31-bridgedesign (1)

8/3/2019 31-bridgedesign (1)

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Part 1

Introduction To Bridge Design


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How Do Bridge Engineers Decide

On What Type Of Bridge To Build?

Bridge Survey flood plain cross sections

inspection reports

existing bridge (scour, etc)

water elevations

photos

existing roadway profile

Geotechnical Report

soil / geological formations

slopes and grading

foundation problemssoil prop.s - phi angles etc

Factors affecting choice of superstructure location, city or rural

span length

vertical clearance

maintainability

environmental concerns transportation to site issues

cost

Factors affecting choice of substructure

location and geometry

subsoil conditions

height of column


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Bridge Design Process

Preliminary Design Process

Bridge Survey Geotechnical Report

1. Determine the most

economical type structure and

span arrangement

2. Hydraulic Analysis3. Preliminary Cost Estimate

4. Foundation Borings

5. Determine Foundation Type

Final Design Process

Top to Bottom Design (twice) Design methods per AASHTO and

MoDOT Bridge Manual

Analysis via

computations

spreadsheetscomputer programs

Detail plans are produced by technicians

(Micro-Station)

Plans are checked

Quantities computed

Special Provisions written

Plans are advertised for bidding

Low Bid Contractor builds the bridge


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Types of Superstructures

Bridges are often referred to by their superstructure types.

The superstructure system of members carry the roadway over a crossing

and transfer load to a substructure.

Superstructures are categorized by;

Support type (simply supported or continuous)

Design type (slab on stringer, slab, arch. Rigid frame, etc) Material type (steel, concrete, timber)


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Slab on Stringer Bridges

Most common type of bridge in Missouri. Consist of a deck, resting on the girders. The deck distributes the

loads transversely to the girders.

The girders carry the loads longitudinally (down the length of the

bridge) to the supports, (abutments and intermediate bents).

Concrete

Deck Girder

Prestressed I Girder Prestressed Double Tee

Prestressed Box

Steel

Plate Girder

Wide Flange

Steel Box Girder


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I - GIRDER

BULB TEE

Prestressed Girders


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Prestressed Concrete I-Girder


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Prestressed Concrete I-Girder Bridge


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Prestressed Concrete Panels


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Prestressed Double Tee Girders


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Steel Plate Girder / Wide Flange Beam / Box Beam


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Steel Plate Girder Bridge


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Slab Bridges

In slab bridges the deck itself is the structural frame or the entire deck is a thin

beam acting entirely as one primary member. These types are used wheredepth of structure is a critical factor.

Typical Slab Bridges : Concrete Box Culverts Solid Slabs Voided Slabs


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Triple Box Culvert


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Voided Slab Bridge


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Solid Slab

Voided Slab Bridge


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Substructures

The substructure transfers the superstructure loads to the foundations.

End Abutments

Integral Abutment - girders on beam supported by piles, girders concreted into the

diaphragm

Non-Integral Abutment - diaphragms of steel cross-frames, uses expansion devices

Semi-Deep Abutment - used when spanning divided highways to help shorten span

Open C.C. Abutment - beam supported by columns and footings, rarely used

Intermediate bents

Open Concrete Bent - beams supported by columns and footings (or drilled shafts)

either a concrete diaphragm (Pre-Stressed Girder) or steel diaphragm (Plate Girder)

This is the most common type of Pier MoDOT uses.

Pile Cap Bent - beams supported by piling (HP or C.I.P.) and are used when the

column height is less than 15 feet and usually in rural areas. Hammer Head Bent - single oval or rectangular column and footing.

Spread footings - are used when rock or soil can support the structure.

Pile footings - rectangular c.c. supported by HP or Cast in Place piles

Drilled Shafts - holes drilled into bedrock filled with concrete


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Integral End Abutment


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Semi-Deep End Abutment


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Prestressed I-girder intermediate bent


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Steel girders with open intermediate

bent diaphragms


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Footing

Pile Cap Column Footing


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Column Footing


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Preliminary Design

Bridge location

Hydraulic design to determine required

bridge length and profile grade

Bridge type selection


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Stream Gage Data


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Flood-Frequency Rating Curve

0

40000

80000

120000

160000

0 20 40 60 80 100

Return period (years)

Discharge(cfs)


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Q = discharge (cfs or m3/s)

kc = constant (1.0 for English units or0.00278 for metric units)

C= Runoff Coefficient

I= Rainfall Intensity (in/hr or mm/hr)

A = Drainage Area (acres or hectares)

