asep summit 2012 - balili apd presentation - design of bridges

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Design of Reinforced Concrete Design of Reinforced Concrete Bridges as per NSCP 2010 Bridges as per NSCP 2010 VolVol 22By Alden Paul D. Balili, MSCEDLSU-M

OutlineOutline

y Overviewy Highlight of Changes per Chaptery Does not include geotechnical provisions

Who is this for?Who is this for?

y Aspiring Bridge Engineersy Bridge Engineers

Aspiring Bridge Engineer Bridge Engineers

INTRODUCTION TO INTRODUCTION TO BRIDGE DESIGN: BRIDGE DESIGN: SUPERSTRUCTURE PARTSSUPERSTRUCTURE PARTS

Design of Reinforced Concrete Bridges as per NSCP 2010 Vol 2

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Please Note:Please Note:

y Longitudinal direction means in the direction parallel to traffic.y Transverse direction means in the direction

perpendicular to traffic

SUPERSTRUCTURESUPERSTRUCTURE

Longitudinal

Transverse


y Superstructure Section


yWEARING SURFACE

WearingSurface

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yWEARING SURFACE is the portion of the deck which resists traffic

wear. Could be a separate layer of bituminous material,

or Is integral with the deck, (additional thickness

added to the deck)


y DECK

Deck


y DECK Its main function is to distribute loads transversely

along the bridge cross section. Usually integrated with the primary members The wearing surface and barriers are placed on top

of this


y PRIMARY MEMBERS

PrimaryMembers

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y PRIMARY MEMBERS Distributes loads longitudinally and are designed to

resist flexure and shear from traffic loads. Otherwise known as stringers or girders.


y SECONDARY MEMBERS

SecondaryMembers


y SECONDARY MEMBERS Bracing between primary members in the

transverse direction. Helps distribute the loads between primary

members. For prestressed concrete bridges, they are often

called diaphragms. Diaphragms between the ends are called internal

diaphragms. While Diaphragms at the ends are called external diaphragm.


y TRAFFIC BARRIERS

TrafficBarriers

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y TRAFFIC BARRIERSis a device which protects wayward vehicles

from running over the bridge. when a pedestrian walkway is present

protects pedestrians from wayward vehicles.

INTRODUCTION TO INTRODUCTION TO BRIDGE DESIGN: BRIDGE DESIGN: SUBSTRUCTURE PARTSSUBSTRUCTURE PARTS


SUBSTRUCTURESUBSTRUCTURE SUBSTRUCTURESUBSTRUCTURE

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SUBSTRUCTURESUBSTRUCTURE

y PIER


y PIER ..are structures which support the superstructure

at intermediate points between the end supports. A pier which has multiple columns with a beam

joining them on top is usually called a column bent.


y CAP BEAM (note: column bent shown)


y CAP BEAM ..the top beam in a bent which ties together the

supporting columns or piles.

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y Abutment


y Abutment ..are earth-retaining structures which support the

superstructure at the beginning and end of the bridge. Comes in a variety of forms


y SHEAR KEY


y SHEAR KEY ..a short element attached to the abutment or pier

cap beam which prevents the superstructure from sliding transversely against lateral loads

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y BEARINGS


y BEARINGS .. are mechanical systems which transmit the

vertical and horizontal loads of the superstructure to the substructure. This is usually composed of flexible material to

accommodate movements of the superstructure and substructure.


y PEDESTAL


y PEDESTAL .. Is a short column under the bearings. Usual function is to provide a level surface and

achieve the desired elevation for the bearing .

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y STEM


y STEM .. A cantilever wall providing protection from the

earth especially if there is a roadway underneath the bridge (an underpass).


y BACKWALL


y BACKWALL .. An extension of the stem which serves as

protection from the earth for the ends of the superstructure.

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yWINGWALL


yWINGWALL .. Is attached to the backwall. is designed to assist in confining the soil behind

the abutment.


y APPROACH SLAB


y Note: Approach is the section of roadway before and after the structurey Approach Slab .. Is a slab located on the approaches and

supported by the abutment used to prevent settlement of the approach pavement.

