seismic performance of buildings and theoretical...

SEISMIC PERFORMANCE OF BUILDINGS AND THEORETICAL BACKGROUND OF

DAMAGE

SEISMIC RESILIENT SCHOOL BUILDING DESIGN OF SCHOOL BUILDINGS FOR ENGINEER

R.K. MALLIK Structural Engineer RND CENTRE PVT. LTD.

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Session Objective

Participant will able to

– List School Building typology

– Understand typical damage pattern

– Understand theoretical background of damage

– Know possible existing seismic resistant elements in buildings

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SCHOOL BUILDING TYPOLOGY

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Structural Categories And Typology

LOAD BEARING MASONRY (LB)

RC FRAME WITH INFILL (RC FRAME)

STEEL FRAME (SF)

TIMBER (T)

Structural Categories Structural Typology

ADOBE (A)

UNCONFINED MASONRY / UNREINFORCED MASONRY

(UCM/URM)

CONFINED MASONRY

NON ENGINEERED RC WITH INFILL

SMRF WITH INFILL

STEEL FRAME MASONRY INFILL

TIMBER ROOF, MASONRY RND CENTRE

Brick in cement

Brick in mud

Stone in mud mortar with cement pointing

Photo credit: Arup

MASONRY WALL TYPE

Rubble masonry wall

Round Stone cut in half

Dressed Stone masonry wall(Ashlar Masonry)

Undressed Flat stones used in a dry stone wall

Semi Dressed Masonry

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DIFFERENT TYPOLOGY

Field Stone in Mud Mortar Rectangular blocks in mud mortar

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Unconfined and Unreinforced masonry (UCM/URM): Rectangular blocks in cement mortar

Examples of brick in cement mortar buildings ( At Tanahu)

Photo credit: Arup

Fired brick in cement mortar are the most common

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Unconfined and Unreinforced masonry (UCM/URM): Rectangular blocks in mud/cement mortar with seismic

Example of RC lintel

Timber tying elements Cast-in-place concrete lintel bands to provide more overall continuity in the structural system.

Example of traditional building with timber tying elements

Arup

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Reinforced Concrete frame with masonry infill walls (Non-Engineered), (RC)

Examples of non-engineered RC Frame buildings

Photo credit: Arup

Photo credit: Arup

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Reinforced Concrete frame with and without masonry infill walls (Engineered), (RC-MF)

Designed with following IS 456;2002 and following ductile detailing code IS 13920

Lincon School, kathmandu

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Metallic -Steel Frame with CGI Roof and masonry walls

Examples of Steel Frame

Photo credit: Arup

Photo credit: Arup

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Masonry Building Timber Post and Rafters

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Typology Definitions – Combined Systems (CS)

Examples of combined (or mixed) typologies

Define in different pieces and define different structural categories for each floor for mixed systems in elevation. Use different form for each pieces

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DAMAGES IN GORKHA EARTHQUAKE

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Overall Damage Percentage

Proportion of school buildings per structural typology in the eight districts of Phase 1

LB: Load-bearing Masonry RC: Reinforced concrete SF: Steel frame TF: Timber frame

Reference: SIDA summary report of

Phase 1 RND CENTRE

Damages: Buildings per typology

Reference: SIDA summary report of Phase 1

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THEORETICAL BACKGROUND OF DAMAGES

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Causes of Failure of Masonry Buildings

Inadequate integrity

Inadequate out of plane flexure capacity

In adequate In-Plane shear resistance

irregular configuration

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Behavior of Masonry Buildings

Masonry Building Components

Ref: IITK EQ Tips

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Behavior of Masonry Buildings

If No proper Connection, Wall B Tends to fail

Advantage of proper Connections

Ref: IITK EQ Tips

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Lack of integrity( Corner Separation followed by out of plane failure)

Corner Separation Leads to out of plane failure RND CENTRE

Long Wall and Short wall

Slenderness Ratio= H/t If H/t> 12, Wall is slender

Height and length of the wall should be kept in a limit to avoid off plane failure

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Buttress for Long Wall

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Effect of Openings

Load transfer zone from weak wall to strong wall

Opening Weakens Walls Single closed band must be provided above openings

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Crack Around opening and Wall behavior modified

Cracking of wall without vertical reinforcement

Modified Wall behavior with vertical reinforcements, No Cracking

(Mahankaleshor Lower Secondary School, Saga) RND CENTRE

Openings in Walls

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In plane Behavior of Pier (Rocking)

Wall behaves as a discrete units during Earthquake

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In-plane behavior of Wall Pier ( Shearing)

