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V 1.1 – Rev. 12.14.07
AASHTO- Load and Resistance Factor Design (LRFD)
Abutments, Piers, and Walls
Andy Foden, P.E., PhD. and Jud Wible.
Credits
The content for this course has been provided by the following PB employees:
With assistance from: Nuno Chao, P.E.
If you have any questions about the content of this course please contact Andrew Foden or email [email protected]. If you have any technical difficulties, please contact your IT Help Desk.
2
• After completing the content within the course you will be asked to take a final test to ensure that you mastered the key training objectives.
• You will need to make a minimum scoreof 80% on the final assessment to receive credit for passing the course.
• Successful completion of the course will earn 0.1 IACET CEU.
• Please refer to your state’s specific continuing education requirements regarding applicability.
Successful Completion
This class is part of the Structures TRC curriculum for LRFD Design, developed internally at PB. The curriculum focuses on the following ten areas of major change introduced by the LRFD Bridge Design Specifications:
• Foundations
• Decks & Deck Systems
• Joints and Bearings
• Abutments, Piers, and Walls
• Railings
• Introduction to LRFD
• Loads and Load Factors
• Concrete Structures
• Steel Structures
• Buried Structures
LRFD Design Curriculum
3
Objectives
After completing the training program, you will be able to identify:
• The differences Between ASD and LRFD design of abutments, piers,and walls
• The allowable movement of structures and stability factors• The design procedures for abutments and wall designs• The design procedures for pier designs• The design procedures for specialty wall designs
1. Abutments, Piers, and Walls Overview– Intro to Substructure Section– Major Differences Between LRFD and Standard Specification– Limit States and Resistance Factors– Design Considerations– Design Loadings
2. Wall Design– Types– LRFD General Design Requirement– Limit States– Design Steps
3. Anchored Walls– Introduction– LRFD vs. ASD– Limit States and Resistance Factors– Design Steps
Course Outline
4
Course Outline
4. Pier Design– Pier Cap Design
• Types• Traditional Pier Cap Design (Concrete Design previously covered
LRFD 103)• Alternative Pier Cap Design
– Pier Column Design• Design Flow Chart• Design Components
5. Prefabricated Modular Walls– Types– Loads– Limit States and Resistance Factors – Design Components
6. MSE Wall Design– Introduction– Loads– Limit States and Resistance Factors – Design steps
LRFD Abutments, Piers and Walls Overview
Narrated by Jud Wible
Lesson 1
5
Introduction to Abutments, Piers and Walls SectionThe Abutments, Piers and Walls design criteria are located within the AASHTO LRFD Bridge Design Specifications, 4th edition in ‘Section 11: Abutments, Piers and Walls.’ The section is broken down to 11 sub-sections from 11.1 to 11.11 then followed by appendices and references. The layout of section 11 is shown below:
• 11.1 - Scope• 11.2 - Definitions• 11.3 - Notation• 11.4 - Soil Properties and Materials• 11.5 - Limit States and Resistance Factors• 11.6 - Abutments and Conventional Retaining Walls• 11.7 - Piers• 11.8 - Nongravity Cantilevered Walls• 11.9 - Anchored Walls• 11.10 – Mechanically Stabilized Earth Walls• 11.11 – Prefabricated Modular Walls• Reference• Appendix A11 Seismic Design of Abutments and Gravity Retaining Structures
Lesson 1: LRFD Overview
General Design Changes for LFRD
1) Different impact factor (IM) is used and impact factor are determined based on the four limit states design criteria
2) Different load combinations are used
3) More loading variables are defined
4) Resistance factors are added
5) Live load distribution factors are determined differently
Lesson 1: LRFD Overview
• Designed minimum service life of 75 years• Designed 100 year service life is more appropriate for walls which support
bridge abutments, buildings, critical utilities, or other facilities for which consequences of poor performance or failure would be severe.
