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Transportation Engineering II

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Presentation on theme: "Transportation Engineering II"— Presentation transcript:

1 Transportation Engineering II
ECGD4228 Transportation Engineering II Summer 2008 Saturdays 15:30-18:30 PM K204 Dr. Wa'el M. Albawwab

2 Dr. Wa'el M. Albawwab
Lecture 6 Pavement Design Methods Design Parameters Flexible Pavement Rigid Pavement Dr. Wa'el M. Albawwab

3 Pavement Design Methods
A pavement consists of a number of layers of different materials Pavement Design Methods: AASHTO Method The Asphalt Institute Method for Flexible Pavements Portland Cement Association (PCA) Method for Concrete Pavements Texas DOT Method Other methods Dr. Wa'el M. Albawwab

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AASHTO Road Test AASHTO: American Association of State Highway and Transportation Officials Objective: To relate axle load repetitions, pavement design configurations & distresses Dr. Wa'el M. Albawwab

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ASSHTO Design Method Pavement Performance Traffic Roadbed soils (subgrade materials) Materials of construction Environment Drainage Reliability Shoulder Design Life-Cycle Costs Dr. Wa'el M. Albawwab

6 AASHTO’s Formula Considers: (1) Pavement Performance
Based on Pavement Serviceability concept Serviceability was defined as the ability of a pavement to serve its intended function under existing conditions During the test, road users rated pavements Pavement Serviceability Rating (PSR) Based on the pavement roughness 0-1: Very Poor; 1-2: Poor; 2-3: Fair; 3-4: Good; and 4-5: Very Good Dr. Wa'el M. Albawwab

7 AASHTO’s Formula Considers: (1) Pavement Performance
PSR’s used to develop design equations to predict Present Serviceability Index (PSI) Initial Serviceability Index = p0 (the servceability immediately after the construction of the pavement, recommended Terminal Serviceability = pt (2.5-major, 2.0-other), the minimum acceptable serviceability before resurfacing or reconstruction is needed. In the formula: Serviceability loss (PSI) = p0 – pt Dr. Wa'el M. Albawwab

8 Pavement Condition Defined by users (drivers)
Develop methods to relate physical attributes to driver ratings Result is usually a numerical scale From the AASHO Road Test (1956 – 1961) Dr. Wa'el M. Albawwab

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Typical PSI vs. Time p0 Serviceability (PSI) p0 - pt Terminal Serviceability Level pt Time Dr. Wa'el M. Albawwab

10 AASHTO’s Formula Considers:
(2) Traffic The concept of ESAL – Equivalent Single-Axel Load The traffic characteristics are determined in terms of the number of repetitions of an 18,000 single-axle load applied to the pavement on two sets of dual tires. Expressed in Equivalent 18-kip Single Axle Loads (W18) Axle load equivalency factor was introduced to convert different axle loads to Equivalent 18,000 lb (18-kip) Single Axle Loads. Dr. Wa'el M. Albawwab

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Vehicle Types Dr. Wa'el M. Albawwab

12 Vehicle Weight & Size Limits
Weight limits for whole vehicle, single axles & tandem axles Size limits for length, width & height Dr. Wa'el M. Albawwab

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ESAL Determination By Load Equivalency Factors (FE), i.e., number of repetition of 18 kip single-axle load. Axels (lb) Single Tandem Tridem 10000 0.0877 0.007 0.002 18000 1.0 0.077 0.017 40000 21.08 2.08 0.487 Dr. Wa'el M. Albawwab

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Load Quantification Load Equivalency Generalized fourth power approximation Dr. Wa'el M. Albawwab

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ESAL Determination For each axle category i; (single, tandem, tridem) For all categories: Dr. Wa'el M. Albawwab

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ESAL Determination fd – design lane factor, which is the portion of total ESAL acting on the design lane (any lane of two lane highway and outside lane of multilane highway), from field data. G – traffic growth factor for a specific design period AADT – first year AADT N – number of axles (each axle will repeat one load when vehicle is moving) FE – Load equivalency factor Dr. Wa'el M. Albawwab

17 AASHTO’s formula considers:
(3) Subgrade materials Resilient Modulus (Mr) of the soil is considered in design, the value of Mr is normally known/given for design Another parameter needs to know but not directly used in the AASHTO’s formula is CBR – California Bearing Ratio, which is a parameter indicative of soil’s strength. Relationship between Mr and CBR (or R value) is given by: Mr = 1500 CBR (for soils with CBR ≤ 10) Mr = CBR ( for 10 < CBR ≤ 20) Dr. Wa'el M. Albawwab

18 AASHTO’s formula considers: (4) Materials of construction
SN – The Structural Number Dr. Wa'el M. Albawwab

19 AASHTO’s formula considers: (4) Materials of construction
SN – The Structural Number for the road profile Di – depth of layer i mi – drainage coefficient for layer i Dr. Wa'el M. Albawwab

20 AASHTO’s formula considers: (4) Materials of construction
Subbase construction materials: layer coefficient a3 is used to represent the quality of the material AND convert the actual thickness of the subbase to Structural Number (SN, is an engineering term indicative of the total pavement thickness). Base construction materials: a2, and Surface Course Construction materials: a1. Dr. Wa'el M. Albawwab

21 AASHTO’s formula considers:
(5) Drainage Purpose: consider the effect of drainage on the performance of flexible pavement Represented by: mi, i =2,3 (represents the base and subbase layer. Dr. Wa'el M. Albawwab

22 AASHTO’s formula considers:
(6) Reliability Reliability level: the reliability that the pavement designed will survive for its design period. E.g., a 50 percent reliability design level implies a 50% chance for successful pavement performance. Presented by FR. Dr. Wa'el M. Albawwab

23 AASHTO’s formula considers:
(6) Reliability ZR : Standard normal variation for a given reliability S0 : Estimated overall standard deviation Dr. Wa'el M. Albawwab

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Other Issues Drainage Joints Grooving (noise vs. hydroplaning) Rumble strips Climate Level and type of usage Failure examples are primarily related to design or life-cycle, not construction Dr. Wa'el M. Albawwab

25 Dr. Wa'el M. Albawwab
Primary References Mannering, F.L.; Kilareski, W.P. and Washburn, S.S. (2005). Principles of Highway Engineering and Traffic Analysis, Third Edition. Chapter 4 Muench, S.T.; Mahoney, J.P. and Pierce, L.M. (2003) The WSDOT Pavement Guide Interactive. WSDOT, Olympia, WA. Muench, S.T. (2002) WAPA Asphalt Pavement Guide. WAPA, Seattle, WA. Dr. Wa'el M. Albawwab

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