## 1 Introduction  
Materials and structures with negative Poisson's ratios (NPRs) have attracted significant scientific interest because of their unique mechanical behaviors, such as increased shear modulus, energy absorption ability, fracture toughness, and vibration control [1; 2; 3; 4; 5]. NPRs are also called \"auxetics\" by [PERSON] [6]. From theoretical analysis, these forms should have good performance under both static and dynamic loading cases, as energy absorbing and antiknock components. In recent decades, since [PERSON] [7] and [PERSON] [6] found the early forms, this field has been intensively investigated. [PERSON] [8] generated the first mechanical model with a NPR configuration. [PERSON] [9] proposed the first simulation of two-dimensional model molecules [10] and published a rigorously solved model (soft cyclic hexamers) with a stable isotropic phase. Well-known planar structures with chiral [11] and rotation [12] behaviors were studied. Simulations of auxetic materials [13], auxetic structures [14], auxetic two-dimensional hard body systems [15], auxetic nano-composite models in two dimensions [16] and in three dimensions [17], and auxetic metamaterials [18] have been performed. Theoretical and numerical modeling of auxetics has also been conducted [19; 20; 21]. Two-dimensional auxetic forms are always periodic and with perforated configurations [22; 23; 24], leading to auxetic behaviors by unit bending or rotating under tension or compression [25; 26; 27]. One of the most important 2D structures is the 2D re-entrant honeycomb form [28; 29; 30]. When fabricatedfrom materials with high ductility, 2D re-entrant honeycomb exhibits good auxetic behavior and load-carrying capacity under static loading. It also shows high stability and ductility under dynamic tensile or compressive loading [31; 32; 33; 34; 35]. Although 2D auxetic structures have been investigated for many years, their applications in civil engineering are still limited. The main reason is that the existing auxetic material strength and stiffness cannot meet the requirements under both static and dynamic loading, e.g., anti-seismic and anti-explosion. In recent years, in order to improve stiffness and strength, auxetic structures have gradually evolved from elastic foam materials to metallic structures. An important characteristic of these metallic structures is that the plasticity of the material is fully utilized to achieve auxetic performance of the structure, since large deformation of metal is commonly developed in the plastic state [36; 37; 38]. Thus, definition of the Poisson's ratio is also extended from the elastic stage to the plastic one. At present, existing metallic auxetic structures are made of brass and aluminum, which are very expensive. On the other hand, structural steel commonly has good ductility, and it can be perforated easily to achieve re-entrant configurations. Although a solid steel structure obviously has stronger bearing capacity under static loading, in dynamic situations such as anti-seismic and anti-explosion, strength is not the only mechanical index. Perforated members can have more plastic deformation to absorb energy under dynamic loading, which can protect the whole structure. There are already applications of perforated steel plates in civil engineering, using its plastic behaviors to dissipate seismic energy and needing to be replaced after a strong earthquake, such as slotted steel plates in shear walls and steel dampers in anti-seismic applications, which rely on the plastic deformation of perforated steel plates [39; 40]. Generally, their holes are well designed and in regular shapes. The novelty of this study is the realization of a metallic auxetic structure using a 2D re-entrant honeycomb form through the perforation of steel plates. Firstly, steel has high strength and plastic deformation capacity, and it is widely used. However, there are few related studies on auxetic structures made of steel.