6
LRFD and Standard Specification
AASHTO StandardSpecification (Old)
Allowable Stress Design (ASD)
• Design based on stress withfactor of safety
ΣΣDLDL ++ ΣΣLLLL ≤≤ RRnn // FSFS
Load Factor Design (LFD)
• Load factors applied to each loadcombinations
γγ((ΣβΣβDLDLDL+DL+ΣβΣβLLLLLL)LL) ≤≤ ФФRRnn
LRFD Specification (New)• Design based on load factors and
load combinations
• Resistance factors are used
• Design will be based onapplicable limit states
ηη((ΣγΣγDLDLDL+DL+ ΣγΣγLLLLLL)LL) ≤≤ ФФRRnn
Lesson 1: LRFD Overview
The Limit States: (as specified in Article 1.3.2)
1) Service Limit States – Shall include: settlements, horizontal movements, overall stability, scour at the design flood. Article 11.5.2
2) Strength Limit States – Shall consider: structural resistance, loss of lateral and vertical support due to scour at the design flood event. Article 11.5.3
3) Extreme Event Limit States – Shall include loadings if applicable: seismic loading, flood for scour, vessel and vehicle collision, and other site-specific situations. Resistance factors taken as 1 when investigating the extreme limit state.
Limit States and Resistance Factors
Lesson 1: LRFD Overview
7
Limit States and Resistance Factors (cont’d)
Lesson 1: LRFD Overview
Lesson 1: LRFD Overview
Design Considerations
1. Performance2. Cost3. Schedule4. Constructability5. Environmental compatibility6. Maintenance7. Aesthetics8. Site Compatibility
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Allowable Abutment Movements
• According to AASHO Section C11.5.2, allowable abutment lateral movement of 1.5” or less can usually be tolerated by bridge superstructures without significant damage. Earth pressures used in design should be selected consistent with this requirement.
Lesson 1: LRFD Overview
Wall Settlements and Movements for Prefabricated Modular Walls
Wall Type ∆V / ∆H
Crib Wall 1/300
Concrete Modular Wall 1/300
Bin Wall 1/300
Gabion Wall 1/50
Tolerance
Lesson 1: LRFD Overview
9
Overturning
• For conventional walls on soil, the location of the resultant of the reaction forces shall be within the middle one-half of the base width.
• For foundations on rock, the location of the resultant shall be within the middle three-fourths of the base width.
Lesson 1: LRFD Overview
• DC – Dead load of components • DW – Dead load of wearing surface • EV – Earth load vertical • EH – Earth load horizontal• EL – Effects of locked-in loads• ES – Earth load surcharge• DD – Downdrag
Permanent Design Loads
Lesson 1: LRFD Overview
10
• LL – Vehicular live load • IM – Vehicular dynamic load allowance• BR – Vehicular braking force• CE – Vehicular centrifugal force• CT – Vehicular collision force• CV – Vessel collision force• FR – Friction• IC – Ice load• WA – Water load (buoyancy) and
stream pressure• WS – Wind load on structure• WL – Wind on live load• TU – Uniform temperature• Seismic Loading
Transient Design Loads
Lesson 1: LRFD Overview
Guidelines on Earth Pressures for CIP Walls
• Use at-rest earth pressures for rigid gravity retaining walls resting on rock or batter piles
• Use average of at-rest and active earth pressures for semi-gravity walls founded on rock or restrained from lateral movements and which are less than 16 ft high
• Use active earth pressures for semi-gravity walls greater than 16 ft high
Lesson 1: LRFD Overview
11
Design for Water Pressure
DrainageDrainageblanketblanket
Backfill soilBackfill soil
LongitudinalLongitudinalDrain pipeDrain pipe
WeepholeWeepholePrefabricatedPrefabricatedDrainageDrainageElementElement
Backfill soilBackfill soil
Lesson 1: LRFD Overview
Design for Seismic Forces
Lesson 1: LRFD Overview
12
1. Abutments, Piers, and Walls Overview– Intro to Substructure Section– Major Differences Between LRFD and Standard Specification– Limit States and Resistance Factors– Design Considerations– Design Loadings
2. Wall Design– Types– LRFD General Design Requirement– Limit States– Design Steps
3. Anchored Walls– Introduction– LRFD vs. ASD– Limit States and Resistance Factors– Design Steps
Course Outline
13
Lesson 2: Wall Design
Cast-In-Place Gravity and Semi-Gravity Walls
Lesson 2
Lesson 2: Wall Design
Different types of rigid gravity and semi-gravity retaining walls may be used:• A gravity wall depends entirely on the weight of the stone or concrete masonry and of any soil resting on the masonry for its stability.
