rigid pavement design details - urban engineers, inc.knowledge.urbanengineers.com/assets/session 07...
TRANSCRIPT
David Peshkin, P.E.Vice PresidentApplied Pavement Technology, [email protected]
Rigid Pavement Design Details
Session Overview• Joint considerations
– Joint types and details– Joint spacing and layout– Joint load transfer– Joint sealant and reservoir
• Reinforcement
Joint Considerations• Concrete expands and contracts• Concrete curls and warps
And as any PCC paving contractor will tell you, “concrete cracks”
Joint Types and DetailsThree general joint types
• Isolation Joints– Type A – Thickened Edge
• Contraction Joints– Type B – Hinged– Type C – Doweled– Type D – Dummy
• Construction Joints– Type E – Doweled
Isolation Joints• Sometimes referred to as “expansion joints”• Used to isolate structures with different
movement• Pavements from fixed structures• Pavements from pavements
• Also consider thickened edge for future expansion
• Isolation joints are not doweled or tied to surrounding pavement!
Thickened EdgeIsolation Joint Detail
Reinforced IsolationJoint Detail
Isolation Joint Sealant Detail
Contraction Joints• Provide “controlled” cracking of
pavement• Reduce slab stresses
Contraction Joints (continued)
Contraction Joints (continued)
Construction Joints• Used at end of day’s paving or
between paving lanes• Required when two adjacent slabs are
constructed at different times• Tie slabs together rather than isolate
Construction Joints
Beveled Joints• Intended to reduce chipping and spalling
attributed to snow plows• May also be used where joint fraying or
sliver spalls are common
Joint Spacing• Function of slab thickness, stiffness of
support, and other factors• Generally 12.5 to 25 ft• Length-to-width ratio < 1.25• FAA study found better performance on
20-ft slabs compared to 25-ft slabs• ACPA recommendations
– 25-ft maximum for granular base– 20-ft maximum for stabilized base
Radius of Relative Stiffness
( )41
2
3
112 ⎟⎟⎠
⎞⎜⎜⎝
⎛−
=ku
Ehl
l = radius of relative stiffness, inchesE = PCC elastic modulus (typically 4,000,000 psi)h = slab thickness, inchesu = Poisson’s ratio for PCC (typically 0.15)k = modulus of subgrade reaction, psi/in
Keep L/l between 4 and 6
Joint Spacing Limits
1.0
2.0
3.0
4.0
5.0
6.0
7.0
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Joint spacing
L/l
ratio
Thickness = 12 inchesThickness = 13 inchesThickness = 14 inchesThickness = 15 inchesThickness = 16 inchesThickness = 17 inchesThickness = 18 inchesThickness = 19 inches
k = 500 psi/inE = 4,000,000 psi
Joint Spacing Limits
1.0
2.0
3.0
4.0
5.0
6.0
7.0
5 10 15 20 25Slab Size, ft
L/l r
atio
k=700
k=500
k=300
Notes:1.Transverse and longitudinal joint spacing.2.For typical runway and taxiway geometries, the corresponding longitudinal joint spacing is 18.75 ft. (5.7 m).
- Joint spacings shown in this table are maximum values that may be acceptable under ideal conditions.- Smaller joint spacings should be used if indicated by past experience - Pavements subject to extreme seasonal temperature differentials or extreme temperature differentials during
placement may require shorter joint spacings.
Joint SpacingTable 3-16. Recommended Maximum Joint Spacing
6.120>229>9
4.615165-2296.5-9
3.812.51526
MetersFeetMillimetersInches
Joint Spacing1Slab Thickness
Part I, without Stabilized Subbase
6.120>406>165.3217.52343-40613.5-164.615267-33010.5-13
3.812.5203-2548–10MetersFeetMillimetersInches
Joint Spacing1Slab ThicknessPart II, with Stabilized Subbase
Joint Layout• Maintain standard size slabs• Minimize odd-shaped slabs (intersections
and fillets)• Saw joints perpendicular to slab edges• Steel reinforcement in odd shaped slabs
Joint Layout
Fillet Construction (Option 1)
Fillet Construction (Option 2)
δL = 20 mils(Loaded)
0% Load transfer
100% Load transfer
δU = 0 mils(Unloaded)
δL = 10 mils(Loaded)
δU = 10 mils(Unloaded)
Joint Load Transfer
• Purpose• Methods• Measurement of Load
Transfer Efficiency
100×=loaded
unloadedLTEδδ
To Dowel or Not to Dowel• Doweled joints
– All construction joints– Within three joints of free edge
• Undoweled joints– Transverse contraction joints
• Tied joints– Intermediate (sawed) longitudinal joints
• Alternative: dowel all joints
Dowel Details• Dowel diameter, length, and spacing a
function of slab thickness and shearing and bending stresses
• Stress on concrete should not cause failure of slab
• Proper performance requires proper construction
Table 3-17 from 5320-6E
18 in24 in2 in21 to 24 in18 in20 in1 ½ in17 to 20 in15 in20 in1 ¼ in13 to 16 in12 in19 in1 in8 to 12 in12 in18 in¾ in6 to 7 in
Dowel SpacingDowel LengthDowel Diameter1Slab Thickness
1 Dowels may be solid bar or high-strength pipe. High-strength pipe dowels must be plugged on each end with a tight-fitting plastic cap or mortar mix.
