bridge components loading codal provisions · -lateral loads due to water and wind, ice, ship...
TRANSCRIPT
Bridge ComponentsBridge Components
Loading Codal ProvisionsLoading Codal Provisions
Suhasini Madhekar Suhasini Madhekar
College of Engineering PuneCollege of Engineering Pune
Faculty Development Program onFaculty Development Program on
Fundamentals of Structural Dynamics and Application to Fundamentals of Structural Dynamics and Application to
Earthquake EngineeringEarthquake Engineering
1212thth December 2015December 2015
Sanjay Sanjay GhodawatGhodawat Group of InstitutionsGroup of Institutions
AtigreAtigre, Kolhapur, Kolhapur 11
Bridge Components Bridge Components
Bridge Bearings: Supported on a bridge pier, which carry the
weight of the bridge and control the movements at the bridge
supports, including the temperature changes.
Types : Metal rockers, rollers or slides or merely rubber or
laminated rubber, POT - PTFE
2
laminated rubber, POT - PTFE
Bridge Dampers & Isolators: To absorb energy generated by
earthquake waves and lateral load
Bridge Pier: A wide column or short wall of masonry or plain
or RCC for carrying loads as a support for a bridge, founded
on firm ground
Bridge Cap: The highest part of a bridge pier on which the
bridge bearings or rollers are seated.
Bridge Deck: The load bearing floor of a bridge which carries
and spreads the loads to the main beams. (RCC / PSC /
Steel plate girder / Composite)
Bridge Components Bridge Components
3
Steel plate girder / Composite)
Abutment: A support of bridge which may carry a horizontal
force as well as weight.
Expansion Joints : These are provided to accommodate the
translations due to possible shrinkage and expansions due to
temperature changes.
Bridge Bridge -- ComponentsComponents
4
Bridge ComponentsBridge Components
Foundation
SubstructureWell Cap
Pier Cap
Superstructure
Soil Stratum
Bearings
(Connections)
5
The FOUR Components::Foundation :: Well and Well Cap; Pile and Pile Cap
Substructure :: Pier(s) and Pier Cap; Wall; Frame
Connections :: Fixed, Free and Guided Bearings
Superstructure :: Slab; Girder-Slab; Box; Truss; Frame
Soil Stratum
Bridge Cap and DamperBridge Cap and Damper
6
Loading on BridgesLoading on Bridges
7
8
Cars on a suspension bridge over a Cars on a suspension bridge over a river : Coloradoriver : Colorado
9
10
• Permanent Loads: remain on the bridge for an
extended period of time (self weight of the bridge)
• Transient Loads: loads which are not permanent
Loading on BridgesLoading on Bridges
11
- gravity loads due to vehicular, railway and
pedestrian traffic
- lateral loads due to water and wind, ice, ship collision,
earthquake, etc.
12
13
14
15
16
17
18
19
20
Mass of deck = 3,278,404 kg ( DL = 32784 kN)
LL = 3850 kN
D = 65658 kN, F= 324 kN
• Bridge Vibration Units:
– Single-span
– Multi-span
• Simply-supported
Behaviour: Longitudinal shakingBehaviour: Longitudinal shaking
21
• Continuous
Overall Structural Behaviour
Behaviour: Transverse shakingBehaviour: Transverse shaking
SuperstructureConnections
•Vertical cantilever action
22
Substructure
Foundation
•Vertical cantilever action
•Mass lumped at the top
•Foundation flexibility
Ductile Link
Plastic Moment
Capacity Design of Bridge ComponentsCapacity Design of Bridge Components
23
Ductile Link
Brittle Link
Moment Hinges
•Damage only in piers: mandatory ductile detailing•Elastic design of other components
Gawana Bridge (1991 Uttarkashi Earthquake)- Shearing off of anchor bolts of roller–cum–rocker bearings
Bridge Performance in past Indian Earthquakes Bridge Performance in past Indian Earthquakes
24
Past EQs...Past EQs...