• A semi-gravity wall requires reinforcement consisting of vertical bars along the inner face and dowels continuing into the footing. It is provided with temperature steel near the exposed face.
• A cantilever wall consists of a concrete stem and a concrete base slab, both of which are relatively thin and fully reinforced to resist the moments and shears to which they are subjected.
• A counterfort wall consists of a thin concrete face slab, usually vertical, supported at intervals on the inner side by vertical slabs or counterforts that meet the face slab at right angles.
14
Cast-In-Place (CIP) Gravity Wall
H
0.5H to 0.7H
Min.Batter1H:48V
MassConcrete
GranularSoilBackfill
Toe Key
Heel
Base slab, footing or pile cap
Batter
Front faceBack face
Key between successive concrete pours for high walls
Stem
Backwall
Lesson 2: Wall Design
variesvaries
HH
Min. BatterMin. Batter(1H:48V)(1H:48V)
88"" minmin(12(12"" preferable)preferable)
HH//1010 to to HH//88 HH//1212 to to HH//1010
HH//1212 totoHH//1010
22//55H to H to 33//55HH
Cantilever WallCantilever WallCounterfortCounterfort WallWall
22//55H to H to 33//55HH
HH//1212
HH//1212
variesvaries
1H:48V1H:48VMin. BatterMin. Batter
88"" minmin(12(12"" preferable)preferable)
88"" minmin
11//33H to H to 22//33HH
Other Wall Types
Lesson 2: Wall Design
Dimensions shown are suggested, and not necessarily required by Dimensions shown are suggested, and not necessarily required by LRFD.LRFD.
15
External Failure Mechanisms
Sliding Limiting Eccentricity (Overturning)
Bearing
Lesson 2: Wall Design
Overall Stability
Strength Limit State Checks
External Stability1. Sliding2. Limiting Eccentricity3. Bearing Resistance
Service Limit State Checks1. Overall Stability2. Wall settlement3. Lateral displacement
Lesson 2: Wall Design
16
Design Steps
Note: See AASHTO Section 11.6.3.2 for vertical stresscalculation for walls on rock
Lesson 2: Wall Design
Determine
Unfactored
Loads
Determine
Load
Factors
CheckEccentricity
Check Bearing Resistance
Check
Sliding
Determine
Load
Factors
Lesson 2: Wall Design
Abutments and retaining walls shall be investigated for:• Lateral earth and water pressures, including any live and dead load
surcharge.
• The self weight of the abutment/wall.
• Loads applied from the bridge superstructure.
• Temperature and shrinkage deformation effects.
• Earthquake loads as specified herein, in section 3, and elsewhere in the Specifications.
In addition, contractions joints shall be provided at intervals not exceeding 30’ and expansion joints at intervals not exceeding 90’.
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1. Abutments, Piers, and Walls Overview– Intro to Substructure Section– Major Differences Between LRFD and Standard Specification– Limit States and Resistance Factors– Design Considerations– Design Loadings
2. Wall Design– Types– LRFD General Design Requirement– Limit States– Design Steps
3. Anchored Walls– Introduction– LRFD vs. ASD– Limit States and Resistance Factors– Design Steps
Course Outline
18
Lesson 3: Anchored Walls
Non-gravity Cantilevered and Anchored Walls
Lesson 3
Introduction
• Anchored Walls are used for situations where the embedment depth is cost prohibitive or unable to be reached due to necessary cantilever depth.
• A Nongravity Cantilever Wall is a soil retaining system that derives lateral resistance through embedment of vertical wall elements and supports retained soil with facing elements.
