## 1 Introduction  
Corrugated paperboard is a sandwiched engineering structure, whose strength characteristic is in accordance with cross-sectional geometry of flute and material properties of linerboard and corrugating medium [1; 2; 3; 4; 5]. Corrugated paperboard is an environmental friendly packaging material with high stiffness and strength [2; 5; 6; 7; 8]. In addition, it is efficient and easy to use to protect the contents of the package. In Korea, linerboard and corrugating medium made by mixing imported old corrugated container (OCC) and Korea OCC at a certain ratio have been widely used for making corrugated paperboard. The corrugated paperboard with AB-flute double-wall (AB/F-DW) is widely used to maintain the strength of corrugated paperboard. Among corrugated paperboard produced in Korea in 2017, approximately 53.4% was the AB/F-DW corrugated paperboard, which was 1.15 times more than the used amount of SW (A/F and B/F) corrugated paperboard (KCCA, 2018). Recently, the application of corrugated paperboard in Korea has gradually expanded because a BB-flute double-wall (BB/F-DW) corrugated paperboard box having similar compressive strength to the AB/F-DW corrugated paperboard box has the advantage of reducing the package size. In addition, the use of corrugated paperboard has extended from the simple material of the box to materials of various cushion structures and pallets. Even though the corrugated paperboard-based structure is efficient to protect package contents, there are still many empirical factors in the design of corrugated paperboard-based structures such as boxes, pallet and cushion. Finite element analysis (FEA) can be used to analyze strength and economic optimization of such structures depending on the factors. Since the analysis of behavior of both paper and corrugated paperboard using FEA was complex, FEA was uncommonly used in the corrugated paperboard industry. However, applications of FEA to corrugated paperboard have recently increased by taking advantage of advanced modeling for composite sandwich structures similar to corrugated paperboard [9]. By applying FEA to structure analysis of corrugated paperboard, it was possible to simulate geometric nonlinearity (large deformation), material nonlinearity (plasticity), and stiffness properties of different structures of corrugated paperboard, which was agreed well with experimental results [8; 10; 11]. Several researchers have applied FEA to the parametric study of the post-buckling strength of corrugated paperboard sandwich panels. [PERSON] [4] used FEA to evaluate the buckling load and collapse load of the sandwich panel. [PERSON] et al. [11] performed linear buckling analysis using FEA on the edgewise compression test (ECT) model to determine the most buckling shape and estimate the critical buckling load. [PERSON] [12] used the FE (finite element) model to analyze the stress fields occurring in the machine direction (MD) of the combined board beam. The FE model has also been applied to the analysis of the bending stiffness and the ECT strength of corrugated paperboard structures, and to the analysis of the board combinations of corrugated paperboard that have advantageous properties [5; 13; 14; 15; 16]. The developed FEA has shown great analysis results of corrugated paperboard-based complex structure; however, a significant time and effort are required for modeling and analysis. By considering both the shape of the corrugated paperboard and the nonlinearity of its constituent boards, the nonlinearity of the corrugated paperboard can be well expressed through FEA. However in this case, it is impossible to realistically analyze the nonlinearity of the corrugated paperboard due to the enormous analysis time and the lack of convergence of the calculation process. To overcome the inherent problem, the structural analysis of the repeating unit cell in corrugated paperboard should be first performed and it is necessary to derive the equivalent (effective) mechanical properties of the entire structure.