting system.

Analyze for forces applied in the

direction that causes the most critical

load effect




General Guidelines for Planning

Building and its Structure Should Have a

Uniform and Continuous Distribution of Mass,

Stiffness, Strength and Ductility




Regular and Irregular ConfigurationsTo perform well in an earthquake, abuilding should

possess four main attributes:

◦ Simple and regular configuration

◦ Adequate lateral strength

◦ Stiffness

◦ Ductility

Buildings having simple regular geometry and uniformly distributed mass and stiffness inplan as well as in elevation, suffer much lessdamage than buildings with irregular configurations.

Buildings with plan irregularity suffer from torsional modes of vibration whose effects may not be adequately represented in the equivalent static seismic coefficientmethod.


earthquake engineering part4 & 5

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