load bearing structure
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Design of load-bearing structures19th lecture
Earthquake and buildings
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Contents
Introduction
The effect of earthquake on buildings
Conceptual design of buildings for earthquake
Design of slabs- the principles of design
- design for vertical forces
- design for horizontal forces
Summary
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Introduction 1.
The earthquakes do not kill men however the collapsed
building does.
Charles Richter
The earthquake does not read codes.
Thomas Paulay
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Introduction 2.
Design for earthquake: (Hungary)
It is a requirement of the building law.
Az OTK elrjaZaj- s rezgsvdelem
55. (1) Az ptmnyt s rszeit, szerkezeteit gy kell mretezni smegvalstani, hogy a krnyezetbl hat zaj- s rezgshatsoknak
(pl. szeizmikus s forgalmi rezgshatsoknak) az elrt mrtkben
ellenlljon, illetleg azt meghatrozott mrtkig csillaptsa.
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Introduction 3.There is earthquake in Hungary too !!!!!!
Date Location Magnitude,
M
EMS
intensity
Damage
2006 11. 23. Beregsurny 4,5 VI. Smalldamage
in buildings
2006 12. 31. Gymr 4,1 V. VI. 10 M Ft
building
damage
2007 03. 03. Rpcelak 2,9 No damage
The judgment of earthquakes by geophysicists are
changed.
2008 11.13 Murony 3,5 No damageIV.
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The earthquake 1.
a
b
Fault rupture
R
PP S
P
The origin of earthquake:
Ground surface
Wood-Anderson
seismograph
hypocenter
epicenter
Focaldepth
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Seismic waves:
Characterization by:
- acceleration
- velocity
- amplitude
The ground surface
moves horizontally
and vertically too.
The earthquake 2.
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The effect of movement
of soil on buildings:VibrationLateral forces, movement,
Internal forces,
Possibility of damage, and
collapse.
Horizontal vibration
Vertical vibration
Movement of the soil
Movement of the soil
Torsional vibration
Movement
of the soil
Movement of
the soil
Role of floors:Horizontal and tensional
vibration: distribution oflateral forces between bracing
elements.
Vertical vibration:balancing lateral forces and
transferring them to the
vertical load-bearing
elements.
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The earthquake 3.Measure of the effect of earthquake:
Magnitude:e.g.: Richter magnitude:
- M=logA; (A measured amplitude in m);
- maximal value: M = 9.
Intensity scale:e.g.: MCS-1917; MSK-1964, 1976, 1978;
newer EMS-1992, 1998
- 12 class; takes into account the effect of earthquakes on man, objectsnature and the extent of damage caused in buildings.
Soil acceleration:- Basic data for design; depends on direction and soil.
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The earthquake 4.Seismic map of Hungary:
The reference, horizontal peak ground acceleration,
agR, on rock.
EC8-NA
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The earthquake 5.
A fldrengs s a hatsa az pletekre.
The seismicity in Hungary:
Similar to Australia, but since the earthquake in Newcastle, 1989,
design for earthquake is part the design process.
4-5.
zone
design according to
EN 1998moderate
2-3.
zone
simplified design
method according to
EN 1998
low1. zone
Design methodSeismicityZone
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The earthquake 6.
A fldrengs s a hatsa az pletekre.
Measure of the effect of earthquake :
EMS M ag/g 2.zone 3.zone 4-5.zone
I. 0,4
II. 1,5 < 0,001
III. 2,5 0,001 0,007
IV. 3,5 0,006 0,03
V. 4,4 0,015 0,06
VI. 5,2 0,03 0,15
VII. 6,0 0,07 0,36
VIII. 6,7 0,15 0,71
IX. 7,4 0,30 1,53
X. 8,0 0,51 3,06
XI. 8,5 1,53 3,56
XII. 8,9 > 2,04
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The earthquake 7.
A fldrengs s a hatsa az pletekre.
European Macroseizmic Scale (EMS):
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The earthquake 8.
A fldrengs s a hatsa az pletekre.
European Macroseizmic Scale (EMS):
VII. class: Damaging
- Most people are frightened and try to run outdoors. Many find it
difficult to stand, especially on the upper floors
- Furniture is shifted and top-heavy furniture may be overturned.
Objects fall from shelves in large numbers. Water splashes from
containers, tanks and pools.
- Masonry buildings: large, long cracks on most of the walls;
partitions, end walls, chimneys are collapsed.
- RC buildings: cracks on columns, beams, walls; cracks on partitions,
infill walls; covers and plaster are falling down.
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Conceptual design 1.Seismic response of the building, the expected
damage are strongly influenced by the architectural
design together with quality of materialand
execution.
Principles:
- simplicity, symmetry and regularity in plan;
- regularity in elevation;
- continuity in resistance and stiffness;
- redundancy and robust behavior;
- rigid floors;
- adequate foundation.
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Conceptual design 2.
Even the cleverest calculations and detailed design cannot
compensate for errors and defects in he conceptual design of
the structural and non-structural elements!
Close collaboration between architect and structural
engineer from the earliest planning stage!
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Conceptual design 3.Cost of the structure designed for earthquake
depends on:
design principles,
applied design method.
No significant extra costs thanks to themodern methods!
EN1998
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Conceptual design 4.
Avoid soft storey
ground floor!
Avoid soft storey
upper floors!
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Conceptual design 5.
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Conceptual design 6.
Avoid asymmetrical
horizontal bracing!
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Conceptual design 9.