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y FOOTING


y Footing .. A component which transmits the loads from the

substructure and superstructure to the soil or the piles underneath. A footing supported without piles and resting on

soil is called a spread footing..A footing supported with piles is called a pile

cap


y PILES


y PILES .. Are used when the bearing capacity under a

footing is incapable of carrying the gravity loads. .. Extend below to a stronger soil layer or the

underlying rock layer to provide adequate support and to prevent settlement.There are different types of piles ranging from

concrete to steel

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INTRODUCTION TO INTRODUCTION TO NEW NEW NSCPNSCP 2010 2010 VOLVOL 2 2 CODECODE


IntroductionIntroduction

y The new NSCP 2010 code adopts the AASHTO LRFD Bridge Design Specifications 2007.y It should be noted that the latest

AASHTO code is 2010. However, revisions from 2007 to 2010 are minimal.

IntroductionIntroduction

y The new NSCP 2010 code adopts the AASHTO LRFD Bridge Design Specifications 2007.y It should be noted that the latest

AASHTO code is 2010. However, revisions from 2007 to 2010 are minimal.

Chapters adapted from Chapters adapted from AASHTO LRFD 2007AASHTO LRFD 2007

AASHTO LRFD BRIDGE 2007 NSCP 2010 Vol 2

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Where are they now?Where are they now?

NSCP Vol 2 - 1997 NSCP 2010 Vol 2

1. General Provisions

2. General Features of Design

3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures

8. Reinforced Concrete

9. Prestressed Concrete

10. Structural Steel

11. Aluminum Design

12. Soil-Corrugated Metal Structure Interaction Systems

13. Timber Structures

14. Elastomeric Bearings

15. TFE Bearing Surface

16. Steel Tunnel Liner Plates

17. Soil Reinforced Concrete Structure Interaction Systems

18. Soil-Thermoplastic Pipe Interaction System

19. Pot Bearings

20. Disc Bearings

21. Seismic Design



1. General Provisions2. General Features of Design

3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures




11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design




2. General Features of Design3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures




11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design





3. Loads4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures




11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design

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3. Loads (Distribution Factors)4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures




11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design





3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures

8. Reinforced Concrete9. Prestressed Concrete10. Structural Steel

11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design





3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures



10. Structural Steel11. Aluminum Design12. Soil-Corrugated Metal Structure Interaction Systems

13. Timber Structures14. Elastomeric Bearings





19. Pot Bearings

20. Disc Bearings

21. Seismic Design





3. Loads4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures

8. Reinforced Concrete9. Prestressed Concrete


11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design

For decks of composite systems

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3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures8. Reinforced Concrete



11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design





3. Loads

4. Foundations

5. Retaining Walls6. Culverts

7. Substructures




11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design (Mononobe Okabe)


NSCP Vol 2 - 1997 NSCP 2010 Vol 21. General Provisions


3. Loads

4. Foundations

5. Retaining Walls

6. Culverts7. Substructures




11. Aluminum Design





16. Steel Tunnel Liner Plates17. Soil Reinforced Concrete Structure

Interaction Systems18. Soil-Thermoplastic Pipe Interaction

System19. Pot Bearings

20. Disc Bearings

21. Seismic Design





3. Loads (Railing load provisions)4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures




11. Aluminum Design








19. Pot Bearings

20. Disc Bearings

21. Seismic Design

(Has a lot of new content regarding railings)

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3. Loads

4. Foundations

5. Retaining Walls

6. Culverts

7. Substructures




11. Aluminum Design



14. Elastomeric Bearings15. TFE Bearing Surface




19. Pot Bearings20. Disc Bearings21. Seismic Design

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 01CHAPTER 01


Chapter 01 HighlightsChapter 01 Highlights

y Description of the different design limit states Service Limit State Fatigue and Fracture Limit State Strength Limit State Extreme Event Limit States


y Description of the different design limit states Service Limit Statex Restrictions on stress, deformation and crack width

under regular service conditions.

Fatigue and Fracture Limit State Strength Limit State Extreme Event Limit States

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y Description of the different design limit states Service Limit State Fatigue and Fracture Limit Statex Restrictions on stress range as a result of a single

design truck occurring at the number of expected stress range cycles. This is to prevent crack growth due to repetitive loading

Strength Limit State Extreme Event Limit States


y Description of the different design limit states Service Limit State Fatigue and Fracture Limit State Strength Limit Statex Strength and stability are provided to resist force

combinations that the bridge is expected to experience.

