This paper presents findings of an analytical study aimed at investigating the effects of unbound aggregate base residual stresses on the resilient response behaviour of geogrid reinforced flexible pavements. In the first step the critical stresses or strains the response in the individual pavement layers are calculated using an analytical model, and in the second step they are compared to permissible stresses or strains. Useful design information such as fatigue life and rut depth are also estimated through empirical equations. Difference between in situ flexible pavement measured and. A finite element fe based mechanistic response model recently developed at the university of illinois was used to predict critical pavement responses of unreinforced and geogrid. Design of flexible pavement is largely based on empirical methods using layered elastic and twodimensional finite element fe analysis. Vesic, respectively, professor and asso ciate professor of civil engineering, georgia institute of technology fullscale static load tests have been made of single, dual, and dual tandem truck tire loads on flexible pavements to. Application of layered system analysis to the design of.
They are 3 normal stresses s z, s r, s t and 6 shearing stresses t rz t zr, t rt t tr, and t tz t zt. These stresses may not exceed the tensile strength of the asphalt but, when repeated over time, cyclic. Stressstrain characteristics of flexible pavement using. The series of finiteelement numerical simulations were carried out for several types of flexible pavements and overlays placed on these pavements. Structural assessment of flexible and rigid airfield pavement. Horizontal tensile strain at bottom of ac layer controls bottom up fatigue cracking. Vertical stresses in subgrades beneath statically loaded. Mechanistic approach requires the accurate evaluation of. Axle loads, wheel loads and contact pressures 69 6. Stresses in layered systems at any point, 9 stresses exist. Nowadays, the failure of the surface of flexible pavement roads is common before the. Vertical stresses in subgrades beneath statically loaded flexible pavements george f.
Structural analysis of flexible pavements stresses and strains reading. Stresses and strains in flexible pavements function of the following. Stresses and deformations in flexible layered pavement systems. The purpose of the work reported is to investigate, in the laboratory, the complete stress and strain distributions set up in the different layers under dynamic loads. Alaska flexible pavement design manual 12 effective 40104 effective 40104 alaska flexible pavement design manual the excess fines design method and the mechanistic design method.
The theory can be used to determine the stresses, strains, and deflections in the subgrade if the modulus ratio between the pavement an d the subgrade is close. It provides guidance on layering, composition, and construction and maintenance issues relating to a range of flexible pavements, as well as typical pavement thickness and. Boussinesq equations are developed for computing stresses in a homogeneous, isotropic and elastic media due to a point load at the surface. Introduction typical flexible pavement section can be idealized as a multilayered system soil subgrade subbase course base course. Pavement stressstrain analysis is an ideal tool for analytical modelling. Stresses in homogeneous mass boussinesq formulated models for the stresses inside an elastic halfspace due to a concentrated load applied on the surface. Charyulu, malati kesaree, theoretical stress distribution in an elastic multilayered medium 1964.
Stresses and strains in flexible pavements civil iitb. Lesson 21 structural responses in flexible pavements. At each point in the system there exists a certain orientation of the element such that the shearing stresses acting on each face are zero. The program computes displacements, stresses and strains within the pavement due to a single circular wheel load. Stress and strain factors for threelayer elastic systems. The stressesstrain distribution and the threedimensional stress state over the height of the asphaltsurfacing layer.
Lecture notes ct 4860 structural pavement design design of. Assumptions in multi layered elastic systems the material properties of each layer are homogeneous property at point ai is the same at bi. Michpave michpave is a userfriendly, nonlinear finite element program for the analysis of flexible pavements. Investigation of thermalinduced strains in flexible pavements authors. A series of equations was proposed by boussinesq to determine stresses, strains, and deflections in a homogeneous, isotropic, linear elastic half space with modulus e and poissons ration. Due to axis symmetry, there are only three normal stresses. Because in the design and analysis of flexible pavements the stresses and strains existing at the bases of the upper two layers can be important, it would be convenient to have the stress fac tors, rrl and rr2, and the strain factors, vz rrlzzl and % rr2 zz2, tabu. Development of a rational probabilistic approach for flexible. The stresses are not transferred from grain to grain to the lower layers as in the ease of flexible pavement layers. The main criteria is the vertical compressive strain in the sub grade because. Stresses and strains in flexible pavement using computer program. Strain and stress distributions in flexible pavements under. Application of support vector machine regression for predicting critical responses of flexible pavements ali reza ghanizadeh1 email. Comparison of stresses and strains in pavements with and without reflective cracking is presented.
Stresses and deformations in flexible layered pavement systems subjected to dynamic loads. Typical twolayer hma pavement stresses as calculated by everflex wu, 2001, a threedimensional finite elements program. But the design methodology has taken rapid strides towards rationality in the past few decades based on an understanding of the stresses and strains in the layers constituting the pavement and application of the concept of reliability in achieving the desired level of service during the pavements design life. Material containing subgrade and environment condition are also responsible for stresses in the pavement. Design flexible and rigid pavements 9design principlespavement components and their roledesign practice for flexible and rigid pavements, ircmethods only. Response models for flexible pavements single layer model. Although the method has gained wide acceptance in this country and is currently used in pennsylvania to design flexible pavements, it is limited in precise application to areas where. Pdf analysis of stressstrain and deflection of flexible.