Lesson 3: Anchored Walls
19
Anchored Wall
Active
Zone
Failu
re pl
ate
(or o
ther c
ritica
l
failur
e sur
face)
Des
ign
Hei
ght (
H)
Ver
tical
Ele
men
tEm
bedm
ent
Overburden cover
as required
Finished Grade
Unbonded Length
BondedLength
Primary Grout
45o + ’/2
Wall (verticalelements withfacing)
Wall bearingelement
Anchor head
Bearing plateAnchor
SheathingGrout
Anchor inclinationas required
Lesson 3: Anchored Walls
Components of a Ground Anchor
Anchor headBearing plate
WallUnbondedTendon
Anchor GroutBonded Tendon
AnchorDiameter
Trumpet
Sheath
Unbonded Length Anchor Bond Length
Tendon Bond Length
Lesson 3: Anchored Walls
20
b.) Failure of wall in bending
d.) Failure of wall due toinsufficient passive resistance
Failure Mechanisms for Anchored Walls
a.) Tensile failure of tendon
c.) Pullout failure of grout/grout bond
Lesson 3: Anchored Walls
Failure Mechanisms for Anchored Walls
e.) Failure due to insufficient axial resistance
f.) Rotational failure ofground mass (Service Limit)
Lesson 3: Anchored Walls
21
Comparison to ASD – Anchor Tensile Rupture
• ASD– 0.8 GUTS > 1.33 Design Load (DL = EH + LS)– 0.8 GUTS > 1.33 EH + 1.33 LS
• LRFD– φ GUTS > γp EH + 1.75 LS– 0.8 GUTS > 1.5 EH + 1.75 LS
• Guaranteed Ultimate Tensile Strength (GUTS)
Lesson 3: Anchored Walls
Limit States for Anchored Walls
Strength Limit State
Tensile resistance of tendon steelGround anchor pulloutFlexural resistance, passive resistance, and bearing resistancesof the vertical wall element, lagging and permanent facing
Service Limit State
Ground surface settlementLateral wall movementOverall stability
Extreme Event State
Lesson 3: Anchored Walls
22
Resistance Factors – Anchor Pullout
Cohesionless (Granular) Soils 0.65(1)
Cohesive Soils 0.70(1)
Rock 0.50(1)
Where Proof Tests Performed 1.00(2)
Lesson 3: Anchored Walls
Anchored Wall Design Steps
Lesson 3: Anchored Walls
DetermineRequirementsand Feasibility
Subsurface profile
Check Corrosion Protection
Requirements
DetermineLateral
Pressure Envelope
DetermineUnfactored
Loads
DetermineLoad
Factors
DetermineInclination
and Spacing
Select Tendon and
Check Resistance
23
Anchored Wall Design Steps, cont.
Lesson 3: Anchored Walls
EvaluateBond
Length
CheckFlexural
Resistance
CheckBearing
Resistance
CheckPassive
Resistance
CheckOverallStability
DesignTimber
Lagging &Facing
CheckWall
MovementsAt Service I
Load Combinations and Load Factors
Calculation of Anchor Load
Anchored Wall Design Steps
HH 4545oo--φφ/2/2 15 f
t (m
in.)
Sv = 8 to 12 ft(commonly used)
Bond length0.2 H (min.)
Minimum freelength = 15 ft
A Typical Anchor Setup
Lesson 3: Anchored Walls
24
Anchor/Soil Type(Grout Pressure)
Soil Compactness or SPT Resistance(1)
Presumptive Ultimate Bond Stress, τn (ksf)
Gravity Grouted Anchors(<50 psi)Sand or Sand-Gravel Mixtures Medium Dense to Dense 11-50 1.5 to 2.9
Pressure Grouted Anchors(50 – 400 psi)Fine to Medium SandMedium to Coarse Sand
w/Gravel
Silty SandsSand Gravel
Glacial Till
Medium Dense to Dense 11-50Medium Dense 11-30Dense to Very Dense 30-50
-----Medium Dense to Dense 11-40Dense to Very Dense 40-50+Dense 31-50
1.7 to 7.92.3 to 145.2 to 20
3.5 to 8.54.4 to 29 5.8 to 296.3 to 11
Ultimate Bond Stress for Anchors in Cohesionless Soils
Lesson 3: Anchored Walls
Timber Lagging
•Do not “design” temporary timber lagging, select from experience or use Table 6.3.3a from Reference Manual
•Facing shall be designed based on Article 11.8.5.2
Lesson 3: Anchored Walls
Check wall movements at Service 1
25
1. Abutments, Piers, and Walls Overview– Intro to Substructure Section– Major Differences Between LRFD and Standard Specification– Limit States and Resistance Factors– Design Considerations– Design Loadings
2. Wall Design– Types– LRFD General Design Requirement– Limit States– Design Steps
3. Anchored Walls– Introduction– LRFD vs. ASD– Limit States and Resistance Factors– Design Steps
Course Outline
26
Lesson 4: Pier Design
Pier Caps and Pier Columns
Lesson 4
Pier Types
Cap
Shaft
Footing
Wall
Footing
Hammerhead pier Wall pier
Column Bents
Cap
Pile (Typ.)
