Evaluation of rigid pavement on apron of terminal 3 Soekarno-Hatta International Airport using finite element method

The development of transportation technology is indicated by the appearance of a new aircraft gear configuration, dual trim. The load repetitions of the movement of aircraft with dualtridem gears, such as B-777-300ER aircraft with MTOW 28 tons, on Terminal 3 Soekarno-Hatta International Airport (SHIA) apron may cause pavement deformation, resulting in long-term fatigue and structural failures. Therefore, the performance of the existing rigid pavements to hold the loads for the next 20 years should be evaluated. Firstly, the equivalent annual departure and coverage of the aircraft in the airport up to 2037 is calculated. Next, the existing rigid pavement structure of the apron in the airport is modeled using a finite element method to calculate thermal stress and fatigue analysis for either the dowel or the slab. Our study result shows that the coverage value for the next 20 years is 86,534 with the maximum deflection of 0.055 mm and the maximum stress of 0.496834 MPa. The calculated thermal stress is 1.55 MPa, resulting in load repetition for the slab 1,241,484 and an infinite load repetition for the dowel.


Background
Indonesia's aviation industry has been growing rapidly for the past few years, for both domestic and international travels. It is characterized by the introduction of various types of larger aircraft into the industry. One of the aircraft is dual-tridem gears-based Boeing 777-300ER, operated by PT. Garuda Indonesia since 2013 to serve long-haul international routes from/to Terminal 3 Soekarno-Hatta International Airport (SHIA). The use of heavier aircraft raises concern regarding the capability of the apron's pavement structure on handling the additional loads.
Unfortunately, the current existing airport pavement design guidelines only specify pavement thickness output. The pavement thickness capability gained in restraining the structural response (stress, strain, and deflection) generated by the aircraft load on the landing gear is not covered yet. Therefore, finite element methods are needed to overcome this problem. In addition, the basic theory of pavement loading developed by Westergaard in 1926 can only be applied to single-wheel aircraft and two-layer pavements. This study is conducted to address the limitations of current existing theories that have not accommodated current technology developments.
This study focuses to measure the ability to exist pavements in the apron of Terminal 3 SHIA to resist structural responses due to temperature and load variation. The analysis was performed using a finite element method with the help of Abaqus software version 6.11.

Objective
The objective of this research is to evaluate of existing rigid pavements on the apron of Terminal 3 Soekarno-Hatta International Airport in support the loads that pass through it during the design life. where : W1 = wheel load of design aircraft (kg), where : R = modulus of rupture of concrete (psi), fc' = compressive strength of concrete (psi).

Thermal stress
Based on Delatte (2008), the thermal stress due to curling and warping is determined by the ratio between slab length (L) and relative stiffness radius (ℓ). The formula to determine the relative stiffness radius (ℓ) is : where : ℓ = relative stiffness radius (mm), E = modulus elasticity of concrete (MPa), D = pavement thickness (mm), k = modulus of subgrade reaction (MPa/m), υ = Poisson's ratio.
The next step is to calculate the stress due to temperature difference using formula : where : C = correction factor E = modulus elasticity of concrete (MPa), αt = thermal expansion of concrete ( 0 C), Δt = temperature difference between top and bottom surface on slab ( 0 C), υ = Poisson's ratio.

Idealization of finite element modelling for pavement structure
Before the computation is performed on the model, the idealization of modeling is firstly carried out to define some modeling conditions in order to represent the actual pavement conditions. In general, the idealization of modeling includes:

Global modelling
The global model is made by using solid elements modeled into 12 slabs, with as many as 4 slabs are connected transversely (x-axis-wise) and 3 slabs are connected longitudinally (y-axis-wise). Due to the limited resources available, the connection between slabs in the global model is not made using dowel. In addition, footprints in the global model are footprints on both sides of main landing gear. The footprint is located on the edge of the slab (edge loading). While the other side's footprint is located on the interior of the slab (interior loading). The dimensions of other parts that have been adjusted can be seen in Table 1 and Figure 1.

Local modelling
The aim of local models is to perform more specific analysis, because it analyzes the stress and deflection on the slab connection, especially the ability of dowel to function properly in transferring loads. They are made using solid elements which use dowels to hold together 2 connected slabs, and between slabs are given a gap of 10 mm. Footprint made in a local model is a footprint on one side of main landing gear. The footprint is located on the joint between slab (edge loading). The dimensions of other parts that have been adjusted can be seen in Table 2 and Figure 2.

Boundary condition
Boundary condition is one of the conditions that must be defined in a finite element modeling. Boundary conditions explain the limitations that a finite element model must have. Because the analysis carried out is a couple-temp displacement which combines two analysis at a time, which are the displacement and temperature analysis, as explained as follows: a) Displacement (mechanical bouncary condition) The boundary conditions that must be defined in this model are the hinge (joint) on the bottom surface subgrade and roll on the outer surface of the pavement (the x and y fields). The purpose of the roll boundary condition is to lock the pavement model so that it does not have displacement in the x-axis and y-axis direction, even if the displacement still occurs, the value will not be too large. b) Temperature The second boundary condition that must be defined in this model is tmperature on top surface and bottom surface of the concrete. This temperature can have an effect on the structure response that occurs. The temperature value chosen is temperature during the day, because in the daytime, the temperature value are more extreme than at night, as in Table 3 below.

Growth analysis of aircraft movement
The first step in this study is to perform growth analysis of aircraft movement, to predict the movement of aircraft at Soekarno-Hatta International Airport over the next 20 years (up to 2037). The data used in this analysis is the aircraft movement data at SHIA from 2002 to 2017 obtained from PT. Angkasa Pura 2, which can be seen in Table 4. From the data, then the aircraft movement for the next 20 years is extrapolated (Figure 3).

Response structure analysis of local and global modelling
The response structure analysis is conducted on loading and joint areas. Previously, the loading area is divided into 3 area. The areas are located on the intersection of critical point for local modelling and global modelling. Area 1 is located on joint between slab of local modelling. Area 2 and area 3 are located on loading area of global modelling. The area can be seen on Figure 5 and Figure 6.

Deflection a. Deflection on loading area
The deflection magnitude of each loading area deflection is illustrated in Table 7. The maximum deflection is illustrated in the form of deflected bowl in Figure 7. The maximum deflection occurs under the load center and on slab joint that is at a distance of 5,000 mm from the slab edge of 0.055 mm.   0  2017  11,833  2,922  1  2018  12,356  3,051  2  2019  12,755  3,150  3  2020  13,210  3,262  4  2021  13,772  3,401  5  2022  14,334  3,540  6  2023  14,875  3,673  7  2024  15,364  3,794  8  2025  15,776  3,896  9 each dowel can be seen on Table 8 and is illustrated in Figure 8.   (Table  9). According to FAA, the MOR value is calculated as follows: R = 9√fc ′ = 624.53 psi = 4.31 MPa Where fc' = compressive strength of concrete (psi) = 4,815.253 psi b. Stress on slab joint The maximum stress of dowel occurs in dowel #5, as in Table 10. The value is still below the tensile stress of steel.

Thermal stress analysis
The calculation of thermal stress using formula in Delatte (2004). Previously, check the temperature difference that occurs after analysis with Abaqus, as can be seen on Table  11. The thermal stress results are shown in Table 12. The maximum cumulative stress of Abaqus running result and thermal stress, occurs in Area 1 and when the temperature difference of 42.82 0 C still produces value below the MOR of concrete.