1 / 18

Load Equivalency

This document explores the evolution of load equivalency theory in pavement engineering, focusing on key contributions from various researchers. It covers pioneering works by Prickett & Ray (1951) and Kreger (1967), among others, and delves into methodologies like the Equivalent Single Wheel Load (ESWL) and Equivalent Single Axle Load (ESAL) concepts. The declining reliance on the fourth power law and the statistical approaches introduced by AASHO provide critical insights into pavement response analysis under different loading conditions. The text emphasizes the dimensional analysis and mechanistic responses vital for accurate pavement design.

pisces
Download Presentation

Load Equivalency

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Load Equivalency

  2. Load Equivalency Plate theory: solutions limited to a single tire print Prickett & Ray (1951) – provided a graphical extension of Westergaard theory to multiple-wheel loads (pattened after Newmark’s extension of Boussinesq soln.) - resulted in PCA code “Airport”- int. - dimensionless ratios a=loaded radius, s=tire spacing

  3. Kreger (1967) – H51 program - Dense liquid edge stress • Peutz et al (1968) – Burmister linear-elastic theory - BISAR code allowed for multiple-wheel loads • Yoder & Witczak (1975) • Used dimensional analysis in a graphical summary of Pickett & Ray charts d • Edge • Interior • Single, dual, or dual tandem wheel loads L x

  4. Asphalt Institute • - used s/a • FAA • based on tire configuration) • Effort has always been to transform the actual multiple-wheel load into an equivalent loading system consisting of a single wheel. • ESWL: Equivalent Single Wheel Load • ESAL: Equivalent Single Axle Load • ESAR: Equivalent Single Axle Radius

  5. ESWL COE (1940); CBR Design Method(B-29 Aircraft Loading) Load & wheel spacings combinations that yield a LEF of 1 when compared to any “given” single axle. Boussineq soln • LEF depended on: • wheel spacing and dual spacing • mechanistic response • layer thickness & moduli

  6. Equal Vertical Stress (Boyd & Foster - 1950)

  7. Maximum Vertical Stress or Deflections

  8. Equal Vertical Deflection (Boyd & Ahlvin - 1958) As long as Sd/a and h1/a remain the same, the load factor will be the same. • Dimensional analysis • s/a • r/a • z/a

  9. Equal Tensile Strain

  10. Equal Contact Pressure

  11. Gerrand & Harrison – 1970 • used all responses. • used super positioning • abandoned constant pressure assumption • equated the contact area of the ESWL to that of one wheel of the assembly

  12. ESAL • AASHTO (AASHO) Rd Test • ESAL concept developed in 1940 – adopted by the Calif. Div of Highways • AASHO based it on PSI; mainly roughness (but intended originally for fatigue induced distress) Nonetheless, AASHO’s entirely statistical-empirical ESAL concept is based on the assumption that the destructive effect of a number of applications of a given axle group (defined in terms of load magnitude and configuration) can be expressed in terms of a different number of applications of a standard or base load. (Ioannides et al 1993) Linear cumulative damage (Miner’s fatigue hypothesis) - been used for everything from rutting to erosion & pumping.

  13. ESAL Approach was less mechanistic; more statistical • Decon (1969): attempted to ‘prove’ the ESAL, i.e. EALF = Wt18/Wtx=(εx/ε18)γ; γ=4 • Suggested using γ = 5.5 • Proof of ESWL concept never done • Irick & Hudson (1964) • Stated 4th power law applied to a ratio of deflections • Scala (1970): LEF based on load induced deflection but is not independent of pavement structure.

  14. OECD (1988) • Refuted 4th power law • concluded that not possible to prove the existence of a law of equivalence between loads in terms of their damaging effects on pavements. • the power () is different for each pvmt type. •  = 4 Rutting & Fatigue •  = 11 to 33 for semi-rigid •  is sensitive to infrequent heavy loads •  varies from 1.2 to 8 if the standard load is well chosen • Every country has a different  for the same design !

  15. ESAR • The radius of an equivalent single wheel that gives the same response as a dual assembly for the same load. • governed by For interior loading(Tayabji et al 1987)Max bending stress (superposition) (Ioannioes et al 1993)

  16. Equate (For equal P)

  17. Traffic Analysis • ni = (n0)i(G)(D)(L)365(Y) (n0)i = initial number or reps/day (G) = growth factor (D) = directional distribution factor (L) = lane distribution factor (Y) = design period - yrs

  18. Traffic Analysis pi = % of total reps for the ith load group Fi = EALF for the ith load group (ADT)0= initial avg daily truck traffic T = % of trucks A = avg axles per truck Tf = truck factor = # of 18k SAL applications per truck

More Related