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This 16 page Class Notes was uploaded by Leonor Langosh on Friday September 18, 2015. The Class Notes belongs to TTE 4811 at University of Florida taught by Staff in Fall. Since its upload, it has received 17 views. For similar materials see /class/206883/tte-4811-university-of-florida in Engineering and Tech at University of Florida.
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Date Created: 09/18/15
AASHTO Flexible Design Procedure Dr Christos Drakos University of Florida so SC r nk G A T o R 66 Topic 7 AASHTO Flexible Pavement Design 1 Development AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS httpwwwaashtoorg 11 AASHO Road Test 0 Late 50 s road test in Illinois 0 Objective was to determine the relationship between the number of load repetitions with the performance of various pavements 0 Provided data for the design criteria 12 Performance Measurements Establishment of performance criteria is critical FunctionalCZI AASHTO VS AI IgtStructura l i21 lk lllll Topic 7 AASHTO Flexible Pavement Design 12 Performance Measurements cont AASHO Road Test performance based on user assessment Dif cult to quantify subjective Highly variable Present Serviceability Rating PSR 01 V Poor 12 Poor 23 Fair A panel of experts drove around In standard 34 Good vehicles and gave a rating for the pavement 45 V Good Measurable characteristics performance indicators sible distress cracking amp rut ing Surface friction Roughness slope varianoe Masure of how much slope varies from horizontal along the direction of traf c Topic 7 AASHTO Flegtltible Pavement Design 13 AASHTO Performance Relations Establish correlation between user assessment ride experience an 39n icators quot 39 39 39 USER ASSBSMENT PERFORMANCE INDICATOIE 01 V Poor Measure of Roughness 12 Poor Measure of Rutting 23 Fair Measure of Cracking 34 Good 45 V Good Present seeroeablll Index PSI How does the tme user performance PSI A0 AlF1 AZF2 AEF3 correlate to the measured performance A3 Regression Coef cients F1 Measure of roug ness F2 Measure of rutting F Measure ofcracking calculated the regrssion coefficienis for the PSI equation Topic 7 AASHTO Flexible Pavement Design 13 AASHTO Design Eguations 131 Perfoa quot 39 amp Design Life PSI scale 1 V Poor 9 5 0 Good PSIU p51 APSI PSI0 PSIt PSIt Terminal PSI known 9 Pvt is no longer functional Time age Design Life AASHTO performance requirement APSI o APSI is such that PSIt is NOT reached before end ofdesign life Topic 7 AASHTO Flegtltible Pavement Design 132 Performance Relation ESAL PERFORMANCE St ct Eff m gmFluency Structural Number SN Raff NW J What are the three factors affecting performance APSI APSI fnc MRem ESAL MRE Aocounis for the environment SN Index relating effectiveness of PVT stmcture known known known Solve for SN Topic 7 AASHTO Flexible Pavement Design 133 Definition of Structural Number Ac D1 a1 SND1xa1 Structural Coefficient a BASE D2 a2 SNZD2X32 SN a fnc E position in PVT m SN SN1 SN2 SN3 W Basic Procedure 0 Determine the traffic ESAL Calculate the effective subgrade modulus MRe Select the performance level APSI Solve forthe required SN needed to protect the subgrade Topic 7 AASHTO Flegtltible Pavement Design 134 Design Notes i Different combination of materials ampthicknesses may result in the same SN ii Yourjob as a designer is to select the most economical combination using available materials and considering the following 0 Geometry requirements CutFill Drainage requirements 0 Frost requirements iiiAASHTO assumes that pavement structural layers will not be overstressed Must check that individual layers meet structural requirements Topic 7 AASHTO Flexible Pavement Design 2 W 21 General Design Variables Design Life Material Properties Traffic Reliability Degree of certainty that the pavement will last the design period Uncertainty in Traffic prediction Performance prediction Materials amp construction Topic 7 AASHTO Flegtltible Pavement Design 22 AASHTO Reliabili Factor FR Adjust traffic for reliability FR fnc R So W18W18gtltFR Reliability level Overall Standard DeVIatIon Where chosen 0 Tra Ic Variation W18 Design ESAl o Performanoe prediction w18 Predicted ESAL ananon Stegs 0 Materials subgrade 1 Define functional class InterstateLocal 2 Select reliability level R Table 1114 3 Select a standard deviation SD 0 Flexible No traf c variation S0035 With traf c variation S0045 0 Rigid No traf c variation S0025 With traf c variation S0035 Topic 7 AASHTO Flexible Pavement Design 23 Performance Criteria Design for serviceability change APSI PSI0 PSIt PSI0 Initial serviceability index 0 Flexible 42 0 Rigid 45 PSIt Terminal serviceability index 0 Major highways gt25 0 Lower volume 20 24 Material Properties 241 Effective Subgrade Resilient Modulus Obtain MR values over entire year 0 Separate year into time intervals 0 Compute the relative damage value uf for each modulus 32 u 118x108 XMR Z Topic 7 AASHTO Flegtltible Pavement Design 241 Effective Sub rade Resilient Modulus cont 0 Compute average uf for entire year 0 Determine effective MR using average uf uf 118x108 XMR m Topic 7 AASHTO Flexible Pavement Design 242 Pavement Structural Layers Layer coefficient ai relative quality as a structural unit 2quot of material with a02 provides the same protection as 1quot material a0 Initially layer coefficients were derived from AASHO road test results have subsequently been related to resilient modulus HotMix Asphalt E AASHTO dos not require test to determine HMA modulus usually assume aHMA0 um mum mm It YMivuns pm Topic 7 AASHTO Flegtltible