SESSION 7 Joint Design. ObjectivesObjectives Identify types of joints Determine suitable joint...
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Transcript of SESSION 7 Joint Design. ObjectivesObjectives Identify types of joints Determine suitable joint...
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SESSION 7SESSION 7SESSION 7SESSION 7
Joint Design
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ObjectivesObjectivesObjectivesObjectives
Identify types of joints
Determine suitable joint spacings
Determine load transfer requirements
Develop joint reservoir designs
Define tie bar requirements for longitudinal joints
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Types of JointsTypes of JointsTypes of JointsTypes of Joints
Contraction joint
Construction joint
Expansion joint
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Joint Type?Joint Type?Joint Type?Joint Type?
Construction Joint (transverse or longitudinal)
Butt Joint
SlabThickness
Dowel or Tie Bar
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Joint Type?Joint Type?Joint Type?Joint Type?
Contraction Joint (transverse or longitudinal)
SlabThickness
Dowel Baror Tie Bar
InitialSawcut
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Joint Type?Joint Type?Joint Type?Joint Type?
Expansion Joint
Expansion Joint with Filler Material
SlabThickness
Dowel Bar
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Elements of Joint Elements of Joint DesignDesignElements of Joint Elements of Joint DesignDesign
Transverse joints
Joint spacing
Load transfer design
Sealant reservoir design
Longitudinal joints
Tie bar design
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JPCP Joint SpacingJPCP Joint SpacingJPCP Joint SpacingJPCP Joint Spacing
Short enough to prevent mid-slab cracking
Intricately linked with:
Slab thickness
Base support
Climatic conditions
Generally between 3.6 and 6.1 m (12 and 20 ft)
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Example JointExample JointSpacing GuidelinesSpacing GuidelinesExample JointExample JointSpacing GuidelinesSpacing Guidelines
Wet-Freeze/Dry Freeze
12
14
16
18
20
10 11 12 13 14 15 16Slab Thickness, in
Ma
x.
Jo
int
Sp
aci
ng
, ft
k = 75 psi/in k = 150 psi/in k = 300 psi/in
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Uniformity of Joint Uniformity of Joint SpacingSpacingUniformity of Joint Uniformity of Joint SpacingSpacing
Uniform joint spacing
Joints spaced at fixed intervals
Variable joint spacing
3 or 4 joint spacings in a repeating pattern, e.g., 3.7 - 4.6 - 4.0 - 4.3 m (12 -15 - 13 - 14 ft)
Intended to reduce rhythmic response of vehicles
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Joint OrientationJoint OrientationJoint OrientationJoint Orientation
Perpendicular Joints perpendicular to centerline
Skewed Joints placed at an angle to pavement
centerline (counterclockwise skew) May be beneficial for nondoweled joints Limit skew to minimize corner breaks
(maximum 1:10)
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4.6 m 4.3 m4.0 m3.6 m
Traffic
Traffic
1
10
(12 ft) (15 ft) (13 ft) (14 ft)
Example Variable Example Variable Spacing and Skewed Spacing and Skewed JointsJoints
Example Variable Example Variable Spacing and Skewed Spacing and Skewed JointsJoints
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Skewed JointsSkewed JointsSkewed JointsSkewed Joints
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LoadLoadTransferTransferLoadLoadTransferTransfer
Ability of joint to convey wheel load from one side to the next
Reduces deflections
Reduces pumping, faulting
Methods
Dowels
Aggregate interlock
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WheelLoad
0% Load Transfer
Direction of Traffic
Approach Slab Leave Slab
100% Load Transfer
Approach Slab
Wheel
LoadDirection of Traffic
Leave Slab
Load TransferLoad TransferIllustrationIllustrationLoad TransferLoad TransferIllustrationIllustration
UnloadedLT =
Loaded
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Load TransferLoad TransferRecommendationsRecommendationsLoad TransferLoad TransferRecommendationsRecommendations
Dowels recommended for most highway pavements (slab thickness > 200 mm [8 in])
Minimum 32 mm diameter (38 mm preferred)
Corrosion inhibitor required
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Dowel LayoutDowel LayoutDowel LayoutDowel Layout
Outer Traffic LaneInner Traffic Lane
12 dowels @ 0.3 m (1 ft) center to center
12 dowels @ 0.3 m (1 ft) center to center
Conventional Spacing
TrafficTraffic
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Alternative Dowel Alternative Dowel LayoutLayoutAlternative Dowel Alternative Dowel LayoutLayout
Cluster Spacing
Outer Traffic LaneInner Traffic Lane
5 dowels @ 0.3 m(1 ft) center to center
4 dowels @ 0.3 m(1 ft) center to center
TrafficTraffic
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Joint Sealing and Joint Sealing and Reservoir DesignReservoir DesignJoint Sealing and Joint Sealing and Reservoir DesignReservoir Design
Purposes of joint sealing
Reduce moisture infiltration
Keep out incompressibles
Cost-effectiveness of sealing?
