Aircraft Multiple Wheel Gear Load Interaction Effects on Airport Flexible Pavement Responses: Fid-Bau Portal

Aircraft Multiple Wheel Gear Load Interaction Effects on Airport Flexible Pavement Responses

Gomez-Ramirez, Franco M. / Thompson, Marshall

The arrival of "New Generation Aircraft" (NGA) landing gear configurations, such as Boeing's 777 Dual-Tridem gears, has generated wide-spread concern about the effects of Multiple Wheel Load Interaction (MWLI) on airport flexible pavement response and performance. In mechanistic-empirical design, pavement responses (stresses, strains and deflections) are used to estimate the development of pavement distress (rutting and asphalt concrete fatigue cracking). Various standardized methods (FAA and ICAO), based on the CBR approach, do not provide a realistic representation of MWLI effects on pavement responses (deflection, stresses and strains). It is believed that more advanced structural models are capable of better representing the response interaction from NGA landing gears, but these have not yet been verified with field data. In 1999 the FAA's National Airport Pavement Test Facility (NAPTF) initiated full-scale testing to establish design criteria for the current trend in NGA gears. Typical flexible airport pavement sections were constructed over 3 different subgrade support levels (Low, Medium and High). Sensor installation includes Multi-Depth Deflectometers (MDDs) and Pressure Cells (PCs) to capture critical pavement responses under Dual, Dual-Tandem or Dual-Tridem gears. This paper presents an analysis of the flexible pavement response data for slow-rolling gears (0.34 mph), gathered at the NAPTF. The data can be used to quantify the degree of MWLI. Responses were obtained for various longitudinal and transverse gear offsets from the specific sensor (MDD and PC) for 3 different wheel load levels (24, 30 and 36 kips). Additional analyses of the NAPTF response test results are currently in progress at the University of Illinois Center Of Excellence for Airport Technology (UofILCOE). One of the primary objectives of this on-going study is to validate the principle of superposition for flexible airport pavements. Chou and Ledbetter conducted a re-analysis of the 1971 US Corps of Engineers Multiple Wheel Heavy Gear Load Tests (MWHGL) where they concluded that multiple wheel gear responses can be reasonably approximated by superposing single wheel responses provided that the single wheel responses were accurately measured or computed. Therefore, an accurate structural model of a single wheel load can be used to determine pavement responses for multiple wheel gears. These results will serve to quantify MWLI, validate/calibrate flexible pavement structural response models, and, hence, aid in the development of better tools for the design/evaluation of airport pavement systems subjected to NGA gear loads.