Theoretical stress distribution in an elastic multi. For rigid pavements the slab support conditions at the slabs edge or midspan position are backcalculated. The analyticalempirical or mechanisticempirical approach to design of flexible pavements has two steps, as implied by the name. Perpetual pavements ohio study of flexible pavements examined performance on 4 interstate routes hma pavements up to 34 years without rehabilitation or reconstruction no significant quantity of work. Hankel transforms of the stresses and displacements 54 vertical stress 5. Oct 12, 2019 rigid pavements are those which posses note worthy flexural strength or flexural rigidity. Difference between in situ flexible pavement measured and calculated stresses and strains article in journal of transportation engineering 27. The rigid pavements are made of portland cement concreteeither. Rigid pavements are those which posses note worthy flexural strength or flexural rigidity. There are various types of stresses yields in flexible and rigid pavements under the applied live load.
For flexible pavements that is the determination of the distinct layer moduli of constructed layers and the subgrade from known layer thickness. The complex stress and strains for a twolayer flexible pavement structure are shown graphically in figure 2 using a threedimensional finite elements model. Comparison of stress and strain states in pavements with. Strain and stress distributions in flexible pavements under moving loads.
As stresses and strains are used more an d more to predict pavement. A flexible pavement structure is typically composed of several layers of materials. Most roads found in ethiopia are flexible pavements. Analysis of stressstrain and deflection of flexible pavements. Aggregate base residual stresses affecting geogrid. Sp024 manual for condition rating of flexible pavements. The purpose of the work reported is to investigate, in the. The horizontal tensile stresses and strains in the bottom zone h1mm of the asphalt surfacing. To calculate stresses, strains and deflections of a. However, not all distress manifestations are accompanied by distortion or unevenness. The pavement surface deflections measured by benkel man beam are in close agreement with the values predicted by the computer program. Stresses are the response of loading on the pavement.
Nature of responses under flexible and rigid plates. Nowadays, the failure of surface of flexible pavement roads are common before the expected design period. Material properties of each layer thickness of each layer loading conditions environmental impact pavement responses generally of interest. Onelayer theory can be applied as an approximation for a conventional flexible pavement with granular basesubbase with a thin asphaltic layer on a stiff. Investigation of thermalinduced strains in flexible pavements. The horizontal tensile stresses and strains in the bottom zone h1mm of the asphalt surfacing layer which are the failure distress parameters for pavement fatigue cracking. Results and graphs 73 an approach to the design of flexible pavements 9 effect of repetitive loads 95 method of design 96 summary 103. To calculate stresses, strains and deflections of a layered elastic system gradually became more sophisticated in capability to handle linear elastic materials nonlinear elastic granular materials vertical and horizontal loads elastic multilayer systems under multiple wheel loads stress dependent materials. Theoretical stress distribution in an elastic multilayered. The rigid pavements are made of portland cement concreteeither plain, reinforced or prestressed concrete.
Many of the proposed rational design methods for flexible pavements are concerned with the stresses and strains which occur in the various layers of the structure. Onelayer theory can be applied as an approximation for a conventional flexible pavement with granular basesubbase with a thin asphaltic layer on. The purpose of this guide is to assist in the selection, specification and design of flexible road pavements for a variety of applications. Boussinesq 1885 was the first to examine the pavements response to a load.
Design of pavements has been based on experience and judgment in the past. Statistical analysis of stresses in rigid pavement c. Strain measurements in flexible pavements under heavy. A halfspace has an infinitely large area and an infinite depth with a top plane on which the loads are applied. The thermal stresses induced in the top of the basecourse in this model by a severe winters day are shown to reach maximum tensile values of the order of 50 knrn 2 the induced stresses during the rest of the year are very much smaller. Flexible pavements are so named because the total pavement structure deflects, or flexes, under loading. Chapter 3 presents the kenlayer computer program, based on burmisters layered theory, including theoretical developments, program description, comparison with available solutions, and sensitivity analysis on the effect of various factors on pavement responses. The top most paved surface of such type of pavement is flexible, that is extremely dependent on the underlying layers. Each layer receives loads from the above layer, spreads them out, and passes on these loads to the next layer below. Seection and design of flexible pavements 1, introduction the purpose of this guide is to assist in the selection, specification and design of flexible road pavements for a variety of applications. Application of support vector machine regression for. The stresses strain distribution and the threedimensional stress state over the height of the asphaltsurfacing layer. Stresses in flexible pavement rutting engineering intro.
Stresses and deformations in flexible layered pavement. Chapter 2 discusses stresses and strains in flexible pavements. Strain measurements in flexible pavements under heavy vehicle. Two systems have been investigated, a single layer of clay and a. Pdf stresses and strains in flexible pavement using.
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