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Consideration FactorsConsideration FactorsConsideration FactorsConsideration Factors
New or rehabilitation design
Climate
Joint design
Base and subgrade type and drainability
Local experience
Others?
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Joint Channel DesignJoint Channel DesignJoint Channel DesignJoint Channel Design
Unsealed joints
Crack control sawcut (3 mm [1/8 in]
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Joint Channel Design Joint Channel Design (continued)(continued)Joint Channel Design Joint Channel Design (continued)(continued)
Sealed joints
Crack control sawcut (3 mm [1/8 in])
Joint reservoir sawcut (typ. 10 to 15 mm [0.4 to 0.6 in] wide)
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ReservoirWidening Cut
Joint Reservoir Joint Reservoir SawcutSawcutJoint Reservoir Joint Reservoir SawcutSawcut
Crack Control Sawcut
Depth of Widening Cut (25 to 38 mm)
(1 to 1.5 in)
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Joint Reservoir DesignJoint Reservoir DesignJoint Reservoir DesignJoint Reservoir Design
Selection of sealant material
Estimation of joint movements
Determination of required joint width
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Sealant MaterialsSealant MaterialsSealant MaterialsSealant Materials
Rubberized asphalt (ASTM D3405)
Silicone
Preformed compression seals
Placed in state of compression
Must be compressed 20 to 50% of normal width over service life
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3 to 6 mm(1/8 to 1/4 in) Recess
Width
Backer
Rod
Depth
Joint ReservoirJoint ReservoirJoint ReservoirJoint Reservoir
Shape Factor = W / D
Joint Sealant
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Compressed Width
Reservoir Depth
Example Example Compression Seal Compression Seal InstallationInstallation
Example Example Compression Seal Compression Seal InstallationInstallation
Preformed Compression
Seal
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Estimating Joint Estimating Joint MovementsMovementsEstimating Joint Estimating Joint MovementsMovements
L = C L ( T + )L = Joint opening, in
C = Adj. factor (0.8 gran. base, 0.65 stab.)
L = Joint spacing, in
= Thermal coef. of expansion (3.8 to
6.6 x 10-6), in/in/oF
T = Temperature range, oF
= Drying shrinkage coefficient (2 to
8 x 10-4), in/in
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Required Joint ReservoirRequired Joint ReservoirRequired Joint ReservoirRequired Joint Reservoir
Hot-poured/silicone sealants
Required joint width
W = L / S
W = Required joint width
L = Joint opening
S = Allowable sealant strain
Required sealant depth
Apply proper shape factors
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Required Joint Reservoir Required Joint Reservoir (continued)(continued)Required Joint Reservoir Required Joint Reservoir (continued)(continued)
Compression seals
Select uncompressed seal width
USW > L / (Cmax - Cmin)
Cmax = 0.5 (typ); Cmin = 0.2 (typ)
Determine width of sawcut
W = (1 - Pc) * USW
Pc = % of compression at installation
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Longitudinal Joint Longitudinal Joint DesignDesignLongitudinal Joint Longitudinal Joint DesignDesign
Contraction (sawed) joints
Between lanes or between lane - shoulder
Adequate sawing depth/timing
Effective tie bar system
Construction (butt) joint
Commonly between lane and shoulder
Effective tie bar system
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Longitudinal Longitudinal Contraction JointContraction JointLongitudinal Longitudinal Contraction JointContraction Joint
D/3 Joint Formed by Sawing
DD/2
Deformed Tie Bar(Minimum No. 5 Bar)
Mainline Pavement
Mainline Pavement or PCC Shoulder
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Longitudinal Longitudinal Construction JointConstruction JointLongitudinal Longitudinal Construction JointConstruction Joint
D
D/2
Deformed Tie Bar(Minimum No. 5 Bar)
Butt Joint
Possible Key Way
PCC Shoulder
Mainline Pavement
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SummarySummarySummarySummary
Joint types Joint spacing guidelines Load transfer recommendations Joint sealant system Longitudinal joint requirements