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of ESAL is used as a traffic loading input in the design of pavement structure.Ĭlimate or environment affect the behavior & performance of materials used in pavements Temperature: high temp. Tire pressure & contact area.Įquivalent Standard Axle Load ESAL (80 kN (18,000 lb or 18 kips) single axle load. Volume & composition of axle load (Traffic survey, load meters, & growth rate). Magnitude of axle loads (controlled by legal load limits). Pavement must withstand the large umber of repeated loads of variable magnitudes Primary loading factors: Traffic Loading Climate or Environment Material Characteristics Others: Cost, Construction, Maintenance, Design period.  Most commonly used methods: Īsphalt Institute Method AASHTO method California method  These criteria are considered in terms of repeated load applications. The design of the pavement is therefore generally based on on strain criteria that limit both horizontal and vertical strain below those that will cause excessive cracking and permanent deformation.  The temperature distribution within the pavement structure will also have an effect on the magnitude of the stressesįigure 20.2 Typical stresses and temperature distribution in flexible pavements under wheel load  When the load and pavement thickness are within certain ranges, horizontal compressive stresses will occur above the neutral axis, whereas horizontal tensile stresses will occur below the neutral axis.  The maximum horizontal stress also occurs directly under the wheel load but can be either tensile or compressive.  Stresses decrease with increase in depth from the surface. The maximum vertical stresses are compressive and occur directly under the wheel load. Principles of Flexible Pavement Design Cont. The application of the wheel load causes a stress distribution (See Figure 20.2). Other layers are finite the vertical direction and infinite in the horizontal direction. It assumes that subgrade is infinite in both the vertical and horizontal directions. Materials in each layers is characterized by certain physical properties (Mr, E,….). Pavement structure is considered as a multilayered elastic system. Principles of Flexible Pavement Design  

Typical Cross Section for Conventional Flexible Pavement

 It is assumed to posses considerable flexural strength that will permit it to act as a beam and allow it to bridge minor irregularities in base and subgrade. Rigid pavement:  Pavement constructed of Portland cement concrete.  A structure that maintains intimate contact with subgrade and distribute loads to it, and depends on aggregate interlock, particle friction, and cohesion for stability. Pavement Types Flexible Pavement:  Pavement constructed of bituminous & granular materials. Chapter 16: Highway Engineering, by Paul Wright & Karen Dixon, 7th Edition, Wiley & sons Instructor: Flexible Pavement Thickness Design / Asphalt Institute Method Source: Chapter 20: Traffic & Highway Engineering by Nicholas Garber and Lester Hoel, Third Edition, Brooks/Cole.