Extreme Event Limit States


y Description of the different design limit states Service Limit State Fatigue and Fracture Limit State Strength Limit State Extreme Event Limit Statesx Ensures structural survival of a bridge during the

following extreme events (Earthquake, floor, ship and vehicle collision)

FYI: FatigueFYI: Fatigue

yWhat is fatigue? Slow degradation of materials due to

repetitive loading and resulting stress reversals. A good example is a paper clip bent back and

forth till failure

Bend up

Bend down

Repeat to failure!

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FYI: FatigueFYI: Fatigue

yWhat is fatigue? Hence, the term stress range is used to

indicate the extreme stresses (+ or - ) a member goes through. Ex: Higher stress range is experienced, when a

section undergoes both positive and negative moment!

-

+

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 02: GENERAL CHAPTER 02: GENERAL DESIGN FEATURESDESIGN FEATURES


Chapter 02Chapter 02

y Generally, this chapter indicates required clearances and geometric requirements for bridges as specified by AASHTO.y Requirements for Hydrology analysis are

also indicated.

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 03: LOADS CHAPTER 03: LOADS AND LOAD FACTORSAND LOAD FACTORS


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Chapter 03 LoadsChapter 03 Loads

y Things to be discussed Loads and Load Combinations The New Design Truck New Seismic Load Provisions Shrinkage, Creep and Temperature


y Load listPERMANENT LOADS TRANSIENT LOADS


y Load Combinations Strength Strength I Normal vehicular use w/o wind Strength II Special vehicle use w/o wind Strength III No vehicle use with wind

velocity > 90 km/h Strength IV High dead load to live load ratio Strength V Normal vehicular use with wind

= 90 km/h


y Load Combinations Strength

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y Load Combinations Extreme Event Extreme Event 1 Earthquake combination Extreme Event II Load combination

considering the extreme effects of the following (vessel colission, extreme flood) with reduced live load.


y Load Combinations Extreme Event


y Load Combinations Service Service I Normal Bridge Operation w/ 90

kph wind. Used for Reinforced Concrete Crack Control Service II Control of yielding of steel

structures and slip of slip-critical connections Service III Crack control for prestressed

concrete superstructures Service IV Crack control for prestressed

columns/piles


y Load Combinations Service

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y Variable load factors. For certain combinations, variable factors are

used to ensure that members have adequate strength for all possible conditions.


y Variable load factors.


y Example of Variable Load Factors

1.25 DC +LL+WA+FR+EQ0.9 DC +LL+WA+FR+EQ

Ex: Lower gravity loads might result in more conservative column design


y The New Design Truck

Subject to Dynamic Load Allowance (or impact factor)

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y Lane Load = 9.3 kN/m distributed over 3m width

Not subject to Dynamic Load Allowance (or impact factor)

9.3 kN/m

3m

Bridges Bridges Standard Trucks LRFDStandard Trucks LRFD

y Note that the new truck used by the latest LRFD code is called the HL 93. Note that the new code prescribes that truck and lane load are concurrenty HL-93 Standard Shown Below

9.3 kN/m lane load

Bridges Bridges Standard Trucks LRFDStandard Trucks LRFDy For HL93 a new truck for negative moment is

also prescribed. The axle loads are 90% of that for the single trucky HL-93 for Negative moment and interior pier

reactions Shown Below

4300mm 4300mm15000mm MIN

31.5 kN 130.5 kN 130.5 kN 31.5 kN 130.5 kN 130.5 kN

9.3 kN/m lane load

Chapter 03 LoadsChapter 03 Loadsy To take into account dynamic effects (aka the

additional force due to vibration), Dynamic Load allowance (DLA) factor is added.y The dynamic factor to be used are shown

below

Note that the impact factor is now constant and not variable with the span.

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y To apply the DLA, the wheel loads could be multiplied by (1+DLA Factor) prior to analysis

Before DLA

After DLA = 33%(Multiply original value by 1.33)

46550 N 192850 N 192850 N

Chapter 03 Loads Chapter 03 Loads -- EarthquakeEarthquake

y In Chapter 3, the basic parameters are specified for EQ load computation. These are Acceleration Coefficient Importance Categories Site Effects Response Modification Factor

Bridges : Earthquake loadsBridges : Earthquake loads

y Earthquake Majority of the Philippines is classified as seismic zone 4

(Acceleration Coefficient = 0.4) Earthquake Inertia forces are caused by lateral and vertical

movement of the ground AASHTO 2007 adopts spectral maps for the design

acceleration coefficient As of the moment, spectral maps are still unavailable for the

Philippines and most of the country will still be using an acceleration coefficient of 0.4 (except for the Palawan area).