Pile Bents
Lesson 4: Pier Design
27
Pier Cap Design Flowchart
ObtainDesignCriteria
SelectOptimumPier Type
Select Preliminary Pier Dimensions
Compute Load
Effects
Analyze and Combine
Force Effects
Design Pier Cap and Column
Determine Foundation
Design Pier Footing or Other
Foundation Elements
Lesson 4: Pier Design
Traditional Pier Cap Design
• Reinforcement only depends on separate values of Vu, Mu and Tu• Mechanical interaction of force effects not considered• Should not be used for:
– Deep Beams• Where the point of 0 shear to the face of the support is less
than 2d or components in which a load causing more than one-third of the shear at a support is closer than 2d from the face of the support.
– Regions Near Discontinuities
Lesson 4: Pier Design
28
Alternative Pier Cap Design
Strut and Tie Method
The strut-and-tie model is used principally in regions of concentrated forces and geometric discontinuities to determine concrete proportions and reinforcement quantities and patterns based on assumed compressive struts in the concrete, tensile ties in the reinforcement, and the geometry of nodes at their points of intersection.
Lesson 4: Pier Design
Strut and Tie Usage
• Concrete “struts” resist compressive forces
• Steel “ties” resist tensile forces • Struts and ties meet at the points of
load application (also known as nodes.)
Thic
knes
s
A Deep Flexural Member
Lesson 4: Pier Design
29
Strut and Tie Basics
• Tension ties yield before compressive struts crush
• Forces in the struts and ties are uniaxial• External forces are applied at the points
(or nodes) of the beam. P
P P
P
Legend:CompressionTension
Lesson 4: Pier Design
Strut and Tie Pier Cap Design
Draw IdealTruss Model
Check Size of Bearings
AASHTO 5.6.3.5 and 5.7.5
Solve Member Forces AASHTO5.5.4.2.1, 5.6.3.5
Choose Tension Tie
Reinforcement
Check Capacity of
StrutsAASHTO5.6.3.3
Check Anchorage of Tension Ties
AASHTO 5.6.3.4
Check nodal stresses
AASHTO 5.6.3.5
Design Crack Control
Reinforcement AASHTO 5.6.3.6
Lesson 4: Pier Design
30
Nodes
Legend:CompressionTension
CCC nodesCCT node
CTT nodes
• CCC node – nodal zone bounded by compressive struts and bearing areas• CCT node – nodal zone anchoring a one-direction tension tie• CTT or TTT node – nodal zone anchoring tension ties in more than one
direction
Lesson 4: Pier Design
Label Element Limiting Concrete Compressive Stress
1 CCC node 0.85φf’c
2 CCT node 0.75φf’c
3 CTT or TTT node 0.65φf’c
4 Compressive strut fcu
5 Tension tie fy or (fpe+fy)
Strut and Tie (Nodal) Design
Lesson 4: Pier Design
31
Strut and Tie Pier Design
Choose the tension tie reinforcement
– Determine the Top Reinforcement over Column– Calculate required area of tension tie reinforcement– Determine the Required Stirrup Reinforcement– Calculate the Required Stirrup Size and Spacing– Maintain bar spacing as per AASHTO 5.10.3
Lesson 4: Pier Design
Crack Control Reinforcement Detailing
• Orthogonal grids• Spacing not to exceed 12”• Ratio of As/Ag ≥ 0.003• Tension reinforcement can be included
Lesson 4: Pier Design
32
Region Types
• D-region – disturbed region (strut and tie applicable)
• B-region – normal design region
D-region B-region
D
D
B
B
2 - No. 9
10 - No. 92 - No. 6
4 - No. 6
4-legged No. 6stirrups at 12"
2-legged No. 5stirrups at 12"
Section D-D
10 - No. 9Bottom
8 - No. 9 Top
4 - No. 6 (Typ.)
