|
Roy D. McQueen & Associates, Ltd | ||
| Experts in pavement evaluation, engineering, testing, and research. | |||
| About RDM |
Contact RDM |
Services | NDT Equipment |
Experience | Certifications | Qualifications | Career Center |
News & Events |
Nondestructive Testing | LEDGA |
Due to the limitations of current Federal Aviation Administration (FAA) design methods for GA airport pavements - particularly the ability to handle "overload" aircraft conditions - the new design procedures for GA airport pavements and accompanying LEDGA software are based on layered elastic methods. To provide a degree of reliability, short of conducting a series of expensive full scale tests, the layered elastic subgrade strain failure criterion was based on thickness designs that comply with current FAA pavement design methods contained in FAA Advisory Circular 150/5320-6D. Therefore, it is believed that the new design methods will provide North Carolina Division of Aviation (NCDOA) with increased flexibility to handle additional design cases (e.g., overload, varying departure levels) with the same degree of reliability that exists with current FAA design methods. LEDGA is a computer program designed for use by experienced engineers to perform structural analyses of GA. airport pavements. The design analyses that LEDGA produces are based on modifications to the FAA LEDFAA computer program and the results of the aforementioned study for ITRE. The LEDFAA program is described in FAA Advisory Circular (AC) 150/5320-16. Modifications to the LEDFAA program that are incorporated in the LEDGA program include revised subgrade strain failure criterion, elimination of rigid pavement analysis capability, revised CBR-Esub transformation, revised fleet mix including GA and "overload aircraft", and procedures for assessing the effect of overload aircraft on GA airport pavements. Other familiar elements of the LEDFAA program were retained for ease of use and continuity. These include design for fatigue failure expressed in terms of a cumulative damage factor (CDF) using Miner's rule, similar graphical screens for the pavement structure and traffic, characterization of material properties of pavement layers and subgrade in terms of the elastic modulus, and same defaults for elastic modulus, Poisson's ratio, and layer interface. The LEDGA program also offers other enhancements to the evaluation and design procedures for GA airport pavements. These include the ability to vary the operational frequency of individual aircraft in the GA and overload fleet mix, input back-calculated subgrade elastic modulus from nondestructive tests (NDT), vary the thickness of the asphalt concrete surface layer, and incorporate layered elastic design methods for the design of GA airport pavements. Documentation on the development of the revised failure criterion, computational logic and other program elements can be found in the aforementioned study for ITRE. The LEDGA program is not intended to replace the services of professional engineers. As with any design procedure, all pavement designs must be accompanied by sound engineering design. It should also be stressed that, although layered elastic based design procedures are normally considered to be mechanistic and more rational than previous methods, a considerable amount of engineering judgement is still required. Designs produced by LEDGA should also comply with the detailed requirements of FAA AC 150/5320-6 and other applicable FAA, NCDOA and industry standards. The program does not automatically satisfy all of these requirements and the recommendations in the Advisory Circulars and other applicable standards should be followed. It is the designer's responsibility to use the program and standards in conjunction with each other. RDM, the FAA, ITRE, and North Carolina Department of Transportation represent to the best of their knowledge that the LEDGA software does not infringe upon any copyrights, trade secrets, or patents. The software is made available on an "as is" basis. No other representation or warranty is expressed or implied. It is the user's responsibility to properly select inputs, interpret output and adhere to all applicable or governing standards. | |
During the period of August 6, 1997 to June 30, 1999, Roy D. McQueen & Associates, Ltd. (RDM) performed the study entitled "Development of a Reliable Methodology to Determine In-Situ Pavement Strength of General Aviation Airport Pavements" under Contract No. NCSU 97-1312-01 with the Institute for Transportation Research and Education (ITRE) of the North Carolina State University (NCSU), Raleigh, NC. The basic objectives of the study were to develop standardized procedures for nondestructive testing (NDT), evaluation and design of General Aviation (GA) airport pavements in North Carolina using analytical software developed for this purpose. The resultant evaluation/design procedures and software were to permit evaluating the effects of allowing a one time or periodic overload operations on the airport pavements.