Bridges : Bridges : Earthquake LoadsEarthquake Loadsy Spectral Map from

NSCP 1997 Vol 2 Bridges

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Bridges : Earthquake LoadsBridges : Earthquake Loads

y Earthquake Earthquake can attack in the two principal directions:

longitudinal and transverse. Codes specify the following load cases for earthquake to

cover earthquakes which attack in a diagonal direction

x 100% Long + 30% Transx 30% Long + 100% Trans


y Earthquake (Procedure using Single Mode) 1) Apply a unit uniform load on the structure. Call this

po(x)


y Earthquake (Procedure using Single Mode) 1) Apply a unit uniform load on the structure. Call this

po(x)


y Earthquake (Procedure using Single Mode) 2) Compute the corresponding deflections due to unit

uniform load. Call these deflection vs(x)

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y Earthquake (Procedure using Single Mode) 3) Compute uniform load per unit length of structure. Call

it w(x)

W(x)


y Earthquake (Procedure using Single Mode) 4)


y Earthquake (Procedure using Single Mode) 5) Compute the Period of vibration


y Earthquake (Procedure using Single Mode) 5) Compute the Elastic Seismic Response coefficient.

A = Acceleration coefficient S = Site coefficient, this is dependent on the soil of the site

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y Earthquake (Procedure using Single Mode) 5) Site coefficient valuesx S = 1.0 for rock type foundationx S = 1.2 for stiff clay or deep cohesionless soilx S = 1.5 for soft to medium-stiff claysx S = 2.0 or soft clays or silts


y Earthquake (Procedure using Single Mode) 6) Compute the actual uniform load on the bridge due to

earthquake


y Earthquake (Procedure using Single Mode) 6) It should be noted, that the procedure computes the

elastic response of the structure. To consider the dissipation of the earthquake force due to

formation of plastic hinges, the forces computed must be divided by R (the response modification factor)


y Earthquake (Procedure using Single Mode) 6) R factors

Note the different factors given the importance of the bridge

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Bridges: Earthquake LoadsBridges: Earthquake Loads

y Multiple column bent

Bridges: Earthquake LoadsBridges: Earthquake Loads

y Single Column


y Lateral Loads come from the following Earthquake (Procedure for estimating forces)x 7) Finally, we must check the overstrength requirements so that the

columns yield first before the cap beam


y Lateral Loads come from the following Earthquake (Procedure for estimating forces)x 7) Why column hinging? (Contrary to buildings)

As per the Paper Structural rehabilitation with advanced composites by F. Seible

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y Lateral Loads come from the following Earthquake (Procedure for estimating forces)x 7) The plastic hinges must form in the column before the beamx To do this we require that the Mn of the cap beam is greater than 1.3

x Mn of the column at a joint.x Also in computing Mn of the column, fy = 1.25 x original value of fy to

account for strain hardeningx Also to prevent the occurrence of shear failure before flexural failure,

the whole pier system must be designed for a lateral shear force which gives a moment equal to 1.3 Mn of the column (with yield strength 1.25fy)


y Designing a pier for ductility. Moment failure must precede shear failure Plastic hinges in the columns and not the beams


y Designing a pier for ductility Longitudinal Forces. Compute EQ forces in the pier Get the dead load on the columns (Use Combination Get corresponding 1.3 Mn for axial load due to dead load Get Shear force at top (Call it Vo), that would produce a

moment in the columns equal to 1.3 Mn

Compare Vo with the EQ forces to get max shear


y Designing a pier for ductility Transverse Forces. 1. Compute EQ forces in the pier2. Get the dead load on the columns (Use Combination 3. Get corresponding 1.3 Mn for axial load for each column due to

dead load4. Get corresponding V that would produce a moment 1.3 Mn for each

column. Add all these Vs to produce Vo5. Using Vo and the dead loads, compute the new axial loads on the

structure.6. Recompute the 1.3Mn for each column given the new axial loads.

Compute the corresponding Vo as per step 57. The recomputed Vo will now be compared with the shear in step 4.

If not within 10% repeat step 3.

