I. Header November 29, 2015 To: Professor John Harvey University of California, Davis One Shields Ave. Davis, CA 95616 From: Samuel Ray 999576030 Subject: Pavement Analysis and Design, Bogota International Airport I am submitting a report on the design of a newly reconstructed takeoff taxiway. The taxiway will only carry the loads of the following aircraft: Boeing 777-300 ER (B777) Airbus A350-900 (WV001) (A350)
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I.HeaderNovember 29, 2015To: Professor John HarveyUniversity of California, DavisOne Shields Ave. Davis, CA 95616From: Samuel Ray 999576030Subject: Pavement Analysis and Design,Bogota International Airport
I am submitting a report on the design of a newly reconstructed takeoff taxiway. The taxiway will only carry the loads of the following aircraft: Boeing 777-300 ER (B777) Airbus A350-900 (WV001) (A350)
II.Purpose:The Bogota International Airport is considering expanding a terminal in order to accommodate new flights by the above mentioned aircraft B777 and A350. The Mechanistic-Empirical design method was used to create alternate pavement designs. Both asphalt concrete and Portland cement concrete were used. The results were acquired by using both openpave and EverFe for each new design. Openpave was used for the design of the asphalt concrete (AC) and EverFe was used for the design of the Portland cement concrete (PCC).III. Summary of Data:Flexible:It is expected that 3 B777 and 4 A350 will use the terminal every day. The main speed on the taxiways is 25 km/hour. It will be used 365 days per year and will be evenly divided between winter and summer, and between day and night. Expected pavement temperatures at the site are 20ºC during summer days, 15ºC during summer nights and winter days, and 4ºC during winter nights, all at 1/3 depth in the asphalt concrete.The following two tables were provided by Consultant John Harvey.Table S1: Proposed Pavement Structure:Existing Layer Thickness DescriptionAsphalt Concrete 150 mm Dense graded AC, badly crackedAggregate Base 300 mm Imported aggregate base, compacted to 98 percent modified ProctorSubgrade Very thick fill. Original design CBR values of 4-6Table S2: Deflections of existing taxiwaysSensor location (mm) 0 200 300 600 900 1200 1500Deflection (m) 777 704 649 499 385 302 242
Table 1 specifies the existing layers (Asphalt Concrete, Aggregate base, and subgrade) and their thicknesses. The shear strengths of the unbound layers are
100 kPa for the subgrade, and 420 kPa or 350 kPa for the aggregate base. The design life for this pavement is 20 years. A Heavyweight Deflectometer was used to test the deflections in the existing runway. The load was 100kN on the 150 mm radius plate. The results are shown above in Table 2. PCC Design:For the alternative concrete design we assumed a doweled (50 mm diameter) plain slab with dimensions of 4m by 4m, with the PCC having a stiffness of 28 GPa and a MR of 5 MPa. The nighttime temperature gradient is -5ºC for summer and -3 ºC for winter, and daytime temperature gradients of +4 ºC for both seasons. The slab would also have a constant equivalent temperature of -2 ºC from moisture.IV. Summary of MethodsAsphalt ConcreteUsing the deflections in table 2, the stiffness of the subgrade and aggregate base were obtained by back calculation in openpave. Given values of viscosity and penetration (Viscosity at 60 C is 18,000 poises and penetration at 25 C is 45 dmm) The Shell method was used to calculate the Asphalt Stiffness. Intermediate steps of finding loading time, diameter at 1/3 depth, percent by volume of aggregate and bitumen were needed to complete the shell method. Stiffness was found for all 4 season conditions for both air craft.Given dimensions/positions of tires and their given loads and pressures were put into openpave. Critical points were determined and analyzed to find max tensile strains and vertical stresses. 4 open paves for each season condition were created. With the max tensile strains, for each plane, for each season condition, fatigue life (Nf) was found for each pass of each wheel. Expected number of repetitions for each plane for each season condition (n) was found with the given information. Miner’s law was used to check if the pavement failed due to fatigue. The pavement does fail due to fatigue under the tires of both the B777 and the A350. Simultaneously at the critical points determined, vertical stress was obtained from each openpave created. The thickness of the aggregate base (AB) was to be designed to protect the subgrade (SG) from rutting. Iterations in open pave were used to find this thickness based on the criteria of .4saturated shear strength >.5 vertical stress. The thickness found that satisfies this criteria is 1225 mm. Same procedure was done for rutting of the AB but, it seems that the AB will rut regardless of any changes made. PCC k-value was found using the funky chart and previously back calculated subgrade stiffness modulus. Overall temperature gradient was found for each season temperature. The dimensions of the wheels were placed into EverFe along with the configurations of the wheel with its corresponding loads.