Rational Method

AICkQc


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Drainage Area Delineation


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n1 n2 n3

LeftOverbank

RightOverbank

Channel

Stream Valley Cross-sections


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Mannings Equation

0

32486.1

SRAn

Q

n = Roughness Coefficient

A = Area

R = Hydraulic Radius = A / P

P = Wetted Perimeter

S = Hydraulic Gradient (channel slope)


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n1 n2 n3

LeftOverbank

RightOverbank

Channel

Stream Valley Cross-sections


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Energy Equation

Elevation

1 2

Datum

Elevation

Pressure

Pressure

Velocity

Velocity

HeadlossEGL

HGL

z1

z2

y1

y2

V12/2g

V22/2g

hl

lhg

Vyz

g

Vyz

22

2

2

22

2

1

11


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Constriction of Valley by Bridge

Opening Length

Bridge Deck/Roadway


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Encroachment by Roadway Fill

Flood elevationbefore encroachmenton floodplain

Fill Fill

Bridge Opening Encroachment

Backwater

Encroachment


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Backwater

Normal WaterSurface

Water Surface through Structure

Affect of Bridge on Flood

ElevationsDesign High WaterSurface (DHW)


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Part 2

Slab Design


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Geometry & Loads

16k 16k

Deck Weight = Width x Thickness x Unit Weight

1 ft x (8.5in x12 in/ft) x 150 lb/cf = 106 lb/ft


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Design Moment

MDL1 = wS2/10 = 0.106 x 82/ 10 = 0.678

MDL2 = wS2/10 = 0.035 x 82/ 10 = 0.224

MLL = 0.8(S+2)P/32 = 0.8(8+2)(16)/32 = 4

MImp = 30% x MLL = 1.2

Mu

= 1.3[0.678+0.224+1.67(4+1.2)] = 12.4

Design For 12.4 k-ft/ft


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Statics, Moment, Shear, Stress?


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Reinforced Concrete Design

Basic Equations For Moment Utilize Whitney

Stress Block Concept

Design Moment = Capacity

12.4 k-ft/ft = fAsfy(d-a/2) f= 0.90

Compression = Tension

0.85fcba = Asfy

Two Simultaneous Equations, Two Unknowns (a & As)

d

c

Comp.

Tens.

c = a /b1


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Reinforced Concrete Design

(0.85)(4ksi)(12in)(a)=(As)(60ksi) a=1.47As

12.4k-ft=(0.9)(As)(60ksi)(6in-1.47As/2)/(12in/ft)

12.4=27As-3.31As2

ax2+bx+c=0 a=3.31, b=-27, c=12.4, x=As

As = [-b - (b2 - 4ac)1/2]/2a

As = [-27 - ((-27)2-(4)(3.31)(12.4))1/2]/[(2)(3.31)]

As = 0.49 in2/ft

5/8 rebar at 7.5 in centersd

c

Comp.

Tens.

c = a /b1


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Part 3

Steel Beam Design


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Simple Span Beam50 ft span


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Dead Load = Beam Weight + Deck Weight


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Live Load = HS20 Truck x Distribution Factor

Distribution Factor = S/5.5


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Design Moment = 2358 kip-ft


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Design Shear = 214 kips

S l Gi d D i


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Steel Girder Design Design Moment = 2358 k-ft

Design Shear = 214 kips

Limit Bending Stress

Due To Moment

Limit Shear Stress

Due to Shear


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Gi d D i


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Girder Design

Moment Of Inertia (I)

1/12bh3+Ad2

Parallel Axis Theorem

Section Modulus = S = I/c

Stress = Moment/Section Modulus (M/S)

For Strength DesignLimit Stress to Fy

Find Shape With S > M/Fy

S > (2358k-ft)(12in/ft)/50ksi = 566 in3

A W36x170 Provides 580 in3


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Part 4

Intermediate Bent Design


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Load Cases

Permanent Loads:

DD = Downdrag

DC = Dead LoadComponent

DW = Dead Load

Wearing Surface

EH = Horizontal Earth ES = Earth Surcharge

EV = Vertical Earth

EL = Locked In Forces

Transient Loads:

SE = Settlement

BR = Braking CE = Centrifugal Force

CT = Vehicular

Collision

CV = Vessel Collision EQ = Earthquake

IC = Ice Load

FR = Friction


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Load Cases (Cont.)