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Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey For integral bridges, it is important to

compute the effect of creep, shrinkage and temperature due to secondary effects induced by the fixed ends.y The next slides will illustrate the effect of

secondary stresses on the structure

FYI: Secondary StressesFYI: Secondary Stresses

y Given a Bar with length L with one side with no restraints.y If hotter, bar will expandy If colder, bar will contracty The additional or subtracted length, could be expressed as D 'T L

y Please note that under these conditions, no stress is induced on the bar

FYI: Secondary StressesFYI: Secondary Stresses

y Given a Bar with length L with restraints at both ends.y If hotter, bar cant expand, because of this what kind of stress is induced? Compression!

y If colder, bar cant contract, because of this tension stress is induced at each unit element of the bar

Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey As shown on the previous slides, due to

restraint, there are stresses induced due to creep shrinkage and temperature.y For RC bridges, since we are controlling

tension, the combination with shrinkage and colder temperature will govern the design!

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Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey The major induced deformation loads are

the following

y The magnitude of these forces were not previously given in the standard specifications for bridges (NSCP Vol2 1997)

Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey Uniform Temperature Change (TU) Describes the seasonal change in temperature

for a bridge. Ex: If a bridge in PH was constructed at a

temperature of 30o during summer, TU effects would be large during the cold months like December (say 20o temperatures).

Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey Temperature Gradient

(TG) Due to the difference of

exposure to the elements of the surface and the underside of the bridge, difference in temperature could occur. Common occurrence is

the surface is hotter than the rest of the depth of the bridge or the surface is colder than the rest of the depth.

Hotter at top

Less hot at the bottom

Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey Shrinkage (SH) Shrinkage occurs in concrete and is due to

the loss of moisture. Shrinkage is composed of two partsx Overall Shrinkagex Differential shrinkage for Composite Decks

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Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey Shrinkage (SH) Overall shrinkage is the general shrinkage

being experienced by the section Differential shrinkage occurs due to the

difference in age of concrete in composite members. In the section below, the deck slab would shrink more because it is newer.

Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey Creep (CR) Creep is the additional deformation due to

sustained loading. Since dead load and internal prestress forces

are intended to be there forever, they induce siginificant amount of creep effects.

Chapter 03 Chapter 03 -- Creep, Shrinkage and Creep, Shrinkage and TemperatureTemperaturey Creep (CR) If the ends of a beam are restrained, creep

due to dead load + prestress may induce positive moments at the ends. SECTION HIGHLIGHTS SECTION HIGHLIGHTS

CHAPTER 04: LOADS CHAPTER 04: LOADS AND LOAD FACTORSAND LOAD FACTORS


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y This chapter recommends analysis techniques to be used for bridges.y Things to be discussed: Equivalent Strips for Deck Analysis Distribution Factors for Gravity Loads Dynamic Analysis Specifications for EQ Loads


y Equivalent Strips for deck analysis. It is common for deck slabs to primarily span

in the transverse direction The bridge code specifies the equivalent

width of this strip

Moment Diagram

A A

Section A-A

Gir

der

Gir

der

P

Eq. W

idth


y Equivalent Strips for deck analysis. Equivalent widths as per code


y Distribution Factors approximate the amount of shear and moment that would go to each girder

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Chapter 4Chapter 4

y Common Steps for Moment and Shear1. Get the moment produced by the axle

loads of the truck (note that previously, we use wheel loads for the moment)

2. Multiply the moment by the distribution factor prescribed by the AASHTO code

Live LoadsLive Loads

y Some important terms to note:

Axle Load Wheel Load

Chapter 04 Chapter 04 Distribution FactorsDistribution Factors

y Table of Distribution factors for moment in interior concrete girders.

WhereS = Spacing, mmTs = thickness of slab, mmL = Span, mmNb = number of beamsKg = factor as detailed on the next page

Limitations

Interior


y Factor Kg

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y Table of Distribution factors for Shear in interior concrete girders.

WhereS = Spacing, mmTs = thickness of slab, mmL = Span, mmNb = number of beamsKg = factor as detailed on the next page

Interior


y For exterior girders, the moment and shear is computed by getting the reaction on the exterior girder when the wheel loads are placed 0.6m from the parapet.

0.6m

Chapter 04 Chapter 04 Dynamic AnalysisDynamic Analysisy The latest code requires a different

refinement of analysis depending on the bridge importance.y Before we proceed the following acronyms

are used SM Single Mode UL Uniform load elastic method (simplest

method for EQ loads) MM Multimode Elastic Method (similar to

response spectrum analysis) TH Time History Method

Chapter 04 Chapter 04 Dynamic AnalysisDynamic Analysis

y Requirements as per code for seismic zone 4

Note that TH = time history is required for critical bridges. However, this would most likely be revised due to the lack of a time history record for the Philippines.

