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Concrete Roundabout Design And Construction
Indiana Concrete Pavement Workshop
February 27, 2015
Eric Ferrebee American Concrete Pavement Association
Technical Services Engineer
Why a Roundabout?
According to FHWA: Up to 90% reduction in fatalities 76% reduction in injury crashes 30-40% reduction in pedestrian crashes 75% fewer conflict points than 4-way intersections 30-50% increase in traffic capacity No signal equipment to install/maintain No left-turn lane and reduced need for storage lanes
Design of Concrete Roundabouts
Thickness Design Joint Design
Layout Locations Allow Adjustment in the Field
Construction
Why Concrete Roundabouts?
Let’s ask a couple questions… 1. Where do we historically use concrete pavement?
(situations, traffic conditions, applications, etc.) 2. What performance characteristics of concrete
pavement make it the best choice for roundabouts?
Where are Concrete Pavements Historically Used?
Answers: High traffic areas Areas with lots of turning movements Situations where we need a “long-term fix” Situations where future maintenance must be kept to an absolute minimum Areas where future disruption to traffic must be kept to a minimum Areas where safety is a priority
Why Concrete for Roundabouts?
Answers: Long service life Minimal maintenance requirements Resistance to surface deformation
Doesn’t rut or shove Maintains surface/drainage characteristics No future overlays required (grade issues)
Ease of construction (constructability) Roundabouts typically hand placed but some have been constructed with slipform paving machines
Why Concrete (cont.)
Answers: Superior safety aspects
Drainage Skid resistance Lighting
More aesthetically pleasing Faster construction Economical over long-term (LCC)
Pavement Thickness Design
AASHTO 1993 Pavement Design Guide
Most commonly used by state DOTs
Pavement ME Design (MEPDG) Under calibration/implementation in many states
ACPA (PCA) StreetPave software: http://www.pavement.com/streetpave/
MUST CONSIDER CUMULATIVE TRAFFIC!!
Concrete Intersections: Thickness
Physical Area Functional Area
Low ADTT (T1)
Low ADTT (T1)
High ADTT (T3)
T2
T3
T3 + 0.5 to 1 in.
Physical Area Thickness Roadway 1
Low ADTT (T2)
High ADTT (T3)
High ADTT (T3)
Roadway 2
T3>T2>T1
Jointing
Decide on joint layout philosophy Like normal intersection Isolate circle from legs Pave-through, isolate two legs Other philosophy, based on experience
Follow 6-step method Joints in circular portion radiate from center Joints in legs are normal (perpendicular)
Concrete Roundabout Jointing
Develop a jointing plan Bird’s eye view
Remember rules Follow the steps Be practical!
Rules for Joint Layout
Things to Do Match existing joints or cracks – location AND type! Cut joints at the proper time Place joints to meet in-pavement structures Remember maximum joint spacing Place isolation joints where needed Understand that joint locations can be adjusted in the field! Be Practical
Type Location
Rules for Joint Layout
Things to Avoid: Slabs < 2 ft wide Slabs > 15 ft wide Angles < 60º (90º is best)
Dog-leg joints through curve radius points
Creating interior corners Odd Shapes (keep slabs near-square or pie-shaped)
Recommended Maximum Joint Spacing
ML = T x Cs ML = Maximum length between joints (in.) T = Slab thickness (in.) Cs = Support constant Use 24 for subgrades or unstabilized [granular] subbases; Use 21 for stabilized subbases (ATB, CTB, lean concrete) or existing
concrete or asphalt pavement; Use 12 to 15 for thin bonded overlays on asphalt
Joint Spacing Recommendations
For Streets, Roads, and Highways: Use ML = T x Cs
Keep ratio of transverse to longitudinal spacing at less than 1.5 Keep maximum spacing of transverse joints to 15 ft for plain concrete unless local history shows longer panels work
What About Load Transfer?
Aggregate Interlock Maximum aggregate size is important
Mechanical connection Dowel bars Tiebars
Subbase support
Dowel Bar Recommendations
Pavement Thickness Dowel Diameter Less than 7.0 in. None 7.0 – 7.9 in. 1 in. 8.0 – 9.9 in. 1-1/4 in. Greater than 10.0 in. 1-1/2 in.
www.pavement.com/dowelcad
Jointing a Roundabout
Step 2: Draw all lane lines on the legs and in the circular portion, accounting for roundabout type.
Jointing a Roundabout
Step 3: Add “transverse” joints in the circle, being mindful of the maximum joint spacing.
Jointing a Roundabout
Step 5: Add transverse joints between those added in Step 4, minding the maximum joint spacing.
Jointing a Roundabout
Step 5: Add transverse joints between those added in Step 4, minding the maximum joint spacing.
Jointing a Roundabout
Step 6: Make adjustments for in-pavement objects, fixtures, and to eliminate odd shaped slabs.
More Information?
“Concrete Pavement Field Reference: Prepaving,” EB237P, ACPA, 2007. “Concrete Roundabouts: Rigid Pavement Well-Suited to Increasingly Popular Intersection Type, “ R&T Update #6.03, ACPA, June 2005. “Roundabouts: An Informational Guide,” FHWA-RD-00-068, FHWA, March 2000. “Kansas Roundabout Guide”: http://www.ksdot.org/burTrafficEng/Roundabouts/Roundabout_Guide/RoundaboutGuide.asp Various agency standards…KS, WI, IA, OH, etc…
Thank you. Questions?
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Eric Ferrebee Technical Services Engineer
American Concrete Pavement Association [email protected] | 847.423.8709