Gawana Bridge…- Unseating of superstructure from abutments
25
Past EQs…Past EQs…
Gawana Bridge…
26
Past EQs…Past EQs…
Old Surajbadi Bridge (2001 Bhuj Earthquake)- Bearing damage due to jumping of superstructure
27
Past EQs…Past EQs…
New Surajbadi Bridge (2001 Bhuj Earthquake)- Jumping of Girders – Damage to girders
28
Toe Crushing of Stone Wall Masonry Piers- Old Highway bridge (2001 Bhuj earthquake)
Past EQs…Past EQs…
29
Vertical Splitting of Stone Wall Masonry Piers- Old Highway bridge (2001 Bhuj earthquake)
Past EQs…Past EQs…
30
Collapse of Superstructure- Aman Setu (2005 Kashmir earthquake)
Past EQs…Past EQs…
31
Analysis of Bridges : Issues in ModelingAnalysis of Bridges : Issues in Modeling
• Superstructure– No ductility demand – Usually, stiff in vertical direction
• Connections– Simple Bearings :: Rocker, Roller
• Model as rigid, with usual freedom
– Flexible Bearings :: Neoprene/Rubber/Lead Rubber
32
– Flexible Bearings :: Neoprene/Rubber/Lead Rubber• Model as Flexible
• Substructure– Only structural component with ductility
• Detailed idealisation required
– Effect of shear deformations to be included
• Foundation– Main concern is modeling soil
• Levels of earthquake shaking
– LOW :: Functional Evaluation Earthquake
• Un-cracked Section (EIgross)
– HIGH :: Safety Evaluation Earthquake
• Cracked Section (EIeff)
Properties for ModelingProperties for Modeling
M
EI
EIgross
33
Natural Period T (sec)
0.0
0.5
1.0
1.5
2.0
0 1 2 3 4
Sp
ectr
al A
ccele
rati
on
Sa/g Safety
Functional
Mu
0.6Mu
EIeff
ϕ
• Modulus of Subgrade Reaction k
– Layered Soil
– “N” Value
Properties for modeling…Properties for modeling…
Rigid Foundation
34
Distributed Springs Lumped Springs
Foundation
Modeling: SummaryModeling: Summary
35Cantilever model for Transverse Shaking
Overall model
for Longitudinal Shaking
AnalysisAnalysis
• Methods of Dynamic Analysis
Seismic Coefficient method
Response Spectrum analysis for other bridges
36
Time History analysis for special bridges
Push over analysis
Geometric and material nonlinearities
IRC Codes: Flexure and Shear Design IRC Codes: Flexure and Shear Design
• Design lateral force calculation
(Interim IRC: 6-2014)
- Structural flexibility
- Response Reduction Factor (R) for nonlinear response
• Working Stress Design for bridge substructures
37
• Working Stress Design for bridge substructures (IRC:21-2000)
- Not applicable for explaining seismic behaviour
- Contradiction with the lateral force calculation method
IRC Codes: Flexure and Shear Design… IRC Codes: Flexure and Shear Design…
• No provision on explicit design against lateral shear force (IRC:21-2000)
- Shear design prescribed only for beams and slabs
- Horizontal steel provided as per the prescribed minimum amount
- No provision on confinement of concrete
38
- No provision on confinement of concrete
• Capacity design not prescribed for any bridge component (IRC:21-2000, IRC:78-2000)
- No plastic hinge formation in case of extreme seismic event
• Limit State Design for bridge (IRC:112 -2011)
IRC Codes: Flexure and Shear Design… IRC Codes: Flexure and Shear Design…
• Wall piers and column piers (IRC:78-2000)
- No difference in design methodologies
Pier Cap
Pier Cap
39
:: Flexural deformations:: Plastic Hinge Region
Column Pier
Pile Cap
Wall Pier
Pile Cap
:: Shear deformations:: No plastic hinge
IRC Codes: Flexure and Shear Design… IRC Codes: Flexure and Shear Design…
• Well Foundations (IRC:78-2000)
- Three dimensional finite element analysis of the foundation
- Tensile and compressive stresses checked at the critical
sections
- No formal flexure and shear design methodology prescribed
40
prescribed
- Nominal vertical and horizontal steel prescribed
- Proportioning of foundation prescribed on an empirical basis
- Seismic design procedure not available
•Generated where the mass is (at deck level)
• Needs to be transferred safely to ground
Earthquake Force…Earthquake Force…
41
• Vertical vibrations
– Vertical inertia force
– Adds and subtracts to the gravity force
– Generally not a problem due to FS in gravity design
Ground vibrations…Ground vibrations…
42Gravity LoadsGravity Loads Vertical EQ-Induced Inertia ForceVertical EQ-Induced Inertia Force
•Horizontal vibrations
Horizontal inertia force
Need load transfer path
Need adequate strength
Ground vibrations…Ground vibrations…
Deck Slab
Piers
Inertia Forces
43Flow of EQ inertia forces through all componentsFlow of EQ inertia forces through all components
Soil
Earthquake Shaking
Piers
Foundations
SuperstructureSuperstructure
ConnectionsConnections
• The Bridge Example
Capacity Design ConceptCapacity Design Concept
EQ Design– Good Ductility
44
SubstructureSubstructure
FoundationFoundation
– Good Ductility
– Adequate Strength
(FEQ)max
P
• The Bridge Example…
The Example…The Example…
45
M(FEQ)max
P
Shear Design
( )max
0
EQ
MF
H=
(FEQ)max
PH
• The Bridge Example…
The Example…The Example…
46
0H
M(FEQ)max
PH0
( )max
EQ uIf F V>
design additional steel for the balance shear
Plastic
The Example…The Example…
47
Ductile Link
