Rigid Pavement ESAL Equation

From Pavement Interactive

Contents 1 Example Calculation

At first glance, this equation looks quite complex - it is. 

Where:	W	=	axle applications inverse of equivalency factors (where W18 = number of 18,000 lb (80 kN) single axle loads)
	Lx	=	axle load being evaluated (kips)
	L18	=	18 (standard axle load in kips)
	L2	=	code for axle configuration 1 = single axle 2 = tandem axle 3 = triple axle (added in the 1986 AASHTO Guide) x = axle load equivalency factor being evaluated s = code for standard axle = 1 (single axle)
	G	=	a function of the ratio of loss in serviceability at time, t, to the potential loss taken at a point where pt = 1.5
	pt	=	"terminal" serviceability index (point at which the pavement is considered to be at the end of its useful life)
	b	=	function which determines the relationship between serviceability and axle load applications D = Slab Depth in inches

Example Calculation

• Assumptions: Single axle, 30,000 lb (133 kN), D = 7 in., p_t = 2.5
• Answer: (Table D.13, p. D-15, 1993 AASHTO Guide) = 7.7
• Calculations

where :	W18	=	predicted number of 18,000 lb (80 kN) single axle load applications
	W30	=	predicted number of 30,000 lb (133 kN) single axle load applications
	Lx	=	L30 = 30
	L2x	=	1 (single axle)
	G	=	serviceability loss factor
		=
	b30	=	curve slope factor
		=
and	G/b30	=	-0.1761/5.7298 = -0.03073
	b18	=
	G/b18	=	-0.1761/1.3709 = -0.12845
Thus,
and		of W18 loads allowable with a 30,000 lb. single axle
Finally,	LEF	=	(same as contained in 1993 AASHTO Guide âcol Appendix D)