Four iterations were made for each plane and for each season temperature making a total of 12 iterations. The max tensile stresses and the deflections at the corners were recorded for each iteration. Flexural Strength (MR) was equal to 5 meaning the acceptable max tensile stress would be 2.75.The design thickness was found to be 605.5 mm with a deflection of 2.848 mm and a maximum stress approximately 2.75 MPa. The critical plane was A350 during summer/winter day because this combination had the largest max stresses. Plots were then made to show the relationship between thickness of PCC and deflection as well as max tensile stress.*All calculations, tables and figures are in the Attachments section with step by step methods.V. Final RecommendationFlexibleMy final recommendation would be to design the AB to a thickness of 1225 mm to protect the SB from rutting. Due to the large loads and the thin required AC thickness, the AB will rut regardless of thickness. I’d recommend using the AB with a saturated shear strength of 420 kPa because it will rut less than the alternative. The pavement also fatigues due to the large loads of the tires and the slow velocity as well. Because minors law for the max critical point was around 6 the pavement cannot be expected to last 20 years but around 6 times less than 20 years. The pavement will fatigue after 3-4 years so preventive maintenance before these years could be an option. The thin asphalt, heavy loads and slow speeds of the planes will cause the AB to rut and the AC to fatigue. Changing one of those variables could greatly increase the life of this pavement.RigidMy final recommendation would be to design the PCC to a thickness of 605.5 mm to achieve allowable tensile stresses. Rigid pavement design would be better to handle the heavy loads of the aircraft however, it is more expensive and a considerable large thickness would be required. If the money is there I’d suggest using PCC instead of the thin asphalt.
VI. ClosureThere are many issues with the Asphalt pavement such as fatigue and rutting of the AB. The PC however when designed correctly did not fail. The PCC however, costs more and more of it is used. The PCC would be a better option because the AC will fail and a reliable expensive pavement is better than a failing inexpensive one.
Using the sensor and deflection measurements stiffness can be found using open pave. Stiffness of asphalt concrete is given for this back calculation as 10500 MPa. Thickness of aggregate base (AB), radius and load were also given. When you enter in the load and radius openpave calculates the pressure.Table 2Location X (mm) Y (mm) Load (kN) Pressure (kPa) Radius (mm)
1 0 0 100 1414.7106 150 Using the given information and iterations the stiffness of the AB and the subgrade (SG) can be found.Table 3
z (mm) 0.7776996 0.7035079 0.6491723 0.4994464 0.3846662 0.301618 0.2421815Therefore the elastic modulus of AB=280 MPa and SG=80 MPaStep 2: Find stiffness of ACWe must find the Stiffness of the asphalt concrete (AC). First Plot Viscosity at 60 C: 18,000 poisesPenetration at 25 C: 45 dmmOn the Bitumen Test Data Chart
Figure 1¿chart
T r∧b=62° C
T 1=25 °C
Penetration@T 1=45dmm
PI calculation
20−PI10+PI
=log (800 )−log (Penetration@T 1 )
Tr∧b−T 1
20−PI10+PI
=log (800 )−log (45 )
62−25
PI=1.16
Find area of tire cross-section on the surface LoadB777=288120N
Pressur eB777=1520550Pa
A= LoadPressure
= 2881521
= .189m2
Find the Diamter of tire cross-section on the surfaceA=
dsurface2 π4
.189=d surface2 ∗π4
dsurface=.49mFind Diameter at 1/3 depth13thickess=.058m
d 13 depth
=dsurface+2∗13
thickness
d 13depth
=.49+2∗.058=.608m
Find loading time (t)velocity (v )=6.9m
s
t=d 13depth
v
t= .6086.9
=.09 sec
Table 6max tire Mass (kg) P/g (kg/m^2) Area (m^2) diameter (m) thickness (m)
With calculated values of stiffness modulus of bitumen, volume of bitumen and volume of aggregate we can find stiffness modulus of bituminous mix.Plot these values on nomograph for mixed stiffness.
