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.
RND CENTRE
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
RND CENTRE
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
RND CENTRE
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
RND CENTRE
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
RND CENTRE
Reinforced Concrete frame with masonry infill walls (Non-Engineered), (RC)
Examples of non-engineered RC Frame buildings
Photo credit: Arup
Photo credit: Arup
RND CENTRE
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
RND CENTRE
Metallic -Steel Frame with CGI Roof and masonry walls
Examples of Steel Frame
Photo credit: Arup
Photo credit: Arup
RND CENTRE
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
RND CENTRE
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
Causes of Failure of Masonry Buildings
Inadequate integrity
Inadequate out of plane flexure capacity
In adequate In-Plane shear resistance
irregular configuration
RND CENTRE
Behavior of Masonry Buildings
If No proper Connection, Wall B Tends to fail
Advantage of proper Connections
Ref: IITK EQ Tips
RND CENTRE
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
RND CENTRE
Effect of Openings
Load transfer zone from weak wall to strong wall
Opening Weakens Walls Single closed band must be provided above openings
RND CENTRE
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
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
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.
RND CENTRE
Photo credit: Arup
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
RND CENTRE
Seismic Enhancement
Example of RC lintel Example of traditional building with timber tying elements
Arup
RND CENTRE
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
RND CENTRE
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)
RND CENTRE
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
RND CENTRE
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
20 story 2.0 seconds
30 story 3.0 seconds
RND CENTRE
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
RND CENTRE
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 ???????????????????????
RND CENTRE
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
RND CENTRE
Beam
Two types of Damage: Flexure & Shear Flexure Damage is Acceptable Stirrups prevents buckling of L Bar
RND CENTRE
Shear Stirrups Details
Stirrups in Lapping Zone
Stirrups spacing Need not less than 100 mm
RND CENTRE
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
RND CENTRE
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
RND CENTRE
End Column
Anchorage of beam bars in end column joint Insert beam bar up to 60 times the dia of bar in column
RND CENTRE
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
RND CENTRE
Soft and weak story Collapse (Poor reinforcement
detailing, poor quality of construction material,
faulty construction practices)
RND CENTRE
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
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
RND CENTRE
Building behavior in Earthquake
Unbalanced mass can cause torsion in regular configuration Building.
RND CENTRE
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
RND CENTRE
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.
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 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
RND CENTRE
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)
RND CENTRE
Session Objective
Participant will able to
– List SIDA Form Parameter
– Understand Masonry typical damage pattern
– Understand theoretical background of damage
– Know possible existing seismic resistant elements in masonry buildings
– Identify existing retrofitting if any
RND CENTRE