Dowel Bars at Slab Corners• Issue: spacing pattern at joint intersection can
lock joint
Tie Bars• Used at longitudinal contraction joints• Inhibit instead of allow movement• Allows load transfer by aggregate interlock• Common use is #5 (5/8 in) deformed bars,
30 in long on 30-in centers• Do not tie together more than 75 ft
Jointing Arrangement
Joint Sealant• All joints sealed• Sealant types
– Hot-poured– Silicone– Preformed– Fuel resistant sealants– Jet blast resistant sealants
Joint Seal Details
Joint Seal Details
Reinforcement• Purpose• Types• Use for
– Odd shaped slabs– Where L:W exceeds 1.25
• Jointed reinforced concrete pavements (JRCP)
• Continuously reinforced concrete pavements (CRCP)
Reinforcement does not increase strength!
Purpose• Does not prevent cracking• Keeps cracks that form tightly closed• Maintains joint interlock• Minimizes infiltration of debris• Allows longer joint spacing/fewer joints
Types• Welded wire fabric or bar mats
• End laps• Minimum of 12 inches, but not < 30 times the
diameter of reinforcement• Side laps
• Minimum of 6 inches, but not < 20 times the diameter of reinforcement
• Side and end clearance• Maximum of 6 inches and minimum of 2 inches
to allow for adequate concrete cover
Spacing• Longitudinal
• Not less than 4 inches nor more than 12 inches apart
• Transverse• Not less than 4 inches nor more than 24
inches apart
Odd-Shaped Slabs• Amount of steel
• 0.050 percent steel in both directions• When L:W exceeds 1.25
• Location• Per the spacing guidelines, but enough to
fulfill the area of steel requirement
Amount of Steel
where:
As = area of steel per foot of width or length, square inches
Ps = percentage of steel based on length of slab, %
L = length or width of slab, feet
t = thickness of slab, inches
fs = allowable tensile stress in steel, psi
ss
fLtLA )7.3(
=s
sft
LLP
8.30(%) =
Minimum percentage of embedded steel is 0.05 percent!
Table 3-18 from 5320-6E
Based on current specifications and accounting for 2/3 of the yield strength of the steel to calculate the fs.
Table 3-19 from 5320-6E
Table 3-20 from 5320-6E
Welded Wire Fabric• Use of smooth or deformed wire is option
of designer• Minimum sizes
• Transverse: not < W4 or D4• Longitudinal: not < W5 or D5
• Minimum area should not be < 0.05 %
JRCP• Steel contents typically 0.15 to 0.20% of
cross sectional area• Can use up to maximum 75 feet joint
spacing with load transfer• Use spacing details shown in Figure 3-11
Figure 3-11 from 5320-6E
CRCP• Steel contents typically 0.6 to 0.7% of
cross sectional area• Eliminates transverse joints• Develops transverse cracks every 2 to
10 feet• Continuous reinforcement keeps cracks
tightly closed
CRCP Design• Foundation requirements per rigid design• Thickness requirements same as plain
PCC• Transverse Steel Design
• Located either above or below longitudinal steel but must have a minimum of 3 inches cover
• Spacing at 12 inches or greater
CRCP Design (continued)• Longitudinal Steel Design
• Resist subgrade restraint• Resist temperature effects• Concrete to steel strength ratio• Located mid-depth of slab or above• Spacing every 6 to 12 inches• Overlap greater of 25 bar diameters or 16
inches
Steel to Resist Subgrade Restraint
where:
Ps = percentage of embedded steel, %
F = friction factor of subgrade
ft = tensile strength of concrete, psi
fs = allowable working stress in steel, psi
s
ts
ffFP )2.03.1((%) −=
Recommended friction factor is 1.8Recommended fs is 75 percent of specified minimum yield strengthft may be estimated at 67 percent of concrete flexural strength
Steel to Resist Temperature Effects
where:
Ps = percentage of embedded steel, %
T = maximum seasonal temperature differential for pavement, °F
ft = tensile strength of concrete, psi
fs = allowable working stress in steel, psi
TffP
s
ts
19550(%)−
=
Recommended fs is 75 percent of specified minimum yield strengthft may be estimated at 67 percent of concrete flexural strength
Concrete to Steel Strength Ratio
where:
Ps = percentage of embedded steel, %
ft = tensile strength of concrete, psi
fy = minimum yield strength of steel, psi
y
ts
ffP 100(%) =
Transverse Steel Design
where:
Ps = percentage of embedded steel, %
fs = allowable working stress in steel, psi
Ws = width of slab, feet
F = friction factor of subgrade
1002
(%)s
ss
fFWP =
Recommended fs is 75 percent of yield strength
CRCP Jointing• Construction joints
• Longitudinal joints between paving lanes• Transverse construction joints between
paving days• Warping joints
• See Figures 3-12 and 3-13
Figure 3-12 from 5320-6E
Figure 3-13 from 5320-6E
CRCP Terminal Treatment• Needed when CRCP meets other
pavements or structures• End movements can be expected around
2 inches• Allows ends to expand and contract• Figure 3-14 shows the detail with a
flange beam
Figure 3-14 from 5320-6E
Summary• Many other features to consider in FAA
design besides thickness• All components need to be considered
together
Questions?