Brittle Link
Plastic Moment Hinges
Reinforced concrete bridgeReinforced concrete bridge ::
Slab bridge: span < 12 m
Carriageway
48
48
Slab
Cross section of solid slab bridge deckCross section of solid slab bridge deck
Reinforced concrete bridgeReinforced concrete bridge ::
T-Beam bridge : span 12 to 24 m
Carriageway
Footpath
49
49Cross section of TCross section of T--beam bridge deckbeam bridge deck
D=1200-1800 mm
T-beam Cross beam
Reinforced concrete bridgeReinforced concrete bridge ::
Slab on girder bridge :Footpath
Carriageway
50
50Cross section of ICross section of I--beam bridge deck beam bridge deck
I-beam
D=1200-3000 mm
Cross beam (Diaphragm)
Reinforced concrete bridgeReinforced concrete bridge ::
Box girder bridge : span: 20 to 50 m
Carriageway
Footpath
51
51Cross section of box girder bridge deck Cross section of box girder bridge deck
D= 1000-3000 mm
Steel bridgeSteel bridge ::
Steel I-beam bridge : Span: upto 20 m
Footpath
Carriageway
52
52Cross section of steel ICross section of steel I--beam bridge deck beam bridge deck
Common types of failure observed under seismic excitation:Common types of failure observed under seismic excitation:
Seismic displacement failure
Abutment slumping failure
53
53
Abutment slumping failure
Column failure
Joint failure
Displacement failure : UnseatingDisplacement failure : Unseating
54
54
Unseating failure of main approach of Nishinomiyako bridge in Kobe earthquake (Japan)
Displacement failure: Pounding Displacement failure: Pounding
55
55
The longitudinal movement of the new Surajbadi bridge superstructures led to pounding at the deck slab
level in Bhuj Earthquake, 2001 India.
Abutment Slumping failure Abutment Slumping failure
56
56
Pile foundation
Deck
Column failure due to improper detailing of plastic hinge region Column failure due to improper detailing of plastic hinge region
57
57
Crushed column of Santa Monica Freeway
Northridge earthquake 1994 (USA)
Column failure due to improper detailing of plastic hinge regionColumn failure due to improper detailing of plastic hinge region
58
58
Column failure in Mission-Gothic under crossing at Simi Valley
San Fernando Freeway in Northridge earthquake 1994, USA
Column shear failure.Column shear failure.
59
59
Failure of column of Hanshin Expressway, Japan in
Kobe Earthquake, 1995 Japan.
Joint failure due to poor detailing Joint failure due to poor detailing
60
Cypress viaduct joint failure in
Northridge earthquake in 1994 USA .
Conceptual seismic designConceptual seismic design::
The bridge should be straight as curve bridge complicates the
seismic response.
Deck should be continuous with few movement joints. Simply
supported spans are prone to unseating.
Foundation material should be of rock or firm alluvial. Soft soil
61
61
Foundation material should be of rock or firm alluvial. Soft soil
amplifies seismic response.
Pier height should be constant along the bridge. Non-uniform
height results in stiffness variation and attraction of more
forces to stiffer pier.
Pier stiffness should be uniform in all direction.
Conceptual seismic designConceptual seismic design::
Span length should be kept short. Long span results in
high axial forces on the column with potential for reduced
ductility.
Plastic hinges should be developed in the column rather
62
Plastic hinges should be developed in the column rather
than in the cap beam or in superstructure.
The abutment and the pier should be oriented
perpendicular to the bridge axis. Skew supports tend to
cause rotational response with increased displacement.
Connection of pier and superstructure Connection of pier and superstructure ::
Bearing
63
(a) Moment resisting conection
Bearing
(b) Bearing supported connection
Support alternative for pier and superstructure
Beneficial effect of consideration of soil flexibility Beneficial effect of consideration of soil flexibility
Consideration of soil flexibility effect on foundation gives
64
64
lesser forces due to shift of period of vibration of structure
because of added flexibility by soil from higher acceleration
zone to lower acceleration zone of design spectrum.
Outcome:Outcome:
The substructure of bridge are more vulnerable under
seismic excitation.
Non consideration of inelastic action of structure led to the
failures in plastic hinge region of column.
65
65
Seismic deflection of bridge calculated using elastic theory
of design will lead to underestimation of actual deflection
and will result into unseating or pounding of girders during
seismic excitation.
Outcome (contd..) Outcome (contd..)
Comparative study of possible alternative models of same
type of bridge are required
Comparative results of fixed base and detailed model for
bridge with well foundation considering SSI
Difference in seismic response of bridge model with actual
66
66
Difference in seismic response of bridge model with actual
and simplified location of bearing
Effect of scour of river bed on seismic response
Effect of hydrodynamic pressure on seismic response using
global model.
67
Thank you..