4-legged No. 6stirrups at 12"
Section B-B
10 - No. 9Bottom
2 - No. 9 Top
2 - No. 6 (Typ.)2-legged No. 5stirrups at 12"
8 - No. 9
A Crack Controlled Reinforcement Example
Crack Control Reinforcement
Lesson 4: Pier Design
33
Pier Columns
Lesson 4: Pier Design
Failure of a Bridge Failure of a Bridge Pier After a 2004 Pier After a 2004
EarthquakeEarthquake
Column Design Flowchart
Analyze Shaft/ Columns
Determine Max Moment/Shear
Check Compression
Reinforcement Limits
AASHTO 5.7.4.2
Develop Column
Interaction Curve
Check Slenderness
AASHTO 5.7.4.3
Calculate Axial Resistance
AASHTO 5.7.4.4
Check Biaxial Flexure
AASHTO 5.7.4.5
Determine Transverse
ReinforcementAASHTO 5.10.6
Lesson 4: Pier Design
34
Interaction Diagrams and DataTypical column Interaction DiagramColumn Interaction Diagram – Tabulated
FormφPn(kip)
φMn(kip-ft.)
φPn (kip) (cont.)
φMn (kip-ft.) (cont.)
Pmax = 2,555
764 799 1,354
2,396 907 639 1,289
2,236 1,031 479 1,192
2,076 1,135 319 1,124
1,917 1,222 160 1,037
1,757 1,291 0 928
1,597 1,348 -137 766
1,437 1,389 -273 594
1,278 1,419 -410 410
1,118 1,424 -546 212
958 1,404 -683 0
Lesson 4: Pier Design
Biaxial Bending Reinforcement
Ast(Typ.)
Spiralor Tie
Ag
Y
Y
XX
Y
Y
Detailing of a Typical Column
Lesson 4: Pier Design
35
Course Outline
4. Pier Design– Pier Cap Design
• Types• Traditional Pier Cap Design (Concrete Design previously covered
LRFD 103)• Alternative Pier Cap Design
– Pier Column Design• Design Flow Chart• Design Components
5. Prefabricated Modular Walls– Types– Loads– Limit States and Resistance Factors – Design Components
6. MSE Wall Design– Introduction– Loads– Limit States and Resistance Factors – Design steps
Lesson 5: Prefabricated Modular Walls
Lesson 5
36
Metal Bin WallCrib WallConcrete Module Gabion Wall
Types of Modular Walls
Lesson 5: Prefabricated Modular Walls
Vertical Back Slope
Positive Back Slope
Lateral Earth Pressure
VerticalBack Slope
Lesson 5: Prefabricated Modular Walls
Negative Back Slope
37
Estimate required base widthDetermine unfactored loads and moments used for analyses
Unfactored Loads
Lesson 5: Prefabricated Modular Walls
Load Distribution for Bearing Analysis
Lesson 5: Prefabricated Modular Walls
38
GROUP γDC γEV γEH(Active)
γES γLS
Strength – Ia 0.90
1.25
1.00 1.50
1.00
1.75
Strength – Ib 1.35 1.50
1.50
1.50 1.75
Service – I 1.001.00 1.00 1.00
Load Factors and Limit States for Factored Loads & Moments
Strength Limit States for Modular WallsService Limit States for Modular Walls
Lesson 5: Prefabricated Modular Walls
Assume rectangular distribution of soil pressure over supports (leveling pad or footing)Assume 80% of soil weight inside modules is transferred to supportsCalculate the nominal bearing resistance based on methods for spread footings
Check Bearing Resistance
Lesson 5: Prefabricated Modular Walls
39
Assume 20% of soil fill weight (WF) is effective as soil-to-soil sliding resistance between the supportsAll the remaining vertical loads are effective in sliding resistance acting as footing material-to-foundation within the soil sliding resistanceSoil-to-soil interface strength is the lesser of strength of backfill soil or foundation soil
Assumptions for Sliding Analysis
Lesson 5: Prefabricated Modular Walls
40
Course Outline
4. Pier Design– Pier Cap Design
• Types• Traditional Pier Cap Design (Concrete Design previously covered
LRFD 103)• Alternative Pier Cap Design
– Pier Column Design• Design Flow Chart• Design Components
5. Prefabricated Modular Walls– Types– Loads– Limit States and Resistance Factors – Design Components
6. MSE Wall Design– Introduction– Loads– Limit States and Resistance Factors – Design steps
Lesson 6: MSE Wall Design
Lesson 6
41
MSE Walls
A Mechanically Stabilized Earth (MSE) Wall is constructed by placing alternating layers of reinforcing elements and compacted backfill behind a facing. The soil and the structural elements act in unison to form a composite structure that constitutes the wall.