Transient Loads:

LL = Live Load

IM = Dynamic Load LS = Live Load

Surcharge

PL = Pedestrian Load

WL = Wind On LiveLoad

WS = Wind On

Structure

Transient Loads:

TG = Temperature

Gradient

TU = Uniform

Temperature

CR = Creep

SH = Shrinkage WA = Water Load


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Load Combinations

Load Combination

Limit State

DC

DD

DW

EH

EV

ES

EL

LL

IM

CE

BR

PL

LS WA WS WL FR

TU

CR

SH TG SE

Use One of These at a Time

EQ IC CT CV

STRENGTH I

(unless noted)gp 1.75 1.00 -- -- 1.00 0.50/1.20 gTG gSE -- -- -- --

STRENGTH II gp 1.35 1.00 -- -- 1.00 0.50/1.20 gTG gSE -- -- -- --STRENGTH III gp -- 1.00 1.40 -- 1.00 0.50/1.20 gTG gSE -- -- -- --STRENGTH IV gp -- 1.00 -- -- 1.00 0.50/1.20 -- -- -- -- -- --STRENGTH V gp 1.35 1.00 0.40 1.0 1.00 0.50/1.20 gTG gSE -- -- -- --EXTREME EVENT I gp gEQ 1.00 -- -- 1.00 -- -- -- 1.00 -- -- --EXTREME EVENT II gp 0.50 1.00 -- -- 1.00 -- -- -- -- 1.00 1.00 1.00SERVICE I 1.00 1.00 1.00 0.30 1.0 1.00 0.50/1.20 gTG gSE -- -- -- --SERVICE II 1.00 1.30 1.00 -- -- 1.00 0.50/1.20 -- -- -- -- -- --

SERVICE III 1.00 0.80 1.00 -- -- 1.00 0.50/1.20 gTG gSE -- -- -- --SERVIE IV 1.00 -- 1.00 0.70 -- 1.00 0.50/1.20 -- 1.0 -- -- -- --

FATIGUELL, IM &

CE ONLY-- 0.75 -- -- -- -- -- -- -- -- -- -- --


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Water (WA)Strength

M = (Pbh)(h)= Pbh2

h

Resultant

P

ContractionS

cour

100year

PierSco

ur

100yea

r

Q100

b

M


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Water (WA) - Extreme Event

(Cont.)

(b)1000

0.7VForce2

ContractionScou

r

500year

PierScour

500year

Q500

b

B

A (B)1000

0.5VForce2

A = Of Water Depth 10

B = Sum Of Adjacent Span Length 45

Drift Mat

Pressure = CDV2/1000

CD=0.7

CD=0.5


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Wind on Structure (WS)

P(WS)Vert.

W

W

P(WS)Trans. HH

P(WS)Long.

PSub.

PVert. = (20psf)(W)(L)PTrans. = (50psf)(H)(L)

PLong. = (12psf)(H)(LT)(%)

PSub. = (40psf)(b)

L = Tributary Length

LT = Total Bridge Length

% = Long. Distribution %

b = Column Or Cap Width


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Wind on Live Load (WL)PTrans. = (100plf)(L)

PLong. = (40plf)(LT)(%)

L = Tributary Length

LT = Total Bridge Length

% = Long. Distribution %

P(WL)Trans.P(WL)Long.

6


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Int. Bent Analysis


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Cap Beam - Strength Limit State

Basic Equations For Moment Utilize Whitney

Stress Block Concept

fMn

= fAs

fy

(d-a/2)

f= 0.90

de

c

Comp.

Tens.

c = a /b1


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Cap BeamService Limit State Crack Control

dc = Concrete Cover To Center Of Closest Bar fs = Service Tensile Stress In Reinforcement

h = Overall Section Thickness

ge= 1.00 For Class 1 Exposure (Crack Width = 0.017)= 0.75 For Class 2 Exposure (Crack Width = 0.013)

)d0.7(h

d1

c

cs

2dc700sss

e f

g


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Cap Beam Service Limit State

Crack Control Is Based On A Physical Model

x

h dc

fc1

fc2

fs/n

l lCrackSpacing

Primary TensionReinforcement

fc1

fc2

fs/n

fc1

fc2

fs/n

l= =16.03

s s

22c2

sd2

dc


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Simplified Shear Design

LRFD

fVn = f(Vc + Vs + Vp)(kips) f= 0.90

a Set At 90 Set: b=2.0, q =45

Results In:

vvcc db'0.0316V f s

)sincot(cotdA

Vvyv

s

a

f

LbsToConvertTo1000ByMultiply V c

vvcc db'2.00V fs

dAV

vyv

s

f

0.0

Si lif d Sh i


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Simplifed Shear Design

Section A-A

5-#6s

(E

achFace)

6 - #9s

6 - #9s

#5s @

12 or 6A

A

-400

-200

0

200

400


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Column Design

Column42 Diameter

-1000

3500P (kip)

(P max)

(P min)

1800

M (k-ft)

Controlling Point

Axial Load Moment Interaction Diagram

18-#9 Bars

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31-bridgedesign (1)