If vertical reinforcement is absent

X-Cracking

Sliding above Sill Level RND CENTRE

strong mortar weak units

through masonry units

Associated NCMA TEK Note

low vertical compressive stress

sliding along bed joints

weak mortar strong units

stair step through bed and head joints

Possible Shear Cracking Modes

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Damage to In-Plane Wall

(Mahankaleshor Lower Secondary School, Saga) RND CENTRE

Severity of Crack

Guidance: After surveying the piece, estimate the percentage of openings that have cracking. If cracking is observed at openings, record the typical severity of cracking: - Severe ¼ inch cracks or greater - Moderate – around 1/8 inch cracks - Minor or Hairline cracks – around 1/16 inch cracks or cracks in

the finish only

Cracking at openings is generally less of a concern for Life Safety but can be uneconomical to repair.

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Photo credit: Arup

Out of plane failure Mode

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Off Plane Failure of Wall

Darbaar School, 2015 Nepal Earthquake

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Off Plane Failure of Wall

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Out of plane damage to Parapets

1994 Northridge Earthquake, Filmore

1996 Urbana Summer

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Gable Wall Damage

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Delamination of Wall

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Complete Collapsed Wall

SHREE MAHANKAL PS (KASHIKHANDA)

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Wall behavior modified( Seismic enhancement)

Rocking of pier Bending of pier in place of Rocking

Sliding of masonry No Sliding of masonry RND CENTRE

Box Action for Better performance

For Box Action Lintel band, Sill band, Foundation band Small openings in wall Good connection between wall and roof and wall and foundation

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Horizontal Bands

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Off Plane Behavior of Lintel Band

Detailing of Reinforcement in Lintel bands

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Timber Band

Use of through stone in stone masonry wall RND CENTRE

Seismic Enhancement

Example of RC lintel Example of traditional building with timber tying elements

Arup

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CONFIGURATION

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Redundancy

Redundant building> 2 Nos of wall in any direction

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Making Complex Span Simple

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Restriction on Plan Projection

K 1, K 2 < {0.25 A ,0.25 B} min

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Plan Aspect ratio

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Improper Vertical configuration

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Regular vertical configuration

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RCC BUILDING SEISMIC PERFORMANCE

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Causes of Failure of RCC Buildings

Lack of Ductility

Poor Non Ductile Detailing Weak Column Strong beam

Lack of Strength Beam Column Joint Failure Inadequate column shear strength Infill Wall Failure Short Column Effect

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LACK OF DUCTILITY

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Seismic Effects on Building

Foundation is constrained by ground

Roof tries to remain in its position (inertia)

Roof has to oscillate with different acceleration than ground, a

Roof and foundation are interconnected by flexible columns

If Lump mass at roof = m Then Inertia force imposed = m X a ( Newton’s second low)

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Flow of Inertia Forces

Inertia force is higher at high mass zone( at floors)

Inertia force from slab transferred to wall or column by floor

And finally from foundation to the subgrade soil

From wall /column to the foundations

Floor slab, walls, columns, foundations must be designed to transfer inertia force safely to subgrade soil

Walls and columns need special attention while designing seismic resistant building

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Strength and Stiffness

FEMA 454, Chapter 4

Force Distribution is as per stiffness

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Centre of Mass and Centre of stiffness

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Natural Period of Buildings

• Each building has its own natural period (frequency)

Building

Height

Approx

Natural

Period

Natural

Frequency

2 story 0.2 seconds 5 cycles/sec

5 story 0.5 seconds 2 cycles/sec

10 story 1.0 seconds



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Resonance • Resonance = frequency content of the

ground motion is close to building's natural frequency

– tends to increase or amplify building response

– building suffers the greatest damage from ground motion at a frequency close or equal to its own natural frequency

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RESPONSE SPECTRA

Building Response spectra for 300 YRP Earthquake

Building acceleration is in average 2.5 times the ground acceleration We can not afford design of building with 0.8g times Mass Horizontal seismic coefficient for residential moment RC frame as per NBC105 is : 0.08 g ???????????????????????

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Reduced Design forces

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Ductility

Ductility Allows to decrease design force to get economical building

Reduce design force and allow deformation within acceptable limit

IF YOU DECREASE LOAD ….BE SURE ABOUT DUCTILITY

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Ductility

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Brittle and ductile performance of Building

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Strong Beam weak column Unacceptable

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LACK OF STRENGTH

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Effect of Gravity load and Earthquake load in RC Frame

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Beam

Two types of Damage: Flexure & Shear Flexure Damage is Acceptable Stirrups prevents buckling of L Bar

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Shear Stirrups Details

Stirrups in Lapping Zone

Stirrups spacing Need not less than 100 mm

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Column

Closure ties spacing improves seismic resistance of Column Larger spacing of stirrups and lack of

135 degree hooks RND CENTRE

Column failure Shear failure, Diagonal cracks Column looses vertical load carrying capacity

Effect of stirrups spacing

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Additional Open stirrups required to prevent bulging of larger stirrups.

