10/1/13
Roadway and Pavement Design References: AASHTO Guide for Design of Pavement Structures, 1993 Huang s Pavement Analysis and Design, 1993 (
!"#$ = !%& '&
&=!
m = number of axle load groups F = the equivalent axle load factor (EALF) for the ith axle load group n = the number of passes of the ith axle load group during the design period Class
1
Description
Motorcycles (optional)
2
Passenger Cars
3
4
Other Two-Axle, Four Tire Single Unit Vehicles
Buses
5
Two-Axle, Six Tire, Single Unit Trucks
6
Three-Axle Single Unit Trucks
7
Four or More Axle Single Unit Trucks
8
Four or Less Axle Single Trailer Trucks
9
10
Five-Axle Single Trailer Trucks
Six or More Axle Single Trailer Trucks
11
Five or Less Axle Multi-Trailer Trucks
12
Six-Axle Multi-Trailer Trucks
13
Seven or More Axle Multi-Trailer Trucks
1
10/1/13
80 kN 100 kN 18 kN 18,000 lb 22,000 lb 4,000 lb 1 ESAL 2.2 ESAL .002 ESAL 2
10/1/13
160 kN 36,000 lb Tandem Axle 160 kN 36,000 lb Single Axle 13.93 ESAL 1.38 ESAL Little Truck 67 kN 27 kN 15,000 lb + 6,000 lb 0.48 ESAL 0.01 ESAL = 0.49 ESAL BIG TRUCK 151 kN 34,000 lb +
1.10 Pavement Type 54 kN 151 kN 34,000 lb + 12,000 lb = 2.39 ESAL 0.19 1.10 Single Unit Multiple Unit Flexible 0.600 1.300 Rigid 0.900 2.000 3
10/1/13
 
We need to know:   Average daily traffic (ADT)   Average daily truck traffic (ADTT)   Traffic mixture (number of vehicles in each class)   Average weight of the vehicles in each class  
Given: ADT = 3500 VPD, Class 9 – 30%, Class 5 – 5% Use the ESAL data from earlier slide  
ESALo = [(0.49)(0.05) + (2.39)(0.30)](3500)(365) ESALo = 947,266  
Initial traffic in two directions   Must correct for one direction   Usually a factor of 0.5 is used   This can vary depending on the traffic 4
10/1/13
 
 
 
100% for two lane highways Outside lane is design lane for multilane facilities (truck or driving lane) AASHTO, PCA, and Asphalt Institute all recommend slightly different methods 5
10/1/13
 
 
 
Used to project total design traffic from the estimated first year traffic Multiply initial year traffic by appropriate growth factor Note that growth factors can be different for the different vehicle classes 6
10/1/13
 
Should consider:   Expected traffic attracted or diverted due to new/improved facility   Normal growth due to increased activity   Number of motor vehicles and their use   Future development (land use)  
Given   Four lane highway, traffic measured in two directions   Flexible pavement with pt = 2.5 and SN = 5   Traffic measurements over a 24-­‐hour period   Traffic data as previously shown   Growth factor = 2% Find   20 year design ESAL ignoring light traffic (eg. passenger cars) using AASHTO method  
 
Assumptions:   Traffic volume (all vehicle types) will increase at 2% per year   Axle weights of various vehicle types will remain constant over design period 7
10/1/13
ESALD = (947,266)(0.5)(0.9)(24.30) ESALD = 10,358,354 8