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Evaluation of the Impact of Aircraft Lateral Turning Forces on Pavement Design and Performance

Description:

The introduction of a new generation of very large aircraft, capable of traveling very long distances on intercontinental flights, has created new challenges to airport pavements worldwide. Aircraft such as the Boeing B777, or the Airbus A340 and A380, have gross weight well over 750,000 pounds at maximum takeoff weight. The vertical load applied on the landing gears is used to design the pavement structure. However, the design assumes only static loading. There is no consideration of lateral forces induced at the surface of the pavement. This problem gets more complicated when the vertical load is amplified due to surface roughness and the normal dynamic forces during taxiing operations. There are two main situations when these forces are critical for the pavement. During taxiing to takeoff, the aircraft turns or pivots to align with the runway center. At maximum takeoff weight, this turn generates very large localized shear forces at the surface where tire and pavement interact. The second situation is during fast exits after landing. In this case the centripetal acceleration during the fast exit creates large lateral forces at the surface or near surface of the pavement. Shear forces in both situations cause the pavement to deform and ultimately delaminate, which is a serious distress in runway pavements, capable of producing large cracks, potholes, foreign object debris (FOD), and at the worst case a partial or complete delamination of the surface layer. There have been several instances of catastrophic failure of the surface layer during pivot turning in airports around the world. Delamination near fast exits has also become a source of problems for airport administrators trying to maintain the runway in good structural condition and free of FOD. Currently, the Federal Aviation Administration (FAA) does not have specifications in its design procedure to include the shear failure of the surface of subsurface layers induced by pinned landing gear movements at runway ends, or fast exit turns on the middle of the runway build as flexible pavement. Understanding the problem and its consequences is the first step in developing a design procedure--or modifying an existing design procedure--in which lateral shear failure is mitigated.

Objective:

The objectives of this research would be to

1)

Understand, qualify and quantify lateral shear forces within the surface or subsurface layers of flexible pavements induced by landing gear lateral turning movements.

2)

Develop models to take the excessive lateral shear forces into consideration in the design of runway asphalt concrete surface layers.

3)

Formulate recommendations to include shear resistant asphalt concrete layer (or sublayer) in the pavement structure to minimize shear failures and avoid layer delamination in areas within the runway/taxiway that are more likely to experience excessive lateral shear forces;

4)

Recommend existing or revised test standards and threshold values to reduce the risk of such failures.

Related Research:

Although the issue of lateral shear forces is a frequent problem, there aren’t many efforts of investigating it reported in the literature. This project would build on some scattered research related below:

(a) Airfield Asphalt Pavement Technology Program (AAPTP) Project 06-04: Identification Non-destructive Testing to Identify Presence and Extent of Delamination of HMA Airfield Pavements.

(b) Airfield Asphalt Pavement Technology Program (AAPTP) Project 07-04 Evaluation of Failure Mechanisms for HMA Airfield Pavements and Project 07-01: Improved Shear Strength to Accommodate Higher Tire Pressures

(c) Federal Aviation Administration: few articles and publications on delamination of HMA airfield pavements and instrumentation of fast-exit taxiways.

Tasks:

Based on the objectives above and the overall goal of this research, the following tasks are proposed:

(a) Conduct detailed review of, but not limited to, existing research, literature, case studies, airport regulations and best practices related to lateral shear damage on pavement structures. As a minimum, the review should focus on:

a. Understanding damages induced by excessive lateral forces.

b. Examples of failures and corrective measures adopted by the industry.

c. Pavement mechanics and the structural behavior as it relates to shear stresses.

d. Pavement design procedures and how they can be modified to include shear stress resistance.

e. Mapping the interaction load-pavement response to understand and define loading threshold in which the problem must be investigated during the design.

(b) Load characterization

a. Types of landing gear and loading magnitudes.

b. Gear speed and loading duration.

c. Operational characteristics and limiting conditions.

(c) Pavement mechanics

a. Investigation of best constitutive models and type of pavement simulations required to effectively evaluate the high shear stress problem. (Note: not a model development, but rather a model search from the ones commonly used in practice.)

(d) Aircraft-Pavement interaction

a. Investigate the interaction between various aircrafts and gear/loading configurations and the pavement structure.

b. Identify critical conditions and limiting cases in which the evaluation of high lateral shear stress is required.

c. Investigate pavement structure concepts to minimize lateral shear damage.

(e) Pavement design recommendation

a. Evaluate pavement design methods, including FAA, to propose ways to incorporate a procedure to evaluate high lateral shear stress damage and failure.

(f) Materials and construction practices

a. Recommendations of asphalt concrete mixture requirements to produce shear resistant materials (including lab tests of such materials).

b. Construction good practices to avoid creating areas more susceptible to damage induced by shear forces.

(g) Prepare guidebook to assist airport pavement engineers in dealing with the design, construction and maintenance of pavement structures subjected to high levels of surface or subsurface lateral forces.

Relevance:

American Society of Civil Engineers (ASCE) Airfield Pavement Committee, Federal Aviation Administration Technical Center, and Engineer Research & Development Center at U.S. Army Corps of Engineers.

Sponsoring Committee:AKP30, Design and Rehabilitation of Asphalt Pavements
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Dr. Regis Carvalho from Oaken Consult and Dr. Danny Xiao from the University of Wisconsin-Platteville
Date Posted:10/04/2017
Date Modified:10/16/2017
Index Terms:Pavement design, Pavement performance, Delamination, Airport runways, Dynamic loads,
Cosponsoring Committees: 
Subjects    
Aviation
Design
Pavements

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