Table 12 Stiffness of AC (Pa)day/summer 1900000000night/summer 3200000000day/winter 3200000000night/winter 8000000000
Step 3: Find position of wheels on open paveDetermine vertical StressSet up openpave with loads for B777 and A350Only one side of the plane is needed to be evaluated due to symmetry.Loads and Pressures were calculated before.Table 13Load (N) Pressure (Pa) 288119.7 1520550 B777334643.6 1661637.16 A350Positions of wheels and critical points with loads were calculated and put in openpave for the A350 and B777Table 14: Wheel LoadsA350 Location X (mm) Y (mm) Load (kN) Pressure (kPa) Radius (mm)
Figure 5Step 4: Find Thickness of AB to protect SG from rutting.*we only have to check for rutting for Summer Day because that is the time that is most susceptible to rutting.find desiredmax value for σ zz (vertical stress )
.4∗shear strength>.5σ zz
s sSG=100 kPa
σ zz<80 kPaVarying the depths we got these values*note through observation using openpave the B777 caused more vertical stress therefore this was the plane used to determine if there will be rutting in the SG.Table 18SG SG SG SG AB AB AB AB
Looking at AB 1200 mm and AB 1300mm we have just above and below 80 kPa respectively, when looking at the max vertical stress.
200 300 400 500 600 700 800 900 10000
50
100
150
200
250
A350 AB thickness to protect Subgrade
Stress vs ThicknessDesign thickness
Thickness of AB (mm)
verti
cal S
tres
s (k
Pa)
Figure 6: AB thickness vs rutting in subgrade A350
200 400 600 800 1000 1200 14000
20
40
60
80
100
120
B777 Actual Design Thickness
(vertical stress)/2 vs depthDesign thickness
thickness of AB (mm)
(ver
tical
str
ess)
/2 k
Pa
Figure 7: AB thickness vs rutting in subgrade B777Through interpolation we get a design thickness of 1225 mmTable 19
SG SG SG SG AB AB AB ABpoint 5 6 7 8 9 10 11 12
AB 1225 mm szz (kPa) -75.987 -79.928 -70.912 -75.237 -799.811 -39.3083 -32.46416 -0.80931
B) Determine if Subgrade ruts Find desired σ zz
samemethodas before
σ zz<336 kPaBy looking at point 9, on table 19, it shows a vertical stress of 800 kPa therefore, the AB will rut. Changing any thickness of the AB will not protect the AB.
0 200 400 600 800 1000 1200 14000
100
200
300
400
500
600
700
800
900
1000
Check for Rutting in AB1 & AB2
A-350
B777
Saturated Shear Stress for AB1
Saturated Shear Stress for AB2
Thickness (mm)
Verti
cal S
tres
s (kP
a)
Figure 8: Rutting in AB vs Thickness of ABC) Determine if the AC fails due to fatigueStep 1: find the tensile strains due to passing of planesUsing open Pave the following micro strains were calculated at the bottom of the asphalt layer.
Table 20 B777 wheel
A350 wheel critcal point A B C DA350 summer day (micro strain) 358 124 797 125A350 summer night (micro strain) 327 90.4 659 95.9A350 winter day (micro strain) 327 90.4 659 95.9A350 winter night (micro strain) 244 102 421 83.9B777 summer day (micro strain) 677 168 269 137B777 summer night (micro strain) 568 76.9 479 125B777 winter day (micro strain) 568 76.9 479 125B777 winter night (micro strain) 370 88.2 364 116Step 2: find allowed number of repetitions
for A 350 summer day point A
ϵ tension=358∗10−6
N field=SF∗e−23.63−4.2913∗ln (ϵ tension)
N field=5∗e−23.63−4.2913 ln(358∗10−6)=167847allowed repititions
Table 21wheel B777 wheel A350
critcal point NA NB NC NDA350 summer day (micro strain) 167846.8382 15881478.1 5412.06872 15343394.73A350 summer night (micro strain) 247578.3282 61643290.2 12237.9428 47842427.57A350 winter day (micro strain) 247578.3282 61643290.2 12237.9428 47842427.57A350 winter night (micro strain) 869731.9717 36718546.4 83716.2255 84908602.8B777 summer day (micro strain) 10901.4996 4314412.61 572262.698 10353386.51B777 summer night (micro strain) 23155.6184 123400152 48113.5729 15343394.73B777 winter day (micro strain) 23155.6184 123400152 48113.5729 15343394.73B777 winter night (micro strain) 145702.6124 68517586.6 156292.101 21143789.56
Step 3: find actual repetitionsnactual for each season forB777=
365∗20∗3∗32
2=16425
*n will only change between the different planesTable 22
