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Smoothness to RoughnessTechniques, Tips and 26 Years of Insight
Michael Gerardi
APR Consultants, Inc.
The Primary Reason We Strive to Build
and Maintain Smooth Pavements is to Minimize Aircraft Dynamic Response and to Maximize Aircraft and Pavement Performance.
Courtesy F. Seggie
Smoothness Acceptance Testing
New Pavement Acceptance Specifications –Grade Control
• Responsible for Long Wavelength “Smoothness”
• .5-Inch Maximum Deviation from Design
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Full Length Centerline, 2013
Ele
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(in
)
Distance (feet)
APR’s Experience With Smoothness Criteria
• Criteria▫ .25-Inch to a 12-Foot Straightedge (FAA) or 3mm in a 3-
Meter Straightedge (ICAO)
▫ PI of 15 Inches per Mile (Profilograph)
• From an Aircraft Ride Quality Perspective▫ Generally these Thresholds are Overly Conservative
These Methods Apply to Construction Quality. As a Result, Their Usefulness to Identify Roughness That Affect Aircraft Response is Limited.
Types of Roughness
• Shock Loading▫ Elevated Slabs or Spalling
• Single Axel Loading▫ Short to Medium Wavelength
▫ Multiple Events in Succession
• Whole Aircraft Loading▫ Long Wavelength Event
▫ Up to 300 Feet (91m) Long
Methods to Evaluate RoughnessMethod Very Short WL
Shock LoadingShort WL
Single AxleLong WL
Whole Aircraft
Visual (PCI)
Drive by in Car
Pilot Reported
Physical Straightedge
California Profilograph
IRI
BBI
Analytical Straightedge
Aircraft Simulation
Forget About What You Know.
Change Your Perspective.
Keep the Aircraft in Mind
85 Feet (26m)12-Foot Straightedge
Boeing 777-200
25-Foot Profilograph
IRI (Quarter-Car Model)
Old Technology Vs New Aircraft
Current Smoothness Acceptance Testing Devices and Methods Do not Identify Long Wavelength Events that Can
Affect Aircraft Dynamic Response
Dispute Case Study
• New Asphalt Overlay
• Owner Concerned About Higher PI Values
• What Effect Will it Have on Aircraft Ride Quality?
Start
Distance
(ft)
Stop
Distance
(ft)
Profile
Index
17 528 7.23
529 1,056.00 1.00
1,057.00 1,584.00 0.00
1,585.00 2,112.00 2.00
2,113.00 2,640.00 4.51
2,641.00 3,168.00 2.00
3,169.00 3,696.00 1.50
3,697.00 4,224.00 5.51
4,225.00 4,752.00 0.50
4,753.00 5,280.00 3.51
5,281.00 5,808.00 2.00
5,809.00 6,336.00 2.00
6,337.00 6,864.00 3.51
6,865.00 6,938.00 30.46
Dispute Case Study
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Runway 02-20
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Distance (feet)
PI = 7.23
PI = 30.46
Dispute Case Study
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Taxi: Boeing 737-800 Aircraft 172500 lbs GW95-Knot Constant Speed Taxi
Air Temperature = 59 (°F) Field Elevation = 0 (ft) Headwind = 0 (kts)Profile Filename = Line J - 90 West.dat Sim. Start = 0 (ft) RQF = 2.407217Output Filename = Sim1.out Taxiing Speed = 95 (knots) Complete Simulation = Yes
Pilo
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Acc
(g'
s)C
G V
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Acc
(g'
s)El
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in)
Distance (feet)
The Problem with Indexes
• Aircraft Response is Complex
• Indexes Can Not Take Into Account the Variability of the Situation▫ Aircraft Size
▫ Aircraft Speed
▫ Location on The Runway
▫ Operation Type
• One Generalized Number Can Mischaracterize the Event in Question
The Problem with Indexes
• Imagine You Encounter a Speed Bump while Driving Your Car▫ Encountered at 3 mph - No
Worries
▫ Encountered at 50 mph - It Would Be a Problem!
• Indexes Don’t Take Speed into Account
New Tools You Can Use
• Understanding that New Pavements Should Meet Smoothness Guidance / Criteria▫ There Are Devices and Methods that can Evaluate the
Pavement for Smoothness AND Help Evaluate Airfield Pavements for Content That Affects Aircraft Response.