Avoid short
columns!
nagy meredeksg
nyomatkbra
nyrsi
tnkremenetel!
Avoid partially
infilled frames!
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Conceptual design 10.
Gap is needed!
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Conceptual design 12.
Use the slabs to tie in
the elements and
distribute the forces!
Rigid floor.
disadvantegous advantageous
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Supporting load:
- as a plate: - loads due to gravity;- lateral load due to vertical
vibration;
support: vertical structural elements- as a diaphragm: - wind load;
- lateral load due to horizontal
vibration;
- lateral load due to torsional
vibration;
support: vertical bracing elements
Floors 1.
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Floors 2.Floor as a diaphragm:
RIGID FLOOR:Relative idea: depends on the
rigidity (deformation) of the
floor and bracing elements.
Displacement: rigid body
translation, rotation.
FLEXIBLE
FLOOR
SEMI RIGID
FLOOR
Simple calculation methods. 3D building model.
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Floors 3.Making rigid floor:
Building material, building construction
method:
Rigid floors: - cast in situ RC floors;
- prefabricated RC composite floor;
- corrugated metal sheet composite
floor.
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Floors 4.Making rigid floor:
By seismic joints:
NOYES
NO YES
Rigid unitsVertical
displacement
Horizontal
displacem
ent
Changing ground motion
x < 4y
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Floors 5.Making rigid floor:
By additional bracing elements:
Flexible floor Rigid floor
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Floors 6.Making rigid floor:
Avoiding stress concentration:
Locations for stress concentration
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Floors 7.Making rigid floor:
NO
NO
NO
NO
NO
NO NO
NO
NOYES
YES
YES YES
YES
YES
YES
YES
YES YES
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Floors 8.Making rigid floor:
NO NO
NO
NO
YESIGEN
YES
YES
YES
NO
YES YES YESYES YESNO YES
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Analysis 1.
Design of floors for earthquake
according to Eurocode 8
EN 1998 Design of structures for earthquakeresistance: supplement to the other Eurocodestandards and should be used together them.
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Analysis 2.Ultimate Limit State: Resistance
Ed RdEd effect of action for seismic action,
Combination according to: EN 1990: 6.4.3.4
Ed=E{Gk,j; P; Aed; 2,iQk,i}, Gk,j+ Aed+ 2,iQk,i
Design value of seismic action: Aed= IAek,
I importance factor
Rd design resistance of structural elements.
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Analysis 3.
Guidance:
Mass of the building used for dynamic analysis:
Gk,j+ E,iQk,i , E,i= 2,i
Residential building (A):E=0,15; 2=0,3; =0,5 (independently occupied stories)
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Analysis 4.Analysis of the stiffening system:
Static analysis: lateral force method of analysis
Dynamic analysis: modal response spectrum analysis
Both uses response spectra, which considers:
- the effect of soil: soil factor
- type of building: importance class
- the behavior of the stiffening system: behavior factor
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Analysis 5.
Design response spectra:
Period (s)
Designresponsespectra(Sd
/ag
)
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Analysis 6.Analysis of floors for vertical acceleration:
- The vertical mass forces are defined by, avg,
vertical response spectra.
- avg is at most 45 90 % of the horizontal
acceleration.
- avg, max= 0,15gx 0.9 = 0,13g, that is 13% of the
total mass.
- Not necessary to take into account.
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Analysis 7.Analysis of floors for horizontal acceleration :- Analysis of stiffening system results the forces acting
on the shear walls.
1. Find the forces acting on the floor. Calculation of the bending
moment and the shear force in the plane of the floor. (Membranemodel, strut and tie model.)
2. Checking of shear resistance of the floor in its plane.
3. Analysis of thejoint between the floor and the stiffening
elements.
4. Calculation of edge reinforcement, reinforcement in ring beams.
5. Calculation the deflection of the floor in its plane. Is the floor
rigid?
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Analysis 8.Analysis of floors for horizontal acceleration:
Edge reinforcement, reinforcement in ring beams:
Reinforcement of the ring beam is lapped as usual.
Edge beams and cross beams are used.
Crossbeams
Cross
beams
Edge beam
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Analysis 9.Analysis of floors for horizontal acceleration:
Example: four storey building, stiffened by RC walls, (Dulcska-Kollr)
1. zone: ag = 0,08g
320 kN
641 kN
1112 kN
961 kN
Continuous ring beam
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Analysis 10.Example: four storey building, stiffened by RC walls, (Dulcska-Kollr)
V
M
111,2
444,8
222,4
3336
27,8
1112
416
Compressed column
283
Top floor:
Continuous ring beam
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Composite floor 1.
szls tmaszkzbens tmasz
a fels vasals 33%-avasals a tmasz felett
vasals a tmasz felett
a fvasals 33%-a
kapcsol vasals
a kregpanel feltmaszkodik a falra
a kregpanel nem tmaszkodik fel a falra
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Composite floor 2.
Joint between prefabricated element and cast in situ concrete:
Direct connection is needed for the dynamic load.
Friction is diminishes, plates may buckle.
kapcsol elemekacl trrcs
egyttdolgozst biztost elemek elrendezse
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Composite floor 3.
Free edge:
Edge beam is important.
No Yes Yes
fggnyfal fggnyfal fggnyfal
A szabadszegly kialaktsa
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Literature:Chopra, A.K.:Dynamics of structures. Theory and
applications to earthquake engineering.
Prentice Hall, New Jersey 1995.
Charleson, A.: Seismic Design for Architects.
Elsevier Ltd., Architectural Press 2008.
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