concrete roundabout design and construction · concrete roundabout design and construction indiana...

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? Concrete Roundabout Design And 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)

Why Concrete Roundabouts?

Concrete is the perfect material for roundabout applications.

THICKNESS DESIGN Design and Jointing of Concrete Roundabouts

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!!

http://www.pavement.com/streetpave/

Concrete Intersections: Thickness

Physical Area

Functional Area

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 ROUNDABOUTS Concrete Roundabout Design And Construction

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)

Layout Joints as Normal

Good for small roundabouts or traffic circles?

Proper Jointing of Roundabouts

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

6-STEP METHOD FOR JOINTING ROUNDABOUTS

Concrete Roundabout Design And Construction

Jointing a Roundabout

Step 1: Draw all pavement edges and back-of-curb lines in plan view.


Step 2: Draw all lane lines on the legs and in the circular portion, accounting for roundabout type.


Step 3: Add “transverse” joints in the circle, being mindful of the maximum joint spacing.


Step 4: On the legs, add transverse joints where width changes occur.


Step 5: Add transverse joints between those added in Step 4, minding the maximum joint spacing.

Doglegs

Layout Joints as Normal

Good for small roundabouts or traffic circles?


Step 5: Add transverse joints between those added in Step 4, minding the maximum joint spacing.


Step 6: Make adjustments for in-pavement objects, fixtures, and to eliminate odd shaped slabs.

…And Box Out Fixtures Properly!

If You DO Box Out Properly…

If You DON’T Box Out Properly…

Good Practice…

What If I Have to Dead-end a Joint?

EXAMPLE IN KANSAS Concrete Roundabout Design And Construction

110th Street & Lamar Avenue Overland Park, Kansas

Rough Grading

Grading of Subgrade

Subbase & Curb Const.

Curb Placement – Widened Gutter

Field Joint Layout Plan

Inner Pavement Ring Formed

Dowel Basket Placement

Start Concrete Placement

Hand Placement with Roller Screed

Hand Finishing

Half Way Done!

Outer Ring…

1 inch Isolation Joint

Approach Lanes…

Approach Lane Sequence

Finishing Approach Lanes

Open to Traffic!

Properly Jointed Roundabout

Another Kansas Example…

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…

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