▫ APPROVED in FAA AC 150-5370-10H
Various Profiling Devices
▫ Sufficient Accuracy for Airfield Evaluation▫ Relatively Inexpensive▫ Can Track All Event Wavelengths▫ Some Units are Slow to Operate
Inclinometers
Various Profiling Devices
▫ Van, Truck or ATV Mounted▫ Faster Than Walking Type▫ Sub Millimeter Accuracy▫ Texture Can Adversely
Affect Ride Readings
▫ More Expensive▫ Difficulty Tracking Longer
Wavelengths▫ Requires Accel / Decel Room▫ Will not Measure Grade
Inertial Profilers
Various Profiling Devices
▫ Captures “True” Profile▫ Can Be Faster than
Inclinometer▫ Millimeter Accuracy▫ Texture is Not Detected
▫ Very Repeatable▫ Wide Range of Prices
Depending upon the Unit
External Reference Profilers
Robotic Total Station Scanning Laser
Walking External Reference
Limitations of a Physical Straightedge
• Profile Index (PI)▫ Effective for Short Wavelength. Misses Long
Wavelength Content.
• 12-Foot Straightedge (3-Meter)▫ Effective for Short Wavelength. Misses Long
Wavelength Content.
• Analytical Straightedge▫ Uses Any Length Straightedge. Effective for All
Wavelengths.
Straightedge Comparison
2 Inches
120 Feet
Straightedge Comparison
Straightedge Comparison
Additional Evaluation Methods
• Boeing Bump Index▫ Can Be Used as a “First Look” Method
▫ Is Limited in What it Can Accurately Identify It’s an Index
▫ Can Produce False Sense of Security
• Aircraft Simulation▫ Detects Short and Long Wavelength Events
▫ Not Subjective
Thresholds of Acceptability
• .40G in Vertical Response is an Unofficial Threshold of Acceptability
▫ Shock and Vibration and Human Discomfort
Shock and Vibration Handbook, Chapter 44 “Effects of Shock and Vibration on Man” by D. E. Goldman and H. E. Von Gierke
▫ Boeing Study on Structural Fatigue
Boeing Report D6-81746
Boeing’s Levels of Roughness Based on Accelerations at the Aircraft’s CG
• Level 1 Roughness▫ .25G to .54G
▫ Acceptable
• Level 2 Roughness▫ .55G to .79G
▫ Excessive
• Level 3 Roughness▫ .80G and Up
▫ Unacceptable
Boeing Criteria
• Acceptable – Minor impact on aircraft fatigue damage and minimal passenger discomfort
• Excessive – Pavement repair recommended. Immediate closure not required
• Unacceptable – Immediate closure of the affected pavement
Predicting an Aircraft’s Response
• Aircraft Simulation is Used to Predict Responses at the Pilot’s Station and the Aircraft’s CG to the Measured Profile.
Concerns With BBI
Because BBI is a Simple Wavelength Vs. Amplitude
Evaluation Tool, It Cannot Detect Multiple Events
Pavement Roughness
Takeoff with Roughness in the Overrun
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Takeoff: Boeing 737-800 Aircraft 172500 lbs GWRoughness in the Overrun
Air Temperature = 59 (°F) Headwind = 0 (kts)Field Elevation = 0 (ft) RQF = 2.996531Sim. Start = 0 (ft)
Pilo
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(g'
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in)
Distance (feet)
Takeoff with Roughness at 2,000 Feet
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Takeoff: Boeing 737-800 Aircraft 172500 lbs GWRoughness Beginning at 2,000 Ft
Air Temperature = 59 (°F) Headwind = 0 (kts)Field Elevation = 0 (ft) RQF = 3.951038Sim. Start = 0 (ft)
Pilo
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(g'
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(g'
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in)
Distance (feet)
A Runway’s Profile Changes Over Time
Settlement of a Concrete Runway
2006
2010
2014
3.50 Inches
4.50 Inches
1.0 Inch
Settlement of a PCC Runway
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CVG 18R CL, 2005 Baseline CVG 18R Centerline 2013 CVG 18R Centerline 2017Pavement Settlement over 12 Years
2013 Update Profile
2005 Baseline Profile
2017 Update Profile
Downward Spiral of Ride Quality• Overtime, the Pavement’s Profile Shape Can Change
• Depending upon the Wavelength, Aircraft Begin to Respond to These Changes – Increasing Dynamic Loading
• Deteriorating Ride Quality Produces More Pavement Roughness
Integrate Profile Monitoring into PMS
• Using Profile Measurement Devices Discussed in this Presentation, Changes to the Profile can be Tracked
• Like Other PMS Elements, Measure and Assess Periodically
▫ 3-5 Years
• Allows Managers to Predict Problems and Manage Maintenance
Wrap Up
• Existing Guidance and Criteria Will Provide you with Degrees of “Smoothness”
• Limitations in the Methods and Devices Allowable Will Not Identify “Roughness”
• Newer Technology Profiling Devices Will Provide You With Answers for Both - Smoothness and Roughness
Wrap Up
• Devices that Capture “True” Profile have Proven Very Useful in Tracking Profile Shape
• Profile Shape Changes Appear to be Common Place As the Pavement Ages
• Shape Changes can Create Roughness and Poor Aircraft Response
• Airports are Choosing to Enhance their PMS using Profile Monitoring Services.
The End