Pavement Design 242 Pavement Structural La ers cont Untreated and Stabilized Bases Can estimate the base layer coefficient from Figure 715 for Untreated base Bituminoustreated base Oementtrated base 0 For untreated base can also use the following instead of interpolating from the figure 0249X10gE27 0977 Granular Subbases Can estimate the subbase layer coefficient from Figure 716 0 Can also use the following instead of interpolating from the figure a3 0227X10gE37 0839 Topic 7 AASHTO Flexible Pavement Design 25 Drainage 0 AASHTO guide provides means to adjust layer coefficients depending on the effectiveness of the drainage 0 Define quality of drainage of each layer based upon Time required for drainage Percent time moisture levels approach saturation 0 Determine drainage modifying factor m from Table 1120 SN Percenlage uf lime pavemenl slruciure is exposed Quality of drainage to moisture levels approaching saturation Waler removed Less lhan Greater than Raling wilhin l 5 5 25 25 Excellent 2 hours LAO 135 35vl30 130 120 l20 Good I day l35 125 125415 ll5 IUD 00 Fair I week 254I5 115105 LOO030 080 Poor I month ll57I05 LBS 181 080 060 060 Very poor Never drain 105 095 095 075 075040 040 Source After AASHTO 986 M Topic 7 AASHTO Flexible Pavement Design 26 Computation of Reguired Pavement Thickness 261 Basic Approach 0 Determine the required SN for design traffic 0 Identify trial designs that meet required SN 262 Nomograph to Solve for SN x a cm 5mm mm 5 Topic 7 AASHTO Flexible Pavement Design 26 Computation of Reguired Pavement Thickness cont 263 Solving the Equation I l 1 ogkzur 15 1094 04 logw 18 ZR so 936 logSN 1 r 02 232 logM R r 807 SN 1519 Declare the known variables W18 ZR S0 PSI amp MR 0 Give an initial estimate forthe SN 0 Allow the equation solver Matlab Maple Mathcad Egtltcel etc to iterate for the solution Topic 7 AASHTO Flegtltible Pavement Design 264 Pavement Structural Layers SN alD1 aZDzm2 o No Unique Solution Many design configurations will meet the required SN Optimize the design consider the following Design oonstraints drainage minimum thickness available materials Construction oonstraints minimum layer thickness EDDanllS 265 Layered Design Analysis Nomograph determines the SN required to protect the subgrade However each structural layer must be protected against overstressing Procedure developed using the AASHTO design nomograph Determine the SN required to protect each layer by entering the nomograph using the MR of the layer in question Topic 7 AASHTO Flexible Pavement Design First we need to protect the subgrade use the nomograph to get SN needed to provide adequate protection BUT have to protect each layer from overstressing need to get required SN level of protection for each layer 0 Only top AC layer does not need protection For example Base needs SN1 protection BUT SN1 alD1 D 1 a1 E2 32 quot 2 E3 33 m3 Topic 7 AASHTO Flegtltible Pavement Design 266 General Procedure 1 Using E2 as the MR value determine from Figure 1125 the structural number SN1 required to protect the base and oompute the thickness of layer 1 by SN D 1 1 31 2 Using E3 as the MR value determine from Figure 1125 the structural number SN2 required to protect the subbase and compute the thickness of layer 2 by o D ZSNzialDl 2 a2quotquot2 3 Based on the roadbed soil resilient modulus MRem determine from Figure 1125 e total structural number SN3 required and oompute the thickness of layer 3 by o D 2SN3ra1D17a2D2m2 3 a3m3 Topic 7 AASHTO Flexible Pavement Design 27 Other Thickness Considerations 271 AASHTO Suggested Minimums ESAL Asphalt Concrete Aggregate Base 1 4 50000 150000 2quot 4quot 150000 500000 25quot 4quot 500000 2000000 3quot 6quot 2000000 7000000 35quot 6quot gt 7000000 4quot 6quot 271 Construction Stability Layer must be thick enough to act as a unit 0 Thickness gt 2 Maximum Aggregate Size Topic 7 AASHTO Flegtltible Pavement Design 28 Cost Considerations 0 Consider Different combination of materials Cost of materials Cost of excavation cut areas Egtltpress cost as a unit contribution 016X080 312 Magtltimize crushed stone thickness minimize AC thickness Can also stabilize base to use less H A 0 Use gravel only for fill or frost Topic 7 AASHTO Flexible Pavement Design 29 AASHTO Design Example 1 Given 0 Reliability 90 0 Overall Sid Dev 035 0 W18 10 million 0 Design Serviceability Loss 20 WORK EXAMPLE ON THE BOARD Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 Given 0 Reliability 90 0 Design Serviceability Loss 20 Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Construct a material information table Material Layer sqydin m Unit SN Next step is to fill in the information Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Asphalt Concrete structural coefficient a Figure 713 0 mains Idspsi a Surface Course Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Bituminous treated base structural coefficient a Figure 715 ulnaMan ml39 9 E 5mm mm m mumquot mvany onquot b Bituminous Treated Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Cement stabilized base structural coef cient a Figure 715 summi nominalu mm MD7 any mar c Cement Treated iii3m Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Crushed stone base structural coefficient a Figure 715 mm mm in Mmulusdm In a Unirealed Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Crushed stone subbase structural coefficient a Figure 716 Modulus1W psi Topic 7 AASHTO Flexible Pavement Design 210 AASHTO Design Example 2 cont Material Layer lsqvdin Are there any obvious oonclusions Unit SN
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