Lesson 6: MSE Walls
Lesson 6: MSE Walls
MSE Walls Uses
• May be used in locations where conventional gravity, cantilever, counterforted or prefabricated modular walls are considered. • Shall not be used under the following conditions– Where Utilities (other than drainage) shall be within the
reinforcement zone– Where erosion or scour may undermine the fill or facing– Where reinforcement is exposed to surface or ground water
contaminated by corrosive chemicals or aggressive environmental conditions.
42
Principal Components of an MSE Wall
Lesson 6: MSE Walls
Strength Limit States for MSE Walls
Soil Failure Modes (External Stability)– Sliding– Limiting Eccentricity– Bearing Resistance
Lesson 6: MSE Walls
Structural Failure Modes (Internal Stability)– Tensile Resistance of Reinforcement– Pullout Resistance of Reinforcement– Structural Resistance of Face Elements– Structural Resistance of Face Element Connections
43
MSE Wall External Failure Mechanisms
Sliding Overturning
Bearing
Lesson 6: LRFD Overview
Overall Stability
Service Limit States - Wall Facing Design
• Durability• Flexibility• Strength• Compatibility• Adequate Anchorage
• Wall Settlement
• Lateral Displacement
• Facing Must Provide:
Lesson 6: MSE Walls
44
Unfactored Loads
• Estimate reinforcement length
• Determine earth pressures and surcharges
• Determine unfactored loads and moments
Lesson 6: MSE Walls
Preliminary Sizing of Reinforcement
• Minimum reinforcement length– > 0.7H or 8 ft.
• Sloping fill or surcharges– use 0.8H to 1.1H
• With walls on slopes– minimum of 4-ft wide bench in front of wall– See AASHTO Table C11.10.2.2-1 for minimum
embedment depths
Lesson 6: MSE Walls
45
Pressure Diagram for External Stability AnalysisHorizontal Backslope with Traffic Surcharge
Lesson 6: MSE Walls
Pressure Diagram for External Stability Analysis
Sloping Backslope
Lesson 6: MSE Walls
46
Extensible Reinforcement
Lesson 6: MSE Walls
Inextensible Reinforcement
Lesson 6: MSE Walls
47
Limiting Differential Settlements
MSE walls with Panel Size Less than 30 ft2
Joint Width (in.)
Limiting Differential Settlement
0.75 1/1000.5 1/2000.25 1/300
Lesson 6: MSE Walls
Lateral Wall Displacement
• Usually occurs during construction• Differential movements along base and lateral wall
movements
• Greater displacement with extensible reinforcements• Cantilever type movements because walls are built
from bottom up
Lesson 6: MSE Walls
48
Objectives
You should now be able to identify:
• The differences Between ASD and LRFD design of abutments, piers,and walls
• The allowable movement of structures and stability factors• The design procedures for abutments and wall designs• The design procedures for pier designs• The design procedures for specialty wall designs
49
Instructions
• The assessment consists of 10 multiple choice questions.
• You will need to achieve a minimum score of 80% to receive credit for passing the course.
• If you score below 80%, please go back and review the content of this course, and then retake the assessment to achieve a passing score.
You are now ready to begin the final assessment.
When ready, click the Right arrow below to advance to the assessment.
Final Assessment
50
Thank you for completing this course. If you received a passing score on the assessment, simply close this window to exit the course. Your score will be recorded on your transcript. If you did not achieve a passing score, please review the content of this course and thenretake the assessment to achieve a passing score.
You may print a certificate from the My Transcript area of PBUniversity by clicking the cert. icon.
If you need a certificate that specifically states the IACET certification and credit hours, please email a request to us at [email protected].
Conclusion