SESSION 8 Shoulder Considerations

Objectives Identify shoulder/edge support types Describe benefits of each type Discuss how edge support conditions are considered in structural design Describe benefits provided by shoulder rumble strips

Functions of Shoulder Safety zone Auxiliary area Lateral support to mainline pavement Potential traffic lane during rehabilitation

Shoulder / Edge Support Types Widened concrete slab Tied concrete shoulder AC shoulder

Widened Concrete Slabs Slab paved m (1-3 ft) wider than usual Lane striped at normal 3.6-m (12-ft) width Reduces edge and corner loadings

Tied Concrete Shoulder Paved concrete slab tied to concrete mainline pavement Benefits: Reduced edge stresses/deflections Improved lateral support Reduced moisture infiltration

Design of Tied Concrete Shoulder Same thickness as mainline, if paved together urban: full depth, full lane width rural: if lesser thickness, granular fill below Effective tie system required minimum No mm (30 in) Transverse joints match mainline joints

Concrete Shoulder and Slab Paved Monolithically D / 3 Sawed JointD D / 2 Deformed tie bar (Minimum No. 5 ) Concrete ShoulderMainline Pavement

Concrete Shoulder and Slab Paved Separately D D / 2 Butt Joint Concrete ShoulderMainline Pavement Deformed tie bar (Minimum No. 5 ) Possible Keyway

Improper Tie Bar Installation

Asphalt Shoulder AC surface course or surface treatment Reduced structural capacity No structural support to mainline pavement Lane-shoulder joint difficult to seal Better visible delineation at night Lower initial cost

Consideration of Edge Support in Thickness Design 1986/1993 AASHTO Procedure J factor Concrete shoulder only 1998 AASHTO Supplement Edge support adjustment factor Widened slab or concrete shoulder PCA Concrete shoulder reduces edge stress

Shoulder Rumble Strips Indentations in shoulder Create noise and vibration to alert drivers of wayward vehicles Effective in reducing vehicle-leaving-the- road crashes

Summary Types of shoulders Benefits of widened slabs and tied shoulders Advantages and disadvantages of asphalt shoulders Benefits of shoulder rumble strips