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SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 05: CONCRETE CHAPTER 05: CONCRETE STRUCTURESSTRUCTURES


Chapter 05 Chapter 05 Concrete StructuresConcrete Structures

y Provisions for both reinforced and prestressed concrete are now included in this chapter.y Since equations given for this chapter are

common for RC design, only the following will be discussed: Provisions for Crack Control Allowable Stresses for Prestressed Beams Cover Requirements for Reinforcement


y To limit cracking in concrete, the bridge code specifies a minimum amount of spacing which depends on the stress on the steel reinforcement.

Chapter 05 Chapter 05 Concrete StructuresConcrete Structuresy Note that Class 1 exposure is equivalent to

limiting the crack width to 0.43mm. The factor Je can be changed accordingly to the desired crack width. (Ex: a Je = 0.5 corresponds to crack width of 0.22mm.)

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y Recall that there are multiple stages in the design of a prestress concrete girder.These are Transfer Stage Deck is Cast Service Stage


y Transfer Stage Forces


y Deck is Cast


y Service Stage

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y For each stage the bridge code specifies limits on the stresses on the girder. Limits for Compressive Stress at Transfer


y For each stage the bridge code specifies limits on the stresses on the girder. Limits for Tensile Stress at transfer


y For each stage the bridge code specifies limits on the stresses on the girder. Limits for Compressive Stress at Service


y For each stage the bridge code specifies limits on the stresses on the girder. Limits for Tensile Stress at Service

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y For concrete cover, the bridge code recommends the following Min cover to main bars > 25mm Cover to ties and stirrups may be 12mm less

than the ones specified on the table shown on the next slide.


y For concrete cover, the bridge code recommends the following.

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 09: DECKS CHAPTER 09: DECKS AND DECK SYSTEMSAND DECK SYSTEMS


Chapter 09: Deck SlabsChapter 09: Deck Slabs

y For this chapter, only provisions for concrete deck slabs will be discussed.

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y Depth > 175mm unless specified by the bridge owneryWhen deck skew does not exceed 25o,

the transverse reinforcement may be parallel to the skew. Otherwise, it should be perpendicular.


y Skew less than 25o.


y Skew > 25o. Transverse reinforcement now perpendicular to longitudinal.

Skew Angle


y The reinforcement may be designed empirically as long as the following conditions are satisfied Supporting components are made of steel or

concrete The deck is fully cast-in-place and water cured The deck has a uniform depth

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y The reinforcement may be designed empirically as long as the following conditions are satisfied The ratio of effective length to design depth

does not exceed 18 and is not less than 6.0 Core depth of the slab is not less than

100mm


y The reinforcement may be designed empirically as long as the following conditions are satisfied Effective length (s effective) does not exceed

4100mm


y The reinforcement may be designed empirically as long as the following conditions are satisfied There is an overhang beyond the external

girder with a span of 5xSlabThickness. 28 day strength of the deck = 28 MPa Deck is composite with the deck

components. Minimum 4 layers of reinf.


y Minimum reinforcement as per empirical requirements 0.570mm2/mm for steel in bottom layer 0.380mm2/mm for steel in top layer

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y Traditional design It is still permitted to design the slabs as

conventional flexure elements. Distribution reinforcement is recommended

as follows

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 11: CHAPTER 11: ABUTMENTS, PIERS AND ABUTMENTS, PIERS AND WALLSWALLS


Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy This chapter provides the provisions for

earth pressure forces for conventional and MSE-type retaining walls.

Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy This chapter also specifies the capacity of

typical soil nails into soil or concrete.

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Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy Typical checks for conventional retaining

walls are as follows Bearing Resistance Overturning Subsurface Erosion Passive Resistance Sliding

Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy Of particular importance in this chapter is

the appendix regarding Seismic Design of Abutments and Gravity Retaining Structuresy This appendix details the Mononobe Okabe

method for retaining walls.

Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy An illustration of the Mononobe-Okabe

loads for the active wedge

Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy Variables relevant with figure on the

previous slide

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Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy Important things to note from Appendix

of Chapter 11 For nonyielding abutments, it is recommended

to multiply the acceleration coefficient by 1.5

For seismic zone 4 it is recommended to have monolithic/integral abutments to minimize damage

Chapter 11: Abutments, Piers and Chapter 11: Abutments, Piers and WallsWallsy Example of Non-yielding abutments.

w/ Raked Piles w/ Soil Nails

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 13: CHAPTER 13: RAILINGSRAILINGS


Chapter 13: RailingsChapter 13: Railings

y Railings are intended for two things To prevent wayward vehicles from going over

the bridge and protect adjacent property To protect pedestrians from wayward vehicles

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y Railings are intended for the following To prevent wayward vehicles from going over

the bridge and protect adjacent property To protect pedestrians from wayward vehicles Protection of other vehicles near the

collission

Chapter 13: RailingsChapter 13: Railingsy Railings are intended to have different

levels of protection according to the use of the road. Test Level One (TL-1) Areas w/ low speed

and low traffic volume TL-2 Collector roads with favorable site

conditions w/ a small number of heavy vehicles TL-3 Generally acceptable for many high

speed arterial highways w/ favorable site conditions.

Chapter 13: RailingsChapter 13: Railingsy Railings are intended to have different

levels of protection according to the use of the road. TL-4 Generally acceptable for high speed

highways with a mixture of trucks and heavy vehicles TL-5 Similar to TL-4 but with unfavorable

site conditions (Ex: A wayward vehicle may collide with valuable property) TL-6 similar to TL-6 but traffic is expected

to have tanker type trucks


y The height of railing has a requirement depending on the TL level.

TL Height (mm)

1 685

2 685

3 685

4 810

5 1070

6 2290

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Chapter 13: RailingsChapter 13: Railingsy Design forces prescribed for railings are

as follows

SECTION HIGHLIGHTS SECTION HIGHLIGHTS CHAPTER 14: JOINTS CHAPTER 14: JOINTS AND BEARINGSAND BEARINGS


Chapter 14: Joints and BearingsChapter 14: Joints and Bearings

y Though integral bridges are recommended by the latest bridge code, expansion joints are still needed for very long bridges


y Commonly used bearings for expansion joints are Elastomeric Bearing Pads made of rubber.y To add the capacity of Elastomeric

Bearing Pads, they are often reinforced with steel plates as shown below.

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y The following limits govern the design of Elastomeric Bearing Pads Shape Factor Allowable Compressive Stress and Deflection Allowable Shear (Lateral) Deformation Allowable Rotation Stability


y The following limits govern the design of Elastomeric Bearing Pads AASHTO 2007 recommends two methods

named Method A and Method B. For this presentation only excerpts from

Method B will be shown.


y The following limits govern the design of Elastomeric Bearing Pads Properties recommended for bearing pads are

shown below.

Shear Modulus G for each hardness


y The following limits govern the design of Elastomeric Bearing Pads Shape Factorx The shape factor is defined as the ratio of the area

to the side area free to bulge.x Looking at one sample below.

L

W

hriArea

Side Area Free to Bulge=

Note that this is done for each layer for reinforced bearing pads

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y The following limits govern the design of Elastomeric Bearing Pads Compressive stress (allowable values shown

below)

Vs = Service Stress due to total loadVL = Service stress due to live load


y The following limits govern the design of Elastomeric Bearing Pads Compressive deflection (Live load)


y The following limits govern the design of Elastomeric Bearing Pads Compressive deflection (Dead load)


y The following limits govern the design of Elastomeric Bearing Pads Compressive deflection (Strain)

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y The following limits govern the design of Elastomeric Bearing Pads Since stress is non-linear for

reinforced/laminated bearings, the following graphs can also be used to compute strain


y The following limits govern the design of Elastomeric Bearing Pads Allowable shear deformation limit


y The following limits govern the design of Elastomeric Bearing Pads Allowable Rotation for Combined

Compression and rotationx Uplift requirements are satisfied if

n = number of interior layers


y The following limits govern the design of Elastomeric Bearing Pads Allowable Rotation for Combined

Compression and rotationx Bearings subject to shear deformation shall satisfy

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y The following limits govern the design of Elastomeric Bearing Pads Stabilityx Bearings are considered stable if

Where

Design of Reinforced Concrete Design of Reinforced Concrete Bridges as per NSCP 2010 Bridges as per NSCP 2010 VolVol 22THE END! Thank you for listening

By Alden Paul D. Balili, MSCEDLSU-M

asep summit 2012 - balili apd presentation - design of bridges

Documents

bridge design

traffic loads

bridge cross section

prestressed concrete

y transverse direction

direction perpendicular

direction parallel

y longitudinal direction