SESSION 10 Special Design Considerations for Reinforced Concrete Pavements

ObjectivesObjectives  Identify design and construction aspects unique to reinforced pavements  Define reinforced pavement joint types  Describe the amount and type of reinforcement used in JRCP and CRCP

IntroductionIntroduction  JRCP designs  Jointed pavements  Longer joint spacing  Distributed steel in slabs ( %)  CRCP  No transverse contraction joints  Heavy longitudinal steel carried through the pavement ( %)

JRCPJRCP PLAN VIEW 7.6 to 18.3 m (typ) (25 to 60 ft) Transverse Joints (with dowels) Welded Wire Fabric Reinforcing Longitudinal Joint (with tiebars)

CRCPCRCP PLAN VIEW Typical Crack Spacing (0.9 to 2.4 m) (3 to 8 ft) Longitudinal Joint (with tiebars) Continuous Longitudinal Reinforcement (Deformed Bars)

Special Considerations — Foundation  Subgrade characterization  Same as JPCP  Drainage and base type  JRCP: same as JPCP  CRCP: uniform base support  CRCP: approach use of permeable base with caution

Special Considerations — Thickness  Thickness design not differentiated by pavement type  Applicability of current procedures to reinforced pavements  1998 AASHTO supplement design:  Use 9 m (30 ft) joint spacing for JRCP  Assume 4.6 m (15 ft) joint spacing for CRCP (for design purposes only)

Special Considerations — Joints  JRCP contraction joints  Maximum spacings of 9.1 to 13.7 m (30 to 45 ft)  Doweled  Properly designed reservoir

Special Considerations — Joints (continued)  CRCP  No transverse contraction joints  Construction joints  Terminal joints äLug anchors äWide Flange (WF) steel beam

Lug Anchor Side View Six No. 5 Bars No. 5 Bars at longitudinal steel spacing 2 ft 3 ft (min) Permissible Raised Key Construction Joint

Wide Flange Steel Beam Side View No in c-c Sleeper Slab Beam Stiffener WF Steel Beam 10 in 1 in Expansion Joint Material 10 ft No. 5 8 in c-c No. 5 6 in c-c

Special Considerations — JRCP Reinforcement  JRCP longitudinal steel reinforcing  Holds cracks tightly together  Deformed welded wire fabric (WWF) or deformed bars recommended  0.19% minimum steel content

JRCP Steel Design  JRCP steel design often based on “subgrade drag” theory  “Subgrade Drag” theory considers:  Friction between slab and base  Slab length  Working stress in steel

Key Factors for JRCP Steel Design  In addition to “subgrade drag” factors, other research suggests:  Expected crack widths  Traffic loadings  PCC/steel thermal properties  Fatigue characteristics of steel

Typical JRCP Steel Layout Longitudinal wires or bars on 152-mm (6 -in) centers (typical) Transverse wires or bars on 305- m m (12 -in) centers (typical) Traffic

Special Considerations — CRCP Reinforcement  CRCP longitudinal steel reinforcing  Induce the formation of transverse cracks at desired intervals and hold those cracks tight  Only deformed bars  Minimum 0.6% steel recommended  For thick slabs, some agencies have used double layers of steel

AASHTO CRCP Steel Design  Determines recommended steel content assuming a given bar diameter  Design criteria:  Crack spacing between 0.9 and 2.4 m (3 to 8 ft)  Crack width < 1 mm (0.04 in)  Steel stress < 75% of ultimate tensile strength

Typical CRCP Steel Layout Deformed longitudinal bars on 127 to 203 mm (5 to 8 in) centers Optional deformed transverse bars on 610 to 1220 mm (24 to 48 in) centers Traffic

Special Considerations — Transverse Reinforcement  Intended for control of longitudinal cracking  Generally included for JRCP because of use of WWF  Often used on CRCP as a means of facilitating longitudinal steel placement

Special Considerations — Shoulders  Transverse joints in shoulder match those of pavement  Jointed PCC shoulders or ramps adjacent to CRCP can be problematic

Special Considerations — Construction  JRCP steel  Placed between lifts or vibrated into fresh concrete  CRCP steel  Placed on chairs or placed using tube feeders (chairs more precise position)  Stagger steel splices  Minimum 64 mm (2.5 in ) cover

CRCP Steel Placement

Longitudinal Steel Laps Outside Pavement Edge PLAN VIEW Lap Spacing of Longitudinal Bars

SummarySummary Foundation DESIGN ITEM TREATMENT IN REINFORCED PAVEMENTS Same Slab ThicknessSame Joint DesignSpecial Considerations Reinforcement DesignSpecial Considerations ShoulderSame/Some Special ConstructionSame/Some Special