n (repetitions)A350 14600B777 16425Step 3: use minors law to find whether pavement fails due to fatigue
nN
for A350 summer day at critical point A
nN
= 14600167847
=.087
*same process for each minor law calculationTable 23
wheel B777 wheel A350critcal point minors A minors B minors C minors DA350 summer day (micro strain) 0.086984063 0.00091931 2.69767454 0.00095155A350 summer night (micro strain) 0.058971236 0.00023685 1.19301097 0.000305168A350 winter day (micro strain) 0.058971236 0.00023685 1.19301097 0.000305168A350 winter night (micro strain) 0.016786781 0.00039762 0.17439869 0.00017195B777 summer day (micro strain) 1.506673449 0.00380701 0.02870185 0.001586437B777 summer night (micro strain) 0.709331088 0.0001331 0.34137976 0.001070493B777 winter day (micro strain) 0.709331088 0.0001331 0.34137976 0.001070493B777 winter night (micro strain) 0.112729619 0.00023972 0.10509168 0.000776824
Now sum up n/N at each critical pointsum A sum B sum C sum D
3.259778561 0.006104 6.074648 0.006238AC fails due to fatigue at A and C
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50
1
2
3
4
5
6
7
Minors Law for design thickness
Path AMinors Law Failure linePath BPath CPath D
Path
n/N
sum
Figure 9
0 500 1000 1500 2000 25000
0.2
0.4
0.6
0.8
1
1.2
Minors Law vs AB thickness for A350 & B777
1225mm
300mm
2000mm
Max Strain before Fatigue
Thickness (mm)
Σn/N
Figure 10: Minors Law vs AB thicknessAs you can see here the AC will rut no matter what even if you change the thickness of the AB. It levels off. AB cannot protect the AC.Part 2A) Find k-value
=210 psi¿Using the funky chart and the back calculated stiffness modulus of SG, we can find the k-value. K-value=210 psi/in
210 psi¿ =.0543 MPa
mm=k−value
B) Find design thickness of asphaltStep 1: Find wheel dimensions
Area B777=.189m2
¿ B777 infowebsite we found thewidthW of thewheel¿ be .53m
L= AW
=. 189.53
=.357m
*same procedure for A350Table 24:wheel dimentions
W (m) L (m)B777 0.53 0.357516738A350 0.53 0.379988533
Step 2: set up wheel configuration.
Figure 12:B777 configuration in EverFe
Figure13: A350 configuration in EverFeStep 3: Find Changes of Temperature
Figure 14Step 4: iterate to find design thicknessDo 4 iterations for each temperature gradient and for each plane.Check the deflections and the max stress by using visualize for pointsHere is a table of all the iterations of PCC thickness and corresponding plane/season/thickness/deflection and Max tensile stress.
Table25:Thickness and respective stresses and deflectionsthickness (mm) Max (Mpa) Displacement (mm)
Looking at chart we can see that the design thickness would be for the A350 summer day between 600 and 615Step 5: find design thicknessHere is the criteria for Max stressstress<.55∗MR=.55∗5MPa=2.75MPaThrough interpolation of A350 between 600 and 615 mmm.Design thickness will be 605.5mm
Table 26 Design Thicknessthickness (mm) Max (Mpa) Displacement (mm)
605.5 2.75 2.848
Figure 15: results for points
Figure 16: results for stressesC) Plots of deflections and Max stress vs thickness for each season and each plane.
0 100 200 300 400 500 600 700 8000
1
2
3
4
5
6
7
8
B777 Stress vs Thickness
B777 Max Stress Summer/Winter DayB777 Max Stress Summer NightB777 Max Stress Winter NightMax allowable stress
thickness (mm)
stre
ss (M
Pa)
Figure 17
200 250 300 350 400 450 500 550 600 6500
0.51
1.52
2.53
3.54
4.5
B777 Deflections vs Thickness
B777 Defliction Summer/Winter DayB777 Deflection Summer NightB777 Deflection Winter Night
thickness (mm)
Defle
ction
s (m
m)
Figure 18
200 250 300 350 400 450 500 550 600 6500
0.5
1
1.5
2
2.5
3
3.5
4
4.5
A350 Deflections vs Thickness
A350 Deflections Winter NightA350 Deflections Summer NightA350 Deflections Summer/Winter Day
thickness (mm)
Defle
ction
s (m
m)
Figure 19
0 100 200 300 400 500 600 700 800 9000
1
2
3
4
5
6
7
8
9
A350 Max Stress vs Thickness
A350 Max Stress Winter NightA350 Max Stress Summer NightA350 Max Stresses Summer/Winter NightMax Allowable Stress
Thickess (mm)
Max
Str
ess (
MPa
)
Figure 20
Full openpaveTable 26: B777 summer day 1225 mm AB2 FALSE