Protect column end and lap zone with close lateral stirrups. RND CENTRE

Beam Column Joint

Beam Column Joints are critical

Stirrups in joint with 135 degree hoop prevents joint failure

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how to insert joint stirrups

Damage due to beam bar outside of column bars RND CENTRE

Beam column joint failure

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End Column

Anchorage of beam bars in end column joint Insert beam bar up to 60 times the dia of bar in column

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In Design Wall is not considered This mistakes can not predict the possibility of damage of ground storey column.

Preventing open ground problem

Soft storey

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Soft storey

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Soft and weak story Collapse (Poor reinforcement

detailing, poor quality of construction material,

faulty construction practices)

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Short Column

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Short Column Effect

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Solving Short Column Effect

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FRAME –INFILL WALL INTERACTION

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Infill Wall

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Lateral load Transfer Mechanism due to infill

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Hybrid Frame

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INFILL WALL FAILURE MODE

CC and DC Mode

SS ,FF,DK Mode

The Corner Crushing (CC) mode The Diagonal Compression (DC) mode The Sliding Shear (SS) mode The Diagonal Cracking (DK) mode,

The Frame Failure (FF) mode RND CENTRE

SS, FF and DK Mode of Failure

SHREE MANDALI DEVI PS (DHULIKHEL) SS , FF, DK Mode RND CENTRE

FAILURE OF INFILL WALL

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Session Objective


– List School Building typology

– Understand typical damage pattern


– Know possible existing seismic resistant elements in buildings

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THANK YOU

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Buildings per typology

Reference: SIDA summary report of

Phase 1 RND CENTRE

Configuration

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Aspect ratio

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Vertical irregularity

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Pounding Effect

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Building behavior in Earthquake

Unbalanced mass can cause torsion in regular configuration Building.

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Irregular column height

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Larger displacement causes farther column to fail.

Unbalanced Stiffness

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Damage intensity vs thickness of soil deposit

Larger soil deposit depth > greater time period affects high rise buildings

lesser soil deposit depth > lesser time period affects high low rise buildings

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Slab Constraining Action

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CONFIGURATION

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Redundancy

Redundant building> 2 Nos of wall in any direction

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Making Complex Span Simple

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Restriction on Plan Projection

K 1, K 2 < {0.25 A ,0.25 B} min

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Plan Aspect ratio

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Improper Vertical configuration

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Regular vertical configuration

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CONFINED MASONRY

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Key Components of a Confined Masonry Building :

• Masonry walls made either of clay brick or concrete block units

• Tie-columns = vertical RC confining elements which resemble columns in reinforced concrete frame construction.

• Tie-beams = horizontal RC confining elements which resemble beams in reinforced concrete frame construction.

Components of a Confined Masonry Building:

Reinforced Concrete Frame Construction

Confined Masonry Construction

Confined Masonry versus Infilled RC frames:

Confined Masonry

– Walls first

– Concrete later

Reinforced Concrete Infilled Frame

– Concrete first

– Walls later

Source: Tom Schacher

-construction sequence

- integrity between masonry and frame

Confined Masonry vs RC Frames with Infills – Key Differences

Location of Confining Elements is Very Important!

Key Elements – Layout Rules

Confined Masonry Panel Under Lateral Loading: Shear Failure

Displacement

She

ar

forc

e

1 2 3

12

3

P P PV

Vm

Vm

V 'm

Vc

Vc

VcV 'm

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Confined Masonry Construction: Toothing at the Wall-to-Tie-Column Interface

Toothing enhances interaction between masonry walls and RC confining elements

Existing Possible Retrofitting in past

Strengthening to floor / roof

Seismic Belts Single vertical reinforcement in walls

Reinforcement with welded wire mesh Post tensioning

Wall jacketing Bamboo reinforcing

External cane and rope mesh

External wre mesh reinforcement

External polymer reinforcement

Used car tyre straps

Strengthening to foundations RC jacketing of columns and other elements Steel jacketing of columns and oterh elements

Addition of RC shear wall

Addition of steel bracing other (please specify)

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Session Objective


– List SIDA Form Parameter

– Understand Masonry typical damage pattern


– Know possible existing seismic resistant elements in masonry buildings

– Identify existing retrofitting if any

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THANK YOU

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seismic performance of buildings and theoretical...

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