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1 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.

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Page 1: Abutments, Piers, and Walls - WSP Groupondemandweb.pbworld.net/pbucontent/aicc/LRFD_Abutments/data/... · • The design procedures for specialty wall designs 1. Abutments, Piers,

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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.

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• 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

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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

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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

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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.

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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

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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

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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

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• 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

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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

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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

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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.

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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.

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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.

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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

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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

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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

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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

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Extensible Reinforcement

Lesson 6: MSE Walls

Inextensible Reinforcement

Lesson 6: MSE Walls

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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

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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

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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

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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